Micro-spring structure column grid array high-precision high-strength plate-level assembling method

Abstract

The invention discloses a high-precision and high-strength plate-level assembly method and structure for a micro-spring structure column grid array, and belongs to the field of integrated circuit packaging. According to the method, additional auxiliary alignment jigs and steel mesh jigs for processing printing solder paste do not need to be processed, PVD, photoetching and electroplating processes compatible with a substrate preparation process are adopted, the prepared Pilllar type protrusions serve as limiting columns, and the micro-spring structure is rapidly positioned in the assembling stage, so that rapid and high-precision positioning alignment is achieved; and in the reflow stage, the top solder layer in the Pilllar type bulge is fused to be subjected to alloying reaction with the micro-spring structure and wrap and fill a welding spot gap, so that high-strength bonding interconnection is realized. The plate-level assembly scheme of the micro-spring structure has the advantages of simple assembly process, rapid positioning, high-precision alignment, high-strength bonding and the like from the aspect of process; from the perspective of jig processing cost, a special alignment jig and a printing screen plate do not need to be processed, and the advantages of low cost and high efficiency are achieved.

Description

Technical Field

[0001] This invention relates to the field of integrated circuit packaging technology, and in particular to a high-precision, high-strength board-level assembly method for a micro-spring structure pillar gate array. Background Technology

[0002] With the continuous advancement of innovative research and development in areas such as deep space exploration, long-term space stay, and reusable rockets, the special requirements for long lifespan of airborne products that undergo frequent flight tests under multiple physical field loads such as force, heat, high temperature, high humidity, and electricity have placed more stringent and higher demands on the reliability of component solder joints and service life.

[0003] First, in environments with large temperature variations and cycling, the stress caused by thermal mismatch reduces the reliability of traditional packaged solder joints, especially for large-size CBGA and CCGA packages. Second, under high-intensity impacts, solder joints in traditional packages are also prone to problems due to stress concentration. Furthermore, under long-term vibration environments, solder joints in traditional packages suffer from stress fatigue, making it difficult to guarantee long-term reliability. Under these harsh conditions, traditional PBGA, CBGA, and CCGA packages can no longer meet the requirements for high reliability and long service life.

[0004] As a novel form of bonded column grid array (CCGA), the micro-spring structure offers flexible connections and shows promising application prospects in the aforementioned specific scenarios. However, due to its hollow structure and light weight, the micro-spring structure is susceptible to vibration during material transfer or hot air disturbance in the reflow oven during board-level assembly, leading to alignment misalignment. Furthermore, the self-calibration effect during subsequent reflow can cause some micro-spring structures to twist and deform, affecting the bonding quality and reliability of the product. Summary of the Invention

[0005] The purpose of this invention is to provide a high-precision, high-strength plate-level assembly method and structure for micro-spring structure column grid arrays, so as to solve the problems in the background art.

[0006] To address the aforementioned technical problems, this invention provides a high-precision, high-strength plate-level assembly method and structure for a micro-spring structure column grid array, comprising the following steps: Step 1: Provide a substrate or PCB board with surface pads; deposit a conductive layer on the surface of the substrate or PCB board using a PVD process. Step 2: Cover the conductive layer with a layer of photoresist to create grooves corresponding to the surface pads; Step 3: The Pillar-type protrusion is prepared in the groove by electroplating process. The Pillar-type protrusion includes a conductive layer, a Cu layer, a Ni layer and a solder layer. Step 4: Apply a layer of active flux to the surface of the Pillar-shaped protrusion; Step 5: Another component is provided. The bottom of the component has an arrayed micro-spring structure. It is installed according to the assembly drawings and the corresponding Pillar-type protrusions covered with flux. No additional auxiliary alignment fixtures are required. Step 6: After the assembly is completed, the structure is placed in a reflow oven. After the solder layer melts, it undergoes an alloying reaction with the micro-spring structure and fills the gap between the solder joints, completing the high-precision and high-strength bonding and interconnection between the micro-spring structure and the Pillar-type protrusion. Step 7: Conduct quality checks on the assembled samples through cleaning processes and various testing methods to ensure the effectiveness of the bonding and interconnection between the devices and the substrate or PCB board.

[0007] In one embodiment, the flux is sprayed onto the top surface of the Pillar-shaped protrusion or covers the entire surface of the device, including the top and sides of the Pillar-shaped protrusion and the exposed portion of the substrate, by spraying, spin coating or printing.

[0008] In one embodiment, in step one, a conductive layer covers the surface pads, and the conductive layer is a TiW / Cu or Ti / Cu structure.

[0009] In one embodiment, after step three, the method further includes: removing the remaining photoresist and the exposed conductive layer through a process of resist removal, etching, and cleaning.

[0010] In one embodiment, the solder layer is made of SAC series, SnPb series and SnAg series, and the height of the solder layer is not less than 150μm.

[0011] In one embodiment, the surface pad is made of Al / Cu / CuNiPdAu / CuNiAu / CuNiSnAgCu / CuNiSnPb material.

[0012] In one embodiment, the diameter of the Pillar-type protrusion is set smaller than the size of the surface pad.

[0013] In one embodiment, the substrate or PCB board is made of FR4 / BT / ABF / silicon substrate / epoxy resin substrate / glass substrate rigid substrate.

[0014] In one embodiment, the micro-spring structure is made of SnPb alloy, BeCu alloy, or Cu.

[0015] The present invention provides a high-precision, high-strength plate-level assembly method and structure for a micro-spring structure column grid array, which has the following beneficial effects: (1) Unlike the micro-spring structure alignment process which uses special alignment fixtures or pre-made limiting balls, this method uses PVD, photolithography and electroplating processes that are compatible with the substrate preparation process to prepare Pillar-type protrusions as limiting posts, so as to achieve rapid and high-precision positioning and alignment of the micro-spring array. It does not require machining alignment fixtures, saving the cost of machining special alignment fixtures; it does not require the sample to be repeatedly switched between mechanical fixtures, reducing the risk of scratches and contamination on the surface of the substrate to be bonded; it does not require the pre-made limiting balls to undergo high and low temperature environments, which greatly reduces the warping caused by the accumulation of internal stress after the substrate has undergone high and low temperature environments. (2) Unlike the process of printing a layer of solder paste on the surface of the substrate or PCB board pads by printing a stencil in the board-level assembly of the micro-spring structure, this assembly process produces Pillar-type protrusions. The top of this structure is a solder layer with selectable height and material. After melting in reflow, it can directly alloy with the micro-spring structure. There is no need for additional stencil jigs for printing solder paste, saving the cost of processing stencils for printing solder paste. (3) The assembly process produces Pillar-type protrusions. During the reflow stage, the top solder layer in the Pillar structure melts and undergoes an alloying reaction with the micro-spring structure, which then wraps and fills the gap between the solder joints. This results in better wetting effect, higher bonding strength of the solder joints, and the realization of high-strength bonding interconnection. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of a high-precision, high-strength plate-level assembly structure of a micro-spring structure column grid array provided by the present invention; Figure 2 This is a schematic diagram of the substrate or PCB board structure to be assembled; Figure 3 This is a schematic diagram of creating a conductive layer on the surface of a substrate or PCB board. Figure 4 This is a schematic diagram of the groove structure corresponding to the surface pads being prepared in photoresist. Figure 5 This is a schematic diagram of fabricating a Pillar-type protrusion structure in a groove structure; Figure 6 This is a schematic diagram of covering the surface of a Pillar-type raised structure with a layer of active flux. Figure 7 This is a schematic diagram of the rapid and high-precision overlay of Pillar-type protrusions on the arrayed micro-spring structure at the bottom of the device. Figure 8 This is a schematic diagram showing how the solder layer fully fills and wraps the gaps between solder joints in the Pillar-shaped protrusions after reflow. Detailed Implementation

[0017] The following detailed description, in conjunction with the accompanying drawings and specific embodiments, provides a high-precision, high-strength plate-level assembly method and structure for a micro-spring structure column grid array proposed in this invention. The advantages and features of this invention will become clearer from the following description. It should be noted that the accompanying drawings are all in a very simplified form and use non-precise proportions, and are only used to facilitate and clarify the illustration of the embodiments of this invention.

[0018] Example 1 This invention provides a high-precision, high-strength plate-level assembly method for a micro-spring structure column grid array, comprising the following steps: S11, Provide as follows Figure 2 The substrate 100 shown has surface pads 103; the substrate can also be replaced by a PCB board. A conductive layer 101 is deposited on the surface of the substrate 100 to be assembled using a PVD process, such as... Figure 3 As shown, the conductive layer 101 covers the surface pad 103; S12. A layer of photoresist 102 is coated on the surface of the conductive layer 101, and grooves 104 corresponding to the surface pads 103 are prepared through processes such as exposure and development. Figure 4 As shown; S13. A Pillar-type protrusion 105 is fabricated within the groove 104 via electroplating. The Pillar-type protrusion 105 is structurally designed from bottom to top as a conductive layer 101, a Cu layer 106, a Ni layer 107, and a solder layer 108. Further, the remaining photoresist 102 and the exposed conductive layer 101 are removed through processes such as resist removal, etching, and cleaning. Figure 5 As shown; The role of the Ni layer 107 is to slow down the diffusion rate of Cu atoms into the solder layer, reduce the risk of voids caused by Cu atom migration on the bonding surface, and improve the reliability of the product. The thickness is set to 3μm. S14. A layer of active flux 109 is applied to the surface of the Pillar-type protrusion 105; such as Figure 6 As shown, flux 109 can be sprayed only on the top surface of Pillar-type protrusion 105, or it can cover the entire device surface, including the top and sides of Pillar-type protrusion 105 and the exposed portion of substrate 100. S15. The micro-spring structure 111, already arrayed at the bottom of device 110, is aligned and installed according to the assembly drawings with the Pillar-type protrusion 105 covered with flux 109. This achieves rapid, high-precision alignment and assembly without the need for additional auxiliary alignment fixtures. Figure 7 As shown; S16. The structure after assembly is as follows: Figure 8As shown, it is placed in a reflow oven. After the solder layer 108 structure melts, it undergoes an alloying reaction with the micro-spring structure 111. At the same time, the molten solder has a climbing rod effect, filling and wrapping the gap of the solder joint, thus completing the high-precision and high-strength bonding interconnection between the micro-spring structure 111 and the Pillar-type protrusion 105. S17. After assembly, the sample quality is checked through cleaning process and various testing methods to ensure the effectiveness of bonding and interconnection between device 110 and substrate 100.

[0019] Example 2 Based on the method in Example 1, a high-precision, high-strength plate-level assembly structure of a micro-spring structure column grid array was fabricated, such as... Figure 1 As shown, the substrate includes a substrate 100. The upper surface of the substrate 100 has surface pads 103. Pillar-type bumps 105 are formed on the surface pads 103. The pillar-type bumps 105 are composed of a conductive layer 101, a Cu layer 106, a Ni layer 107, and a solder layer 108 from bottom to top. The conductive layer 101 is a TiW / Cu or Ti / Cu layer. The surface of the pillar-type bumps 105 is covered with an active flux 109.

[0020] Pillar-shaped protrusions 105 provide rapid positioning and limiting for the bottom arrayed micro-spring structure 111 of the device 110 structure. Inserting Pillar-shaped protrusions 105 into the micro-spring structure 111 limits the micro-spring structure 111 from shifting due to vibration or heat flow disturbance, thus ensuring the alignment accuracy before reflow soldering.

[0021] Through the reflow process, the solder layer 108 structure at the top of the Pillar-type protrusion 105 melts and undergoes an alloying reaction with the micro-spring structure 111, filling and wrapping the gaps between the solder joints to complete a high-strength bonded interconnection.

[0022] This invention provides a high-precision, high-strength board-level assembly method and structure for a micro-spring structure pillar grid array. Unlike the micro-spring structure alignment process which uses special alignment fixtures or pre-fabricated limiting balls, this assembly process uses PVD, photolithography, and electroplating processes compatible with the substrate preparation process to prepare Pillar-shaped protrusions as limiting pillar structures, which can achieve rapid and high-precision positioning and alignment of the micro-spring array.

[0023] Using the prepared Pillar-shaped protrusions as limiting posts eliminates the need for machining alignment fixtures, saving the cost of dedicated alignment fixtures. It also eliminates the need for repeated switching of samples between mechanical fixtures, reducing the risk of scratches and contamination on the substrate surface to be bonded. Furthermore, it avoids the need for pre-fabricated limiting balls to withstand high and low temperature environments, significantly reducing warping caused by stress accumulation on the substrate after exposure to such environments. Unlike micro-spring structures that require printing a layer of solder paste onto the substrate or PCB pads using a stencil during board-level assembly, this process produces Pillar-shaped limiting post structures with a solder layer at the top, the height and material of which can be selected. After melting during reflow, this layer can directly alloy with the micro-spring structure and fill the gaps between solder joints, resulting in better wetting and higher solder joint bonding strength. This achieves high-strength bonding interconnection without the need for additional stencil fixtures for solder paste printing, saving the cost of stencil printing.

[0024] The above description is merely a description of preferred embodiments of the present invention and is not intended to limit the scope of the present invention in any way. Any changes or modifications made by those skilled in the art based on the above disclosure shall fall within the protection scope of the claims.

Claims

1. A high-precision, high-strength plate-level assembly method for a micro-spring structure column grid array, characterized in that, Includes the following steps: Step 1: Provide a substrate or PCB board with surface pads; deposit a conductive layer on the surface of the substrate or PCB board using a PVD process. Step 2: Cover the conductive layer with a layer of photoresist to create grooves corresponding to the surface pads; Step 3: The Pillar-type protrusion is prepared in the groove by electroplating process. The Pillar-type protrusion includes a conductive layer, a Cu layer, a Ni layer and a solder layer. Step 4: Apply a layer of active flux to the surface of the Pillar-shaped protrusion; Step 5: Another component is provided. The bottom of the component has an arrayed micro-spring structure. It is installed according to the assembly drawings and the corresponding Pillar-type protrusions covered with flux. No additional auxiliary alignment fixtures are required. Step 6: After the assembly is completed, the structure is placed in a reflow oven. After the solder layer melts, it undergoes an alloying reaction with the micro-spring structure and fills the gap between the solder joints, completing the high-precision and high-strength bonding and interconnection between the micro-spring structure and the Pillar-type protrusion. Step 7: Conduct quality checks on the assembled samples through cleaning processes and various testing methods to ensure the effectiveness of the bonding and interconnection between the devices and the substrate or PCB board.

2. The high-precision, high-strength plate-level assembly method for micro-spring structure column grid arrays as described in claim 1, characterized in that, The flux is sprayed onto the top surface of the Pillar-shaped protrusion or covers the entire surface of the device, including the top and sides of the Pillar-shaped protrusion and the exposed portion of the substrate, by spraying, spin coating or printing.

3. The high-precision, high-strength plate-level assembly method for micro-spring structure column grid arrays as described in claim 1, characterized in that, In step one, the conductive layer covers the surface pads, and the conductive layer is a TiW / Cu or Ti / Cu structure.

4. The high-precision, high-strength plate-level assembly method for micro-spring structure column grid array as described in claim 1, characterized in that, After step three, the process further includes removing the remaining photoresist and exposed conductive layer through a process of resist removal, etching, and cleaning.

5. The high-precision, high-strength plate-level assembly method for micro-spring structure column grid array as described in claim 1, characterized in that, The solder layer is made of SAC series, SnPb series and SnAg series, and the height of the solder layer is not less than 150μm.

6. The high-precision, high-strength plate-level assembly method for micro-spring structure column grid array as described in claim 1, characterized in that, The surface pads are made of Al / Cu / CuNiPdAu / CuNiAu / CuNiSnAgCu / CuNiSnPb material.

7. The high-precision, high-strength plate-level assembly method for micro-spring structure column grid array as described in claim 1, characterized in that, The diameter of the Pillar-type protrusion is set smaller than the size of the surface pad.

8. The high-precision, high-strength plate-level assembly method for micro-spring structure column grid array as described in claim 1, characterized in that, The substrate or PCB board is made of FR4 / BT / ABF / silicon substrate / epoxy resin substrate / glass substrate, a rigid substrate.

9. The high-precision, high-strength plate-level assembly method for micro-spring structure column grid array as described in claim 1, characterized in that, The micro-spring structure is made of SnPb alloy, BeCu alloy, or Cu.

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