Method for testing a packaging substrate with at least one electron beam column and apparatus for testing a packaging substrate

Abstract

A method for testing a packaged substrate using at least one electron beam post is described. The method includes placing the packaged substrate on a stage in a vacuum chamber; testing one or more networks on the packaged substrate in the vacuum chamber using at least one electron beam post; and discharging one or more networks while testing them.

Description

Method for testing package substrate, and device for testing package substrate The present disclosure relates to a method and apparatus for testing packaging substrates. More specifically, embodiments described herein relate to non-contact testing of electrical interconnects in packaging substrates (i.e., panel-level packaging (PLP) substrates or advanced packaging (AP) substrates) using an electron beam, specifically for identifying, characterizing, detecting, and / or classifying defects such as shorts, opens, and / or leaks. In many applications, it is necessary to inspect substrates to monitor their quality. Since defects may occur, for example, during processing of the substrate (e.g., during structuring or coating of the substrate), inspecting the substrate to detect defects and monitor quality may be beneficial. Semiconductor package substrates and printed circuit boards used to manufacture complex microelectronic and / or micromechanical components are often tested during and / or after manufacturing to determine defects, such as shorts or opens, in the metal paths and interconnects provided on the substrate. For example, a substrate used to manufacture complex microelectronic components may include a plurality of interconnect paths for connecting semiconductor dies or other electrical components to be mounted on the package substrate. Various methods are known for testing such components. For example, contact probes can be used to contact the contact pads of the component under test to determine whether the component is defective. However, due to the increasing miniaturization of components, components and contact pads are becoming increasingly smaller. Therefore, contacting the contact pads with a contact probe can be difficult and may even risk damaging the component under test during testing. The complexity of package substrates is increasing, and design rules (feature size) are decreasing significantly. Within these substrates, surface contacts (for later flip-chip or other die mounting) connect to other surface contacts on the package substrate to interconnect semiconductor (or other) components. Standard electrical testing methods, such as electromechanical probing, are no longer sufficient for mass production test due to reduced throughput (flying probes, higher test point counts) and reduced contact reliability (electrical probes, smaller contact sizes). Beyond the issues of reduced size and potential damage to contact pads, the topography of the package substrate also presents challenges for other test methods, such as those using capacitive or electric field detectors, which benefit from small mechanical spacing. Non-contact electrical testing using an electron beam utilizes voltage signal readings, specifically voltage comparison measurements via secondary electron sensing. Furthermore, test points or networks can be charged with the electron beam. Before or after a test sequence, the substrate can be discharged, for example, using a discharge step, to define or recreate predetermined substrate conditions. Discharge steps have disadvantages, including, but not limited to, reduced throughput due to the time required for the discharge step. Therefore, it would be beneficial to provide improved testing methods and testing apparatus suitable for reliably and quickly testing complex microelectronic components, particularly packaging substrates such as advanced packaging (AP) substrates and panel-level packaging (PLP) substrates. In view of the above, according to the independent claims, a method and apparatus for testing a package substrate are provided. Additional aspects, advantages and beneficial features may be apparent from the dependent claims, the description and the accompanying drawings. According to an embodiment, a method for testing a package substrate using at least one electron beam column is provided. The method includes placing the package substrate on a stage in a vacuum chamber; testing one or more nets on the package substrate in the vacuum chamber using the at least one electron beam column; and discharging the one or more nets while testing the one or more nets. According to an embodiment, an apparatus for testing a package substrate according to the method according to an embodiment of the present disclosure is provided. According to an embodiment, an apparatus for testing a package substrate is provided, wherein the apparatus includes a controller having a processor and a memory storing instructions, wherein when executed by the processor, the instructions cause the apparatus to perform a method according to an embodiment of the present disclosure. According to an embodiment, a device for testing a packaging substrate is provided. The device includes a vacuum chamber; a stage within the vacuum chamber, the stage configured to support a packaging substrate, specifically, a panel-level packaging substrate or an advanced packaging substrate; and a charged particle beam column configured to generate an electron beam. The charged particle beam column includes an objective lens configured to focus the electron beam on the packaging substrate; a scanner configured to scan the electron beam to different locations on the packaging substrate; and an electron detector for detecting signal electrons emitted when the electron beam strikes the packaging substrate. The device further includes an ion source for providing positive ions and / or negative charges into at least a portion of the vacuum chamber; one or more electrodes configured to generate an electric field between the one or more electrodes and the packaging substrate, the electric field configured to move the positive ions or negative charges toward the packaging substrate; a controller configured to control the density of the positive ions and / or negative charges in the vacuum chamber during testing; and an analysis unit for determining whether a first component-to-component electrical interconnection path is defective based on the signal electrons. Embodiments are also directed to apparatuses for performing the disclosed methods, and include apparatus components for performing each of the described method aspects. Method aspects may be performed by hardware components, a computer programmed by appropriate software, any combination of the two, or in any other manner. Furthermore, embodiments according to the present disclosure are also directed to methods for operating the described apparatuses and methods for manufacturing the apparatuses and components described herein. Methods for operating the described apparatuses include method aspects for performing apparatus functions. Reference will now be made in detail to various exemplary embodiments, one or more of which are illustrated in each figure. Each example is provided by way of explanation and is not intended to be limiting. For example, features illustrated or described as part of one embodiment may be used in or in conjunction with other embodiments to produce still further embodiments. This disclosure is intended to include such modifications and variations. In the following description of the figures, the same reference numerals refer to the same components. Only the differences with respect to individual embodiments are described. The structures shown in the figures are not necessarily drawn to scale, but are provided to provide a better understanding of the embodiments. Embodiments of the present disclosure relate to testing and / or defect review of package substrates (i.e., panel-level packaging (PLP) substrates or advanced packaging (AP) substrates) according to methods described herein. At least one electron beam is used to write and read charge on the package substrate, particularly for identifying and characterizing defects such as shorts, opens, and / or leaks. Non-contact electrical testing using the electron beam can be provided, providing a voltage signal reading (e.g., a voltage comparison performed by sensing signal electrons). According to some embodiments, which can be combined with other embodiments described herein, the voltage comparison on the package substrate can be determined by detecting signal electrons. According to some embodiments, which can be combined with other embodiments described herein, the signal electrons can, in particular, be secondary electrons. Furthermore, test points or contacts can be non-contact charged on the AP or PLP substrate. Non-contact testing avoids or reduces damage to the AP / PLP substrate. Detection and classification of electrical defects is enabled. To further improve the voltage comparison in methods and devices according to embodiments of the present disclosure, charge control is provided. According to some embodiments, the package substrate can be discharged prior to testing. By discharging the test substrate to defined starting conditions with respect to potential and charge distribution, it provides repeatable voltage contrast signals obtained by signal electrons (SE) and improved defect detection success rates (S / N ratio, signal-to-noise ratio) on several substrates, as well as improved defect detection success rates after repeated electron beam scanning and test sequences. Furthermore, according to the embodiments described herein, the package substrate can be continuously discharged during testing. By discharging the test substrate, a repeatable voltage contrast signal obtained by signal electrons (SE) and an improved defect detection success rate (S / N ratio, signal-to-noise ratio) on multiple substrates can be provided, as well as an improved defect detection success rate after repeated electron beam scanning and test sequences. According to embodiments of the present disclosure, an ion source can be utilized to control the charging conditions of the AP or PLP substrate. A defined directional electric field is provided. The electric field separates positive ions from negative ions (or negative charge) and directs the positive ions toward the substrate. According to some embodiments that can be combined with other embodiments described herein, the ion source and the electric field electrodes can be integrated into a vacuum test chamber. For AP / PLP substrates, each network type can be limited to a specific time at a defined test voltage. This limitation can be based on the failure rate characteristics of the electrical networks on the substrate or component (wafer, panel), particularly within any particular substrate or component. Embodiments of the present disclosure allow for discharging networks and / or test points and / or, for example, embedded active or passive electrical components, before reaching a limit of the product of the test voltage V and the charging time t (V*t). Additionally or alternatively, the same charge can be applied to different networks or test points for the same duration. Furthermore, additional discharge operations can be reduced, additionally or alternatively. Specifically, additional discharge operations across the entire area can be avoided. Instead of completely discharging the substrate or the entire substrate area, a "tail discharge" can be provided, for example by applying a VUV flash to all networks. This means that VUV discharge is eliminated or the need for VUB discharge is reduced. A permanent supply of charge carriers can discharge the test points or networks over time, but (for example) at a slower rate. Discharging can be performed in parallel with an ongoing test sequence, thus avoiding a separate discharge step. According to embodiments, a method for testing a package substrate using at least one electron beam column is provided. The method includes placing the package substrate on a stage within a vacuum chamber. Testing one or more nets on the package substrate within the vacuum chamber using the at least one electron beam column. While testing the one or more nets, the one or more nets are discharged. Specifically, active discharge can be provided, for example, by providing charge carriers to discharge the substrate while testing the one or more nets. According to some embodiments, discharging includes providing charge adjacent to the substrate. FIG1 shows a schematic diagram of an apparatus according to an embodiment of the present disclosure and illustrates the concept of charge control according to the embodiments described herein. The packaging substrate 10 is supported on a stage 105. The packaging substrate is supported in a vacuum chamber 110. According to some embodiments that can be combined with other embodiments described herein, one or more ion sources 152 are located within the vacuum chamber 110 or at least partially within the vacuum chamber. In addition, a remote ion source can be provided and the conduit of the remote ion source can be at least partially located within the vacuum chamber. The ion source 152 generates positive ions and negative charges. The vacuum chamber or at least part of the vacuum chamber is filled with positive ions and negative charges. According to an embodiment of the present disclosure, the negative charges can be electrons or negative ions. In the following, the acceleration of positive ions towards the substrate is described. However, by changing the potential of the component, negative ions or electrons can also be accelerated towards the substrate. One or more electrodes 154 generate an electric field. The potential difference between the one or more electrodes and the substrate or stage 105 can be provided by the one or more electrodes, respectively. As shown in FIG1 , the electric field accelerates positive ions toward the package substrate 10, thereby imparting a positive charge to the package substrate 10. Since the electrodes 154 are at a negative potential relative to the substrate, negative ions or electrons are accelerated toward the package substrate, thereby imparting a negative charge to the package substrate. According to some embodiments, which can be combined with other embodiments described herein, the ion source 152 can be selected from an ion source with a gas supply, a UV source (such as a VUV source), a spark generating unit, or another ion generating unit. For example, a VUV source generating ions can ionize residual gas in the vacuum chamber, wherein the ion density can be controlled, for example, by the base pressure and the free path of the ion general trajectory. According to some embodiments, which can be combined with other embodiments described herein, the filling of the vacuum chamber with positive ions and / or negative charges is provided by an ion source that is at least partially provided in the vacuum chamber (e.g., an ion source connected to the vacuum chamber). As shown in FIG. 1 , ions are released from ion source 152 and distributed within vacuum chamber 110 . Specifically, the ions can be distributed between stage 105 and one or more electrodes 154 . The electric field separates positive ions and negative ions or electrons, respectively. According to some embodiments, which can be combined with other embodiments described herein, package substrate 10 can be placed on stage 105 at ground potential and positively charged electrode 154 . The voltage between one or more electrodes 154 and the stage can be provided by power supply 106 . As shown in FIG. 1 , one or more electrodes 154 can be integrated into a charged particle beam column, as shown in FIG. 1 . Electron beam testing offers a suitable solution, as it allows testing of test points smaller than 60μm or 10μm and below. It is capable of voltage contrast imaging. To this end, the electron beam can be used to positively or negatively charge the test structure. The voltage contrast principle can then be used to determine the test point potential for defect detection and sample parameter monitoring (such as capacitance and resistance). 1 , a charged particle beam column 120 may be provided on a first side of the stage 105. In some embodiments, which may be combined with other embodiments described herein, the charged particle beam column 120 may have an electron source 121 for generating an electron beam and beam optics, such as a scanning deflector 122 and / or an objective lens 124, for directing the electron beam onto a substrate disposed on the stage 105. The objective lens 124 may be an electrostatic objective lens, a magnetic objective lens, or a magnetic-electrostatic objective lens. The apparatus 100 further includes an electron detector 140 for detecting signal electrons 113 emitted when the second electron beam strikes the package substrate, and an analysis unit 141 configured to determine, based on the signal electrons 113 , whether, for example, the component-to-component electrical interconnection path 20 of the package substrate is defective. The charged particle beam column 120 shown in FIG. 1 includes a first plurality of electrodes 146 and a second plurality of electrodes 148 . The first plurality of electrodes 146 can generate a multipolar field, such as an octopole field, to direct the signal electrons 113 toward the electron detector 140 . For example, the first plurality of electrodes can include eight or more electrodes for generating an octopole field. Specifically, the multipolar field generated by the first plurality of electrodes 146 can be dynamically adjusted to the position of the electron beam 111 on the package substrate 10 . The second plurality of electrodes 148 can generate a multipolar field, such as an octopole field, to direct the signal electrons 113 toward the electron detector 140 . For example, the second plurality of electrodes can include eight or more electrodes for generating an octopole field. Specifically, the multipolar field generated by the second plurality of electrodes 148 can be static. According to some embodiments, which can be combined with other embodiments described herein, one or more electrodes in the charged particle beam column 120 may be at least one component of four or eight electrodes (or more) configured to generate a multipole field for guiding signal electrons. FIG. 1 further illustrates an ion source 152 and a gap 153. The gap 153 allows positive ions to be distributed above the package substrate 10. During charge control operation of the device 100, the first plurality of electrodes 146 and / or the second plurality of electrodes 148 can be charged to generate an electric field configured to accelerate positive ions or negative charges toward the substrate. The first plurality of electrodes 146 and / or the second plurality of electrodes 148 can be biased to generate a uniform electric field, particularly at or adjacent to the upper surface of the package substrate 10. According to an embodiment, an apparatus for contactless testing of package substrates is provided. The apparatus includes a vacuum chamber 110 and a stage 105 within the vacuum chamber. The stage is configured to support the package substrate 10, which may be a panel-level package substrate or an advanced package substrate. The apparatus further includes a charged particle beam column 120 configured to generate an electron beam. The charged particle beam column includes an objective lens 124 configured to focus the electron beam on the package substrate, a scanner configured to scan the electron beam to different locations on the package substrate, and an electron detector 140 for detecting signal electrons 113 emitted when the electron beam strikes the package substrate. The apparatus further includes an ion source for providing positive ions and / or negative charges into at least a portion of the vacuum chamber, and one or more electrodes configured to generate an electric field between the one or more electrodes and the package substrate, the electric field configured to accelerate the positive ions or negative charges toward the substrate. A controller is configured to control the density of the positive ions and / or negative charges in the vacuum chamber during testing. Furthermore, an analysis unit 141 is provided. The analysis unit decides based on the signal electronics 113 whether, for example, the component-to-component electrical interconnection path 20 is defective. According to some embodiments, which can be combined with other embodiments described herein, and as shown in FIG1 , one or more electrodes can be provided in the charged particle beam column. For example, one or more electrodes, or at least some of the one or more electrodes, such as the top electrode, can be positioned to direct signal electrons toward a detector. According to some embodiments, which can be combined with other embodiments described herein, a gap can be provided between one or more electrodes and the packaging substrate. In particular, a gap can be provided between at least one electron beam column and the packaging substrate. FIG. 2A shows an exemplary test method for a discharge operation according to the state of the art. There are n number of test points or networks, which are then charged by a charged particle beam. Thus, for a charging time t c , the delay of the nth test point or network to be charged is n*t c The test point or network is charged to the test voltage V h As can be seen from the graph shown in Figure 2A, the test t h The test voltage holding time in t varies between different networks that are subsequently charged. For example, the first network is tested at t max The maximum voltage is maintained during the mid-charge period, and the network charging is then charged for a shorter period of time. cThis situation will cause the hold time of the first test point and the last test point to change. h to (t h +n*t c ). As shown in FIG2B, embodiments of the present disclosure allow tailing or continuous discharge. The test point or network can be tested using a test voltage V h For example, the test voltage can be the maximum allowable test voltage V max Because charge carriers are provided adjacent to the substrate, a permanent discharge can be provided in parallel with the test. The integral under the test voltage curve over time can provide the same area A for a plurality of test points or networks. According to embodiments of the present disclosure, the area A corresponding to the product V*t of the constant charge distribution before discharge can be constant for a predetermined set of networks or test points, specifically for all networks or test points. During testing of a test point or network, a tailing or continuous discharge can be provided by having a predetermined ion density in an area adjacent to or above a substrate. According to embodiments, a method for testing a package substrate using at least one electron beam column is provided. The method includes placing the package substrate on a stage within a vacuum chamber. One or more networks on the package substrate within the vacuum chamber are tested using the at least one electron beam column. While testing the one or more networks, the one or more networks are discharged. In particular, an active discharge can be provided, for example, by providing charge carriers to discharge the substrate while testing the one or more networks. According to some embodiments, the discharge includes providing a charge adjacent to the substrate. According to the embodiments described in this disclosure, positive ions are forced toward the substrate, while negative ions or electrons are accelerated toward the positively charged electrode 154. This provides a self-aligned process that achieves a uniform charge distribution. For example, if a first region of the package substrate 10 is more positively charged than a second region of the package substrate 10, the first region will experience a smaller electric field and, therefore, a reduced positive charge during sequential charge control operations. In any region of the substrate within the uniform electric field, ion deposition on the substrate (which provides a continuous discharge) will cease when ions are applied to the electrode to compensate for the applied electric field. Therefore, by controlling the strength of the electric field, the substrate can be charged to a defined potential. For example, the electrode 154 charged to +100 V will generate a zero electric field when charges accumulate on the substrate 10, causing the substrate to also be biased to +100 V. Thus, the substrate potential can be adjusted to a predefined value. According to some embodiments, which can be combined with other embodiments described herein, during testing of a packaging substrate, residual positive or negative charges on or in a loaded test substrate can be neutralized by negative or positive ions, for example, by directing an electron beam onto portions of the packaging substrate using a charged particle beam column. As described with respect to FIG. 1 and FIG. 7 and FIG. 8 , a method for testing a package substrate is provided. The package substrate is a panel-level package substrate or an advanced package substrate. The method, performed using at least one electron beam column, includes placing the package substrate on a stage within a vacuum chamber. According to some embodiments, which can be combined with other embodiments described herein, at least one electron beam is directed onto at least a first portion at a first landing energy and onto at least a second portion at a second landing energy different from the first charging landing energy. For example, when the at least one electron beam strikes at the second energy to read the charge on the package substrate, signal electrons can be detected. This provides tailing or continuous charge control by generating positive ions to neutralize negative charge on the package substrate, for example, during testing. Over the years, the complexity of packaging substrates has continued to increase, aiming to reduce the space requirements of semiconductor packages. To reduce manufacturing costs, packaging technologies such as 2.5D ICs, 3D-ICs, and wafer-level packaging (WLP), such as fan-out WLP, have been introduced. In WLP, integrated circuits are packaged before the wafer is cut. As used herein, the term "package substrate" refers to packaging substrates configured for advanced packaging technologies, particularly WLP or panel-level packaging (PLP). 2.5D integrated circuits (2.5D ICs) and 3D integrated circuits (3D ICs) combine multiple dies into a single, integrated package. Here, two or more dies are placed on a packaging substrate, such as a silicon interposer or panel-level packaging substrate. In 2.5D ICs, the dies are placed side by side on the packaging substrate, while in 3D ICs, at least some of the dies are stacked on top of each other. Compared to conventional 2D circuit board assemblies, these assemblies can be packaged as a single component, reducing cost and size. The package substrate typically includes a plurality of component-to-component electrical interconnect paths that provide electrical connections between the chips or dies to be placed on the package substrate. The component-to-component electrical interconnect paths may extend vertically (perpendicular to the surface of the package substrate) and / or horizontally (parallel to the surface of the package substrate) through the body of the package substrate in a complex network of connections, with endpoints (referred to herein as surface contacts) exposed at the surface of the package substrate. Advanced packaging (AP) substrates provide component-to-component electrical interconnects on or within a wafer (such as a silicon wafer). For example, an AP substrate may include through-silicon vias (TSVs), such as those provided in a silicon interposer, and other conductive lines extending through the AP substrate. Panel-level packaging substrates are made of composite materials, including ceramic and glass. A PLP substrate is fabricated that is configured to integrate multiple components (e.g., potentially heterogeneous chips / dies, e.g., potentially of different sizes and configurations) into a single integrated package. Furthermore, an AP substrate may be incorporated onto the PLP substrate. A panel-level substrate typically provides a site for multiple chips, dies, or AP substrates to be placed on its surface (e.g., one or both sides), as well as multiple component-to-component electrical interconnect paths extending through the bulk of the PLP substrate. Embodiments of the present disclosure are specifically directed to an advanced packaging substrate or panel-level packaging substrate. Compared to printed circuit boards, the packaging substrate according to embodiments of the present disclosure may include different materials, such as semiconductor materials, ceramics, or glass. Additionally or alternatively, the packaging substrate may include or embed active or passive electronic components, such as capacitors, coils, transformers, or transistors. In addition, various other active and passive components may be embedded in the substrate, which components also require electrical testing. Furthermore, the line width of the electrical interconnect path may be 20 μm or less, such as in the range of 20 μm to 2 μm, or even less. Additionally or alternatively, the size of the contact pad may be 60 μm or less, or even about 10 μm or less. Therefore, the failure rate characteristics of AP / PLP substrates are more critical than those of printed circuit boards. Embodiments of the present disclosure improve the control of the test voltage V and the test voltage hold time t, and in particular the control of the product of the test voltage and the test voltage hold time V*t. Compared to PCBs, the coating and etching (structuring) processes used in AP / PLP manufacturing are more complex and introduce a greater potential for process-related electrical failures. Furthermore, embedded active and passive electrical components (such as capacitors and other components) present a higher probability of defects and are more susceptible to failure. Due to the higher value of semiconductor components installed later, electrical testing of all networks and embedded components on AP / PLP substrates is beneficial. Standard PCBs can be tested using a probe tester, as mechanical damage to contact pads (scratches caused by the probe) does not result in significant yield loss. However, on AP / PLP, the contacts are very small, and any scratches can lead to reduced connectivity and yield loss. It's important to note that the size of a panel-level substrate is not limited to the size of a wafer. For example, a panel-level substrate can be rectangular or have other shapes. Specifically, a panel-level substrate can provide a surface area larger than a typical wafer, for example, 1000 cm² or greater. For example, a panel-level substrate can have a size of 30 cm x 30 cm or greater, 60 cm x 30 cm or greater, or 60 cm x 60 cm or greater. According to embodiments of the present disclosure, e-beam testing and / or e-beam inspection provide testing of contact pads of 60 µm or less, or even approximately 10 µm or less. Voltage contrast test imaging can be provided. Testing can be performed at or between "surface contacts" on a package substrate. A "surface contact" is understood to be an endpoint of an electrical interconnection path exposed on the surface of a package substrate, such that an electron beam can be directed onto the surface contact for contactless charging or probing of the electrical interconnection path. The surface contact is configured to make electrical contact with a chip, die, smaller package, or other electrical component (such as a capacitor, resistor, coil, or the like) that is placed on the surface of the package substrate, for example, by soldering. The electrical component may also include an active electrical component, such as a transformer that changes the voltage in a region of the package. In some embodiments, the surface contact may be or may include a solder bump. According to embodiments of the present disclosure, 100% of the electrical interconnect paths are tested. The cost of ownership for component packages containing chips such as processors, memory, or the like (microelectronic components) is primarily determined by the highly integrated microelectronic components. Therefore, mounting a defect-free microelectronic component on a defective packaging substrate is disadvantageous in terms of manufacturing costs. A completely defect-free packaging substrate is required before mounting the microelectronic component. FIG3 shows a so-called “bathtub” curve 310. The bathtub distribution shows the failure behavior over time, for example for a panel-level packaging substrate or an advanced packaging substrate. The dashed lines separate the different regions. Region I is the “infant mortality” region. Region III is the “end of life wear” region. Region II is an intermediate region, suitable for testing, for example. Region II corresponds to the normal life or service life, for example, with a lower constant failure rate. The test parameters affect the “infant mortality” and “end of life wear” failure rates. When the product V*t of the test voltage V and the test voltage holding time t increases, the bathtub distribution changes, as shown by the dashed line 312. For example, a further increase in the product V*t leads to a bathtub distribution, as shown by the dashed line 314. To improve testing, the product V*t can be set as an improved parameter to catch early failures without increasing the wearout failure rate. Therefore, it is beneficial to have a suitable product V*t, and for the product to be similar or constant for similar nets or test points. Embodiments of the present disclosure with tailing or continuous discharge allow the product V*t to be adapted while providing a constant V*t. Assume that the failure rate and time are described in the "bathtub curve" and related mathematical functions. In order to avoid excessive stress on the test network, it is allowed to max The maximum test voltage V max , and the network must be discharged after reaching this limit. In fact, all tested networks must be discharged after reaching V max *t max Post-discharge. This results in many discharge steps in the test sequence on each AP / PLP substrate and slows down the overall test due to the many discharge cycles. Another disadvantage of performing a separate discharge operation after the test sequence is that similar networks will have different product V*ts because the V*t of the first network under test in the test sequence is longer than the V*t of the last network under test in the test sequence. Instead of achieving a complete discharge of the substrate by, for example, performing a VUV flash on all networks, embodiments of the present disclosure provide a "tail discharge" or continuous discharge. No VUV discharge operation (VUV flash) is provided, or the number of VUB discharge operations performed on all networks can be significantly reduced. A permanent supply of charge carriers (e.g., ions) is provided to allow the network to discharge slowly over time. The discharge is provided in parallel with the running test sequence. Embodiments of the present disclosure provide for discharging one or more networks under test while testing one or more networks. The present disclosure relates to methods and apparatus for testing package substrates that are configured to integrate multiple components into an integrated package and include at least one component-to-component electrical interconnect path. According to embodiments of the present disclosure, a test system, test apparatus, or test method can detect and / or classify defective electrical connections in a package substrate, such as open circuits, short circuits, leakage defects, or other defects. In particular, the test method and test system can provide non-contact testing. Mechanical probing of contact pads with a pitch of 60 µm or less, or even approximately 10 µm or less, is difficult or even impossible. Furthermore, the small contact pads must not be damaged by any scratches. Non-contact testing is advantageous. According to some embodiments, which can be combined with other embodiments described herein, further charge control can be provided during charge writing by operating the electron beam column with a defined landing energy. In particular, the landing energy, i.e., the energy of the electron beam when it strikes the package substrate, can be varied to control the charge provided on the package substrate. By varying the landing energy, the area impacted by the electron beam can be positively charged, negatively charged, or uncharged. During the writing operation, no charge is advantageously provided to the package substrate. The electron beam can be used to provide non-contact electrical testing, in which a charge can be placed, for example, at a first surface contact point, and the charge can be read, for example, at a second surface contact point. This enables the detection and classification of electrical defects in the package substrate. Different electron beam landing energies (Upe) control the SE yield (secondary electron yield) and, thereby, the total electron yield. Embodiments of the present disclosure provide for testing advanced or panel-level packaging substrates using a charged particle beam (e.g., an electron beam), wherein substrate charge control can be provided by charge carriers (particularly ions). Substrate charge control can be provided when testing test points or networks on a package substrate. The package substrate can be loaded into a test chamber, such as a vacuum chamber. For example, the package substrate can be loaded onto a grounded platform. The substrate is moved beneath one or more electrodes and / or an electron beam column, and the vacuum chamber is filled with ions. Consequently, ions fly between the test substrate and one or more electrodes (e.g., a positive electrode). The positive electrode can provide the electron beam column. Positive ions can be accelerated in an electric field, while negative ions or electrons are attracted to the positive electrode. The positive ions slowly discharge negatively charged test points or networks at a defined discharge rate. The discharge rate can be controlled by the number of charge carriers (i.e., the number of available ions). Discharge automatically ceases when the network reaches ground potential or another potential defined by the electric field and one or more electrodes. Discharge occurs concurrently with testing of the network or test points. A constant product V*t of the test voltage V and the test voltage holding time t (or the corresponding integral of the test voltage curve over time) can be provided. According to some embodiments that can be combined with other embodiments described herein, a predetermined test voltage and a predetermined test voltage hold time can be provided. For example, the predetermined test voltage hold time and the predetermined test voltage can be entered in a graphical user interface and provided to a controller. The density of positive ions and / or negative charges can be controlled based on the predetermined test voltage and the predetermined test voltage hold time. According to another optional implementation, the electron beam energy of the electron beam and / or the electric field generated by one or more electrodes and the substrate stage can be controlled based on the predetermined test voltage. During one or more first test sequences, the density of positive ions and / or negative charges can be maintained at a constant level. The product V*t described herein can remain constant. According to some embodiments that can be combined with other embodiments described herein, the density of positive ions and / or negative charges can be varied for one or more second test sequences that are different from the one or more first test sequences. The density of positive ions and / or negative ions can be adapted to the predetermined product V*t and can also vary between one test sequence and a subsequent test sequence. According to some embodiments, which can be combined with other embodiments described herein, discharging one or more test points or networks may include providing positive ions and / or negative charges in at least a portion of the vacuum chamber when testing the package substrate, and generating an electric field between one or more electrodes and the package substrate when testing the package substrate, the electric field being configured to accelerate the positive ions or negative charges toward the substrate. Testing of features of a package substrate (e.g., electrical interconnect paths) can be provided, wherein charging of the features and / or the package substrate can be controlled. In particular, the product of the test voltage and the charge retention time can be controlled and / or limited. The charge on the package substrate or a corresponding portion thereof can be controlled by varying the electron beam primary energy (Upe), i.e., the energy at which the electron beam lands on the package substrate. The test can include a voltage signal reading, i.e., a voltage comparison measurement when signal electrons (e.g., secondary electrons) are detected. Test locations (i.e., surface contacts) on advanced or panel-level package substrates can be charged contactlessly to avoid damaging the surface contacts. As schematically depicted in FIG. 1 , the package substrate 10 includes a first component-to-component electrical interconnection path 20 extending between a first surface contact 21 and a second surface contact 22 of the package substrate 10. Optionally, the first component-to-component electrical interconnection path 20 may extend between three or more surface contacts, which may be provided on the same surface or on two opposing surfaces of the package substrate. The component-to-component electrical interconnection path 20 depicted in FIG. 1 extends only between the first surface contact 21 and the second surface contact 22. Both are arranged at the top surface of the package substrate, but the present disclosure is not limited to such component-to-component electrical interconnection paths, and the component-to-component electrical interconnection path may be a complex network of vias, pillars, and / or conductor lines extending through the package substrate and having a plurality of surface contacts. The package substrate 10 may include a plurality of component-to-component electrical interconnection paths for connecting a plurality of components to be placed on the package substrate 10. In FIG1 , three component-to-component electrical interconnection paths are exemplarily depicted, but the package substrate 10 may include thousands or tens of thousands of such component-to-component electrical interconnection paths. If no short circuit exists between two electrical interconnection paths, the paths are generally electrically isolated from each other. According to the embodiments described herein, a packaging substrate 10 is placed on a stage 105 in a vacuum chamber 110. The stage may be movable, in particular in the z-direction (i.e., a direction perpendicular to the stage surface) and / or in the x- and y-directions (i.e., in the plane of the stage surface). The stage 105 is provided in the vacuum chamber and is configured to support a packaging substrate, which is one of a panel-level packaging substrate and an advanced packaging substrate. An electron beam 111 is directed onto a first surface contact 21. The electron beam may be scanned to direct it to a second surface contact 22. Signal electrons 113 emitted from the second surface contact 22 are detected for testing the first component-to-component electrical interconnection path 20. The signal electrons may be secondary electrons and / or backscattered electrons. For example, it may be determined whether the first component-to-component electrical interconnection path 20 has an "open circuit" defect. Additionally or alternatively, electron beam 111 is directed to a more distant surface contact 27 that is not the end point of first component-to-component electrical interconnection path 20. That is, it is directed to a second component-to-component electrical interconnection path 23 that may extend through the package substrate and adjacent to first component-to-component electrical interconnection path 20. Signal electrons emitted from more distant surface contact 27 are detected for testing first component-to-component electrical interconnection path 20. The signal electrons may be secondary electrons and / or backscattered electrons. For example, it can be determined whether first component-to-component electrical interconnection path 20 has a "short" defect. Specifically, by detecting signal electrons 113 emitted when electron beam 111 strikes the package substrate (specifically, by determining the energy of signal electrons 113, which depends on the potential of second surface contact 22 or further surface contact 27), it is possible to determine whether first component-to-component electrical interconnection path 20 is defective in a "voltage comparison measurement." Specifically, defective connections in the package substrate, such as open circuits, short circuits, and / or leakage defects, can be determined and classified. In some embodiments, the analysis unit 141 may be configured to determine whether an electrical interconnection path of the package substrate has a defect, such as a short circuit, an open circuit, and / or a leak, based on the detected signal electrons. Optionally, the analysis unit 141 may be configured to classify the detected defects. In some embodiments, the analysis unit 141 may be configured to determine whether a short circuit or a leak exists between two or more electrical interconnection paths based on the signal electrons detected from subsequent measurements. In some implementations, the signal electrons 113 detected by the electron detector 140 may provide information about the potential of the substrate location from which the signal electrons 113 were emitted or reflected, and the analysis unit 141 may be configured to determine from this information whether the component-to-component electrical interconnection path 20 is defective. The analysis unit 141 may further be configured to classify the determined defects. Specifically, the test may include determining, by the analysis unit 141, whether the first component-to-component electrical interconnection path 20 has any of a short circuit, an open circuit, and / or a leak. An “open circuit” is understood as a disconnected electrical interconnection path that does not actually electrically connect the first surface contact point 21 and the second surface contact point 22. A “short circuit” is understood as an electrical connection between two electrical interconnection paths that are actually electrically separated. In some embodiments, which may be combined with other embodiments described herein, one or more electrical connections extending between surface contacts on different sides of a substrate are inspected. In further embodiments, a first plurality of electrical connections extending between surface contacts on a first side of the substrate, a second plurality of electrical connections extending between surface contacts on a second side of the substrate, and / or a third plurality of electrical connections extending between surface contacts on different sides of the substrate are inspected. For example, one or more electron beam columns may be positioned on both sides of the substrate (not shown) so that surface contacts on both sides of the substrate can be charged and / or discharged to inspect and test the corresponding electrical connections. According to the embodiments described herein, charging and probing are provided using an electron beam, specifically a scanning electron beam. Other testing methods (such as electrical and / or mechanical probing) cannot provide the throughput offered by the methods and systems described herein. In particular, avoiding additional discharge operations after the test sequence can further improve throughput. The methods and systems described herein rely on contactless charging and probing using an electron beam. Furthermore, the contact reliability of electrical and / or mechanical testers decreases with decreasing size and increasing density and number of surface contacts to be tested in advanced package substrates. For example, contact pad sizes of 30 μm or less are difficult to mechanically probe. Furthermore, the topography of the package substrate and the topography of the package substrate's surface contacts can pose problems for other testing methods (such as capacitive detectors or electric field detectors). For example, having a charged electron beam offers advantages over flood-type electron gun electron charging. Given the complexity of package substrates, the ability to locally charge improves the available test procedures compared to charging the entire area with a flood-type electron gun. Furthermore, localized charging reduces the total charge accumulation on the package substrate. Thus, the product of the test voltage V and the test voltage hold time t can be provided separately for different nets. Furthermore, different charging of different regions may result in a reduction in the total charge provided on the substrate. According to some embodiments, which can be combined with other embodiments described herein, different charge patterns can be provided on multiple portions of the package substrate. The test method described herein is suitable for testing package substrates for integration into multi-component packages, particularly PLP substrates or AP substrates, and uses an electron beam to charge, for example, component-to-component electrical interconnect paths 20 and read the voltage of the live circuit system, particularly by probing second surface contacts and / or further surface contacts. In other words, both "electrical actuation" and "probing" are performed by the electron beam, allowing for reliable and rapid defect detection. Testing by electron beam charging and electron beam probing (e.g., using an EBT column or an EBR column) is topography-independent, fast, and flexible in terms of contact location, size, and geometry, whereas the topography of the package substrate can be a problem for other test methods (e.g., capacitive detectors or electric field detectors). A packaging substrate (such as a PLP substrate) may include a plurality of component-to-component connections, for example, 5,000 or more, 10,000 or more, 20,000 or more, or even 50,000 or more. The connections may include through-silicon vias (TSVs), for example, provided in a silicon interposer along with other conductor lines extending through the packaging substrate, and / or may include multi-die interconnect bridges that may be embedded in the packaging substrate. The packaging substrate may be a multi-layer substrate, including electrical interconnects in a plurality of layers arranged one above the other (e.g., in a layer stack). In some embodiments, the package substrate 10 includes a plurality of component-to-component electrical interconnection paths extending between corresponding first and second surface contacts, and optionally, additional contacts. The method may also include testing the plurality of component-to-component electrical interconnection paths sequentially or in parallel. As used herein, "sequential testing" refers to the subsequent testing of the plurality of component-to-component electrical interconnection paths of the package substrate. For example, 5,000 or more component-to-component electrical interconnection paths may be tested one after the other. As used herein, "parallel testing" may refer to the simultaneous testing of two or more component-to-component electrical interconnection paths. "Parallel testing" may also refer to testing a plurality of component-to-component electrical interconnection paths by scanning an electron beam to charge a plurality of first surface contacts within a field of view while simultaneously scanning an electron beam to probe a plurality of corresponding second surface contacts within the field of view. Specifically, for sequential testing, embodiments of tailing or sequentially discharging the component-to-component electrical interconnection paths (i.e., nets) may result in a more even distribution of charging time between nets. In some embodiments, directing the electron beam 111 to the first surface contact includes focusing the electron beam 111 on the first surface contact 21, for example, using a beam probe diameter of 30 μm or less (specifically, 10 μm or less) on the package substrate. Focusing the charged electron beam on the package substrate (e.g., via an objective lens) can prevent charging of substrate surface areas other than the surface contact and provide more accurate test results. Additionally or alternatively, particularly for signal electron beam detection, the electron beam can be scanned across a portion of the package substrate to generate an image of the portion of the package substrate. The image can include voltage contrast information. For example, pattern recognition in the image can be used to provide defect detection or defect classification for one or more electrical interconnect paths. While conventional PCBs typically include relatively large, flat metal pads that form surface contacts for testing, package substrates tested according to the embodiments described herein may include a large number of small, convexly shaped solder bumps to be tested, which makes testing more challenging. In particular, the first surface contact 21 and the second surface contact 22 may each have a maximum dimension of 25 μm or less, particularly 10 μm or less. For example, the first and second surface contacts may be substantially circular, particularly hemispherical, with a diameter of 25 μm or less, particularly 10 μm or less. According to some embodiments, which may be combined with other embodiments described herein, the surface contacts may have a three-dimensional topography, particularly a substantially hemispherical shape. In contrast to mechanical testers, an electron beam can be accurately directed to these small surface areas because it can be focused to a very small probe diameter and can be precisely directed to a predetermined point on the substrate, for example, by a scanning deflector with sub-μm accuracy. While other testers may slide or glide across surfaces with protruding geometries, the electron beam can be accurately focused onto arbitrary geometries, making the test method described herein geometry-independent and topography-independent. According to some embodiments, which may be combined with other embodiments described herein, the electric field generated by one or more electrodes, such as the first plurality of electrodes and / or the second plurality of electrodes, can be uniform, particularly across the surface of the package substrate. The electric field between the package substrate surface and the one or more electrodes can also be uniform. A uniform electric field within a region is constant at every point within that region. A uniform electric field has the same intensity and direction at every point and is consistent with homogeneity, meaning that all points experience the same physical properties. Therefore, a uniform electric field can also be referred to as a homogeneous electric field. The first plurality of electrodes and / or the second plurality of electrodes can be used to guide signal electrons during detection of signal electrons and can be used to generate an electric field for charge control. According to additional or alternative modifications, the electric field can be generated by another electrode, such as electrode 154, or by a combination of another electrode and the first plurality of electrodes and / or the second plurality of electrodes. In some embodiments, which may be combined with other embodiments described herein, electron detector 140 comprises an Everhard-Thornley detector. An energy filter 142 for signal electrons 113 can be positioned, for example, in front of electron detector 140, specifically in front of the Everhard-Thornley detector, as schematically depicted in FIG. 1 . The energy filter can include a gate configured to be set at a predetermined potential. Energy filter 142 can suppress low-energy signal electrons. Energy filter 142 can suppress signal electrons that are not relevant to the voltage comparison measurement being performed. In some implementations, energy filter 142 can suppress signal electrons emitted from uncharged surface areas and only allow signal electrons emitted from charged surface contacts to pass. Consequently, the signal current detected by the electron detector can depend on the energy of the signal electrons, indicating whether the probed surface contact is defective. In some embodiments, the apparatus 100 may include a scanning controller 123 connected to a scanning deflector 122 of the charged particle beam column 120. The scanning deflector 122 may be configured to scan the electron beam over the substrate surface. The electron beam may be directed to a portion of the packaging substrate, for example, by a first beam probe diameter. The portion of the packaging substrate may be an area of ​​the packaging substrate over which the electron beam is scanned. The electron beam may be raster scanned over the portion of the packaging substrate. For example, one or more scanning deflectors 122 may scan the electron beam over the portion of the packaging substrate. The portion of the packaging substrate may also be a surface contact point. The electron beam may be vector-scanned to one or more surface contact points of the packaging substrate. For example, one or more scanning deflectors may be used to vector-scan the electron beam to one or more surface contact points. For example, the scan controller 123 can be configured to control the scan deflector so that the electron beam is sequentially directed to the pairs of first and second surface contacts to test the corresponding component-to-component electrical interconnection paths extending between the respective pairs of first and second surface contacts. This allows for rapid and reliable testing of multiple electrical interconnection paths extending through the package substrate. According to some embodiments that can be combined with other embodiments described herein, the electron beam can be vector-scanned to individual locations, such as surface contacts of a package substrate, for charging, and can be vector-scanned to individual locations for detecting signal electrons. Alternatively, the electron beam can be vector-scanned to individual locations, such as surface contacts of a package substrate, and a region of the package substrate can be raster-scanned for detecting signal electrons. According to some embodiments that can be combined with other embodiments described herein, the electron beam of a charged particle beam column can be scanned to one or more locations on a package substrate for charging and detecting signal electrons. As schematically depicted in FIG. 1 , the electron source 121 is connected to a power supply 130 . This power supply can provide a high voltage to the electron source, thereby emitting an electron beam, also known as a primary electron beam, from the electron source. According to some embodiments, which can be combined with other embodiments described herein, the voltage provided by the power supply 130 can be varied to change the energy of the electron beam, thereby varying the landing energy of the electron beam on the package substrate. According to some embodiments, which can be combined with other embodiments described herein, one or more power supplies can be connected to various components of the electron beam column. For example, the power supply can be connected to the electron source (as shown in FIG. 1 ), the electron source's extractor, the electron source's anode, a deceleration electrode configured to decelerate electrons before impacting the package substrate, and / or the stage 105 . The landing energy of the electron beam on the package substrate is determined by the potential difference between the electron source's emitter tip and the package substrate or the stage 105 . Therefore, one or more power supplies can be provided to vary the landing energy of the electron beam. According to an embodiment, an apparatus for contactless testing of a packaging substrate is provided. The packaging substrate is a packaging substrate as described herein, and in particular, a panel-level packaging substrate or an advanced packaging substrate. The apparatus includes a vacuum chamber 110 and a stage 105 within the vacuum chamber, wherein the stage is configured to support a packaging substrate, such as a panel-level packaging substrate or an advanced packaging substrate. The apparatus further includes an electron beam column configured to generate an electron beam, wherein the electron beam column includes an objective lens configured to focus the electron beam on the packaging substrate, a scanner configured to scan the electron beam to different locations on the packaging substrate, and an electron detector for detecting signal electrons emitted when the electron beam strikes the packaging substrate. The apparatus further includes an ion source for providing positive ions and / or negative charges into at least a portion of the vacuum chamber, and one or more electrodes configured to generate an electric field between the one or more electrodes and the packaging substrate, wherein the electric field is configured to accelerate the positive ions or negative charges toward the substrate. Further, a controller is provided that is configured to control the density of positive ions and / or negative charges in the vacuum chamber during testing. FIG1 exemplarily illustrates a grounded stage 105. The stage can be directly grounded, can be grounded via a DC power supply (as exemplarily shown in FIG1 ), or can be grounded via an AC power supply. According to some embodiments, which can be combined with other embodiments described herein, the stage can include a conductive stage surface that is directly or indirectly grounded to provide a reference potential. When the packaging substrate is placed on the stage 105, the packaging substrate provides a defined charge thereon. In any case, the stage can be conductive. Therefore, the stage can be provided with a defined potential. For example, the defined potential can be ground potential, or can be a negative potential or a positive potential relative to the ground. For example, a DC power supply can be provided between the ground and the conductive stage. Alternatively, an AC power supply can be provided between the ground and the conductive stage, wherein a defined alternating potential can be provided. According to some embodiments that can be combined with other embodiments described herein, the surface of the stage 105 is provided with a non-conductive material. For example, a layer of dielectric material can be provided as the surface of the stage. Having a non-conductive stage surface allows the charge applied to the packaging substrate to remain on the packaging substrate so that it can be detected during testing operations or defect review operations. According to some embodiments, which can be combined with other embodiments described herein, the stage includes a conductive stage surface that is directly or indirectly grounded to provide a reference potential. According to further additional or alternative modifications, the package substrate can be partially grounded, for example, via the stage. For example, some circuitry can be connected to GND, while some circuitry is not. According to further modifications, which can be combined with other embodiments described herein, the package substrate can be capacitively grounded, for example, via the stage. In some embodiments, no ohmic connection is present. The defined potential of the stage (especially a conductive stage) provides electric field lines, especially on the stage surface and non-conductive parts of the package substrate. The defined potential can be used to influence the electron beam of the electron beam column. According to further modifications that can be combined with other embodiments described herein, capacitive coupling of the package substrate to the stage 105 can place the package substrate at a defined potential. For example, a grounded conductive stage 105 can provide capacitive coupling to ground. Additionally or alternatively, a set of predetermined structures on the package substrate can be grounded. However, due to the grounding, the set of predetermined structures may not be charged and can be used as a reference potential. FIG1 illustrates a controller 180. According to some embodiments, which may be combined with other embodiments described herein, the controller can be connected to one or more components of apparatus 100 for non-contact testing and charge control of package substrates. As exemplarily shown in FIG1 , the controller can be connected to power supply 130, scan controller 123, analysis unit 141, ion source 152, and stage 105. The controller can also be connected to electron detector 140. Controller 180 includes a central processing unit (CPU), memory, and support circuitry. To facilitate control of the apparatus for testing packaged substrates, the CPU can be any general-purpose computer processor that can be used in an industrial environment to control various chambers and subprocessors. Memory is coupled to the CPU. The memory or computer-readable medium can be one or more readily available memory devices, such as random access memory, read-only memory, a hard drive, or any other form of local or remote digital storage. Support circuitry can be coupled to the CPU to support the processor in a conventional manner. Such circuits include cache memory, power supplies, clock circuitry, input / output circuitry and related subsystems, and the like. Inspection process instructions are typically stored in memory as software routines, often referred to as recipes. The software routines can also be stored and / or executed by a second CPU (not shown) that is remote from the hardware controlled by the CPU. A software general purpose program, when executed by a CPU, can convert a general purpose computer into a special purpose computer (controller) for controlling the operation of an apparatus, such as a computer for controlling trailing or continuous discharge control, landing energy, stage positioning, and / or charged particle beam scanning during test operations. Although the methods and / or processes of the present disclosure are discussed and implemented as software general purpose programs, some of the method steps disclosed therein can be implemented in hardware and performed by a software controller. As such, embodiments of the present invention can be implemented as software executed on a computer system, as hardware implemented as application specific integrated circuits or other types of hardware, or as a combination of software and hardware. A controller may execute or perform a method for testing a package substrate using an electron beam column. The method, according to some embodiments, includes generating ions and generating an electric field to perform tailing or continuous discharge control. Furthermore, the method includes testing the package substrate, specifically by directing an electron beam from at least one electron beam column toward at least a first portion of the package substrate and directing an electron beam from at least one electron beam column onto the package substrate. The method further includes detecting signal electrons emitted upon impact of the electron beam to test at least one first component-to-component electrical interconnect path of the package substrate. According to an embodiment, an apparatus for testing a package substrate using any of the methods described herein is provided. The apparatus may include a controller 180. The controller includes a processor and a memory storing instructions that, when executed by the processor, cause the apparatus to perform a method according to an embodiment of the present disclosure. Figures 4A and 4B illustrate enlarged cross-sectional views of a package substrate during the testing method described herein. Package substrate 10 may be an AP substrate or a PLP substrate used to manufacture a multi-die integrated package and includes a first die connection interface for attaching a first die 301 and a second die connection interface for attaching a second die 302. A plurality of component-to-component electrical interconnection paths (four of which are illustratively shown in Figures 4A and 4B) extend between corresponding first surface contacts of the first die connection interface and corresponding second surface contacts of the second die connection interface. The surface contacts may be formed as or include solder bumps having a three-dimensional geometry, such as, for example, a substantially hemispherical shape. In FIG. 4A , a first component-to-component electrical interconnection path 20 extending between first and second surface contacts 21, 22 is tested by directing a charged electron beam 111 toward first surface contact 21 and an electron beam 112 toward second surface contact 22. Because first surface contact 21 is electrically connected to second surface contact 22 via first component-to-component electrical interconnection path 20, after charging first surface contact 21, second surface contact 22 should be at the same potential as first surface contact 21. Signal electrons 113 emitted from second surface contact 22 are detected. These signal electrons carry information about the potential of second surface contact 22, which should be the same as the potential of first surface contact 21. If the potential of second surface contact 22 is determined to be different from the potential of first surface contact 21, a defect is detected. The detected voltage comparison can be used to characterize the defect. Furthermore, the detected voltages of subsequently measured adjacent electrical interconnect paths may be compared to find out short circuits or leakages between different electrical interconnect paths. After testing the first component-to-component electrical interconnection path 20, the electron beam 111 can be directed to two surface contact points of the second component-to-component electrical interconnection path 23, for example, by scanning the electron beam (vector scanning) to other locations using corresponding scanning deflectors and / or by moving the stage supporting the package substrate. Subsequently, multiple component-to-component electrical interconnections can be tested using the charging electron beam and the probing electron beam. Thus, multiple test points can be tested sequentially and / or in parallel. 4B, an open circuit 151 exists in the first component-to-component electrical interconnection path 20. The open circuit 151 may be determined because the second surface contact 22 is not charged after or during charging of the first surface contact 21 by the charged electron beam 111. In FIG4B , a short circuit 155 exists between the second component-to-component electrical interconnection path 23 and the third component-to-component electrical interconnection path 24. Because the third component-to-component electrical interconnection path 24 is charged together with the second component-to-component electrical interconnection path 23, this can be detected by a probe electron beam directed to the more distant surface contact point 27 of the third component-to-component electrical interconnection path 24 after or during the charging of the second component-to-component electrical interconnection path 23, thereby determining the short circuit. For evaluation and defect classification, metrology signals of adjacent interconnect paths and / or previously collected data can be compared, allowing the identification of opens, shorts, and leaks in the package substrate. FIG5 is a schematic top view of a package substrate 10 under test described herein. The package substrate has a top surface with a plurality of surface contacts arranged in a two-dimensional pattern. The package substrate 10 includes a first die connection interface 31 for attaching a first die (specifically, by flip-chip mounting), a second die connection interface 32 for attaching a second die (specifically, by flip-chip mounting), and optional additional die connection interfaces that may be arranged adjacent to each other in pairs. The first die connection interface 31 may include a plurality of first surface contacts, for example, formed as solder bumps, and the second die connection interface 32 may include a plurality of second surface contacts, for example, formed as solder bumps. In some embodiments, each first surface contact of the first die connection interface 31 is connected to a corresponding second surface contact of the second die connection interface 32 via an element-to-element electrical interconnection path. For clarity, only the element-to-element electrical interconnection paths connecting the first and second die connection interfaces are depicted. According to some embodiments, which may be combined with other embodiments described herein, a first surface contact can be connected to one second surface contact. Alternatively, a first surface contact can be connected to two or more second surface contacts. For example, after applying a charge to the first surface contact, the two or more second surface contacts can be probed with an electron beam. According to the testing method described herein, a charged electron beam 111 is directed (specifically, focused) onto a first surface contact of a first die-connect interface 31, and a charged electron beam 111 is directed (specifically, focused) onto an associated second surface contact of a second die-connect interface 32. Signal electrons emitted from the second surface contact are detected to test for an "open" defect in the electrical interconnection path connecting the first and second surface contacts. Subsequently, additional surface contacts of the first and second die-connect interfaces can be tested, particularly in pairs. Additionally or alternatively, a test can be performed in parallel or subsequently to determine whether charging of one component-to-component electrical interconnect path causes charging of a surface contact point of another component-to-component electrical interconnect path, thereby determining a "short" defect. For example, an electron beam can be raster-scanned across a portion of a package substrate to generate an image of that portion of the package substrate. The image can be evaluated, for example, by pattern recognition. The package substrate 10 depicted in FIG. 6A has surface contacts on both major surfaces of the package substrate. For example, a first plurality of component-to-component electrical interconnection paths may extend between first and second surface contacts exposed on the upper substrate surface, and a second plurality of component-to-component electrical interconnection paths may extend between first and second surface contacts exposed on the lower substrate surface. The dashed box exemplarily illustrates a wafer or the like mounted on top of the package substrate after substrate testing is complete. The package substrate 10 depicted in FIG. 6B has at least one component-to-component electrical interconnection path extending between at least three surface contacts 25 (ie, a first surface contact, a second surface contact, and at least a third surface contact). The package substrate 10 depicted in FIG6C has at least one component-to-component electrical interconnection path extending between at least three surface contacts 25 exposed on different major surfaces of the substrate in a complex connection network. This component-to-component electrical interconnection path can be configured to interconnect three or more dies through the package substrate. The package substrate 10 depicted in FIG6D has at least one interconnect bridge 29 embedded therein. At least one component-to-component electrical interconnection path extends through the at least one interconnect bridge 29. Specifically, a plurality of component-to-component electrical interconnection paths extending between a first die connection interface and a second die connection interface of the package substrate extend through the interconnect bridge. The interconnect bridge can be embedded in the package substrate during its manufacture. The interconnect bridge can be a bridge wafer embedded in the package substrate to increase the connection speed between multiple dies. According to some embodiments, which can be combined with other embodiments described herein, the testing methods and / or apparatus according to the present disclosure can be utilized during and / or after the manufacturing of a package substrate. For example, testing can be applied to a package substrate that does not yet include all layers or structures. For example, testing can be performed after the fabrication of a redistribution layer (RDL) and / or a via layer. RDL testing and / or via testing can be provided. Furthermore, testing can be provided for a finished package substrate. Testing can be provided by charging (writing) one or more parts (such as surface contacts) and detecting the charge on the package substrate by means of signal electrons (reading). The number of electrons emitted from the surface of the package substrate by each irradiating electron (i.e., the total electron yield) depends on the energy. For a total electron yield of 1, the number of electrons reaching the surface of the package substrate is the same as the number of signal electrons emitted or scattered from the surface of the package substrate. There are two neutral energy values, a first neutral energy value and a second neutral energy value, whose total electron yield is equal to 1, i.e., no charge. According to some embodiments that can be combined with other embodiments described herein, the surface of the package substrate can be read by an electron beam having one of the neutral energy values, i.e., detecting signal electrons. According to some embodiments, which can be combined with other embodiments described herein, directing an electron beam having a first landing energy onto a portion of a package substrate can be a charging operation. The charging operation "writes" charge into an electrical interconnect or a network of electrical interconnects. Furthermore, directing an electron beam having a second landing energy onto a portion of the package substrate can be an operation for detecting signal electrons. The electron beam at the second landing energy can "read" the charge of the electrical interconnect or the network of electrical interconnects. According to some embodiments, which can be combined with other embodiments described herein, charging of portions of a package substrate is reduced or avoided during detection of signal electrons, i.e., during charge reading. In particular, the influence of the charge of an electrical interconnection path or a network of electrical interconnections is avoided or minimized when detecting signal electrons, e.g., detecting previously provided charge. For example, an electrical interconnection network may include five surface contacts (or any number greater than two). Charge can be applied (i.e., "written") to the first surface contact. The applied charge can be "read" from the electrical interconnection network at the second surface contact. When "reading" the charge at the second through fifth surface contacts, it is advantageous to leave the charge of the electrical interconnection network having five surface contacts unchanged. Therefore, during the detection of signal electrons, the neutral energy value of the landing energy can be utilized to reduce or prevent charge generation. The neutral energy value depends on the material. The material of the packaging substrate or the material of the packaging substrate surface is known, and the landing energy can be adapted to the packaging substrate material to suit the method of testing the packaging substrate. The first neutral energy value can be several hundred eV. For a typical packaging substrate or a typical surface contact point on the packaging substrate, the second neutral energy value can be between 1.5 keV and 2.5 keV. According to some embodiments, which can be combined with other embodiments described herein, the landing energy used for the testing method can be selected to be higher than the second neutral energy value, between the first and second neutral energy values, or lower than the first neutral energy value. The landing energy can be adapted depending on the test strategy, the material of the packaging substrate and / or the material of the surface contact point. For landing energies below the first neutral energy value, negative charging occurs, meaning the total electron yield is less than 1. For landing energies between the first and second neutral energy values, positive charging occurs, meaning the total electron yield is greater than 1. A total electron yield greater than 1 indicates that more electrons leave the surface than impact the surface. Therefore, the package substrate or structure is positively charged. For landing energies above the second neutral energy value, negative charging occurs, meaning the total electron yield is less than 1. A total electron yield less than 1 indicates that fewer electrons leave the surface than impact the surface. Therefore, the package substrate or structure is negatively charged. According to embodiments of the present disclosure, test structures (e.g., regions of a packaging substrate and / or surface contacts) can be charged positively or negatively by electron beam impact. Depending on the primary energy level (i.e., the landing energy), the total electron yield can be controlled relative to the secondary electron yield. The potential at the test point can be determined. The voltage comparison principle can be used for defect detection. Furthermore, sample parameter monitoring (such as capacitance and resistance) can be provided. According to some embodiments, which can be combined with other embodiments described herein, the landing energy can be changed to be higher or lower than the second neutral energy value. The landing energy of the electron beam is set to a predetermined landing energy and positioned on a portion of the packaging substrate, such as a surface contact or test point on the packaging substrate. The electron beam resides on the portion of the packaging substrate for a defined time to charge the portion of the packaging substrate positively or negatively relative to the surroundings of the portion of the packaging substrate. For example, the surroundings of the surface contact to be tested can be one or more adjacent surface contacts. The packaging substrate described herein may be a panel-level packaging substrate or an advanced packaging substrate. As illustrated in FIG. 7 , a method may be provided using an electron beam column and includes (see operation 501 ) placing the packaging substrate on a stage in a vacuum chamber. At operation 502 , one or more nets on the packaging substrate are tested within the vacuum chamber using at least one electron beam column. At operation 503 , while testing the one or more nets, the one or more nets are discharged. In particular, the one or more nets are discharged in parallel with the testing of the one or more nets. A trailing or continuous discharge may be provided. The discharge may be an active discharge, for example, including an operation of providing a charge adjacent to the substrate. Embodiments of the present disclosure provide one or more of the following advantages. In a sequential net test sequence, after reaching the maximum V*t limit, each net needs to be discharged once, resulting in many discharge cycles and slowing the test pace. "Tail discharge" according to embodiments of the present disclosure involves continuously discharging the nets in parallel with the test sequence, saving time and accelerating test throughput. Instead of completely discharging the substrate by, for example, performing a VUV flash on all nets, a "tail" discharge or continuous discharge can be used. This saves time in the discharge operation, thereby accelerating test time. A constant product, V*t, of the test voltage V and the test voltage hold time can be applied to the nets. This provides the same electrical stress, the same failure probability, and the same aging effects (bathtub curve). The product, V*t, can be set to an optimal value to capture early failure rates without increasing the wear-out failure rate. For similar nets, the product, V*t, can be advantageously selected, for example, to be optimal and constant. For testing, at least one electron beam of at least one electron beam column is directed onto at least a first portion of a package substrate, and at least one electron beam of at least one electron beam column is directed onto at least a second portion of the package substrate. Signal electrons emitted upon impact of the at least one electron beam are detected to test a first component-to-component electrical interconnect path of the package substrate. According to some embodiments, which can be combined with other embodiments described herein, at least one electron beam can be directed onto at least a first portion at a first landing energy and onto at least a second portion at a second landing energy different from the first charging landing energy. For example, when the at least one electron beam strikes the package substrate at the second landing energy to read the charge on the package substrate, signal electrons can be detected. For example, the second landing energy can be equal to or close to a neutral energy value. For example, the read landing energy can deviate by less than ±10% from the neutral energy value, which corresponds to a landing energy that results in a total electron yield of 1. According to some embodiments, which can be combined with other embodiments described herein, at least one electron beam can be focused when directed toward at least a first portion of a package substrate and at least a second portion of the package substrate. According to further modifications, which can be combined with embodiments of the present disclosure, the electron beam is scanned to one or more locations on the package substrate to charge and detect signal electrons. Furthermore, the method can additionally or alternatively include energy filtering the signal electrons. Embodiments of the present disclosure provide one or more of the following additional advantages. Non-contact electrical testing of the package substrates disclosed herein can be provided, wherein charge can be controlled for electrical defect detection. Given the flexibility of the electron beam, test speed can be increased. During mass production, testing can be performed that includes 100% of the electrical interconnect paths. Furthermore, the flexibility of the electron beam allows for testing and flexible setup for different AP / PLP substrate layouts. The test methods and apparatus disclosed herein are independent of the test feature size and further allow for scaling to smaller sizes, particularly as technology development moves towards smaller structure sizes. The testing of the package substrate is non-destructive. While the foregoing is directed to certain embodiments, other and further embodiments may be devised without departing from the basic scope thereof, and the scope of the same is determined by the following claims. 10: Package substrate 20: Component-to-component electrical interconnection path 21: First surface contact point 22: Second surface contact point 23: Second component-to-component electrical interconnection path 24: Third component-to-component electrical interconnection path 25: At least three surface contacts 27: Further contact point 29: Interconnection bridge 31: First die connection interface 32: Second die connection interface 100: Apparatus 105: Stage 106: Power supply 110: Vacuum chamber 111: Charged electron beam 112: Electron beam 113: Signal electrons 120: Charged particle beam column 121: Electron source 122: Scanning deflector 123: Scanning controller 124: Objective lens 130: Power supply 140: Electron detector 141: Analysis unit 142: Energy filter 146: First plurality of electrodes 148: Second plurality of electrodes 151: Open circuit 152: Ion source 153: Gap 154: Electrode 155: Short circuit 180: Controller 301: First die 302: Second die 310: Bathtub curve 312: Dashed line 314: Dashed line 501: Operation 502: Operation 503: Operation R: Failure rate t: Test voltage hold time V: Test voltage X: Direction Y: Direction Z: Direction In order to understand in detail how the above features of the present disclosure are used, a more detailed description of the present disclosure, which has been briefly summarized above, can be made with reference to the embodiments. The accompanying drawings relate to the embodiments of the present disclosure and are described below: FIG1 shows a schematic cross-sectional view of an apparatus for testing a package substrate according to any of the testing methods described herein; FIG2A shows a graph illustrating charging of a network or a test point within a network over time according to a known discharge scheme; FIG2B shows a graph illustrating charging of one or more networks or one or more test points within one or more networks over time according to an embodiment of the present disclosure; FIG3 illustrates a bathtub distribution showing failure rates over time; 4A and 4B illustrate enlarged cross-sectional views of a package substrate during any of the testing methods described herein; FIG5 illustrates an enlarged top view of a package substrate during any of the testing methods described herein; 6A through 6D illustrate enlarged cross-sectional views of package substrates that may be tested according to the methods described herein; and FIG. 7 shows a flow chart of a method for testing a package substrate according to embodiments described herein. 10:Packaging substrate 20: Component to component electrical interconnection path 21: First surface contact point 22: Second surface contact point 23: Second component to component electrical interconnection path 27: Further contact points 100: Device 105: Taiwan 106: Power supply 110: Vacuum chamber 111: Charged electron beam 113:Signal Electronics 120: Charged particle beam column 121:Electron Source 122: Scanning deflector 123: Scan Controller 124: Objective lens 130: Power supply 140:Electronic Detector 141:Analysis Unit 142:Energy Filter 146: first plurality of electrodes 148: Second plurality of electrodes 152: ion source 153: Gap 154: Electrode 180:Controller

Claims

1. A method for testing a packaged substrate (10) by means of at least one electron beam post, the method comprising the steps of: placing the packaged substrate (10) on a stand (105) in a vacuum chamber (110); testing one or more networks on the packaged substrate in the vacuum chamber by means of at least one electron beam post; and discharging the one or more networks while testing the one or more networks.

2. The method for testing a packaged substrate (10) by means of at least one electron beam post as described in claim 1, wherein the discharge step is an active discharge.

3. The method for testing a package substrate (10) by means of at least one electron beam column as described in claim 1, wherein the discharge step comprises the step of providing charge adjacent to the package substrate.

4. The method for testing a packaged substrate (10) by means of at least one electron beam column as described in claim 1, further comprising the steps of: providing a predetermined test voltage and a predetermined test voltage holding time; and controlling a density of at least one of positive ions and negative charges based on the predetermined test voltage and the predetermined test voltage holding time.

5. The method for testing a packaged substrate (10) by means of at least one electron beam post as described in claim 4, further comprising the step of: controlling at least one of an electron beam energy and an electric field based on the predetermined test voltage.

6. The method for testing a packaged substrate (10) by means of at least one electron beam column as described in any one of claims 4 to 5, further comprising the step of: maintaining the density of at least one of the positive ions and the negative charges at a constant level during one or more first test sequences.

7. The method for testing a packaged substrate (10) by means of at least one electron beam column as described in claim 6, further comprising the step of: changing the density of at least one of the positive ions and the negative charges of one or more second test sequences different from the one or more first test sequences.

8. The method for testing a packaged substrate (10) by means of at least one electron beam column as described in any one of claims 4 to 5, further comprising the step of: changing the density of at least one of the positive ions and the negative charges from one test sequence to a subsequent test sequence.

9. A method for testing a package substrate (10) by means of at least one electron beam column as claimed in any one of claims 1 to 5, wherein the discharge comprises the steps of: providing at least one of positive ions and negative charges in at least a portion of the vacuum chamber while testing the package substrate; and generating an electric field between one or more electrodes and the package substrate while testing the package substrate, the electric field being configured to accelerate the positive ions or the negative charges toward the package substrate.

10. The method for testing a packaged substrate (10) by means of at least one electron beam column as claimed in claim 9, wherein the step of providing at least one of positive ions and negative charges comprises the following steps: filling the vacuum chamber with at least one of positive ions and negative charges by means of an ion source provided at least partially in the vacuum chamber or an ion source connected to the vacuum chamber.

11. The method for testing a packaged substrate (10) by means of at least one electron beam column as described in claim 10, wherein the ion source is selected from the group consisting of: an ion source having a gas supply, a VUV source, and a spark generating unit.

12. The method for testing a package substrate (10) by means of at least one electron beam column as claimed in claim 9, wherein the electric field is uniform at a surface of the package substrate, or wherein the electric field is uniform between the surface of the package substrate and the one or more electrodes.

13. The method for testing a package substrate (10) by means of at least one electron beam column as described in claim 9, wherein a gap is provided between the one or more electrodes and the package substrate.

14. The method for testing a package substrate (10) by means of at least one electron beam post as described in any one of claims 1 to 5, wherein a gap is provided between the at least one electron beam post and the package substrate.

15. A method for testing a package substrate (10) by means of at least one electron beam post as claimed in any one of claims 1 to 5, wherein the testing of the package substrate comprises the following steps: directing at least one electron beam of the at least one electron beam post to at least one first portion of the package substrate; directing the at least one electron beam of the at least one electron beam post to at least one second portion of the package substrate; and detecting signal electrons emitted when the at least one electron beam strikes, to test a first element-to-element electrical interconnection path of the package substrate.

16. The method for testing a package substrate (10) by means of at least one electron beam column as described in claim 15, wherein the at least one electron beam is directed to at least the first portion with a first landing energy and to at least the second portion with a second landing energy different from the first landing energy.

17. The method for testing a package substrate (10) by means of at least one electron beam column as claimed in claim 16, wherein the signal electrons are detected when the at least one electron beam strikes the package substrate with the second landing energy to read a charge on the package substrate.

18. An apparatus for testing a package substrate according to the method of any one of claims 1 to 5.

19. An apparatus (100) for testing a packaged substrate (10), comprising: a vacuum chamber (110); a table (105) configured to support the packaged substrate within the vacuum chamber; a charged particle beam column (120) configured to generate an electron beam, the charged particle beam column comprising: an objective lens (124) configured to focus the electron beam onto the packaged substrate; a scanner configured to scan the electron beam to different positions on the packaged substrate; and an electron detector (140) for detecting signal electrons (113) emitted when the electron beam strikes the packaged substrate; the apparatus further comprising: an ion source for providing at least one of positive ions and negative charges into at least a portion of the vacuum chamber; and one or more electrodes configured to generate an electric field between the one or more electrodes and the packaged substrate, the electric field being configured to accelerate the positive ions or negative charges toward the packaged substrate. A controller configured to control the density of at least one of positive ions and negative charges in the vacuum chamber during testing; and an analysis unit (141) for determining, based on the signal electronics (113), whether a first element-to-element electrical interconnection path (20) is defective.

20. The apparatus (100) for testing a packaged substrate (10) as described in claim 19, wherein the one or more electrodes are provided in the charged particle beam column.

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