Package carrier with large core lead with lead end inspection feature

Abstract

A carrier for a leadless package wherein the carrier comprises: a component mounting structure for mounting an electronic component on the component mounting structure; and a plurality of leads disposed around at least a portion of the component mounting structure, where a corner lead of the leads is closer to at least one corner of the component mounting structure than an intermediate lead of the leads, the intermediate lead is farther from the at least one corner than the corner lead, where the intermediate lead is located between the at least one corner and the corner lead. The corner leads have a greater width along respective edges of the component mounting structure than the smaller width of the intermediate lead, and wherein at least the corner leads include a lead end inspection feature.

Description

Technical Field

[0001] Various embodiments generally relate to a carrier for a leadless package, a leadless package, and an electronic device. Background Art

[0002] A package may refer to an encapsulated electronic component with electrical connections extending out of the encapsulation material. For example, a package may be connected to peripheral electronic devices, such as mounted on a printed circuit board, and may be connected to a larger system via a connector.

[0003] In order to test the manufactured package after such package is mounted on a mounting base such as a printed circuit board (PCB), the package on the mounting base can be subjected to repeated temperature cycles to simulate the thermal load applied during operation of the package. The temperature cycle test can be performed under predetermined maximum and minimum temperature conditions and in an air-to-air environment. Summary of the invention

[0004] A package that is thermo-mechanically robust may be required, especially with respect to thermal cycling.

[0005] According to an exemplary embodiment, a carrier for a leadless package is provided, wherein the carrier includes: a component mounting structure for mounting an electronic component on the component mounting structure; and a plurality of leads arranged around at least a portion of the component mounting structure, wherein a corner lead of the lead is closer to at least one corner of the component mounting structure than a middle lead of the lead, and the middle lead is farther away from the at least one corner than the corner lead, wherein the corner leads have a larger width along a corresponding edge of the component mounting structure compared to a smaller width of the middle lead, and wherein at least the corner leads include a lead end inspection feature.

[0006] According to another exemplary embodiment, a leadless package is provided, comprising: a carrier having the above-mentioned features; an electronic component mounted on a component mounting structure; and an encapsulation material encapsulating at least a portion of the electronic component, at least a portion of the component mounting structure, and only a portion of the lead.

[0007] According to another exemplary embodiment, an electronic device is provided, which includes a mounting base (eg, a printed circuit board) and a package body having the above features mounted on the mounting base.

[0008] According to an exemplary embodiment, a carrier for a leadless package is provided, which has excellent characteristics in terms of thermomechanical reliability during thermal cycle testing and / or more generally under thermal load. Such a leadless package may include a component mounting structure such as a die pad, on which an electronic component such as a semiconductor chip may be mounted. Partially or completely around the component mounting structure, a plurality of leads may be arranged, which can be used to electrically connect the electronic component to a peripheral electronic device when the electronic component is mounted on the component mounting structure and encapsulated by an encapsulation material such as a molding compound. It has been found that in many cases, solder fatigue failures due to thermal load first occur at the so-called corner leads, i.e., a subset of the leads located near the corners of, for example, a polygonal component mounting structure. Advantageously, according to an exemplary embodiment, two measures are taken to improve the second-level thermal cycle on board (TCoB) test performance or second-level reliability of a package using the above-mentioned carrier. The first measure is to selectively expand the width of the corner pad, while the width of the remaining intermediate leads can be kept small, i.e., less than the adapted width of the corner pad. The intermediate lead may be a lead arranged along the edge of the component mounting structure, for example, between the corner leads, which may be arranged closest to different corners of the component mounting structure. It has been found that by extending the width of the corner leads, second-level solder fatigue failures at the corner leads can be strongly suppressed. At the same time, keeping the intermediate leads smaller than the spatially extended corner leads can ensure that no or at least no significant reduction in the pitch of the lead arrangement structure occurs, which ensures compliance with the specifications of many package applications. Keeping the width of the intermediate leads intact can keep the package size in a small form factor. If the intermediate leads are also enlarged, the pitch may need to be changed to a smaller value so that all leads can still be placed in a defined package. It has been found that the second measure that cooperates with the first measure to achieve excellent second-level solder joint thermal cycle on board (TCoB) test performance is to provide a lead end inspection (LTI) feature for at least a portion of the outer side wall of at least the corner lead. Descriptively speaking, such LTI features of the outer side wall or side wall portion of the corner lead can ensure that the solder fillet wets the LTI feature at the side wall. This may allow a reliable and simple optical inspection of a successful soldering process and may also contribute significantly to enhancing the second-level solder reliability robustness of the entire package. Simulation results show that the combination of the above two measures may improve thermal cycling failure robustness. Thus, the described carrier configuration may obtain a package with excellent second-level solder joint thermal cycling on board (TCoB) test performance, in particular during thermal cycling tests. At the same time, the two measures mentioned may be implemented very easily in the manufacturing process and do not involve significant additional effort.

[0009] Description of Further Exemplary Embodiments

[0010] In the following, further exemplary embodiments of a carrier, a package and an electronic device will be explained.

[0011] In the context of the present application, the term "carrier" may particularly refer to a support structure that serves as a mechanical support for one or more electronic components to be mounted thereon. In other words, the carrier may implement a mechanical support function. Additionally or alternatively, the carrier may also implement an electrical connection function. For this purpose, at least a portion of the carrier may be electrically conductive. The carrier may include or consist of a single component, a plurality of components bonded via encapsulation materials or other package components, or a subassembly of a carrier section. The carrier may also help to remove heat from the electronic components and diffuse out of the package to promote heat dissipation. For example, a metal carrier comprising or consisting of copper and / or aluminum may have a high thermal conductivity and may therefore be excellent in terms of its thermal capacity. A sufficiently high thermal capacity of the carrier may also be advantageous. For example, the carrier may form a part of a lead frame structure.

[0012] In the context of the present application, the term "package" may particularly denote an electronic component that may include one or more electronic components mounted on one or more carriers, wherein the at least one carrier includes or consists of a single component, a plurality of components joined via an encapsulation material or other package components, or a subassembly of the carrier. The components of the package may be at least partially encapsulated by the encapsulation material, wherein the leads may be partially exposed.

[0013] In the context of the present application, the term "leadless package" may particularly refer to a package that is configured without elongated lead legs extending out of the encapsulation material. In contrast, the leads of the leadless package may be completely encapsulated by the encapsulation material, except for the metal surfaces of the leads that are flush or substantially flush with the outer encapsulation material surface and do not significantly protrude beyond the outer encapsulation material surface. More specifically, the leads of the leadless package may be exposed outside the encapsulation material only at the bottom main surface of the encapsulation material and the sidewalls of the encapsulation material, but without circumferentially exposed lead legs extending out of the encapsulation material.

[0014] In the context of the present application, the term "component mounting structure" may particularly denote an at least partially conductive structure, which is used as a support structure for electronic components to be mounted thereon. For example, the electronic components may be mounted on the component mounting structure by welding, sintering or gluing. When the component mounting structure is at least partially conductive, it may also provide an electrical coupling function of the electronic components with peripheral electronic devices. For example, the component mounting structure may be a die pad for carrying a semiconductor die, in particular when the carrier is implemented as a patterned metal plate or a lead frame structure. For example, the component mounting structure may have a polygonal shape, in particular a rectangular shape. Optionally, one or more corners of the polygonal component mounting structure may be rounded, provided with an extension, etc.

[0015] In the context of the present application, the term "electronic component" may include in particular semiconductor chips (in particular power semiconductor chips), active electronic devices (such as transistors), passive electronic devices (such as capacitors or inductors or ohmic resistors), sensors (such as microphones, light sensors or gas sensors), actuators (such as loudspeakers) and micro-electromechanical systems (MEMS). In particular, the electronic component may be a semiconductor chip having at least one integrated circuit element (such as a diode or a transistor) in its surface portion. The electronic component may be a bare die or may have been packaged or encapsulated. The semiconductor chip implemented according to the exemplary embodiment may be formed in particular with silicon technology, gallium nitride technology, silicon carbide technology, gallium oxide technology, etc. Particularly preferred may be one or more power semiconductor chips, chips made of wide bandgap semiconductors, etc.

[0016] In the context of the present application, the term “lead” may particularly denote an electrically conductive structure, which may be electrically coupled to an electronic component and / or a component mounting structure for enabling external access to the electronic component when the electronic component is encapsulated.

[0017] In the context of the present application, the term "corner leads" may particularly refer to a subset of leads that are arranged around at least a portion of the perimeter of a component mounting structure and are arranged directly adjacent to or closest to a corner of the component mounting structure. The corner leads may be arranged closer to the respective nearest corner of the component mounting structure than the intermediate leads.

[0018] In the context of the present application, the term "intermediate leads" may particularly denote a subset of leads that are not the leads closest to a corner of the component mounting structure but are further away from a corner of the component mounting structure than the corresponding corner leads.

[0019] In the context of the present application, the term "lead end inspection feature" may particularly denote any arrangement in and / or on the sidewall surface of a lead, which allows or promotes wetting of solder material on the sidewall surface when the corresponding sidewall portion having the lead end inspection feature is exposed outside the encapsulation material after encapsulation. For example, the lead end inspection feature may include a plated structure on the sidewall or a portion of the sidewall, wherein the material of the plated structure may be suitable for allowing wetting of the solder material on the plated structure. For example, such a plated structure may include tin. Additionally or alternatively, the lead end inspection feature may include at least one recess in the sidewall, which increases the surface area, which may also promote wetting of the molten solder material. Providing the plated structure in the sidewall recess may be a preferred option for the lead end inspection feature.

[0020] In the context of the present application, the term "encapsulation material" may particularly denote an electrically insulating and preferably thermally conductive material surrounding at least a portion of the electronic component and at least a portion of the carrier and a portion of one or more leads. For example, the encapsulation material may be a molding compound and may be manufactured, for example, by transfer molding. It is also possible that the encapsulation material is of gel type, which may be used for encapsulation by potting.

[0021] In the context of the present application, the term "electronic device" may particularly refer to a device having an electronic function, and the device having an electronic function may include a package having one or more electronic components mounted on an encapsulated carrier with exposed leads. The electronic device may have a mounting base carrying the package.

[0022] In the context of the present application, the term "mounting base" may particularly refer to a structure that is electrically and / or mechanically connected to the package. For example, such a mounting base may be a printed circuit board (PCB). The package may be surface mounted on the mounting base.

[0023] Although the corner leads may be closer to at least one corner of the component mounting structure than the center leads, the pitch may remain constant.

[0024] In one embodiment, the lead end inspection feature includes a plating structure, which is configured to be wetted by a solder structure and formed on at least a portion of a corresponding side wall of a corresponding one of at least the corner leads. In particular, the corresponding corner lead can have a vertical or inclined side wall. The side wall can be straight or curved, for example in a convex or concave manner. The plating structure, such as a plating layer, can be formed on a portion of the side wall or on the entire side wall. If the plating structure is formed on only a portion of the side wall of the corresponding corner lead, the plating structure can be formed on the bottom side portion of the lead. For example, 40% to 60% of the side wall surface can be covered by the plating structure. The plating structure can be made of the following material, which has the property of allowing the molten solder on the plating structure to be wetted. For example, for this purpose, the plating layer can include tin. When the package formed based on this carrier is solder-connected to the mounting base below it, the side wall or side wall portion of the corner lead can be covered by a solder material (e.g., a solder fillet). It has been found that such a solder fillet covering at least a portion of the exposed sidewalls of the corner leads or pads significantly improves the robustness of the package against failures when performing thermal cycling tests or more generally when exposing the package to thermal stresses.

[0025] In one embodiment, the lead end inspection feature includes a recess (e.g., at least partially covered by a plated structure) formed in at least a portion of a corresponding side wall of a corresponding one of at least the corner leads. Such a recess in the side wall of the corresponding corner lead may be, for example, an opening, a notch, an undercut, a blind hole, a cavity. A plurality of recesses may also be formed in the side wall. In short, the recess may increase the surface area of ​​the side wall, and thus may additionally promote the wetting of the solder material when the carrier-based package is soldered on the mounting base. Advantageously, a portion of the side wall of the corner lead having the recess may be covered with a plated structure that may be wetted by the solder material. In particular, the plated structure may be formed in the recess. It is also possible that the plated structure is formed in the recess and in another portion of the side wall separated from the recess. In addition, a plurality of recesses may be provided in the side wall. It has been found that the lead end inspection feature based on the recess of the corner lead may significantly improve the reliability of the corresponding package when subjected to thermal cycling testing. When the recess is covered by the plated structure, a fully plated LTI feature may be provided, which may ensure significant and reliable coverage of the solder fillet.

[0026] In one embodiment, the recess is formed in a corner region of the corresponding corner lead (e.g., as a pit or step), the corner region including a bottom portion of the side wall of the corresponding corner lead and a connecting portion of the bottom wall. It has also been found that forming a recess at the bottom end of the side wall extending into the corner of the corner lead and extending all the way to the bottom surface of the corner lead also provides an LTI feature, which significantly improves the robustness of the package against thermal loads or stresses. Preferably, such a recess is coated with a plating structure, such as a plating layer (e.g., including tin), which improves the wettability of the molten solder material. In addition to the corner side recess, a portion of the side wall of the corner lead may also be coated with a plating structure to further improve the wettability.

[0027] In one embodiment, the recess is formed in a central portion of the sidewall of the corresponding corner lead (e.g., as a pit or step). More specifically, one or more recesses may be formed in the middle of the sidewall of the corner lead for improving wettability of the molten solder material. Preferably, the recess in the sidewall may be combined with sidewall plating, wherein the plating material may be selected to wet the molten solder material.

[0028] Those skilled in the art will appreciate that the mentioned embodiments of the recess in the sidewalls of the corner leads are exemplary only and that many modifications are possible. In addition, additional or alternative other LTI features may be created at the sidewalls of the corner leads for improving robustness against thermal loads, particularly thermal cycling loads.

[0029] In one embodiment, each of the leads includes a plating structure, which is configured to be wetted by a solder structure and is at least formed on at least a portion of the bottom wall of the corresponding lead. The plating structure at the exposed bottom side of the lead (preferably corner leads and intermediate leads) may be preferred. This can make such a surface wetted by molten solder material, and thus can promote the bottom side of the lead exposed outside the encapsulation material of the package as one hand and the firm connection between the mounting base such as PCB as another hand. Therefore, when creating a solder connection between the package and the mounting base, the bottom side plating structure on the lead can promote reliable solder connection. Advantageously, a common plating structure can cover at least a portion and the bottom side of the side wall of the lead (particularly corner leads). This can simultaneously ensure reliable solder connection and high robustness for thermal load. In addition, this common plating structure can be formed in a common plating process, so it is very efficient.

[0030] In one embodiment, the middle lead includes a lead end inspection (LTI) feature. Therefore, not only the corner leads, but also the middle leads can optionally be provided with a lead end inspection feature. Although the middle leads are generally less prone to failure than the corner leads under thermal loads (e.g., thermal loads applied during a thermal cycling process), forming LTI features on the side walls of the middle leads can further improve the thermal robustness of the lead. An embodiment of such an LTI feature on the side walls of the middle lead is a plating structure that enhances the wettability of the solder material and / or the recess. Reference is made to the above description of suitable LTI features for the corner leads, which also apply to the middle leads.

[0031] In one embodiment, the greater width of the corner lead is at least 1.1 times, such as at least 1.3 times, preferably at least 1.5 times, the smaller width of the middle lead. Fig.14 The simulation results of Table 1 show that with the mentioned ratios a significant improvement regarding the TCoB behavior can be achieved. By the mentioned selective increase of the corner lead width relative to the middle lead width a significant improvement in robustness against thermal load can be achieved. In one embodiment the mentioned factor may be no greater than 2 in order to avoid changes in the pitch or to avoid the need to adapt the specifications to significantly changed dimensions. However, in other embodiments the factor may even be greater than 2.

[0032] In one embodiment, the greater width of the corner leads is at least 0.37 mm and the lesser width of the middle leads is no greater than 0.33 mm. For example, the width of the corner leads may be at least 0.4 mm and the width of the middle leads may be no greater than 0.3 mm. This may allow for the production of miniature packages while providing efficient robustness against thermal loads.

[0033] In one embodiment, the carrier includes at least one anchoring extension, which is integrally formed with the component mounting structure and extends outward from at least one corner of the component mounting structure. Such an anchoring extension can be an additional measure for improving the performance of the package, which involves preventing failures caused by thermal cycles. Anchoring extensions, such as four anchoring extensions extending radially outward from each of the four corners of the rectangular component mounting structure, can provide strong protection against thermal loads. However, in other embodiments, only one, two, three or more than four anchoring extensions can be foreseen. In short, the anchoring extension can be anchored inside the encapsulation material (e.g., molding compound), and thus can offset mechanical loads that may be caused by CTE (coefficient of thermal expansion) mismatch between a printed circuit board and the package. The at least one anchoring extension is optional. If present, the first failure may occur at at least one anchoring extension that can be implemented as a dummy tie rod, thereby preventing early failures of functional corner leads and intermediate leads.

[0034] In one embodiment, at least one anchor extension may be provided with a lead end inspection (LTI) feature. For example, such an LTI feature may be a recess in the corresponding anchor extension and / or a plated structure on the corresponding anchor extension (preferably, a plated structure on the recess of the corresponding anchor extension) for promoting wetting of the surface of the corresponding anchor extension by molten solder. This may further improve the reliability of the package against second-level solder fatigue failures.

[0035] In one embodiment, the leads extend around the entire perimeter of the component mounting structure, wherein the corner leads are a subset of the leads arranged adjacent to all four corners of the component mounting structure, and the intermediate leads are arranged along the edges of the component mounting structure and are located between the corner leads. In such an embodiment, the rectangular component mounting structure can be completely circumferentially surrounded by leads, i.e., leads extending along each of the four edges of the rectangular or substantially rectangular component mounting structure. In such a package design, the corner leads are typically the weak point of the system in terms of second-level solder fatigue failures. However, when width extension is selectively applied to the corner leads in conjunction with the LTI feature, the robustness of the corresponding package against second-level solder fatigue failures can be significantly improved. At each of the four corners of the rectangular component mounting structure, two corner leads can be provided, which face two angled side walls near the diagonal position of the rectangular component mounting structure, preferably closer to the diagonal position than all the intermediate leads.

[0036] In one embodiment, the carrier is configured for use in a leadless package. In particular, as described above, the leads of such a carrier can be configured to meet the requirements of a leadless package.

[0037] For example, the carrier can be implemented as a lead frame structure. In the context of the present application, the term "lead frame" can particularly refer to a sheet metal structure that can be bent, stamped and / or patterned to form a lead frame body as a mounting section for mounting the chip and a connecting lead for electrically connecting the package to an electronic environment. In one embodiment, the lead frame can be a metal plate (particularly made of copper), which can be patterned, for example, by stamping. Forming the carrier as a lead frame structure is cost-effective and is a highly advantageous configuration mechanically and electrically, in which the low-ohmic connection of the chip can be combined with the solid support capacity of the lead frame. In addition, the lead frame can contribute to the thermal conductivity of the package, and can remove the heat generated during the operation of the chip due to the high thermal conductivity of the metal (particularly copper) material of the lead frame.

[0038] However, the carrier may also be a direct copper bonding (DCB) substrate or a direct aluminum bonding (DAB) substrate. Furthermore, the carrier may also be configured as an active metal brazing (AMB) substrate, or an insulated metal substrate (IMS).

[0039] In one embodiment, the carrier comprises or consists of a patterned metal plate. For example, a metal plate can be provided, which can be made of, for example, copper or aluminum. By patterning only such a plate (e.g., by stamping, punching, embossing, etching and / or wiring), the arrangement of the component mounting structure and the adjacent leads can be obtained with a lower workload. At the same time, the conductive properties of such a patterned metal plate can ensure that not only the leads but also the component mounting structure can contribute to the electrical connection inside the package.

[0040] In one embodiment of the package, at least a portion of the outer sidewalls of at least the corner leads are exposed outside the encapsulation material. When the sidewalls of the corner leads are exposed outside the encapsulation material of the package, the sidewalls of the corner leads may be covered by solder fillets during establishment of a solder connection between the package and a mounting base (e.g., a printed circuit board). Such solder fillets on the sidewalls of the leads may significantly improve the mechanical stability of the package and electronic device, and may serve as a reliable protection against thermal load-induced failures that may otherwise occur during thermal cycling.

[0041] In one embodiment, at least a portion of the outer sidewall of the middle lead is exposed outside the encapsulation material. By also exposing the sidewall of the middle lead after encapsulation with the encapsulation material, the lead end inspection feature of such sidewall can cause such sidewall to also be covered by the solder fillet. This can further increase the mechanical stability of the package and the electronic device.

[0042] In one embodiment, at least a portion of the bottom wall of the leads (more specifically the corner leads and / or the middle leads) is exposed outside the encapsulation material. Thus, the bottom wall of the corner leads may also be exposed outside the encapsulation material so that a solder connection may be established between such bottom wall and a pad of the mounting base. In addition, the bottom wall of the middle lead may also be exposed outside the encapsulation material for establishing a mechanical and electrical connection between the package and the mounting base, preferably by soldering.

[0043] In one embodiment, the electronic device includes a solder structure connecting the leads and / or component mounting structures to a mounting base (particularly a conductive pad of the mounting base). For example, the exposed conductive pads of a mounting base (e.g., a PCB) can be connected to the exposed bottom wall solder of a corner lead and / or an intermediate lead and / or a component mounting structure. This can create a mechanical and / or electrical connection between the exposed conductive pads and the exposed bottom wall of the corner lead and / or the intermediate lead and / or the component mounting structure. When the lead end inspection feature is provided (e.g., by a plating structure and / or surface increase measure, such as forming at least one recess), the molten solder will wet the corresponding surface of the lead. Forming a specific solder fillet on the exposed sidewalls of the corner leads and / or the exposed sidewalls of the intermediate leads can additionally enhance mechanical stability and robustness against heat-induced failures.

[0044] In one embodiment, a portion of the solder structure covers at least a portion of an outer sidewall of at least the corner lead, the at least a portion of the outer sidewall being exposed outside the encapsulation material. Such sidewalls covered by solder material can be a result of the LTI feature on the sidewalls of the corner lead, and optionally also the result of the LTI feature on the sidewalls of the intermediate lead.

[0045] In one embodiment, the package is configured as a power package. The power package can be a package that includes at least one power chip as an encapsulated electronic component. Therefore, the package can be configured as a power module, such as a molded power module such as a semiconductor power package. For example, an exemplary embodiment of the package can be an intelligent power module (IPM). Intelligent IPMs are also possible (including microcontrollers). The package can also provide connection features, such as WiFi, Bluetooth, etc. Another exemplary embodiment of the package is a dual in-line package (DIP).

[0046] Accordingly, the electronic component can be configured as a power semiconductor chip. Therefore, the electronic component (such as a semiconductor chip) can be used for power applications in, for example, the automotive field, and can, for example, have at least one integrated insulated gate bipolar transistor (IGBT) and / or at least one other type of transistor (such as MOSFET, JFET, HEMT, etc.) and / or at least one integrated diode. Such an integrated circuit element can be manufactured, for example, with silicon technology or based on wide bandgap semiconductors (such as silicon carbide, gallium nitride). The semiconductor power chip may include one or more field effect transistors, diodes, inverter circuits, half bridges, full bridges, drivers, logic circuits, other devices, etc. The advantages of the exemplary embodiment regarding enhanced thermal reliability can be significant for power bare chips.

[0047] A semiconductor substrate, such as a silicon substrate, may be used as a substrate or wafer for a semiconductor chip. Alternatively, a silicon oxide or another insulator substrate may be provided. A germanium substrate or a III-V semiconductor material may also be implemented. For example, exemplary embodiments may be implemented in GaN or SiC technology.

[0048] The above and other objects, features and advantages will become apparent from the following description and appended claims taken in conjunction with the accompanying drawings in which like parts or elements are designated by like reference numerals. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] The accompanying drawings, which are included to provide a further understanding of exemplary embodiments and constitute a part of this specification, illustrate exemplary embodiments.

[0050] In the attached picture:

[0051] Figure 1 Different views of a carrier for a leadless package are shown according to an exemplary embodiment.

[0052] Figure 2 A top view of a carrier for a leadless package is shown according to an exemplary embodiment.

[0053] Figure 3 A cross-sectional view of an electronic device according to an exemplary embodiment is shown.

[0054] Figure 4 Shown according to Figure 3 A top view of an electronic device.

[0055] Figure 5 Results of simulations are presented showing improved second level solder joint thermal cycle on board (TCoB) test performance of a package according to an exemplary embodiment compared to other approaches.

[0056] Figure 6A cross-sectional view of a portion of a leadless package showing a lead end inspection feature according to an exemplary embodiment is shown.

[0057] Figure 7 A cross-sectional view of a portion of a leadless package showing a lead end inspection feature according to another exemplary embodiment is shown.

[0058] Figure 8 Different views of an electronic device according to an exemplary embodiment are shown.

[0059] Fig. 9 A three-dimensional view of a lead with a lead end inspection feature according to an exemplary embodiment is shown.

[0060] Fig.10 Various views of a process for manufacturing a lead with a lead end inspection feature are shown according to an exemplary embodiment.

[0061] Fig.11 Various views of a process for manufacturing a lead with a lead end inspection feature are shown according to another exemplary embodiment.

[0062] Fig.12 A top view of a carrier with lead end inspection features for a leadless package is shown according to an exemplary embodiment.

[0063] Fig.13 A top view of a carrier with lead end inspection features for a leadless package is shown according to another exemplary embodiment.

[0064] Fig.14 Results of simulations are shown, which illustrate improved second level solder joint thermal cycle on board (TCoB) test performance of a package according to an exemplary embodiment. DETAILED DESCRIPTION

[0065] The illustrations in the drawings are schematic and not to scale.

[0066] Before the exemplary embodiments will be described in more detail with reference to the accompanying drawings, some general considerations will be outlined based on the exemplary embodiments that have been developed.

[0067] Leadless packages are attractive due to their relatively small size, low manufacturing cost, and excellent thermal and electrical properties. Especially for wide bandgap devices, leadless packages may be preferred due to low inductance. Exposed pads can also help improve electrical performance. However, leadless packages may have board-level issues, such as in solar applications. In particular, solder joint reliability under temperature cycle on board (TCoB) testing may be required. Therefore, it may be desirable to improve package board-level robustness and maintain small size and low manufacturing effort.

[0068] According to an exemplary embodiment, a (preferably metal) carrier for a leadless package, the leadless package, and an electronic device obtained by mounting the leadless package on a mounting base (e.g., a PCB) are provided. The carrier includes a component mounting structure (e.g., a bare die pad) for mounting an electronic component (e.g., a bare die) on the component mounting structure. The carrier may also include a plurality of (preferably metal) leads arranged around a portion of the component mounting structure or even the entire component mounting structure. The corner leads (or corner pads) of the leads may be closer to the corners of the component mounting structure than the middle leads (or middle pads) of the leads, and the middle leads (or middle pads) of the leads may be further away from the corresponding corners than the corner leads. In particular, the corner leads may be closest to the corners, while the middle leads may be further away from the corners or further away from the corners than the corner leads. The corner leads may have a larger width along the corresponding edges of the component mounting structure than the smaller widths of the middle leads along the corresponding edges of the component mounting structure. Furthermore, the corner leads may include a lead end inspection (LTI) feature. Advantageously, such a carrier architecture may provide significant solder joint reliability under temperature cycling on board (TCoB) testing. More specifically, significant improvements in the TCoB performance of a package, in particular a VQFN package (ultra-thin quad flat no-lead package), may be obtained by implementing the LTI feature in conjunction with wider corner leads or corner pin pads. The combination of LTI and wider corner pin pads has been shown to significantly improve the board-level robustness of a VQFN package. In summary, the simulation results confirm that the improvement may be obtained by a combination of the two measures mentioned, namely, spatially extended corner leads and their LTI feature, which may lead to excellent results.

[0069] More specifically, one exemplary embodiment proposes widening the corner leads or corner pin pads (e.g., from 0.3 mm to 0.4 mm) because it is believed that the corner pads are the most critical pads for solder joint fatigue failure. In addition, the LTI feature can be implemented for the corner leads, and preferably also for the smaller intermediate leads. This may result in the formation of solder fillets on the exposed side surfaces of the peripheral leads. Without wishing to be bound by a particular theory, it is currently believed that taking these measures can strongly help suppress undesirable phenomena related to the mismatch in the coefficient of thermal expansion (CTE) between the package material and the mounting base material (i.e., for example, the mismatch between the package and the PCB board). By doing so, simulation results show that this will improve the TCoB performance to become higher. This improvement is significant and very easy to achieve.

[0070] Thus, the exemplary embodiments provide a low-effort solution to provide a thermally robust package. This may be beneficial for many applications, including particularly solar applications. Furthermore, by providing a leadless package, space consumption on a PCB may be reduced compared to a leaded package. Thus, remaining small but more robust may be an advantage of the package according to the exemplary embodiments. Furthermore, the LTI feature at the corner leads may also help control solder joints on a PCB in an electronic device.

[0071] Figure 1 A schematic diagram of a leadless package (see FIG. Figure 3 Different views of a carrier 100 ) shown with reference numeral 102 in FIG.

[0072] The leadframe structure carrier 100 shown is configured to be used in forming a leadless package 102. The carrier 100 includes a central component mounting structure 104 for mounting an electronic component 106 thereon. In addition, the carrier 100 includes a plurality of leads 108, 110 arranged completely circumferentially around the periphery of the component mounting structure 104. Each corner lead 108 of the leads 108, 110 is closer to the corresponding next corner 112 of the component mounting structure 104 than the middle lead 110 of the leads 108, 110. Although Figure 1 The corner 112 of the component mounting structure is shown, but the corner of the entire package body 102 may be located further outward, for example, at the extrapolated intersection of the outer surfaces of the leads 108, 110 of the corresponding two rows of leads 108, 110 (see Figure 2The intermediate leads 110 are located farther or further from the next corner 112 than the corresponding corner leads 108. As shown, the corner leads 108 are a subset of the leads 108, 110 that are arranged adjacent to or closest to all four corners 112 of the component mounting structure 104. Accordingly, the intermediate leads 110 are located along the edge 114 of the component mounting structure 104 and between the corner leads 108. Figure 1 , four linear arrangements of leads 108, 110 are shown, wherein corner leads 108 are arranged at each end of the lead arrangements and intermediate leads 110 are located in the gaps between the outermost corner leads 108 of each lead arrangement.

[0073] While the exemplary embodiment involves a QFN type package 102 having leads 108 , 110 on all four sides of the package 102 , other embodiments encompass leadless packages 102 having leads 108 , 110 on only two adjacent sides or on two opposing sides so that there may be a smaller number of corner leads 108 .

[0074] As shown, the corner leads 108 have a larger width L along the corresponding edge 114 of the component mounting structure 104 than the smaller width l of the middle lead 110 along the corresponding edge 114 of the component mounting structure 104. The larger width L of the corner lead 108 is preferably at least 1.3 times the smaller width l of the middle lead 110. In particular, the larger width L of the corner lead 108 may be at least 0.37 mm (e.g., 0.4 mm), and the smaller width l of the middle lead 110 may be no greater than 0.33 mm (e.g., 0.3 mm).

[0075] Advantageously, each corner lead 108 and each intermediate lead 110 includes a lead end inspection (LTI) feature 116 , as will be described in further detail below.

[0076] in short, Figure 1 Embodiments of the present invention selectively enlarge the corner leads 108 or pads to strengthen the solder joints of the most critical connection structures. By adding LTI features 116 to the leads 108, 110, the bonding strength on the sidewalls 120 of the leads 108, 110 can be further improved. The corresponding solder fillets on the exposed side surfaces of the peripheral leads 108, 110 form structures (see Figure 1 The solder structure 134 in the embodiment helps to absorb the CTE mismatch.

[0077] In addition, the carrier 100 includes an anchor extension 124, one at each corner 112. The anchor extension 124 is integrally formed with the component mounting structure 104 and extends outwardly from the corner 112 of the component mounting structure 104. Figure 1 Although not shown, each anchor extension 124 may also be provided with an LTI feature. The anchor extensions 124, particularly when provided with an LTI feature, may also inhibit secondary solder fatigue failures.

[0078] More specifically, Figure 1 A carrier 100 of lead frame type is shown, for example made of a metal material such as copper or aluminum. Figure 1 In the bottom portion of the figure, a component mounting structure 104 is shown, which is implemented here as a die pad. As shown, the component mounting structure 104 has a substantially rectangular shape with four corners 112 and four edges 114. On the bottom main surface of the component mounting structure 104, a solder structure 150 is shown, which can be made flowable for establishing a connection with a mounting base (see Figure 3 On the top major surface of the component mounting structure 104, an additional conductive connection medium, such as additional solder material ( Figure 1 1 ), for establishing a connection with an electronic component 106 mounted on the component mounting structure 104. In the embodiment shown, the electronic component 106 may be a semiconductor chip, such as a semiconductor power chip.

[0079] Still reference Figure 1 , it can be seen that the plurality of leads 108, 110 are arranged around the entire perimeter of the component mounting structure 104, for example at a common vertical level. In other words, the component mounting structure 104 can be coplanar with the leads 108, 110. Alternatively, they can be arranged in different planes.

[0080] As already mentioned, two different types of leads 108, 110 are foreseen: The first type of leads are corner leads 108, which are located closest to the corners 112 of the component mounting structure 104. More specifically, two corner leads 108 are provided for each corner 112. Thus, two corner leads 108 are arranged along each edge 114 of the component mounting structure 104. The second type of leads are intermediate leads 110, which are located at a greater distance from the corresponding corner 112 than the adjacent corner leads 108. Along each edge 114 of the component mounting structure 104, one or more (two in the illustrated embodiment) intermediate leads 110 are arranged between two designated corner pads 108. Four straight rows of leads 108, 110 are provided along the four edges 114.

[0081] It is believed that the corner pads 108 are most critical to failure under excessive thermal load conditions, such as may occur during thermal cycling testing. More specifically, when based on Figure 1 When the carrier 100 forms a package body 102, Figure 1 The structure shown on the bottom side can be made of encapsulating material (see Figure 3 126 in the figure). When such a package 102 is soldered to a mounting base 132 such as a PCB, two bodies 132, 102 are connected, which can have very different coefficients of thermal expansion (CTE). This may result in a CTE mismatch. Under thermal load, the thermal expansion of the mounting base 132 can therefore be significantly different from the thermal expansion of the components of the package 102. Therefore, high mechanical loads may be applied. In unexpected situations, this may lead to failure of the package 102 or the entire electronic device 130.

[0082] Simulation results show that when both measures are taken in combination, the particularly critical corner leads 108 can be made significantly more robust against second-level solder fatigue failures. Figure 1 152 on the top side of the , which shows the corner lead 108 in more detail. The first measure is that the increase in the width L of the outer sidewall 120 of the corner lead 108 along the extended dimension of the specified edge 114 of the component mounting structure 104 can increase the robustness against second-level solder fatigue failures compared to the smaller width l of the outer sidewall of the middle lead 110 along the extended dimension of the specified edge 114 of the component mounting structure 104. Therefore, the first measure is to provide a width L of the corner lead 108 that is larger than the larger width l of the middle lead 110. For example, a suitable choice is L=0.4mm and l=0.3mm. Of course, the exact values ​​of L, l may depend on the specific application and will be appropriately selected by a person skilled in the art.

[0083] A second feature that significantly improves robustness against second level solder fatigue failures is the provision of end of lead inspection (LTI) features 116 at the vertical sidewalls 120 of the respective corner leads 108, and preferably also at the vertical sidewalls of the respective intermediate leads 110. In the illustrated embodiment, the formation of the end of lead inspection features 116 includes providing a plated structure 118 on the sidewalls 120 (at Figure 6 or Figure 7 As shown, the plated structure 118 may also extend to the bottom wall 128 of the corresponding lead 180, 110. The material of the plated structure 118 is selected to promote wetting of the sidewall 120 by the solder material of the solder structure 134 thereon. Suitable materials for such a plated structure are, for example, tin or an alloy containing tin. In addition, the formation of the LTI feature 116 may include forming one or more recesses 122 ( Figure 1 ), see for example Figure 6 or Figure 7 .

[0084] Surprisingly, it has been found that the combination of these two measures, namely, selectively extending the width of the corner leads 108 and providing the outer sidewalls 120 of the corner leads 108 (and optionally also the middle leads 110), can significantly improve the reliability against second level solder fatigue failures. The presence of the LTI feature 116 will make the solder fillet (see Figure 1 The solder structure 134 in the lead 108, 110 covers at least a portion of the sidewall 120 of the lead 108, 110, which will provide an anchoring effect and thereby prevent second-level solder fatigue failures. At the same time, the increase in width L compared to other widths l further enhances this effect. It has been surprisingly found that, in particular, the combination of these two measures provides a synergistic effect in improving the robustness against second-level solder fatigue failures.

[0085] Likewise Figure 1 As shown, the already mentioned anchor extensions 124 extend radially outwardly from each of the four corners 112 of the component mounting structure 104. These anchor structures 124 have bar-shaped leg sections 154 and bifurcated end sections 156. This geometry provides additional improvement in robustness against secondary solder fatigue failures.

[0086] Figure 2 A top view of a carrier 100 for a leadless package 102 is shown according to an exemplary embodiment.

[0087] No additional process or effort is required to widen the corner leads 108 or corner pin pads for the etched leadframe type carrier 100. Substantially the same manufacturing process as conventional leadframes can be performed, only the dimensions need to be adjusted to ensure sufficient space for the wider corner leads 108 or corner pads.

[0088] The horizontal width D and vertical width d of the component mounting structure 104 are also shown. In addition, the pitch P between adjacent center leads 110 is also shown. In addition, the distance B between the centers of the corner pads 108 associated with the same edge 114 of the component mounting structure 104 is also shown. In the illustrated embodiment, d=B. Figure 2 It can be seen that the design of the leadframe-type carrier 100 has only been adapted in a minor manner in order to achieve the mentioned effects.

[0089] Figure 3 A cross-sectional view of an electronic device 130 is shown according to an exemplary embodiment. Figure 4 Shown according to Figure 3 A top view of the electronic device 130 is shown.

[0090] The electronic device 130 shown includes a mounting base 132, such as a printed circuit board (PCB) or an interposer. The leadless package 102 is mounted on the mounting base 132. A solder structure 134 is provided for connecting the corner leads 108 and the middle leads 110 (not shown) on the one hand, and the component mounting structure 104 to the metal pads (not shown) of the mounting base 132. Advantageously, a portion of the solder structure 134 covers a portion of the outer sidewall 120 of the corner lead 108 and a portion of the outer sidewall 120 of the middle lead 110 (see FIG. Figure 3 The portion of the outer side wall 120 is exposed outside the encapsulation material 126.

[0091] The leadless package 102 includes a carrier 100, which may be, for example, Figure 1 . An electronic component 106, such as a power semiconductor chip, may be mounted on the component mounting structure 104. An encapsulation material 126 (e.g., a molding compound) may encapsulate the electronic component 106, a portion of the component mounting structure 104, and a portion of the leads 108, 110. As shown, the corner leads 108 (and the middle leads 110, Figure 3 and Figure 4 A portion of the outer sidewall 120 of the lead 108, 110 (not shown) is exposed outside the encapsulation material 126. In addition, the bottom wall 128 of the lead 108, 110 is exposed outside the encapsulation material 126 to be connected to the mounting base 132 through the solder structure 134.

[0092] When there is no LTI feature on the sidewall 120 of the leads 108, 110 (see Figure 6 and Figure 7 In the case of the package 102 shown in FIG. 116 , the package 102 may perform free expansion due to the CTE mismatch between the package 102 and the PCB type mounting base 132. Then, the solder joint will be significantly affected by the fatigue shear load during the TCoB process.

[0093] Without wishing to be bound by a particular theory, it is currently believed that by providing the LTI features 116 at the sidewalls 120 of the leads 108, 110, the package expansion freedom can be reduced, so that the shear load on the interface between the leads 108, 110 and the solder structure 134 can be reduced. In addition, it has been found that the wider corner leads 108 or corner pins can provide much stronger support to resist package expansion. Therefore, in particular, the LTI features 116 (such as Figure 6 or Figure 7 ) and wider corner leads 108 (as shown Figure 1 The combination of the above-mentioned methods can increase the welding reliability during TCoB testing.

[0094] Figure 3 The cross-sectional view of the electronic device 130 shows the package 102 mounted on a PCB type mounting base 132 via solder connections. Figure 3 Also shown are solder structures 134 between the pads of the mounting base 132 and the exposed leads 108 (and 110 ) and the exposed component mounting structures 104 of the package body 102 .

[0095] Due to the different materials, the coefficient of thermal expansion of the mounting base 132 may be significantly different from the coefficient of thermal expansion of the package body 102. Therefore, different thermal expansion may occur during the thermal cycling process, which may cause thermal loads. However, by combining the selectively elongated corner leads 108 with the lead end verification features 116 on their sidewalls 120, a solder fillet of the solder structure 134 is obtained, which can significantly improve the robustness against second-level solder fatigue failures.

[0096] Figure 5 Results of simulations are shown, which illustrate improved second level solder joint thermal cycle on board (TCoB) test performance of the leadless package 102 according to an exemplary embodiment compared to other approaches. Figure 5The simulation results for a common design of a corner pad without LTI feature and L=1 (see reference numeral 170) are shown. As shown in reference numeral 172, improvements can be achieved by providing end of lead detection features for the corner leads as well as the middle leads, where L=1 is maintained. As shown in reference numeral 174, a significant improvement can be achieved by combining the provision of end of lead detection features 116 and selective extension of the width of the corner leads 108 (i.e., L>1). This can be derived from the thermal load obtained by simulation, the results of which are shown in FIG. Figure 5 A high load is indicated by reference numeral 178 , while a low load is indicated by reference numeral 180 .

[0097] More specifically, Figure 5 Results of TCoB simulations involving the type of package shown. This package can be used, for example, in a solar microinverter where the TCoB performance needs to be evaluated. Simulations have been performed to estimate the risk of TCoB solder joint failure based on the TCoB predictive lifetime model. The simulations started at a stress-free temperature of 25°C. Three simulation cycles were performed in the temperature range of -40°C to +85°C. This corresponds to 1 hour per thermal cycle test. Figure 5 Simulation results on the damage assessment of solder joints, more specifically, the solder damage distribution under fatigue loading, are shown.

[0098] The creep strain energy density distribution of the solder joint damage parameter after three cycles is shown. The corner solder joint is considered to be critical and involves a high risk of failure. Based on the predictive life model, the first failure of the solder joint of the package may occur at about 3000 cycles (see reference numeral 170). Through the LTI feature, the critical solder joint damage can be made less (see reference numeral 172). The predicted first failure will only occur after 6166 cycles under -40℃ / +85℃ TCoB conditions. With the described LTI design, the solder joint reliability is higher than that of the solder joint without LTI design. The wider corner lead pin with LTI shows the highest solder joint reliability to date (see reference numeral 174). Simulation results show that the wider corner lead pin with 50% LTI sidewall coverage can meet the requirement of no first failure before 10,000 cycles.

[0099] Therefore, according to the simulation results, by combining LTI and wider corner lead pads, the TCoB of the VQFN package can be significantly improved without significantly increasing the workload.

[0100] Figure 6 A cross-sectional view of a portion of a leadless package 102 is shown in accordance with an exemplary embodiment.

[0101] according to Figure 6, the lead end inspection feature 116 includes a recess 122 formed in a portion of a corresponding side wall 120 of a corresponding corner lead 108. Figure 6 As shown, the recess 122 is formed in a corner region of the corresponding corner lead 108 , and the corner region includes a bottom portion of the side wall 120 of the corresponding corner lead 108 and a connecting portion of the bottom wall 128 .

[0102] As shown, in addition to the recess 122, the lead end inspection feature 116 also includes a plating structure 118 that is configured to be wetted by a solder structure 134 and is formed on a portion of the corresponding side wall 120 of the corner lead 108 as shown. In addition, another plating structure 118 that is configured to be wetted by the solder structure 134 is formed on the bottom wall 128 of the corner lead 108 as shown.

[0103] In particular, the illustrated embodiment shows that LTI and widened corner leads 108 are very easy to implement. There are several ways to enable LTI to achieve package sidewall wettability. In the illustrated embodiment, a step-cut method can be used to enable LTI for the corresponding package 102.

[0104] therefore, Figure 6 A corner lead 108 is shown having side walls 120 and a bottom wall 128, both of which are exposed to an encapsulation material 126 (e.g., a molding compound). A recess 122 formed in a corner region of the corner lead 108 that is exposed to the encapsulation material serves as a lead end inspection feature to improve second-level solder joint thermal cycle on board (TCoB) test performance. The lead end inspection feature 116 provided by the recess 122 in the corner region can be further enhanced by covering the recess 122 with a plating structure 118 that promotes solder material 134 ( Figure 6 In addition, the bottom wall 128 of the corner lead 108 is also covered by the plated structure 118, which improves the reliability of the solder connection between the corner lead 108 and the exposed pad of the mounting base 132.

[0105] Figure 7 A cross-sectional view of a portion of a leadless package 102 is shown according to another exemplary embodiment.

[0106] according to Figure 7 In the embodiment of the present invention, the recess 122 is formed in a central portion of the sidewall 120 of the corner lead 108 , ie, away from and above the corner region of the corner lead 108 .

[0107] Figure 7 Shown with Figure 6Similar view, but with a recess 122 disposed in the central portion of the vertical sidewall 120 of the exposed corner lead 108. When covered by the plated structure 118, such a central recess 122 can serve as a strong LTI feature 116, thereby improving the thermal reliability of the package 102, especially the thermal reliability of the corner lead 108 of the package 102.

[0108] Figure 8 1 shows different views of an electronic device 130 according to an exemplary embodiment. More specifically, Figure 8 An exploded view and an assembled view of the electronic device 130 are shown.

[0109] The electronic device 130 includes a PCB type mounting base 132, and the package body 102 is assembled on the PCB type mounting base 132. Figure 8 As shown in the bottom portion of , the sidewalls 120 of the leads 108, 110 are partially exposed and partially covered by the solder fillets of the solder structure 134. Therefore, high mechanical robustness and high robustness against second-order solder fatigue failures can be achieved. The exploded view of the components of the package 102 shows that on the top side is the molding compound forming the encapsulation material 126, and below is the electronic component 106 in the form of a semiconductor die. By means of the solder structure 182, the electronic component 106 can be solder-connected to the component mounting structure 104 of the carrier 100 shown below. The corner leads 108 of the carrier 102 can be provided with LTI features 116 and can be selectively elongated compared to the middle leads 110 between the corner leads 108. Figure 8 Also shown are various elements of solder structures 134 , 150 for connecting the leads 108 , 110 and the component mounting structure 104 to pads (not shown) of the mounting base 132 .

[0110] Fig. 9 A three-dimensional view of the leads 108 , 110 is shown, and the lead end inspection feature 116 is shown, according to an exemplary embodiment.

[0111] On the left side, Fig. 9 One embodiment of a lead end inspection feature 116 is shown in the form of a stepped cutout at the lead corner between the sidewalls 120 and the bottom wall 128 of the leads 108, 110. In this embodiment, the stepped cutout is formed as a recess 122 extending along the entire lead edge between the sidewalls 120 and the bottom wall 128. In addition, a portion of the stepped cutout and a portion of the bottom wall 128 are covered with the plated structure 118.

[0112] In the center plan, Fig. 9One embodiment of a lead end inspection feature 116 is shown in the form of a dimple-type recess 122 at the lead corner between the sidewalls 120 and bottom wall 122 of the leads 108, 110. Additionally, a portion of the bottom wall 128 and the dimple are covered with the plated structure 118.

[0113] on the right, Fig. 9 One embodiment of a lead end inspection feature 116 is shown in the form of a plated structure 118 on a side wall 120 and a portion of a bottom wall 122 of the leads 108, 110. Thus, no recess 122 is provided in this embodiment. Fig. 9 The right side of may involve full plating, where the entire sidewall of the metal lead 108, 110 may be plated.

[0114] Fig.10 Different views of a process of manufacturing leads 108 , 110 having lead end inspection features 116 are shown according to an exemplary embodiment.

[0115] As shown in the first step, the lead frame 197 constituting the preform of the leads 108, 110 is encapsulated in the encapsulation material 126 and subjected to a sawing process by a first blade 190. The first blade 190 saws to a portion (eg, half) of the lead frame depth.

[0116] As shown in the second step, deburring and electroplating are performed on the exposed copper surface to form a plated structure 118 .

[0117] As shown in the third step, a second sawing process is then performed using a second blade 191 that is narrower than the wider first blade 190 .

[0118] As shown in the fourth step, the leads 108 , 110 are accessed through a plated step that constitutes a lead end inspection feature 116 .

[0119] Fig.11 Different views of a process of manufacturing leads 108 , 110 having lead end inspection features 116 are shown according to another exemplary embodiment.

[0120] As shown in the first step, the lead frame 197 constituting the preform of the leads 108 , 110 is encapsulated in the encapsulation material 126 arranged on the dicing tape 193 , and is subjected to a sawing process by a blade 192 to be separated into different pieces.

[0121] As shown in a second step, the encapsulated leads 108 , 110 are subjected to chemical roughening and plating (eg, by electroless nickel immersion gold, ENIG) to form a plated structure 118 .

[0122] As shown in the third step, the dicing tape 193 may be removed and encapsulated leads 108 , 110 with plated structures 118 forming lead end verification features 116 on the sidewalls 120 are obtained.

[0123] Fig.12 A top view of a carrier 100 having a lead end inspection feature 116 for a package 102 is shown in accordance with an exemplary embodiment. Figure 2 In addition to the embodiments, Fig.12 Also shown is a lead end inspection feature 116, such as comprising a stepped corner of the respective lead 108, 110 (preferably in combination with a plated structure 118, in the Fig.12 (not visible in the image).

[0124] Fig.13 A top view of a carrier 100 having a lead end inspection feature 116 for a package 102 is shown according to another exemplary embodiment. Fig.12 In addition to the embodiments, Fig.13 Anchor extension 124 is also shown.

[0125] Fig.14 Results of simulations are shown, which illustrate improved second level solder joint thermal cycle on board (TCoB) test performance of the package 100 according to an exemplary embodiment.

[0126] In the simulation results shown (where, for simplicity, Fig.14 The width l of the middle lead 110 is kept at 0.3 mm, while the width L of the corner lead 108 varies in the range from 0.3 mm to 0.45 mm. The following Table 1 shows the simulation results:

[0127]

[0128] Table 1: Thermal Cycle on Board (TCoB) test performance of second-stage solder joints when the corner lead width is increased while the center lead width is unchanged

[0129] It can be seen from the simulation results in Table 1 that significant improvements can be achieved when increasing the width of the corner lead while keeping the width of the middle lead constant. The larger the width of the corner lead (first column), the larger the predicted number of cycles to first failure (second column), and the larger the TCoB performance percentage (third column) compared to the reference L=l=0.3mm. According to Table 1, the ratio or factor of the corner lead width to the middle lead width varies from 1 to 1.5. Table 1 shows the continuous improvement of the TCoB percentage. For example, a corner lead with a width of 0.375mm can improve TCoB by about 55% (i.e., 155.8%-100%), etc.

[0130] However, it should be said that Table 1 is only a simulation result. In actual production, differences may occur. Therefore, Table 1 should be interpreted only as a simulation result. In addition, the simulation result is only an embodiment for illustrating the effect of the combination of the above two measures, and should not be used to limit the interpretation of the embodiment to a specific number.

[0131] It should be noted that the term "comprising" does not exclude other elements or features, and "one" or "an" does not exclude a plurality. In addition, elements described in association with different embodiments may also be combined. It should also be noted that the reference numerals should not be interpreted as limiting the scope of the claims. In addition, the scope of the present application is not intended to be limited to the specific embodiments of the processes, machines, manufactures, material compositions, means, methods and steps described in the specification. Therefore, the appended claims are intended to include these processes, machines, manufactures, material compositions, means, methods or steps within their scope.

Claims

1. A carrier (100) for a leadless package (102), wherein: The carrier (100) comprises: A component mounting structure (104) for mounting an electronic component (106) on the component mounting structure (104); a plurality of leads (108, 110) arranged around at least a portion of the component mounting structure (104); wherein the corner lead (108) of the leads (108, 110) is larger than the lead (108, The middle lead (110) of the component mounting structure (104) is closer to at least one corner (112), and the middle lead (110) is farther away from the at least one corner (112) than the corner lead (108); The exposed surface area of ​​the sidewalls (120) of the corner leads (108) has a greater width (L) along the corresponding edge (114) of the component mounting structure (104) than the smaller width (L) of the exposed surface area of ​​the sidewalls (120) of the center leads (110); and At least an exposed surface area of ​​a sidewall (120) of the corner lead (108) includes a lead end inspection feature (116).

2. The carrier (100) according to claim 1, wherein: The lead end inspection feature (116) includes a plated structure (118) configured to be wettable by a solder structure (134) and formed on at least a portion of a respective sidewall (120) of at least a respective one of the corner leads (108).

3. The carrier (100) according to claim 1 or 2, wherein: The lead end inspection feature (116) includes a recess (122), such as at least partially covered by a plated structure (118), formed in at least a portion of a corresponding sidewall (120) of at least a corresponding one of the corner leads (108).

4. The carrier (100) according to claim 3, wherein: The recess (122) is formed in a corner region of the corresponding corner lead (108), for example as a pit or a step, and the corner region includes a bottom portion of a side wall (120) of the corresponding corner lead (108) and a connecting portion of the bottom wall (122).

5. The carrier (100) according to claim 3, wherein: The recess (122) is formed in a central portion of a side wall (120) of a corresponding corner lead (108), for example, as a pit or a step.

6. The carrier (100) according to any one of claims 1 to 5, wherein: Each of the leads (108, 110) includes a plated structure (118) configured to be wettable by a solder structure (134) and formed on a bottom wall (122) of the corresponding lead (108, 110).

7. The carrier (100) according to any one of claims 1 to 6, wherein: The intermediate lead (110) includes a lead end inspection feature (116).

8. The carrier (100) according to any one of claims 1 to 7, wherein: The larger width (L) of the exposed surface area of ​​the side wall (120) of the corner lead (108) is at least 1.1 times, for example at least 1.3 times, preferably at least 1.5 times, the smaller width (l) of the exposed surface area of ​​the side wall (120) of the middle lead (110).

9. The carrier (100) according to any one of claims 1 to 8, wherein: The greater width (L) of the exposed surface area of ​​the side wall (120) of the corner lead (108) is at least 0.37 mm, and the smaller width (l) of the exposed surface area of ​​the side wall (120) of the intermediate lead (110) is no greater than 0.33 mm.

10. The carrier (100) according to any one of claims 1 to 9, wherein: The carrier (100) includes at least one anchor extension (124) formed integrally with the component mounting structure (104) and extending outwardly from the at least one corner (112) of the component mounting structure (104).

11. The carrier (100) according to claim 10, wherein: The at least one anchor extension (124) is provided with a lead end inspection feature.

12. The carrier (100) according to any one of claims 1 to 11, wherein the leads (108, 110) extend around the entire periphery of the component mounting structure (104); ·in, The corner leads (108) are a subset of the leads (108, 110) disposed adjacent all four corners (112) of the component mounting structure (104), and the intermediate leads (110) are disposed along the edge (114) of the component mounting structure (104) and between the corner leads (108).

13. The carrier (100) according to any one of claims 1 to 12, wherein: The carrier (100) is configured for use in a leadless package (102).

14. A leadless package (102), comprising: The carrier (100) according to any one of claims 1 to 13; An electronic component (106) mounted on the component mounting structure (104); An encapsulating material (126) encapsulating at least a portion of the electronic component (106), at least a portion of the component mounting structure (104), and only a portion of the leads (108, 110).

15. The package (102) according to claim 14, wherein: At least a portion of an outer sidewall (120) of at least the corner lead (108) is exposed outside the encapsulation material (126).

16. The package (102) according to claim 14 or 15, wherein: At least a portion of the exposed outer sidewall (120) of the intermediate lead (110) is exposed outside the encapsulation material (126).

17. The package (102) according to any one of claims 14 to 16, wherein: The package (102) includes at least one of the following features: At least a portion of the bottom wall (128) of the lead (108, 110) is exposed outside the encapsulation material (126); The electronic component (106) is a semiconductor power chip; The package (102) is a power package.

18. An electronic device (130), comprising: A mounting base (132), such as a printed circuit board; as well as · The package (102) according to any one of claims 14 to 17, mounted on the mounting base (132).

19. The electronic device (130) according to claim 18, wherein: The electronic device (130) includes solder structures (134, 150) connecting the leads (108, 110) and / or the component mounting structure (104) to the mounting base (132).

20. The electronic device (130) according to claim 19, wherein: A portion of the solder structure (134) covers at least a portion of the exposed outer sidewall (120) of at least the corner lead (108), the at least a portion of the exposed outer sidewall (120) being exposed outside the encapsulation material (126).

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