Manufacturing method for increasing HBPOP packaging stacking height

Abstract

The invention discloses a manufacturing method for increasing HBPOP packaging stacking height, and relates to the technical field of a ball mounting technology, the method is used for packaging a substrate bonding pad, the surface of the substrate bonding pad is provided with a plurality of solder mask windows, the method comprises the steps that first solder balls are printed on the solder mask windows, and the height of the first solder balls is larger than that of the solder mask windows; flattening the first solder ball, and forming a solder ball pad on the surface of the first solder ball; a second solder ball is printed on the solder ball pad, the ball diameter of the second solder ball is smaller than that of the first solder ball, and the melting point of the second solder ball is smaller than that of the first solder ball; the temperature peak value of backflow preheating is smaller than the melting point of the first solder ball, and the temperature peak value of backflow preheating is larger than the melting point of the second solder ball; and when the first solder ball and the second solder ball are not completely dissolved, backflow preheating is stopped, and the ball mounting process of HBPOP packaging is completed. According to the invention, the height of the solder ball which can be implanted in the ball implanting process is increased.

Description

Technical Field

[0001] This invention relates to the technical field of ball-mounting processes, and more particularly to a method for increasing the stacking height of HBPOP packages. Background Technology

[0002] In the production process of packaging substrates, the ball-mounting process uses ball-mounting equipment (such as ball-mounting machines and stencil printing machines) to precisely place solder balls on the substrate pads. This is a key step in connecting the packaging substrate and the chip and realizing electrical and mechanical connections.

[0003] The limitations on the size of solder balls used in traditional solder ball placement processes mainly stem from the thickness of the solder mask opening and the bump pitch (usually 100~200um). If the bump height needs to be increased, larger solder balls must be selected, and the spacing requirements between bumps will also increase accordingly.

[0004] However, in current HBPoP (High Bandwidth Stacked Package), the demand for high-performance computing has led to an increasing number of chip layers. This requires a continuous increase in the height of the bump ball and a continuous reduction in the bump spacing to ensure transmission efficiency. Traditional ball-mounting technology is gradually becoming unable to meet these requirements.

[0005] Therefore, how to increase the height of the solder balls that can be implanted in the ball-planting process has become a technical problem that urgently needs to be solved. Summary of the Invention

[0006] The technical problem solved by this invention is that the height of the solder balls that can be implanted in the ball-planting process is too low when the implantation spacing between multiple solder balls is continuously reduced.

[0007] To solve the above-mentioned technical problems, the present invention provides the following technical solution: a method for increasing the stacking height of HBPOP packages, used for packaging substrate pads, wherein the surface of the substrate pads has multiple solder mask openings, including: A first solder ball is printed on the solder resist opening, and the height of the first solder ball is higher than the height of the solder resist opening; Flatten the first solder ball to form a solder ball pad on the surface of the first solder ball; A second solder ball is printed on the solder ball pad. The diameter of the second solder ball is smaller than that of the first solder ball, and the melting point of the second solder ball is smaller than that of the first solder ball. The second solder ball is reflow preheated, wherein the peak temperature of the reflow preheating is lower than the melting point of the first solder ball, and the peak temperature of the reflow preheating is higher than the melting point of the second solder ball; When the first and second solder balls are incompletely dissolved, the reflow preheating is stopped, and the ball-planting process for HBPOP packaging is completed.

[0008] Preferably, printing the first solder ball onto the solder resist opening includes: The flux is printed onto the solder resist window; The first solder ball is printed on the solder resist opening; The first solder ball is filled into the solder resist opening by reflow preheating; The step of printing the second solder ball onto the solder ball pad includes: The flux is printed onto the solder ball pad; The flux on which the second solder ball is printed is applied.

[0009] Preferably, the step of stopping reflow preheating and completing the HBPOP packaging ball-planting process when the first solder ball and the second solder ball do not completely dissolve includes: When the material molecules of the first solder ball diffuse into the liquid phase material of the second solder ball to form an alloy, the reflow preheating is stopped, and the ball-planting process of HBPOP packaging is completed.

[0010] Preferably, the peak reflux temperature range is [170℃, 200℃].

[0011] Preferably, the diameter of the first solder ball is less than 150 micrometers.

[0012] Preferably, the encapsulation substrate pads include encapsulation of an upper substrate plate and a lower substrate plate, both of which have multiple solder resist openings.

[0013] Preferably, the manufacturing method is used to complete the ball-planting process on the lower plate of the substrate, and the manufacturing method includes: The second solder ball is soldered to the solder mask opening on the upper plate of the substrate, thus completing the connection between the upper plate and the lower plate of the substrate.

[0014] Preferably, the manufacturing method is used to complete the ball-planting process on the upper plate and the lower plate of the substrate respectively, and the manufacturing method includes: The second solder balls between the upper and lower substrate plates are fused together to complete the connection between the upper and lower substrate plates.

[0015] Preferably, the first solder ball comprises SAC305 material, and the second solder ball comprises Sn58Bi material; the alloy formed by the diffusion of the material molecules of the first solder ball into the liquid phase material of the second solder ball is a Sn-Ag-Cu-Bi ternary alloy.

[0016] Preferably, the first solder ball comprises Sn3.5Ag material, and the second solder ball comprises Sn58Bi material; the alloy formed by the diffusion of the material molecules of the first solder ball into the liquid phase material of the second solder ball is a Sn-Ag-Bi ternary alloy.

[0017] The beneficial effects of this invention are as follows: By implanting a first solder ball and a second solder ball respectively, the height of the solder ball implanted in the solder mask opening is increased when the implantation spacing of the solder balls is reduced. By setting the melting point of the second solder ball to be lower than that of the first solder ball, and by reflowing and preheating the second solder ball, the peak temperature of the reflow preheating is set to be lower than that of the first solder ball and higher than that of the second solder ball, so that incomplete dissolution occurs between the first solder ball and the second solder ball. When the first solder ball and the second solder ball have incompletely dissolved, the reflow preheating is stopped, and the ball planting process of HBPOP packaging is completed. Thus, the ball planting height of the first solder ball can be increased by the second solder ball, while the bridging risk between the first solder ball and the second solder ball can also be reduced. Attached Figure Description

[0018] Figure 1 A schematic diagram of the basic process of a method for increasing the stacking height of HBPOP packages according to an embodiment of the present invention; Figure 2 A schematic diagram illustrating the printing process of the first solder ball provided by the present invention; Figure 3 A schematic diagram illustrating the printing process of the second solder ball provided by the present invention; Figure 4 A schematic diagram of the molecular motion process of incomplete dissolution provided by the present invention; Figure 5 A schematic diagram of the structure of the incompletely dissolved body provided by the present invention; Figure 6 A schematic diagram of a packaging structure provided by the present invention; Figure 7 for Figure 6 A schematic diagram of an incomplete form corresponding to the encapsulation structure; Figure 8 for Figure 6 A schematic diagram of another incomplete form corresponding to the encapsulation structure; Figure 9 A schematic diagram of another packaging structure provided by the present invention; Figure 10 for Figure 9 A schematic diagram of an incomplete form corresponding to the encapsulation structure; Figure 11 for Figure 9 A schematic diagram of another incomplete form corresponding to the encapsulation structure. Detailed Implementation

[0019] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0020] In the production of packaging substrates, the ball-mounting process, using ball-mounting equipment (such as ball-mounting machines and stencil printers), precisely places solder balls onto the substrate pads. This is a crucial step in connecting the packaging substrate to the chip and achieving electrical and mechanical connections. Traditional ball-mounting processes limit the size of solder balls primarily due to the thickness of the solder mask opening and the bump pitch (typically 100-200µm). Increasing the bump height requires larger solder balls, which in turn increases the required spacing between bumps. However, in current HBPoP (High Bandwidth Stacked Package) systems, the demand for high-performance computing has led to an increasing number of chip layers. This necessitates a continuous increase in bump height while simultaneously reducing bump spacing to maintain transmission efficiency. Traditional ball-mounting processes are gradually becoming inadequate for these requirements.

[0021] Based on this, please refer to Figure 1 As one embodiment of the present invention, a method for increasing the stacking height of HBPOP packages is provided for packaging substrate pads, wherein the substrate pads have multiple solder mask openings on their surface. The method includes: S110, the first solder ball is printed on the solder resist opening, and the height of the first solder ball is higher than the height of the solder resist opening; S120, flatten the first solder ball and form a solder ball pad on the surface of the first solder ball; S130, the second solder ball is printed on the solder ball pad. The diameter of the second solder ball is smaller than that of the first solder ball, and the melting point of the second solder ball is smaller than that of the first solder ball. S140, the second solder ball is reflow preheated. The peak temperature of the reflow preheating is lower than the melting point of the first solder ball, and the peak temperature of the reflow preheating is higher than the melting point of the second solder ball. S150: When the first and second solder balls are incompletely dissolved, the reflow preheating is stopped, and the ball placement process for HBPOP packaging is completed.

[0022] HBPOP (high bandwidth package on package) is used for processors that can be integrated into smartphones, tablets, and other consumer electronics. Its main advantages are high bandwidth and high-performance computing.

[0023] Substrate pads are the basic building blocks of surface mount assembly, used to form the pad pattern of a circuit board.

[0024] Solder mask openings refer to openings left on the substrate pads to facilitate soldering and surface treatment, ensuring that the metal parts on the substrate pads can be effectively connected.

[0025] Specifically, please refer to Figures 2-3 The method includes: S1, the flux is printed on the solder resist window.

[0026] like Figure 2 As shown in step ①, flux is printed onto the solder resist window. Flux is a material used during the soldering process to clean the surfaces being soldered and prevent them from re-oxidizing. It typically has rosin as its main component, which can remove oxides from the metal surface and improve soldering performance.

[0027] S2, the first solder ball is printed on the solder resist opening, and the height of the first solder ball is higher than the height of the solder resist opening.

[0028] like Figure 2 As shown in step ②, the first solder ball is printed on the solder resist window.

[0029] S3, the first solder ball is filled into the solder resist opening by reflow preheating.

[0030] like Figure 2 As shown in step ③, the first solder ball is filled into the solder mask opening by reflow preheating. The purpose of reflow preheating is to activate the solder paste and to avoid the heating behavior that would cause component defects due to rapid high-temperature heating during immersion soldering.

[0031] S4, flatten the first solder ball and form a solder ball pad on the surface of the first solder ball.

[0032] like Figure 2 As shown in step ③, the surface of the first solder ball is flattened to form a solder ball pad, so as to print the second solder ball on the solder ball pad, thereby increasing the height of the solder ball formation in the solder resist opening of the substrate pad.

[0033] S5 is the flux that is printed onto the solder ball pad.

[0034] like Figure 2 As shown in step ④, flux is printed onto the solder pad formed by the first solder ball.

[0035] S6, the second solder ball is printed on the solder ball pad. The diameter of the second solder ball is smaller than that of the first solder ball, and the melting point of the second solder ball is smaller than that of the first solder ball.

[0036] like Figure 3 As shown in step ⑤, the second solder ball is printed onto the solder ball pad.

[0037] S7, reflow preheating is performed on the second solder ball. The peak temperature of the reflow preheating is lower than the melting point of the first solder ball, and the peak temperature of the reflow preheating is higher than the melting point of the second solder ball.

[0038] like Figure 3 As shown in step 6, the second solder ball is fixed to the solder ball pad by reflow preheating.

[0039] To ensure that the second solder ball can be fixed to the solder ball pad while maintaining the shape formed by the first solder ball after reflow in S3, and to prevent the second solder ball from becoming completely liquid, the peak temperature and preheating time of reflow preheating in S7 need to be controlled.

[0040] In this process, the duration of liquefaction of the low-melting-point second solder ball, the peak temperature, and the holding time at the peak temperature are the main characteristics that determine the microstructure and performance of the solder ball during reflow soldering.

[0041] Therefore, by combining high-melting-point (e.g., SAC305, 217°C) and low-melting-point (e.g., Sn58Bi, 138°C) materials, composite solders can complete welding at temperatures below the melting point of conventional solders (peak temperature around 200°C).

[0042] For details, please refer to Figure 7 and Figure 10 The first solder ball comprises SAC305 material, and the second solder ball comprises Sn58Bi material; the alloy formed by the diffusion of the material molecules of the first solder ball into the liquid phase material of the second solder ball is a Sn-Ag-Cu-Bi alloy.

[0043] Preferably, you may also refer to Figures 8-11 The first solder ball comprises Sn3.5Ag material, and the second solder ball comprises Sn58Bi material; the alloy formed by the diffusion of the material molecules of the first solder ball into the liquid phase material of the second solder ball is a Sn-Ag-Bi ternary alloy.

[0044] S8, when the material molecules of the first solder ball diffuse into the liquid phase material of the second solder ball to form an alloy, the reflow preheating is stopped, and the ball-planting process of HBPOP packaging is completed.

[0045] like Figure 3 As shown in step ⑧, for details please refer to [link / reference]. Figure 5 .

[0046] During reflow preheating, the second solder ball melts to form a liquid phase, while the first solder ball does not melt. However, its internal molecules move and diffuse into the liquid phase of the second solder ball, forming an alloy that makes the first and second solder balls ellipsoidal. At this point, preheating can be stopped to increase the height of the solder balls after placement without changing the solder mask opening or thickness. Furthermore, the bridging strength of the alloy formed at the junction of the first and second solder balls is relatively high.

[0047] like Figure 4 As shown and Figure 5 As shown, the key characteristics and mechanisms of incomplete miscibility (taking SAC305 and Sn58Bi as examples): The formation conditions are as follows: when the reflow temperature (e.g., 170-200°C) is lower than the melting point of SAC305 and the holding time is insufficient, SAC305 only partially dissolves in liquid Sn58Bi. The undissolved SAC305 forms a solid core in the solder joint, surrounded by Sn-Ag-Cu-Bi alloy.

[0048] Its microstructure is characterized by: interface gradient, with a higher Sn concentration in the region near undissolved SAC305, fewer eutectic structures (Sn-Bi) and growth direction perpendicular to the interface; Bi distribution, with a granular Bi intermediate layer formed at the interface between SAC305 and Sn-Ag-Cu-Bi, where the high Sn concentration prevents participation in the eutectic reaction; and grain orientation, with EBSD analysis showing that the undissolved SAC305 grains are larger, while the surrounding Sn-Ag-Cu-Bi region has smaller grains with similar orientations.

[0049] Incomplete dissolution can be utilized in low-temperature composite welding. By controlling process parameters (such as temperature and time), partial dissolution can be achieved, which can reduce the process temperature (reduce thermal damage) while retaining the mechanical property advantages of high-melting-point solder.

[0050] The method provided in this application is particularly suitable for situations where the distance between solder resist openings is small, and only small-diameter solder balls can be used. In such cases, traditional soldering methods can only achieve a small solder ball height when the solder ball diameter is small. However, the method provided in this application can increase the height by stacking solder balls when the solder ball diameter is small. Specifically, the diameter of the first solder ball is less than 150 micrometers.

[0051] Preferably, the manufacturing method is used to complete the ball-mounting process on the lower substrate, and the manufacturing method includes: soldering the second solder ball to the solder mask opening on the upper substrate, thereby completing the connection between the upper substrate and the lower substrate. Based on this, the method provided in this application, during packaging, includes multiple packaging methods, such as... Figures 6-8 The diagram shows a packaging structure, such as Figures 9-11 This forms another packaging structure.

[0052] like Figures 6-8 As shown, preferably, the manufacturing method is used to complete the ball-planting process on the lower plate of the substrate. The manufacturing method includes: soldering the second solder ball to the solder mask opening on the upper plate of the substrate to complete the connection between the upper plate and the lower plate of the substrate.

[0053] like Figure 7The lower HBPOP board is ball-mounted according to the above process, and finally welded to the upper HBPOP board to form a bump structure. In this composite structure, the SAC305 portion forms an IMC: Cu6Sn5 at the connection with the lower board's copper PAD, and the Sn58Bi portion forms an IMC: Cu6Sn5 at the connection with the upper board's copper PAD. Due to incomplete miscibility, the contact area between SAC305 and Sn58Bi forms a Sn-Ag-Cu-Bi alloy. Alternatively, the lower HBPOP board is ball-mounted according to the above process, and finally welded to the upper HBPOP board to form a bump structure as shown below. Figure 8 In this composite structure, the Sn3.5Ag (melting point 227℃) portion forms an IMC: Cu6Sn5 at the connection with the lower plate copper PAD, and the Sn58Bi (melting point 138℃) portion forms an IMC: Cu6Sn5 at the connection with the upper plate copper PAD. Due to incomplete mutual solubility, the contact area between SAC305 and Sn58Bi forms a Sn-Ag-Bi ternary alloy system.

[0054] like Figures 9-11 As shown, preferably, the manufacturing method is used to complete the ball-planting process on the upper plate and the lower plate of the substrate respectively. The manufacturing method includes: melting the second solder balls between the upper plate and the lower plate of the substrate to complete the connection between the upper plate and the lower plate of the substrate.

[0055] The upper and lower plates of the HBPOP can be manufactured using the same process, and the final product is as follows: Figure 9 As shown, to complete the soldering of the upper and lower plates of an HBPOP, it is only necessary to control the reflow temperature to ensure that the low-melting-point solder (Sn58Bi, melting point 138℃, used in this example) melts, while the high-melting-point solder (SAC305, melting point 217℃, used in this example) undergoes almost no significant deformation, thus completing the soldering. Figure 10 As shown, since the top solder of the bump is Sn58Bi, it ensures better interfacial bonding between the upper and lower HBPOP boards, making it less prone to voids or breakage; the upper and lower HBPOP boards can be manufactured using the same process, and the final product is as follows. Figure 9 As shown, to complete the soldering of the upper and lower plates of an HBPOP, it is only necessary to control the reflow temperature to ensure that the low-melting-point solder (Sn58Bi, melting point 138℃, used in this example) melts, while the high-melting-point solder (Sn0.7Cu, melting point 227℃, used in this example) undergoes almost no large deformation, thus completing the soldering. Figure 11 As shown, since the top solder of the Bump is all-solder, it can ensure that the upper and lower boards of the HBPOP can better dissolve each other and are less likely to form voids or breakage.

[0056] After the first ball placement and flattening to create the "solder ball pad" using conventional ball placement technology, a second ball placement and reflow (reflow preheating) are performed to increase the bump height. In the above process, the liquidation duration, peak temperature, and holding time at the peak temperature of the low-melting-point solder ball (second solder ball) are the main characteristics that determine the microstructure and performance of the solder ball during reflow soldering. The incomplete miscibility effect produced by two solder balls with different melting points is used to perform multiple ball placements, ensuring that the diameter of the ball used in the later placement is smaller than that used in the previous one. Combining high-melting-point (such as SAC305, 217°C) and low-melting-point (such as Sn58Bi, 138°C) materials, composite solder can complete soldering at a temperature lower than the melting point of conventional solder (peak temperature around 200°C).

[0057] In this application, it is only necessary to ensure that the fixed height during use is greater than the sum of the diameter and height of the solder balls, without the need for additional fixtures; and the height of the solder balls after placement can be increased without changing the solder resist opening and the solder resist thickness, so that at a relatively small bump pitch level (around 100um), the height of the solder balls can be increased while reducing the risk of bridging; by utilizing the temperature and performance differences of various solder materials to create a composite structure for soldering, the shear strength of the solder balls is enhanced, and the heat input during reflow soldering can also be reduced.

[0058] This application embodiment increases the height of the solder balls implanted in the solder mask opening by separately implanting a first solder ball and a second solder ball, when the implantation spacing of the solder balls is reduced. By setting the melting point of the second solder ball to be lower than that of the first solder ball, the second solder ball is reflow preheated. The peak temperature of the reflow preheating is set to be lower than that of the first solder ball and higher than that of the second solder ball, so that the first solder ball and the second solder ball will partially dissolve. When the first solder ball and the second solder ball partially dissolve, the reflow preheating is stopped, and the ball planting process of HBPOP packaging is completed. Thus, the ball planting height of the first solder ball can be increased by the second solder ball, while the bridging risk between the first solder ball and the second solder ball can be reduced.

[0059] Those skilled in the art will understand that embodiments of the present invention can be provided as methods, systems, or computer program products. Therefore, the present invention can take the form of a completely hardware embodiment, a completely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, the present invention can take the form of a computer program product implemented on one or more computer-usable storage media containing computer-usable program code. The storage medium can be implemented by any type of volatile or non-volatile storage device or a combination thereof, such as Static Random Access Memory (SRAM), Electrically Erasable Programmable Read-Only Memory (EEPROM), Erasable Programmable Read Only Memory (EPROM), Programmable Red-Only Memory (PROM), Read-Only Memory (ROM), magnetic storage, flash memory, magnetic disk, or optical disk. These computer program instructions may also be stored in a computer-readable storage medium that can direct a computer or other programmable data processing device to function in a particular manner, such that the instructions stored in the computer-readable storage medium produce an article of manufacture including instruction means, which are implemented in a process Figure 1 One or more processes and / or boxes Figure 1 The function specified in one or more boxes.

[0060] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A method for increasing the stacking height of HBPOP packages, characterized in that, A method for encapsulating a substrate pad, the substrate pad surface having a plurality of anti-solder windows, comprising: printing a first solder ball in the anti-solder window, the first solder ball having a height higher than that of the anti-solder window; flattening the first solder ball to form a solder ball pad on the surface of the first solder ball; printing a second solder ball on the solder ball pad, the second solder ball having a diameter smaller than that of the first solder ball, and the second solder ball having a melting point lower than that of the first solder ball; preheating the second solder ball by reflow, the reflow having a temperature peak lower than the melting point of the first solder ball, and the reflow having a temperature peak higher than the melting point of the second solder ball; stopping the reflow preheating when the first solder ball and the second solder ball are incompletely dissolved, and completing the ball planting process of the HBPOP encapsulation.

2. The method of claim 1, wherein The printing of the first solder ball in the anti-solder window comprises: printing a flux in the anti-solder window; printing the first solder ball in the anti-solder window; filling the first solder ball in the anti-solder window by preheating the first solder ball by reflow; The printing of the second solder ball on the solder ball pad comprises: printing the flux on the solder ball pad; printing the second solder ball on the flux on the solder ball pad.

3. The manufacturing method as described in claim 2, characterized in that, The stopping of the reflow preheating when the first solder ball and the second solder ball are incompletely dissolved, and the completing of the ball planting process of the HBPOP encapsulation, comprises: stopping the reflow preheating when the material molecules of the first solder ball diffuse into the liquid phase material of the second solder ball to form an alloy, and completing the ball planting process of the HBPOP encapsulation.

4. The method of claim 3, wherein The reflow temperature peak ranges from [170℃, 200℃].

5. The manufacturing method as described in claim 4, characterized in that, The diameter of the first solder ball is less than 150 microns.

6. The manufacturing method as described in claim 5, characterized in that, The substrate pad comprises an upper substrate and a lower substrate, both of which have a plurality of anti-solder windows.

7. The manufacturing method as described in claim 6, characterized in that, The manufacturing method is used to complete the ball planting process on the lower substrate, and the manufacturing method comprises: welding the second solder ball to the anti-solder window of the upper substrate to complete the connection of the upper substrate and the lower substrate.

8. The manufacturing method as described in claim 7, characterized in that, The manufacturing method is used to complete the ball planting process on the upper substrate and the lower substrate respectively, and the manufacturing method comprises: intermelting the second solder ball between the upper substrate and the lower substrate to complete the connection of the upper substrate and the lower substrate.

9. The production method according to claim 7 or 8, wherein The first solder ball comprises SAC305 material, and the second solder ball comprises Sn58Bi material; the alloy formed by the diffusion of the material molecules of the first solder ball into the liquid phase material of the second solder ball is Sn-Ag-Cu-Bi alloy.

10. The production method according to claim 7 or 8, wherein The first solder ball comprises Sn3.5Ag material, and the second solder ball comprises Sn58Bi material; the alloy formed by the diffusion of the material molecules of the first solder ball into the liquid phase material of the second solder ball is Sn-Ag-Bi ternary alloy.

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