Packaging welding structure for solving high reliability requirement of 5G GaN chip welding

Abstract

The application relates to a packaging welding structure for solving the high-reliability requirement of 5G GaN chip welding, which comprises a chip and a lead frame base island, the upper surface of the lead frame base island is provided with an annular groove, the inner side of the annular groove forms a welding support table, the upper surface of the welding support table is lower than the upper surface of the lead frame base island, the upper surface of the welding support table is also provided with a plurality of support convex points with the same height in an array, and the chip is welded on the welding support table through sintered silver glue. By adjusting the height difference between the upper surface of the welding support table and the upper surface of the lead frame base island, the overflowed sintered silver glue can be reversely packed to the edge of the chip to form glue climbing, and meanwhile, the glue climbing of the sintered silver glue can be avoided to be too high; the support convex points can effectively help to expel the air in the sintered silver glue, can make the cavity rate of the welding layer be reduced to below 2%, and can guarantee the flatness of the chip when placed, avoid the inclination of the chip, and improve the welding reliability of the product and the heat dissipation of the product.

Description

Technical Field

[0001] This invention relates to the field of chip packaging technology, and in particular to a packaging and welding structure that addresses the high reliability requirements of 5G GaN chip soldering. Background Technology

[0002] 5G applications using gallium nitride / silicon carbide (GaN / SiC) products operate with high current and power, reaching temperatures as high as 250 degrees Celsius. This necessitates high heat dissipation and reliability in the chip packaging. To meet these requirements, especially high heat dissipation, the packaging materials (molding compound and solder) also have high demands, requiring high thermal conductivity. The solder at the bottom of the chip, connecting the chip to the leadframe island, is particularly crucial, as heat generated by the chip is first transferred to the leadframe island and then dissipated into the air. Currently, to meet the high heat dissipation requirements, solder materials with a thermal conductivity greater than 100 W / (mK), i.e., sintered silver paste, are selected. However, this type of material also has some drawbacks. After baking and curing, many voids appear in the solder between the chip and the leadframe island, severely affecting the product's heat dissipation.

[0003] Formulas for calculating heat dissipation at different interfaces: Q = a(tw - to)F Where Q is the heat dissipation in W. tw is the surface temperature of the heat source in °C (e.g., the bottom surface of a chip); to is the temperature of the external heat source in °C (e.g., the base island of a lead frame); and F is the area of ​​the heat dissipation surface in m². 2 The approximate weld layer area; 'a' is the overall heat transfer coefficient, w / (℃×m²). 2The thermal conductivity of the heat exchange material is directly proportional to the thermal conductivity of the heat exchange material, approximating that of sintered silver paste. From the above heat dissipation formula, it can be deduced that when the product material structure is the same, tw, to, and a are all constant values, while F is directly affected by the welding void rate. A 30% welding void rate means that the overall heat dissipation Q will decrease to 70%, significantly impacting the product's heat dissipation. This will cause the product's heat to accumulate due to its inability to dissipate in time, leading to an increase in the product's temperature and affecting its operational stability and reliability. Meanwhile, experiments have also confirmed that the area of ​​solder voids between the chip and the lead frame base island is inversely proportional to the heat dissipation of the product. After the product has been working for a certain period of time, the poor heat dissipation caused by the solder voids will lead to product abnormalities, reduce product life, or even direct failure (Chiriac VA, Yu Y. Impacts of solder voids on PQFN packages' thermal and mechanical performances[C]. Thermal & Thermomechanical Phenomena in Electronic Systems. IEEE, 2010: 1-7; Zheng Gangtao, Chen Supeng, Hu Jun, et al. Influence of solder layer void area on the resistance and thermal resistance of power devices[J]. Semiconductor Technology, 2010(11): 16-20).

[0004] like Figure 1 As shown, this is a chip packaging structure in the prior art, including a lead frame 5, a lead frame base island 2, a chip 1, gold wires 7, solder 3, and molding compound 6. In the prior art, the thickness of the solder 3 is generally 15-20μm. After baking and curing, many voids will appear in the solder 3 between the chip 1 and the lead frame base island 2. The area of ​​the solder voids between the chip 1 and the lead frame base island 2 is significantly inversely proportional to the heat dissipation of the product. This seriously affects the heat dissipation of the chip packaged product. Poor heat dissipation will lead to product abnormalities, reduce product life, or even direct failure.

[0005] Current products generally require a chip solder layer void ratio of less than 25% (JEDECJ-STD-033). However, the special applications of these GaN / SiC products have very high requirements for heat dissipation, and the solder layer void ratio should not exceed 5%. In order to reduce solder voids, after optimization through high thermal conductivity sintered silver paste DOE experiments, it was found that when the amount of solder material reaches a certain requirement, that is, the thickness is greater than 30μm, the solder voids will be significantly reduced, which can reduce the solder voids to below 2%, thus meeting the heat dissipation requirements. When the solder thickness exceeds 30μm, although the solder void problem is solved, it also has an adverse impact on subsequent packaging processes. Due to the large solder thickness, chip tilting is likely to exceed the limit during die assembly, which seriously affects soldering quality and yield. At the same time, chip tilting will also cause uneven heat dissipation and affect heat dissipation stability. Excessive solder overflow at the chip edge and difficulty in controlling solder climb make the production of the product very unstable. This not only makes it difficult to control production quality, but also affects the production capacity. Moreover, as the solder thickness continues to increase, the above problems will become more prominent and serious. Therefore, a better solution is needed to solve these problems. Summary of the Invention

[0006] The purpose of this invention is to provide a packaging and welding structure that addresses the high reliability requirements of 5G GaN chip welding, solving both the problem of welding voids and the problem of excessive chip tilt.

[0007] This invention is implemented as follows: A packaging and welding structure that addresses the high reliability requirements of 5G GaN chip soldering includes a chip and a leadframe base island. An annular groove is provided on the upper surface of the leadframe base island, and a soldering support platform is formed inside the annular groove. The shape and area of ​​the soldering support platform are adapted to the chip. The upper surface of the soldering support platform is lower than the upper surface of the leadframe base island. Multiple support bumps of the same height are arrayed on the upper surface of the soldering support platform. The height of the support bumps is 30-50 μm. The chip is soldered to the soldering support platform using sintered silver paste, the thickness of which is equal to or slightly greater than the height of the support bumps.

[0008] The depth of the annular groove is 80-120 μm, and the width of the annular groove is 100-200 μm.

[0009] The height of the welding support platform is 50-75μm.

[0010] The diameter of the supporting protrusion is 30-60 μm.

[0011] The surface of the lead frame base island is also provided with a silver plating layer.

[0012] The encapsulation and soldering structure further includes pins, gold wires, and a molding compound. The gold wires are used to connect the chip and the pins, and the molding compound is used to encapsulate the entire product.

[0013] The beneficial effects of this invention are as follows: This invention designs a new packaging and soldering structure. An annular groove is set on the upper surface of the lead frame base island. Because the thickness of the sintered silver paste has increased (originally 15-20 μm, now at least 30 μm), the overflow to the chip periphery is more severe than before. The annular groove is used to surround the sintered silver paste, forming a dam structure to control the overflow range. The size of the soldering support platform is adapted to the size of the chip, and the upper surface of the soldering support platform is lower than the upper surface of the lead frame base island, forming a certain height difference. By adjusting this height difference, the overflowing sintered silver paste can wrap around the chip edge, forming a creeping paste, while avoiding excessive creeping of the sintered silver paste, which would contaminate the chip edge and top surface. The support bump is a micro-bump, and its height needs to be designed according to the actual thickness of the adhesive, generally greater than 30 μm. The top of the support bump forms a flat support surface, which can effectively help to squeeze out the air in the sintered silver paste and reduce the void ratio of the solder layer. Within 2%, the support bumps ensure the flatness of the chip during placement, preventing chip tilting. During the curing and soldering process, they also correct chip tilt, minimizing it (tilting is only possible when the sintered silver paste thickness exceeds the support bump height, but even then, it's minimal). They also improve the issue of excessive solder paste overflow. Furthermore, the support bumps increase the contact area with the sintered silver paste, providing more mechanical cross-contamination surfaces, enhancing the bonding strength between the sintered silver paste layer and the leadframe base island, and improving the product's soldering reliability. This, in turn, improves product quality and reliability. The thermal conductivity of the mixed support bump and sintered silver paste soldering layer is far superior to that of a pure sintered silver paste soldering layer (sintered silver paste has a thermal conductivity of 100-200 W / (mK), while copper has a thermal conductivity of 400 W / (mK)). Therefore, it also improves the product's heat dissipation, allowing the resulting product to operate for extended periods at temperatures up to 400 degrees Celsius. Since the support bumps occupy a certain space in the original soldering layer, the amount of sintered silver paste used in the newly designed structure is reduced, lowering costs. Attached Figure Description

[0014] Figure 1 This is a top view of the lead frame base island in the embodiment of the encapsulation and welding structure described in this invention;

[0015] Figure 2 yes Figure 1 Sectional view along the AA direction;

[0016] Figure 3 This is a schematic diagram of the structure after silver paste has been applied to the lead frame base island;

[0017] Figure 4This is a schematic diagram of the structure after the chip is soldered to the leadframe base island;

[0018] Figure 5 This is a schematic cross-sectional view of the lead frame base island before processing, as described in this invention.

[0019] Figure 6 This is a schematic diagram of the structure of the present invention, in which an annular groove is machined on the lead frame base island;

[0020] Figure 7 This is a schematic diagram of the structure of the welding support platform fabricated on the lead frame base island of the present invention;

[0021] Figure 8 This is a schematic diagram of the structure of the present invention in which support protrusions are machined on the base island of the lead frame;

[0022] Figure 9 This is a schematic diagram of the structure in which gold wires connect the chip and pins in an embodiment of the packaging and welding structure described in this invention;

[0023] Figure 10 This is a schematic diagram of the encapsulation and welding structure after plastic sealing in the embodiment of the present invention;

[0024] Figure 11 This is a schematic diagram of the encapsulation and welding structure described in this invention applied to a single-base island single-region welding structure product;

[0025] Figure 12 This is a schematic diagram of the encapsulation and welding structure described in this invention applied to a single-base island multi-region welding structure product;

[0026] Figure 13 This is a schematic diagram of the encapsulation welding structure described in this invention applied to a multi-base island multi-region welding structure product.

[0027] The components are: 1. Chip; 2. Leadframe base island; 21. Annular groove; 22. Welding support platform; 23. Support bump; 3. Sintered silver paste; 4. Lead; 5. Gold wire; 6. Molded package. Detailed Implementation

[0028] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0029] As an embodiment of the packaging and welding structure described in this invention for solving the high reliability requirements of 5G GaN chip welding, such as Figures 1 to 10As shown, the device includes a chip 1 and a lead frame base island 2. The upper surface of the lead frame base island 2 is provided with an annular groove 21. A welding support platform 22 is formed inside the annular groove 21. The shape and area of ​​the welding support platform 22 are adapted to the chip 1. The upper surface of the welding support platform 22 is lower than the upper surface of the lead frame base island 2. The upper surface of the welding support platform 22 is also provided with a plurality of support bumps 23 of the same height. The height of the support bumps 23 is 30-50μm. The chip 1 is welded to the welding support platform 22 by sintering silver paste 3. The thickness of the sintering silver paste 3 is equal to or slightly greater than the height of the support bumps 23.

[0030] This invention designs a novel packaging and soldering structure. An annular groove 21 is formed on the upper surface of the leadframe base island 2. Because the thickness of the sintered silver paste 3 has increased (from 15-20 μm to at least 30 μm), the overflow to the periphery of the chip 1 is more severe than before. The annular groove 21 is used to surround the sintered silver paste 3, forming a dam structure to control the overflow range. The dimensions of the soldering support platform 22 are adapted to the dimensions of the chip 1, and the upper surface of the soldering support platform 22 is lower than that of the leadframe base island 2. The upper surface of the two forms a certain height difference. By adjusting this height difference, the overflowing sintered silver paste 3 can wrap around the edge of the chip 1 to form adhesive creep, while avoiding excessive creep of the sintered silver paste 3, which would cause contamination around the edge and top surface of the chip 1. The support bump 23 is a micro-bump, and its height needs to be designed according to the actual thickness of the adhesive, generally greater than 30μm. The top of the support bump 23 forms a flat support surface, which can effectively help to squeeze out the air in the sintered silver paste 4 and reduce the void ratio of the solder layer. With a tilt rate as low as 2%, the support bumps 23 ensure the flatness of chip 1 during placement, preventing chip 1 from tilting. During the curing and soldering process, they also correct chip 1 tilt, minimizing it (tilting is only possible when the sintered silver paste thickness exceeds the support bump height, but even then, the tilt is minimal). Furthermore, they improve the issue of excessive solder paste overflow. Additionally, the support bumps increase the contact area with the sintered silver paste, providing more mechanical cross-contamination surfaces, enhancing the bonding strength between the sintered silver paste layer and the leadframe base island, and improving product performance. The welding reliability is improved, thereby enhancing the quality and reliability of the product. The thermal conductivity of the mixed welding layer of support bump 23 and sintered silver paste 3 is much better than that of the welding layer of pure sintered silver paste (thermal conductivity of sintered silver paste is 100-200W / (mK) while that of copper is 400W / (mK)). Therefore, it can also improve the heat dissipation of the product. The resulting product can even work for a long time under high temperature conditions of 400 degrees. Since support bump 23 occupies a certain space of the original welding layer, the amount of sintered silver paste 3 used in the new design structure will be reduced, thus reducing costs.

[0031] The packaging and welding structure described in this invention can not only be applied to the welding of GaN / SiC chips with high heat dissipation requirements, but also, due to its high versatility, can be widely used in the packaging and welding structures of ordinary chip products.

[0032] The encapsulation and welding structure described in this invention needs to meet certain structural height design principles to achieve optimal results. The specific structural height principles and relationships are as follows: Generally, the depth of the annular groove 21 is preferably half the thickness of the lead frame base island 1, which is easily achieved using a semi-etching process. Based on the existing conventional selection range for lead frame base island thickness, the preferred depth of the annular groove 21 is 80-120 μm, and the preferred width of the annular groove 21 is 100-200 μm.

[0033] Assuming that the amount of adhesive overflow V after dispensing in the existing leadframe base island structure is approximately 100% (chip adhesive creep) * H (chip thickness) * W (adhesive overflow width) * R (chip outer diameter) * 1 / 2, V = 1 / 2 * 100% * H * W * R. Since the chip outer diameter R and chip thickness H remain constant, to ensure that the adhesive creep of the new package soldering structure base island is approximately 50%, the width of the annular groove is the controlled adhesive overflow width. Assuming the total adhesive amount V1, (B annular groove depth + chip adhesive creep rate * H chip thickness) * W annular groove width * R chip outer diameter * 1 / 2, that is, V1 = 1 / 2 (B + 50% * H) * W * R. With the total amount of adhesive remaining constant, V = V1, 1 / 2 x 100% * H * R * W = 1 / 2 (B + 50% * H) * R * W, therefore B = 1 / 2 H. Since the support protrusions of the welding support platform occupy the space of the welding layer, the actual amount of adhesive overflowing will be more than the original design structure. In order to ensure that the amount of overflowing adhesive is also within the control range, the preferred value of B is between 1 / 3 H and 1 / 2 H.

[0034] In this embodiment, the height of the welding support platform 22 is between 1 / 2 and 2 / 3 of the depth of the annular groove 21, which is a preferred value. Specifically, the value is 50-75 μm. Different products may require different parameters. By adjusting this height difference, the overflowing sintered silver paste 3 can wrap around the edge of the chip 1 to form a creeping paste, while avoiding the sintered silver paste 3 creeping too high, which would cause contamination around the edge and top surface of the chip 1.

[0035] In this embodiment, the diameter of the support bump 23 is 30-60 μm (specifically referring to the top of the support bump), which is relatively small and will not significantly affect the lead frame base island 2 during fabrication. The thickness of the sintered silver paste 3 below needs to be equal to or greater than the height of the support bump 23, ensuring that the thickness of the sintered silver paste 3 is greater than 30 μm. This facilitates control, ensures stable production, and solves the problem of solder voids. The amount of sintered silver paste 3 above the support bump 23 is very small, normally less than 10 μm, thus reducing the tilting during chip mounting.

[0036] In this embodiment, the encapsulation and welding structure further includes pins 4, gold wires 5, and a molding compound 6. The gold wires 5 are used to connect the chip 1 and pins 4, and the molding compound 6 is used to encapsulate the entire product to form a complete encapsulated product.

[0037] Due to the complex structure of the leadframe base island 2 and the high precision requirements of each component, the manufacturing process is more challenging and requires the simultaneous use of multiple processes, including chemical etching, laser etching, and stamping. First, the leadframe needs to be pre-formed to create the leadframe base island 2 and leads 4. Then, detailed structures are processed on the leadframe base island 2, such as... Figures 5 to 8 As shown, the annular groove 21 needs to be fabricated first through semi-etching, and the etching depth can be controlled by adjusting the chemical etching time. Then, the welding support platform 22 is fabricated using laser etching, and the etching depth can be controlled by adjusting the laser's operating current or ablation rate (laser etching has high precision and is easy to control, which can compensate for the inability of stamping or chemical etching processes to achieve fine processing of the welding support platform). Finally, the support bumps 23 are fabricated using stamping or back impact. When applying the sintered silver paste 3, a dispensing or chemical coating method can be used. Even if the amount of dispensing is slightly large, the dam structure formed by the annular groove 21 on the lead frame base island 1 can effectively prevent the sintered silver paste 4 from overflowing. The support bumps 23 help to remove air from the sintered silver paste 3, and the open design of the welding layer area is more conducive to the removal of air during curing.

[0038] In this invention, the design is not only applicable to single-base island, single-region welded structure products (such as...) Figure 11 As shown), it can also be used in single-base island multi-region welded structures (such as...). Figure 12 (as shown) and multi-base island multi-region welded structure products (such as Figure 13 As shown in the figure, the specific design depends on the actual needs of the product, but the results and principles are the same.

[0039] In this invention, it is also necessary to determine whether the welding support platform and support bumps need to be surface coated according to the characteristics of different sintered silver pastes in order to achieve the best welding bonding performance. For example, a silver plating layer is set on the surface of the lead frame base island to enhance the bonding strength between the welding support platform, support bumps and silver-loving sintered silver paste.

[0040] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A packaging solder structure solving the high reliability requirement of 5G GaN chip soldering, characterized in that, The package welding structure comprises a chip and a lead frame base island, the upper surface of the lead frame base island is provided with an annular groove, the inner side of the annular groove forms a welding support platform, the shape and area of the welding support platform are adapted to the chip, the upper surface of the welding support platform is lower than the upper surface of the lead frame base island, and a plurality of support convex points with the same height are arranged on the upper surface of the welding support platform, the height of the support convex points is 30-50 μm, the chip is welded on the welding support platform through sintered silver glue, and the thickness of the sintered silver glue is equal to or slightly greater than the height of the support convex points. The value of B is between 1 / 3H-1 / 2H, wherein B is the depth of the annular groove, and H is the thickness of the chip. The height of the welding support platform is between 1 / 2-2 / 3 of the depth of the annular groove. The diameter size of the support convex points is 30-60 μm.

2. The package solder structure of claim 1, wherein The depth of the annular groove is 80-120 μm, and the width of the annular groove is 100-200 μm.

3. The package solder structure of claim 1, wherein The height of the welding support platform is 50-75 μm.

4. The package solder structure of claim 1, wherein The upper surface of the lead frame base island is further provided with a silver plating layer.

5. The package solder structure of any one of claims 1 to 4, wherein The package welding structure further comprises a pin, a gold wire and a plastic encapsulation body, the gold wire is used for connecting the chip and the pin, and the plastic encapsulation body is used for encapsulating the whole product.

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