A packaging method and applications thereof

Abstract

The application discloses a packaging method and application thereof, and belongs to the technical field of quantum computation. The packaging method for welding a chip and a substrate comprises the following steps: in the state that the chip is heated to ball melting and the substrate is not heated, the chip and the substrate are close to each other face to face so that at least the ball is in contact with the substrate; and cooling to weld the ball and the substrate. When the chip and the substrate are packaged by the above method, the problem of substrate warping can be avoided.

Description

Technical Field

[0001] This application belongs to the field of quantum information, especially the field of quantum computing technology. In particular, this application relates to a packaging method and its application. Background Technology

[0002] Ball Grid Array (BGA) packaging emerged in the early 1990s and was initially used primarily in memory chips to address the challenges of high pin counts and high-frequency requirements. As a high-density, high-reliability chip packaging technology, BGA packaging has significant implications for the development of the chip packaging field.

[0003] With the continuous development of integrated circuit technology, chip size is constantly decreasing. Thanks to its excellent thermal management and reliability, BGA packaging technology is widely used in high-performance fields such as mobile devices and communication equipment.

[0004] The traditional BGA packaging process typically includes:

[0005] The chip to be packaged is fixed on the substrate, and gold wires are used to lead out the pins from the chip. The pins are connected to external connectors and other components through the circuit on the substrate. Then, the chip and the substrate are connected by solder balls. Finally, the chip is sealed with plastic or other materials.

[0006] However, in practice, BGA-packaged chips are prone to warping. Summary of the Invention

[0007] The examples in this application provide a packaging method and its application, which can be used to achieve high-quality chip packaging, thereby forming high-quality (e.g., no substrate warping, no separation between substrate and chip) chip products.

[0008] The solution presented in this application is implemented through the following steps.

[0009] In a first aspect, examples of this application disclose a packaging method for welding a chip to a substrate.

[0010] The encapsulation method includes:

[0011] With the chip heated to the point where the balls melt, and without heating the substrate, the chip and the substrate are brought face to face so that at least the balls are in contact with the substrate;

[0012] In addition, cooling is performed to allow the balls to be soldered to the substrate.

[0013] According to some examples of this application, the packaging method further includes, before bringing the chip and substrate face to face, the following:

[0014] The substrate and the chip with the ball already implanted are positioned face to face, with a preset distance between the substrate and the chip, and the ball does not touch the substrate.

[0015] According to some examples of this application, methods for bringing a chip and a substrate face-to-face such that at least the ball contacts the substrate include:

[0016] Lay the substrate flat and move the chip relative to the substrate along the direction of gravity from a position away from the substrate to a position closer to the substrate.

[0017] According to some examples of this application, flux is formed on the entire surface of the substrate facing the chip;

[0018] Alternatively, flux may form in localized areas on the surfaces of the substrate and the chip that face each other.

[0019] According to some examples of this application, there are multiple local regions and multiple spheres on the chip surface, and each sphere corresponds to a local region.

[0020] According to some examples of this application, in a chip, the individual spheres are at the same height relative to the chip surface;

[0021] And / or, in the substrate, the height of each flux relative to the substrate surface is the same.

[0022] According to some examples of this application, methods for forming flux include: screen printing.

[0023] According to some examples of this application, screen printing controls the amount of flux adhered by the aperture of the mesh and the thickness of the screen.

[0024] According to some examples of this application, the cooling method is natural cooling; and / or, the method of heating the chip to the point of ball melting includes preheating, isothermal treatment, and reflow.

[0025] In a second aspect, examples of this application disclose the application of the aforementioned packaging method in the fabrication of superconducting quantum chips.

[0026] The packaging method described in this application heats the chip but not the substrate, melting the bonding balls on the chip surface that are used for bonding with the substrate. The molten bonding balls then contact the substrate and solidify during cooling to achieve bonding between the chip and the substrate. Because the substrate is not heated, it is less prone to warping (and consequently, less prone to chip and substrate separation), thus ensuring the stability and strength of the chip-substrate bonding. Attached Figure Description

[0027] To illustrate this more clearly, the accompanying drawings used in the description will be briefly introduced below.

[0028] Figure 1This is a schematic diagram of the structure in which the substrate warps when the chip and substrate are soldered by reflow soldering in the example of this application.

[0029] Figure 2 This is a schematic diagram of the process flow for the chip packaging method in the example of this application;

[0030] Figure 3 This is a schematic diagram of the process flow for another chip packaging method in this application example;

[0031] Figure 4 A schematic diagram showing the relative positions and states of the chip and substrate during the implementation of the packaging method of the present application example is shown. Detailed Implementation

[0032] The main characteristic of BGA packaging is the arrangement of a series of tiny solder balls on or around the bottom of the chip. These solder balls are used to connect the chip to pads on the printed circuit board (PCB).

[0033] A BGA package typically consists of the following components.

[0034] Chip: The integrated circuit chip is the core part of BGA packaging, which contains various electronic components and circuit structures.

[0035] Solder Ball: A solder ball is a tiny metal ball used to connect a chip to a PCB, and is typically made of a tin alloy. Solder balls on a chip are arranged in a regular grid array, with each ball connected to a pin on the chip. Creating solder balls on chip pins is commonly referred to as ball bonding, and can include solder paste printing ball bonding, ball bonding, laser ball bonding, etc.

[0036] Substrate: In BGA packaging, the substrate is the bottom structure used to support the chip and solder balls. The substrate is typically made of ceramic or plastic. Furthermore, a series of circuit layers are configured inside the substrate, depending on the specific needs, for transmitting electrical signals and power.

[0037] Pads: Pads are metal contacts on a PCB (PCB) that are soldered to the solder balls of chips. A layer of solder paste is typically applied to the pads to ensure reliable and complete soldering during the soldering process. The main component of solder paste is a tin alloy. Through heating and reflow soldering, the solder paste melts and solidifies to form uniform solder joints, achieving electrical interconnection between electronic components and the circuit board. Solder paste has good wetting properties, effectively covering the pads and chip surfaces to ensure soldering quality.

[0038] The process flow for BGA packaging may include the following steps:

[0039] 1. Substrate preparation:

[0040] (1) Pre-treat the substrate to be packaged to ensure that its surface is clean and free of contamination.

[0041] (2) Design and lay out pads on the substrate to ensure that they correspond to the pin positions and number of the chip to be packaged.

[0042] (3) Using a printing method (such as screen printing), apply an appropriate amount of solder paste evenly to the pads of the substrate.

[0043] 2. Chip installation:

[0044] (1) The packaged chip is accurately placed on the substrate using automated equipment or manual operation, so that the chip's solder balls correspond to the solder pads. During this process, positioning tools or vision-assisted equipment can be used to ensure correct alignment to avoid offset or misalignment.

[0045] 3. Welding:

[0046] Hot air reflow soldering or hot plate soldering is performed. The aforementioned methods involve heating the entire chip and substrate, and controlling the heating temperature and time to melt the solder paste and reach the appropriate soldering temperature for soldering connection.

[0047] 4. Cooling and curing:

[0048] After soldering, allow the chip and substrate to cool naturally, or use cooling equipment or a cooling environment together or independently to accelerate cooling so that the solder paste can solidify and harden.

[0049] In the applicant's practice, BGA packaging is achieved through reflow soldering. The equipment used in the packaging process has an internal heating circuit that heats air or nitrogen to a sufficiently high temperature. The hot air is then blown onto the circuit board where the components have been mounted, causing the solder on both sides of the components to melt and bond to the motherboard.

[0050] The heating temperature can be controlled using a reflow temperature profile. For example, a non-linear temperature profile such as RSS (Ramp-Soak-Spike) can be used. This means the entire reflow process is strictly divided into four temperature zones: preheating, isothermal, reflow, and cooling. The reflow temperature zone has the highest temperature and its specific temperature depends on the solder ball type and material (generally, the reflow temperature should be 40-50 degrees Celsius higher than the solder ball's melting point).

[0051] However, during the testing process after BGA packaging, the applicant found that the above reflow soldering had a relatively poor product yield, or that the process requirements were relatively high, and the packaged devices were also prone to problems during use.

[0052] Research revealed that the applicant believes a significant contributing factor to the above problems was substrate warping during the BGA packaging process in reflow soldering. This substrate warping caused a mismatch between the chip and the substrate, leading to separation at the solder joint, reduced bonding strength, and increased susceptibility to desoldering due to heat buildup during prolonged operation, high-intensity heat generation, or mechanical vibration.

[0053] After analysis and research, the applicant believes that the substrate warping problem that may occur during the heating to cooling process in BGA packaging can manifest in the following ways: Figure 1 As shown.

[0054] according to Figure 1 As shown, the substrate underwent two main types of deformation throughout the process. The first is positive deformation, where the surface facing the chip is concave and the surface away from the chip is convex; the second is negative deformation, where the surface facing the chip is convex and the surface away from the chip is concave.

[0055] It is worth noting that the terms "positive" and "negative" mentioned above are relative. That is, a depression on the chip-facing surface can be described as positive, and a protrusion on the chip-facing surface can be described as negative. Similarly, a depression on the chip-facing surface can be described as negative, and a protrusion on the chip-facing surface can be described as positive. The specific description depends on the perspective from which it is discussed, and there are no particular limitations in this application.

[0056] Furthermore, it can be noted that during the deformation process of heating and cooling, compared with the deformation at higher or lower temperatures, the deformation at the thermally stable state is less than the deformation relative to the heating or cooling process as thermal stability is established.

[0057] After investigation, the applicant believes that the main cause of the above problems lies in the material selection of the substrate (such as a printed circuit board, i.e., PCB). Due to the material properties of PCB materials, they are greatly affected by temperature changes during the packaging process, resulting in abnormal PCB warping. However, adjusting the substrate material is not easy, and in some scenarios, it is even impossible.

[0058] Therefore, in this application, the applicant proposes a new solution to overcome the substrate warping problem in the BGA packaging process.

[0059] Primarily, the applicant believes that heating the substrate during BGA packaging is detrimental. Therefore, avoiding heating the substrate during packaging can alleviate or even eliminate substrate warping problems. Accordingly, the examples in this application choose to heat the chip separately, rather than directly heating the substrate.

[0060] In general, this application proposes a novel BGA soldering method. This novel BGA soldering method does not employ a reflow soldering process, but instead uses a new method (described herein as thermocompression soldering) to complete the soldering.

[0061] In the example of this application, the thermocompression bonding method selects to heat the chip but not the substrate, thereby effectively avoiding the problem of substrate warping while welding and packaging.

[0062] The following will describe in detail the scheme in the example of this application.

[0063] The example discloses a packaging method for soldering a chip to a substrate. This packaging method can achieve effective soldering and packaging while significantly suppressing and mitigating substrate warping, thereby greatly reducing the risk of chip and substrate separation at the solder joint.

[0064] In the example, such as Figure 2 As shown, the encapsulation method includes:

[0065] Step S101: With the chip heated until the balls melt, and without heating the substrate, bring the chip and substrate face to face so that at least the balls contact the substrate; and,

[0066] Step S102: Cooling to allow the chip to be soldered to the substrate via balls.

[0067] In this way, without heating the substrate but heating the chip, the chip and the substrate are thermally pressed together, and the substrate is connected by the molten ball on the chip. The chip is then cooled and solidified to achieve the encapsulation connection between the two.

[0068] For convenience, the chip with ball implantation and the substrate can be pre-positioned to facilitate subsequent hot-pressing. Therefore, before bringing the chip and substrate face to face, the packaging method may also include step S100, positioning the substrate and the chip with ball implantation face to face, with a preset distance between the substrate and the chip, and the balls not contacting the substrate.

[0069] Therefore, see other examples in this application. Figure 3 The encapsulation method may include the following steps:

[0070] Step S100: Position the substrate and the chip with the ball already implanted face to face, with a preset distance between the substrate and the chip, and the ball does not contact the substrate.

[0071] Step S101: With the chip heated until the balls melt, and without heating the substrate, bring the chip and substrate face to face so that at least the balls contact the substrate; and,

[0072] Step S102: Cooling to allow the chip to be soldered to the substrate via balls.

[0073] In step 100, the method of positioning the substrate and the chip face to face is, for example, fixing the substrate, then making the chip's spherical surface face the substrate, and moving the chip to gradually approach the substrate.

[0074] More specifically, in some examples, a flat substrate can be supported by a machine or support platform, and the substrate can be fixed by means of suction cups on the machine or platform or by using clamps for holding. After the substrate is fixed, the chip is moved by the operation of a robotic arm, for example, by adsorbing and fixing the back of the chip, and then moving it toward the substrate. That is, the chip moves in a way that approaches the substrate, or it can be described as a downward movement of the chip to approach the substrate.

[0075] In short, a method of bringing a chip and a substrate face to face so that at least the sphere is in contact with the substrate may include: placing the substrate flat and moving the chip relative to the substrate in the direction of gravity from a position away from the substrate to a position closer to the substrate.

[0076] To improve soldering results, flux can be applied to the entire surface of the substrate and chip facing each other. The flux makes it easier for the chip's solder balls to wet the pads on the substrate surface, thus facilitating chip-to-substrate soldering.

[0077] In practice, the applicant found that the distribution of flux on the substrate surface can also be selected to improve the welding quality.

[0078] For example, flux is formed in localized areas of the substrate and chip surfaces facing each other. That is, instead of applying flux to the entire surface of the substrate, flux is selectively applied to localized areas. A more advantageous approach is to select multiple localized areas, corresponding to multiple spheres on the chip surface, with each sphere corresponding to a specific localized area.

[0079] By avoiding applying flux to the entire PCB soldering area, you can minimize the amount of flux used, reduce flux residue, and still achieve better soldering results due to the use of flux.

[0080] One method for forming flux in a localized area of ​​a substrate is by applying flux through a stencil, creating a thin layer of flux only on the PCB pads. This involves fabricating a stencil tailored to the number, distribution, and size of the pads on the substrate surface. The stencil is then placed over the substrate surface, aligning the mesh openings with the pads. Flux is then applied to the mesh openings using a squeegee, thus adhering to the pads. This method can be simply described as screen printing.

[0081] During the process, in order to control the amount of flux used, the amount of flux applied to the PCB pads is controlled by designing the stencil aperture size (hole diameter) and stencil thickness. For example, the height of the flux can also be controlled in the above way. Preferably, in the substrate, the height of each flux component relative to the substrate surface is the same.

[0082] Exemplary examples show that flux can be made from various materials in the art, and this application does not particularly limit it. Generally, flux consists of activators, solvents, surfactants, and other components (such as corrosion inhibitors, antioxidants, film-forming agents, etc.); and in terms of type, it can include lead-containing, rosin-based, and lead-free, non-rosin-based types, etc.

[0083] In addition to fabricating flux on the substrate surface, the examples in this application also include ball-mounting the leads on the chip surface. As with the aforementioned requirements for flux on the substrate surface, it is possible to arrange the balls within the chip so that each ball is at the same height relative to the chip surface.

[0084] One method of solder ball placement is through screen printing, where solder paste (such as solder paste) is applied to the chip's pin locations. The paste is then heated to form spherical solder balls. Alternatively, solder beads (solid particles) can be placed on the chip's pins using a stencil, then heated to melt and bond to the pins. Another method is laser solder ball placement. Laser solder ball placement allows for precise control over the volume and height of each ball, ensuring stable and consistent chip-substrate bonding.

[0085] Solder paste can also be described as solder paste, solder paste, etc. Its main components include solder powder, flux, and other additives; and the composition of the additives depends mainly on the application scenario of the solder paste. Solder paste has a certain viscosity and can adhere to electronic components (such as chips) at a given location (such as chip pins). As the temperature rises, the solvents and some additives in the solder paste will evaporate, allowing the electronic components and PCB to be soldered together to form a permanent connection.

[0086] The above mainly discussed the scheme of step S100. Next, step S101 will be explained.

[0087] This step primarily involves heating. Specifically, the chip is heated so that the surface-mounted balls are melted, while the substrate remains unheated. This heating can be achieved using a robotic arm that moves the chip. A chuck holds the substrate in place, while the robotic arm holds and heats the chip.

[0088] This process uses a thermoforming welding method. The ARM component first attaches to an inverted chip that has been laser-placed with solder balls; the CHUCK then attaches to a PCB with flux applied.

[0089] The ARM descends, and the descent height is controlled to maintain a certain distance between the solder ball head on the chip and the PCB (at least to avoid contact, for example, within a few centimeters), preventing the solder ball on the chip from contacting the flux on the PCB pads.

[0090] Next, the ARM processor is given a temperature profile for solder ball reflow, with the CHUCK not heated throughout the process. When the reflow temperature range is reached (the temperature profile can include four zones: preheating, isothermal, reflow, and cooling; or a preheating, isothermal, and reflow temperature regime can be set), the ARM processor increases pressure or lowers displacement (window parameters can be pre-set) to bring the molten solder balls into contact with the pads on the soldering substrate. Because the solder balls on the chip surface are heated, when they contact the flux on the substrate surface, the flux is heated and acts to assist the reflow of the solder balls from the chip to the PCB pads. Since the CHUCK is not heated throughout this process, soldering yield issues caused by PCB warping are avoided.

[0091] The temperature profile can be determined based on the specific composition of the balls implanted on the chip surface.

[0092] After completing the heating and contact steps described above, cooling can be performed to achieve welding. This involves executing step S102, which is the fourth stage of the aforementioned temperature profile – cooling.

[0093] In this step, cooling can be natural cooling, which means stopping the heating of the ARM processor on the chip and allowing its heat to dissipate naturally and cool down. Alternatively, in other examples, it can be active cooling, such as air cooling.

[0094] The above welding methods can be referred to Figure 4 As shown. Through this method, the solution in this application example achieves high-quality soldering between the chip and the substrate. Furthermore, separation between the chip and the substrate due to substrate warping is less likely to occur. Correspondingly, separation between the chip and the substrate is less likely to occur after experiencing certain thermal shocks, drops, or impacts. In some scenarios, the aforementioned separation can be described as a cold solder joint.

[0095] As an application example of the above packaging method, this application also discloses a method for manufacturing a superconducting quantum chip. The manufacturing process includes a step of connecting a bare chip to a printed circuit board, and this connection step is performed in accordance with the aforementioned packaging method.

[0096] The embodiments described above with reference to the accompanying drawings are exemplary and are only used to explain this application, and should not be construed as limiting this application.

[0097] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, one or more embodiments have been described above with reference to the accompanying drawings. Throughout the description, similar reference numerals are used to denote similar components. In the foregoing description, numerous specific details have been set forth for illustrative purposes in order to provide a more thorough understanding of one or more embodiments. However, it will be apparent that one or more embodiments may be practiced in various circumstances without these specific details, and the embodiments may be combined with and referenced to each other without contradiction.

[0098] It should be noted that the terms "first," "second," etc., in the specification, claims, and accompanying drawings of this application are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that the embodiments of this application described herein can be implemented in sequences other than those illustrated or described herein.

[0099] Furthermore, the terms “comprising” and “having”, and any variations thereof, are intended to cover non-exclusive inclusion, such that a process, method, system, product, or apparatus that includes a series of steps or units is not necessarily limited to those steps or units that are explicitly listed, but may include other steps or units that are not explicitly listed or that are inherent to such process, method, product, or apparatus.

[0100] The above description of the structure, features and effects of this application is based on the embodiments shown in the drawings. The above are only preferred embodiments of this application. However, this application does not limit the scope of implementation to what is shown in the drawings. Any changes made in accordance with the concept of this application, or modifications to equivalent embodiments, that do not exceed the spirit covered by the specification and drawings, should be within the protection scope of this application.

Claims

1. A packaging method for soldering a chip to a substrate, characterized in that, The encapsulation method includes: With the chip heated to the point where the balls melt, and without heating the substrate, the chip and the substrate are brought face to face so that at least the balls are in contact with the substrate; In addition, cooling is performed to allow the chip to be soldered to the substrate via the ball.

2. The packaging method according to claim 1, characterized in that, The packaging method further includes, before bringing the chip and substrate face-to-face, the following: The substrate and the chip with the ball already implanted are positioned face to face, with a preset distance between the substrate and the chip, and the ball does not contact the substrate.

3. The packaging method according to claim 1 or 2, characterized in that, Methods of bringing the chip and substrate face-to-face so that at least the sphere contacts the substrate include: Lay the substrate flat and move the chip relative to the substrate along the direction of gravity from a position away from the substrate to a position closer to the substrate.

4. The packaging method according to claim 1, characterized in that, The entire surface of the substrate facing the chip is covered with flux. Alternatively, the flux may be formed in a localized area of ​​the surface of the substrate facing the chip.

5. The packaging method according to claim 4, characterized in that, There are multiple local regions and multiple spheres on the chip surface, with each sphere corresponding to a local region.

6. The packaging method according to claim 5, characterized in that, In the chip, all the spheres are at the same height relative to the chip surface; And / or, in the substrate, the height of each flux relative to the substrate surface is the same.

7. The packaging method according to claim 4, 5, or 6, characterized in that, Methods for forming flux include: screen printing.

8. The packaging method according to claim 7, characterized in that, Screen printing controls the amount of flux applied by adjusting the mesh size and thickness.

9. The packaging method according to claim 1, characterized in that, The cooling method is natural cooling; And / or, methods for heating the chip to the point of ball melting include preheating, isothermal treatment, and reflow.

10. The application of the packaging method according to any one of claims 1 to 9 in the manufacture of superconducting quantum chips.

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