CCGA device board-level assembly method

Abstract

The invention belongs to the technical field of integrated circuit manufacturing, and particularly relates to a CCGA device board-level assembling method. Coating solder paste on a bonding pad of the assembly substrate; carrying out high-precision butt joint on a welding column of the CCGA device and the bonding pad; homogenizing the high-energy laser beam to form a homogeneous laser beam; and welding the abutting part of the welding column and the solder paste through a homogeneous laser beam, so that the solder paste is quickly melted and fully infiltrated with the welding column and the bonding pad to form an intermetallic compound. According to the method, rapid local welding is carried out on the welding columns and the bonding pads through homogeneous laser, CCGA device board-level assembly is achieved, internal thermal stress caused by long-time welding of a traditional reflow welding process method is effectively reduced, the process problems of welding column toppling, skewing, bridging, welding spot cracking and the like are effectively solved, and the reliability of the device board-level assembly process is effectively improved.

Description

Technical Field

[0001] The invention belongs to the technical field of integrated circuit manufacturing, and in particular relates to a CCGA device board-level assembly method. Background Art

[0002] As the scale of integrated circuits increases, the number of I / Os in packaged devices continues to increase, while the I / O pitch continues to decrease. The stress mismatch caused by the CTE difference between the ceramic substrate and the assembly substrate after the device is assembled at the board level, and the process and reliability issues induced by this, are becoming increasingly prominent. Compared with the traditional CBGA device that uses solder balls as the connection structure between the ceramic substrate and the assembly substrate, the CCGA device that uses solder pillars as the connection structure between the substrates increases the spacing between the ceramic substrate and the assembly substrate, which can alleviate the thermal stress mismatch effect. However, with the increase in the complexity of integrated circuit functions, the size and number of integrated chips inside the device are increasing, and the size of CCGA devices is increasing accordingly. The stress mismatch effect between the materials inside the assembled device is also becoming more prominent, which is typically manifested in defects such as substrate warping, solder pillar skew / dumping / bridging, and solder joint cracks during the board-level assembly process, which greatly affects the service life of the device.

[0003] In the process of CCGA device board-level assembly, the soldering method of the soldering column on the device is traditionally the reflow soldering process, which is to put all the board-level assembly devices into the reflow equipment for overall heating and soldering. Especially for large-scale CCGA device board-level assembly, during the process of thermal load changes such as heating and cooling, due to the large CTE difference between the substrates, the thermal stress is large, which is very easy to cause substrate deformation, solder column deviation, solder joint cracking and other process problems, reducing the process yield and service life. At the same time, the reflow soldering process takes a long time and the thermal stress accumulation is obvious, which will further aggravate the above process problems and has low processing efficiency. Summary of the invention

[0004] The present invention provides a CCGA device board-level assembly method, which can effectively improve the reliability and production efficiency of the board-level assembly process, thereby solving the technical problems mentioned in the background technology.

[0005] The technical solution of the present invention is as follows: A CCGA device board-level assembly method, comprising: S10: Apply solder paste on the pads of the assembly substrate; S20: performing high-precision docking of the soldering column of the CCGA device with the soldering pad; S30: homogenizing the high energy laser beam to form a homogeneous laser beam.

[0006] S40: welding the abutment between the solder column and the solder paste by a uniform laser beam, so that the solder paste melts quickly and fully infiltrates the solder column and the solder pad to form an intermetallic compound.

[0007] Furthermore, the method of applying solder paste in step S10 includes screen printing or solder paste spraying, and the area of ​​the solder paste is smaller than or equal to the pad area.

[0008] Furthermore, the step S20 includes: performing high-precision alignment of solder pillars and solder pads on the CCGA device by a high-precision patch system and abutting the solder pillars and solder pads.

[0009] Furthermore, the step S30 includes: The diffractive optical element is placed at the laser emitting end of the laser, and the diffractive optical element is spaced apart from the laser emitting end. The high-energy laser beam emitted by the laser passes through the diffractive optical element, and the Gaussian distribution spot is converted into a flat-top spot to form a uniform laser beam.

[0010] Furthermore, the step S40 includes: Irradiate one side of the CCGA device assembly substrate with a uniform laser beam, and adjust the size of the flat-top spot of the uniform laser beam so that the flat-top spot covers all pad positions on the assembly substrate; The laser parameters of the homogeneous laser beam are set, and the laser parameters include: laser type, laser wavelength, laser power density, and laser irradiation time.

[0011] Furthermore, the shape of the flat-top light spot includes one of a square, a rectangle, and a circle.

[0012] Furthermore, the high-energy laser beam is a single transverse laser beam or a multi-mode laser beam. Furthermore, the assembly substrate material includes BT, FR4 or ABF.

[0013] Furthermore, the solder paste material includes SnPb, SnAg or SnAgCu.

[0014] Furthermore, the solder column type is a straight type or a spring type, and the straight solder column includes a pure solder column, a copper tape wrapped type solder column, a copper tape braided type solder column, and a copper column.

[0015] Beneficial effects of the present invention: The present invention uses a uniform laser to perform rapid local welding of solder columns and solder pads to achieve board-level assembly of CCGA devices, effectively reduce the internal thermal stress caused by long-term welding in traditional reflow soldering processes, effectively improve process problems such as solder column tipping, skewing, bridging, and solder joint cracking, and effectively improve the reliability of the device board-level assembly process.

[0016] The assembly welding time of the present invention is shortened from the traditional reflow welding time of 15 minutes to the laser welding time of less than 3 seconds, further reducing the risk of process failures such as solder column tipping, skewing, bridging and solder joint cracking, while greatly shortening the board-level assembly process time and improving the board-level assembly efficiency of CCGA devices. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 It is a flow chart of a CCGA device board-level assembly method provided in one embodiment of the present invention.

[0018] Figure 2 It is a schematic diagram of aligning and fixing the mesh holes of a printed screen and the pads of an assembly substrate provided in one embodiment of the present invention.

[0019] Figure 3 It is a schematic diagram of brushing solder paste into mesh holes of a stencil provided in one embodiment of the present invention.

[0020] Figure 4 It is a schematic diagram of solder paste spraying on the pad of the assembly substrate in one embodiment of the present invention.

[0021] Figure 5a It is a schematic diagram of a CCGA device having straight solder pillars and an assembly substrate solder pad after high-precision alignment in one embodiment of the present invention.

[0022] Figure 5b It is a schematic diagram of a CCGA device with a spring-type solder column and an assembly substrate solder pad after high-precision alignment in one embodiment of the present invention.

[0023] Figure 6 It is a schematic diagram of homogenizing a high-energy laser beam to form a homogeneous laser beam in one embodiment of the present invention.

[0024] Figure 7a It is a schematic diagram of welding a side of a CCGA device assembly substrate having straight solder pillars irradiated by a uniform laser beam in one embodiment of the present invention.

[0025] Figure 7b It is a schematic diagram of welding one side of a CCGA device assembly substrate having a spring-type welding column irradiated by a uniform laser beam in one embodiment of the present invention.

[0026] Figure 8a It is a schematic diagram of a CCGA device with a straight solder column and an assembly substrate after homogeneous laser local welding in one embodiment of the present invention.

[0027] Figure 8b It is a schematic diagram of a CCGA device with a spring-type solder column and an assembly substrate after homogeneous laser local welding in one embodiment of the present invention. DETAILED DESCRIPTION

[0028] In order to enable those skilled in the art to better understand the scheme of the present invention, the technical scheme in the embodiment of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiment of the present invention. The described embodiment is only a part of the embodiment of the present invention, not all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present invention.

[0029] In one embodiment of the present invention, Figure 1 : is a flow chart provided by a CCGA device board-level assembly method according to the present invention, such as Figure 1 As shown, the present invention includes: S10: Apply solder paste on the pads of the assembly substrate.

[0030] Generally speaking, in order to solder the CCGA device to the assembly substrate, a soldering pad needs to be provided on the assembly substrate. Optionally, the number of the soldering pads on the assembly substrate is at least one.

[0031] Generally, the number of pads of the assembly substrate is positively correlated with the area of ​​the assembly substrate, for example, the larger the area of ​​the assembly substrate, the more pads there are. The pads of the assembly substrate are arranged on the side of the assembly substrate that needs to be welded to the CCGA device solder column.

[0032] The method of applying solder paste includes screen printing or solder paste spraying, and the area of ​​the solder paste is smaller than or equal to the pad area.

[0033] Apply solder paste on the pads of the assembled substrate. The options include but are not limited to the following two methods: First, solder paste is applied to the pads of the assembly substrate using screen printing, which includes the following two steps: First, place the solder paste printing stencil on the side of the assembly substrate with the pads. The mesh holes of the solder paste printing stencil are placed one by one with the pads on the assembly substrate, and the relative mesh hole diameter does not exceed the diameter of the pad. Figure 2 As shown, it is a schematic diagram of aligning and fixing the mesh of the printed screen with the pad of the assembly substrate provided in one embodiment of the present invention. Figure 2 In the embodiment, after the printing screen 22 is placed on the assembly substrate 20 , each mesh hole 221 on the printing screen 22 corresponds to the pad 201 on the assembly substrate 20 .

[0034] Then, use a scraper 23 to brush solder paste with an area corresponding to the mesh hole into each mesh hole and remove the printed screen. The area of ​​the solder paste is consistent with the area of ​​the mesh hole, and the height of the solder paste does not exceed the thickness of the stencil. Figure 3 As shown, it is a schematic diagram of brushing solder paste into the mesh of the stencil provided in one embodiment of the present invention. Figure 3 In the process, a certain volume of solder paste 202 is brushed into each mesh hole.

[0035] Optionally, the thickness of the printed stencil can be 0.1mm~0.3mm, and the specific thickness can be determined according to the pitch of the pads of the assembly substrate actually used. For example, the thickness of the printed stencil corresponding to the pads with a pitch of 0.6mm is 0.1mm, and the thickness of the printed stencil corresponding to the pads with a pitch of 1.5mm is 0.3mm. Optionally, the preparation process of the printed stencil of the above specifications includes but is not limited to mechanical processing, electroforming process, laser etching, etc., and this embodiment does not limit the preparation process of the printed stencil.

[0036] S20: performing high-precision docking of the soldering column of the CCGA device with the soldering pad.

[0037] Specifically, a high-precision patch system is used to perform high-precision alignment between solder pillars and solder pads on the CCGA device and to abut the solder pillars and solder pads.

[0038] First, after completing step S10, the assembled substrate is fixed on the carrier of the high-precision mounting system, and the center position of each pad on the assembled substrate is accurately located by the image tool of the high-precision mounting system.

[0039] Then, a CCGA device 21 with solder columns on one side is prepared, and the side of the CCGA device without solder columns is clamped by the clamping tool 25 of the high-precision mounting system, and the side of the CCGA device with solder columns is placed above the assembly substrate. The center position of each solder column on the CCGA device is accurately located by the imaging tool of the high-precision mounting system, and the center position of each solder column is aligned one by one with the center position of each solder pad, thereby completing the high-precision alignment of the solder columns on the CCGA device and the solder pads of the assembly substrate.

[0040] Optionally, the welding column type is straight type or spring type.

[0041] When the solder column type of the CCGA device is a straight type, the schematic diagram after the CCGA device having the straight solder column 211a is aligned with the assembly substrate pad 201 with high precision can be seen in FIG. Figure 5a shown.

[0042] When the solder column type of the CCGA device is a spring type, the schematic diagram after the CCGA device with the spring type solder column 211b is aligned with the assembly substrate pad 201 with high precision can be seen in FIG. Figure 5b shown.

[0043] Optionally, the straight solder column includes but is not limited to a pure solder column, a copper tape wrapped solder column, a copper tape woven solder column, a copper column, etc.

[0044] Optionally, the material of the solder column includes but is not limited to SnPb, BeCu or Cu.

[0045] Optionally, the high-precision mounting system may be a high-precision mounting machine.

[0046] Generally speaking, the diameter of the solder column on the CCGA device is set according to the diameter of the pad on the assembly substrate. In order to achieve effective welding between the CCGA device and the assembly substrate, the diameter of the solder column on the CCGA device shall not exceed the diameter of the pad on the assembly substrate. For example, the diameter of the solder column corresponding to a 0.8mm pad is 0.5mm.

[0047] S30: homogenizing the high energy laser beam to form a homogeneous laser beam.

[0048] The diffractive optical element is placed at the laser emitting end of the laser, and the diffractive optical element is spaced apart from the laser emitting end. The high-energy laser beam emitted by the laser passes through the diffractive optical element, and the Gaussian distribution spot is converted into a flat-top spot to form a uniform laser beam.

[0049] The energy distribution of traditional high-energy laser beams is Gaussian, and the energy distribution of the beam is extremely uneven. The excess energy in the center of the beam causes thermal damage to the ball carrier, and the energy at the edge of the beam is too low to achieve effective welding between the solder column and the solder pad. In a possible implementation, in order to industrially use laser beams on the solder pads of the assembly substrate to achieve efficient and highly reliable board-level assembly of solder columns, a corresponding diffractive optical element can be set for the high-energy laser beam. The diffractive optical element homogenizes the Gaussian distribution high-energy laser beam by controlling the phase of the laser beam to form a homogeneous laser beam with highly uniform energy distribution.

[0050] When a high energy laser beam is homogenized to form a homogeneous laser beam, the following steps may be included: First, the diffractive optical element is placed on the side of the laser emitting the high-energy laser beam. A certain working distance is set between the diffractive optical element and the high-energy laser beam. The specific working distance can be determined based on parameters such as the actual output uniform laser beam spot energy and spot size.

[0051] Then, the high-energy laser beam passes through the diffractive optical element, and the Gaussian distribution spot is transformed into a flat-top spot, forming a homogeneous laser beam. Figure 6 As shown, it is a schematic diagram of homogenizing a high-energy laser beam to form a uniform laser beam provided in one embodiment of the present invention. The high-energy laser beam 27 forms a uniform laser beam 28 after passing through the diffraction optical element 26.

[0052] The shape of the flat-top light spot includes but is not limited to square, rectangle, circle, etc.

[0053] The high-energy laser beam is a single transverse laser beam or a multi-mode laser beam.

[0054] The material of the diffractive optical element includes but is not limited to fused quartz, sapphire, plastic and the like.

[0055] S40: welding the abutment between the solder column and the solder paste by a uniform laser beam, so that the solder paste melts quickly and fully infiltrates the solder column and the solder pad to form an intermetallic compound.

[0056] A homogeneous laser beam is irradiated on one side of the CCGA device assembly substrate, and the size of the flat-top spot of the homogeneous laser beam is adjusted so that the flat-top spot covers all pad positions on the assembly substrate.

[0057] The laser parameters of the homogeneous laser beam are set, and the laser parameters include: laser type, laser wavelength, laser power density, and laser irradiation time.

[0058] The aligned board-level assembly components are subjected to a local welding process using a homogeneous laser beam, so that the solder paste melts quickly and fully infiltrates the solder columns and assembly substrate pads to form intermetallic compounds, completing efficient and highly reliable board-level assembly of CCGA components.

[0059] When the aligned board-level assembly components are subjected to a local welding process by a homogenous laser beam, the following steps may be included: First, after step 103, the clamping tool is removed, and a uniform laser beam is irradiated onto one side of the CCGA device assembly substrate, and the spot size of the uniform laser beam is adjusted so that the spot size can cover all pad positions on the assembly substrate.

[0060] Taking the straight solder column type as an example, the schematic diagram of uniform laser beam irradiating one side of the CCGA device assembly substrate with straight solder columns for welding can be seen in Figure 7a shown.

[0061] Taking the spring-type solder column as an example, the schematic diagram of the uniform laser beam irradiating the side of the CCGA device assembly substrate with the spring-type solder column for welding can be seen in Figure 7b shown.

[0062] Then, the laser type, laser wavelength, laser power density, laser irradiation time and other parameters of the homogeneous laser beam are set to make the solder paste melt quickly and fully infiltrate the solder column and the assembly substrate pad, so that intermetallic compounds are formed at the solder paste, solder column and assembly substrate welding interface. Generally, the laser-assisted welding process is divided into two steps, the preheating process and the welding process, to achieve effective welding.

[0063] The laser type, laser wavelength, laser power density, and laser irradiation time here are to ensure that the solder paste is fully melted, and to form intermetallic compounds with the solder column and the assembly substrate pad, so as to achieve low welding defects (voids, bridges, cold solder joints, etc.) and high welding strength. The setting value is set according to the structure of the CCGA board-level assembly and the composition of the solder paste. Generally speaking, the laser type is near-infrared laser; the laser wavelength is 700nm~1400nm; the laser power of the preheating process is 50W / cm2~100W / cm2, and the laser irradiation time is 0.5~1s; the laser power of the welding process is 100W / cm2~150W / cm2, and the laser irradiation time is 1~2s.

[0064] Taking the straight solder column type as an example, the schematic diagram of the CCGA device with a straight solder column and the assembly substrate after homogeneous laser local welding can be seen in Figure 8a shown.

[0065] Taking the spring type solder column as an example, the schematic diagram after the CCGA device with the spring type solder column and the assembly substrate are uniformly laser partially welded can be seen in Figure 8b shown.

[0066] During the laser welding process, protective gas is introduced to prevent oxidation of the solder column and solder paste.

[0067] Optionally, the protective gas includes but is not limited to nitrogen, helium or argon.

[0068] To sum up, the efficient and highly reliable CCGA device board-level assembly process method provided by the embodiment of the present invention realizes the CCGA device board-level assembly process through a uniform laser local rapid welding method, which greatly reduces the internal thermal stress of the board-level assembled device, improves process problems such as solder column tipping, skewness, bridging, and solder joint cracking, and improves the reliability of the board-level assembly process; at the same time, it greatly shortens the board-level assembly process time and improves the board-level assembly efficiency of CCGA devices.

[0069] Those skilled in the art will readily appreciate other solutions of the invention after considering the specification and practicing the invention invented herein. This application is intended to cover any variations, uses or adaptations of the invention that follow the general principles of the invention and include common knowledge or customary techniques in the art that are not invented by the present invention. The specification and examples are to be regarded as exemplary only, and the true scope and spirit of the invention are indicated by the following claims.

[0070] Finally, it should be noted that the above specific implementation methods are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to examples, those skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the spirit and scope of the technical solution of the present invention, which should be included in the scope of the claims of the present invention.

Claims

1. A CCGA device board-level assembly method, characterized in that: include: S10: Apply solder paste on the pads of the assembly substrate; S20: performing high-precision docking of the soldering column of the CCGA device with the soldering pad; S30: homogenizing the high energy laser beam to form a homogeneous laser beam; S40: welding the abutment between the solder column and the solder paste by a uniform laser beam, so that the solder paste melts quickly and fully infiltrates the solder column and the solder pad to form an intermetallic compound.

2. The CCGA device board-level assembly method according to claim 1, characterized in that: The method of applying solder paste in step S10 includes screen printing or solder paste spraying, and the area of ​​the solder paste is smaller than or equal to the pad area.

3. The CCGA device board-level assembly method according to claim 1, characterized in that: The step S20 includes: performing high-precision alignment between solder pillars and solder pads on the CCGA device by using a high-precision patch system and abutting the solder pillars and solder pads.

4. The CCGA device board-level assembly method according to claim 1, characterized in that: The step S30 comprises: The diffractive optical element is placed at the laser emitting end of the laser, and the diffractive optical element is spaced apart from the laser emitting end. The high-energy laser beam emitted by the laser passes through the diffractive optical element, and the Gaussian distribution spot is converted into a flat-top spot to form a uniform laser beam.

5. The CCGA device board-level assembly method according to claim 4, characterized in that: The step S40 comprises: Irradiate one side of the CCGA device assembly substrate with a uniform laser beam, and adjust the size of the flat-top spot of the uniform laser beam so that the flat-top spot covers all pad positions on the assembly substrate; The laser parameters of the homogeneous laser beam are set, and the laser parameters include: laser type, laser wavelength, laser power density, and laser irradiation time.

6. The CCGA device board-level assembly method according to claim 5, characterized in that: The shape of the flat-top light spot includes one of a square, a rectangle and a circle.

7. The CCGA device board-level assembly method according to claims 1-6, characterized in that: The high-energy laser beam is a single transverse laser beam or a multi-mode laser beam.

8. The CCGA device board-level assembly method according to any one of claims 1 to 6, characterized in that: The assembly substrate material includes BT, FR4 or ABF.

9. The CCGA device board-level assembly method according to any one of claims 1 to 6, characterized in that: The solder paste material includes SnPb, SnAg or SnAgCu.

10. The CCGA device board-level assembly method according to any one of claims 1 to 6, characterized in that: The solder column type is a straight type or a spring type, and the straight solder column includes a pure solder column, a copper tape wrapped solder column, a copper tape braided solder column, and a copper column.

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