Ball placement apparatus for printed circuit board assembly and method of soldering

Abstract

The application provides a ball mounting welding device for printed circuit board assemblies and a welding method thereof, and belongs to the technical field of chip testing equipment manufacturing. The device comprises: a first PCBA and a second PCBA arranged opposite to the first PCBA; a solder ball connecting structure arranged between the first PCBA and the second PCBA and used for connecting the first PCBA and the second PCBA after welding; and a rigid support part arranged between the first PCBA and the second PCBA, comprising a first surface and a second surface opposite to each other and a plurality of support bosses arranged thereon, the rigid support part is provided with a avoiding hole penetrating through the first surface and the second surface, at least part of the solder ball connecting structure penetrates through the avoiding hole, the support bosses are respectively arranged between adjacent avoiding holes, and the rigid support part abuts against the first PCBA and the second PCBA. The application realizes gap control and load bearing of face-to-face welding of PCBAs, and greatly improves the anti-warping capability and the reliability of welding points.

Description

Technical Field

[0001] This invention relates to the technical field of chip testing equipment manufacturing, and in particular to a ball-mounting soldering apparatus and soldering method for printed circuit board assemblies. Background Technology

[0002] With the trend towards miniaturization and high-density integration in electronic products, the electrical interconnection methods between circuit board assemblies have become a key factor restricting product size and reliability. Traditional electrical connections between two printed circuit board assemblies (PCBAs) mainly employ board-to-board connectors and flexible printed circuit (FPC) cabling. However, these solutions have technical defects and application limitations in terms of Z-axis height, signal integrity, and mechanical reliability.

[0003] In the field of chip testing, test PCBAs (also known as test load boards, probe carrier boards, or device under test boards) need to operate under high-temperature conditions for extended periods (e.g., typical temperature range of -40℃ to 150℃), while simultaneously withstanding probe pressure (total downward pressure can reach several kilograms to tens of kilograms) and impact loads from the opening and closing of test sockets. Large-size PCBAs (e.g., 200×300mm and above) are highly susceptible to warping deformation under thermo-mechanical coupling, directly leading to uneven contact force between the probes and chip pads, resulting in deviations in test results. However, existing technologies cannot simultaneously meet the requirements of low Z-axis interconnect height, high anti-warping stiffness, high solder joint reliability, low cost, and high production efficiency in the high-temperature, high-pressure, and large-size PCBA application scenarios of the chip testing industry.

[0004] For example, board-to-board connector solutions have drawbacks such as large Z-axis height (typically 1.5-5mm), increased contact resistance at high temperatures leading to signal integrity degradation, and inability to provide bending stiffness; FPC cabling solutions suffer from accelerated insulation aging at high temperatures, limited impedance control accuracy, and lack of support capabilities; direct pad soldering between PCB boards lacks a rigid support structure, the solder joint height is uncontrollable, and it bears all thermal and mechanical stresses; while ball grid array stacked packaging solutions belong to the chip-level packaging field and cannot be directly applied to large-size PCBA scenarios.

[0005] In view of this, a novel ball-mounting soldering device and soldering method for printed circuit board assemblies are proposed to solve all or part of the above problems. Summary of the Invention

[0006] To address at least one of the aforementioned problems and deficiencies in the prior art, embodiments of the present invention provide a ball-mounting soldering apparatus and method for inter-printed circuit board assemblies. By embedding a rigid support portion with clearance holes between two face-to-face soldered printed circuit board assemblies (PCBAs), the thickness of the rigid support portion precisely controls the soldering gap between the PCBA boards, ensuring consistent solder joint height. This rigid support portion also bears external mechanical loads during the finished PCBA assembly usage stage, minimizing stress on the solder joints. Simultaneously, a surface support formed by a large-area continuous support boss integrates the two PCBAs into a single unit, significantly improving bending stiffness and resisting high-temperature warping deformation. This ensures electrical interconnection while integrating gap control, mechanical load-bearing, and anti-warping support functions. Under high-temperature and high-pressure conditions during chip testing, it offers advantages such as low Z-axis height (more than 70% lower than connector solutions), high reliability (solder joint shear strength retention rate ≥90% at 125℃ / 1000h), and low cost. The technical solution is as follows:

[0007] According to one aspect of the present invention, a ball-mounting soldering apparatus for inter-printed circuit board assemblies is provided. The ball-mounting soldering apparatus includes:

[0008] First printed circuit board assembly;

[0009] The second printed circuit board assembly is disposed opposite to the first printed circuit board assembly;

[0010] A solder ball connection structure is disposed between the first printed circuit board assembly and the second printed circuit board assembly. The solder ball connection structure is used to connect the first printed circuit board assembly and the second printed circuit board assembly after soldering.

[0011] A rigid support portion is disposed between a first printed circuit board assembly and a second printed circuit board assembly. The rigid support portion includes a first surface and a second surface facing away from each other, and a plurality of support bosses disposed on the first surface and / or the second surface. The first surface faces the first printed circuit board assembly, and the second surface faces the second printed circuit board assembly. The rigid support portion has clearance holes that pass through the first surface and the second surface. At least a portion of the solder ball connection structure passes through the clearance holes. The support bosses are respectively located between adjacent clearance holes. The rigid support portion abuts against the first printed circuit board assembly and the second printed circuit board assembly respectively.

[0012] According to another aspect of the present invention, a method for ball bonding between printed circuit board assemblies is provided, the method being used with the ball bonding apparatus described above. The ball bonding method includes the following steps:

[0013] Provide a first printed circuit board assembly and a second printed circuit board assembly;

[0014] Solder balls are implanted on one of the first printed circuit board assembly and the second printed circuit board assembly, and solder paste is applied to the other.

[0015] A rigid support is provided, and a clearance hole is provided on the rigid support. The rigid support is disposed between the first printed circuit board assembly and the second printed circuit board assembly, so that the solder balls pass through the clearance hole.

[0016] Align and join the first printed circuit board assembly and the second printed circuit board assembly so that each solder ball contacts the corresponding solder paste layer.

[0017] During reflow soldering, the thickness of the rigid support limits the minimum spacing between the first and second printed circuit board assemblies to ensure that the height of each solder joint remains consistent.

[0018] The ball-mounting soldering apparatus and soldering method for printed circuit board assemblies provided in the embodiments of the present invention have at least one or a portion of the following advantages:

[0019] (1) By setting a rigid support with clearance holes between the first PCBA and the second PCBA, the relative position and distance between the two PCBAs are limited by the thickness of the rigid support. During the welding process, the welding gap is controlled to ensure that the height of each solder joint is consistent. During the finished product use stage, the external mechanical load is borne so that the solder joints are free from stress to the maximum extent. Thus, the functions of electrical interconnection, gap control, mechanical bearing and anti-warping support are integrated.

[0020] (2) By setting a first pad on the first PCBA and a second pad on the second PCBA, and welding a solder ball array between the two, the pad positions correspond one-to-one, thus realizing reliable electrical interconnection between the two PCBAs;

[0021] (3) By opening clearance holes on the rigid support part that correspond one-to-one with the solder ball array, each solder ball passes through the corresponding clearance hole, which not only ensures the electrical connection function of the solder ball, but also avoids the interference of the rigid support part on the solder ball.

[0022] (4) By setting the diameter of the clearance hole of the rigid support to be greater than the diameter of the solder ball and the difference to be not less than 0.1mm, and leaving a safe distance between the edge of the clearance hole and the edge of the solder pad, and the inner wall of the clearance hole is a rounded corner structure, the short circuit caused by solder crawling and the hole wall damage to the solder ball are effectively avoided.

[0023] (5) The rigid support has a coverage area of ​​not less than 60% of the area of ​​the smaller of the two PCBA boards in the direction parallel to the PCBA board surface, providing continuous surface support, so that the bending stiffness of the PCBA is improved from the PCBA's own stiffness to "PCBA + rigid support composite stiffness", and the overall bending stiffness is significantly improved.

[0024] (6) By setting the matching relationship between the thickness of the rigid support and the diameter of the solder ball: 0.45mm solder ball corresponds to a thickness of 0.3-0.35mm, 0.6mm solder ball corresponds to a thickness of 0.4-0.45mm, and the thickness accuracy is controlled within ±0.02mm to ensure the consistency of the welding gap and the stability of signal transmission;

[0025] (7) By setting a support boss on the surface of the rigid support part and setting the height to 0.05-0.10mm, the total surface area does not exceed 15% of the surface area of ​​the rigid support part body. When the PCBA is flat, the pressing force is borne by the surface of the rigid support part body. When the PCBA is warped, the support boss contacts the warped area to provide local support, thus realizing the adaptive support function of "not intervening when flat and triggering as needed when warped".

[0026] (8) By setting the support boss as a discrete micro-bump structure, the support is provided in the form of point contact. In the flat state, it only maintains "just contact" or "micro-force contact" with the PCBA. The majority of the pressing force is borne by the large area of ​​the rigid support, which effectively avoids stress concentration and lifting effect.

[0027] (9) By setting the support bosses as a continuously distributed frame-type protrusion structure, the adjacent micro-protrusions are connected longitudinally and / or laterally, which enhances the structural lateral connection stiffness and stability of the rigid support in the adjacent clearance hole area.

[0028] (10) By setting a positioning structure on the rigid support, the precise alignment between it and the PCBA is achieved, ensuring the precise alignment of the solder ball and the clearance hole, and the solder pad and the solder ball, and avoiding the solder ball being scratched and damaged by the hole wall;

[0029] (11) By filling the gap between two PCBAs and around the solder joints with bottom filler glue, the thermal fatigue resistance of the solder joints can be improved, the thermal cycle life can be increased by about 16 times, and the drop impact resistance can be increased by 3-5 times.

[0030] (12) The ball-mounting and soldering method of the present invention, through the process of ball-mounting --> paste printing --> installation of rigid support --> alignment and closing --> reflow soldering, the thickness of the rigid support limits the minimum distance between the two PCBAs during the reflow soldering process, so that the height of each solder joint is consistent. The peak temperature of reflow soldering is 240-270℃, and all interconnections are completed in one reflow soldering, without the need for an additional screw-locking process.

[0031] (13) The rigid support part uses a material with a thermal expansion coefficient that matches that of the PCBA substrate. Under high temperature conditions, the two expand and contract synchronously without generating additional thermal stress; and the metal rigid support part also functions as a heat distribution plate, which can eliminate local hot spots.

[0032] (14) In addition to the welding process, X-ray inspection and electrical testing (contact resistance test) were also carried out to ensure the reliability and traceability of the welding quality. Attached Figure Description

[0033] These and / or other aspects and advantages of the present invention will become apparent and readily understood from the following description of preferred embodiments taken in conjunction with the accompanying drawings, in which:

[0034] Figure 1 This is a schematic diagram of the overall structure of a ball-mounting and soldering device for PCBAs according to an embodiment of the present invention;

[0035] Figure 2 for Figure 1 A schematic diagram of the overall structure of the ball-planting welding device from another view direction;

[0036] Figure 3 This is a schematic diagram of the rigid support portion of a ball-planting welding apparatus according to an embodiment of the present invention;

[0037] Figure 4 This is a schematic diagram of the arrangement of clearance holes and support bosses on a rigid support portion according to another embodiment of the present invention.

[0038] Figure 5 This is a schematic diagram of the assembly structure and its partial cross-sectional structure of the ball-planting welding device after welding according to an embodiment of the present invention.

[0039] Figure 6 This is a process flow diagram of a ball-mounting and soldering method for PCBAs according to an embodiment of the present invention;

[0040] Figure 7 This is a schematic diagram of the overall structure of a ball-mounting and soldering device for PCBAs according to another embodiment of the present invention.

[0041] The reference numerals in the attached figures are explained as follows:

[0042] 100-Ball Welding Device;

[0043] 110 - First printed circuit board assembly, 111 - First pad;

[0044] 120 - Second printed circuit board assembly, 121 - Second pad;

[0045] 130 - Ball-joint structure;

[0046] 140 - Rigid support section

[0047] 141-Allowing hole, 142-Positioning boss, 143-Supporting boss, 143a-Frame-type protrusion, 143b-Micro-protrusion structure. Detailed Implementation

[0048] The technical solution of the present invention will be further described in detail below through embodiments and in conjunction with the accompanying drawings. In this specification, the same or similar reference numerals indicate the same or similar components. The following description of the embodiments of the present invention with reference to the accompanying drawings is intended to explain the overall inventive concept of the present invention and should not be construed as a limitation thereof.

[0049] Combination Figures 1-5 As shown, the ball bonding apparatus 100 of the present invention mainly includes a first printed circuit board assembly 110, a second printed circuit board assembly 120, a ball bonding structure 130, and a rigid support portion 140.

[0050] The first printed circuit board assembly 110 is the first printed circuit board assembly to be interconnected, such as a test equipment interface board. It has a plurality of first pads 111 on the side facing the second printed circuit board assembly 120. These first pads 111 require surface treatment, preferably using electroless nickel-gold plating or an organic solder resist. Further, a layer of solder paste is applied to the first pads 111 for fusion bonding with solder balls during reflow soldering. The first printed circuit board assembly 110 has positioning holes and mounting holes.

[0051] The second printed circuit board assembly 120 is a second printed circuit board assembly to be interconnected, such as a device under test (DUT) test board. It has a plurality of second pads 121 on the side facing the first printed circuit board assembly 110. The positions of these second pads 121 correspond one-to-one with the plurality of first pads 111 of the first printed circuit board assembly 110. The surface treatment of the second pads 121 is similar to that of the first pads 111, and will not be described further here. The second printed circuit board assembly 120 also has positioning holes and mounting holes. Other areas, except for specially designed clearances, are designated as no-layout zones and are insulated for mating with the rigid support portion 140.

[0052] A solder ball connection structure 130 is disposed between the first printed circuit board assembly 110 and the second printed circuit board assembly 120 to achieve electrical interconnection between the two. The solder ball connection structure 130 can be disposed on the first pad 111 of the first printed circuit board assembly 110 or on the second pad 121 of the second printed circuit board assembly 120. The positions of the first pad 111 and the second pad 121 are one-to-one, only requiring that the side with the solder ball connection structure 130 is located between the two printed circuit boards. In the following detailed description of the embodiments, the example of disposing of the solder ball connection structure 130 on the second pad 121 of the second printed circuit board assembly 120 is used (a common adaptation requirement of existing equipment).

[0053] Furthermore, the material of the solder ball connection structure 130 is preferably high-temperature solder SAC305 (tin-silver-copper alloy, containing 96.5% tin, 3.0% silver, and 0.5% copper) or high-temperature solder SAC405 (tin-silver-copper alloy, containing 95.5% tin, 4.0% silver, and 0.5% copper), wherein the diameter of the solder ball is in the range of 0.3-0.76 mm.

[0054] A rigid support portion 140 is disposed between the first printed circuit board assembly 110 and the second printed circuit board assembly 120. The rigid support portion 140 has clearance holes 141 through which the solder ball connection structure 130 passes. The rigid support portion 140 defines the relative position between the first printed circuit board assembly 110 and the second printed circuit board assembly 120, and the overall thickness of the rigid support portion 140 defines the distance between the first printed circuit board assembly 110 and the second printed circuit board assembly 120, thereby controlling the solder gap during the soldering process and bearing external mechanical loads during the finished product's use.

[0055] The rigid support 140 can simultaneously achieve the following four main functions: First, it controls the soldering gap between the two printed circuit boards during reflow soldering to ensure that the height of each solder joint is consistent; second, it bears the pressure of the probe and the impact load of the test seat in the finished structure, so that the solder joints are minimally subjected to stress; third, it provides bending stiffness for large-size printed circuit boards as a continuous rigid skeleton to resist board warping deformation under high temperature conditions; fourth, it achieves uniform support between boards through the continuous surface contact of the rigid support 140, avoiding stress concentration caused by discrete support.

[0056] In one specific embodiment, the rigid support portion 140 includes a first surface and a second surface facing away from each other, and a plurality of support bosses 143 disposed on the first surface and / or the second surface. The first surface faces the first printed circuit board assembly 110, and the second surface faces the second printed circuit board assembly 120. The rigid support portion 140 has clearance holes 141 that penetrate the first surface and the second surface. At least a portion of the solder ball connection structure 130 passes through the clearance holes 141. The support bosses 143 are respectively located between adjacent clearance holes 141. The rigid support portion 140 abuts against the first printed circuit board assembly 110 and the second printed circuit board assembly 120 respectively.

[0057] The height of the support boss 143 corresponds to the amount of warping deformation of the PCBA. This correspondence allows the rigid support part 140 to contact the warped area through the top surface of the support boss 143 and provide local support force when the PCBA warps significantly.

[0058] In a preferred embodiment, when a support boss 143 is provided on the first surface and the warping deformation of the first printed circuit board assembly 110 toward the rigid support portion 140 is greater than or equal to the height of the top surface of the support boss 143 protruding from the first surface, the warped area of ​​the first printed circuit board assembly 110 abuts against the first surface.

[0059] In another preferred embodiment, when a support boss 143 is provided on the second surface and the deformation of the second printed circuit board assembly 120 towards the rigid support portion 140 is greater than or equal to the height of the top surface of the support boss 143 protruding from the second surface, the warped area of ​​the second printed circuit board assembly 120 abuts against the second surface.

[0060] Combination Figures 3-5 As shown, the specific structural design of the rigid support 140 is described below:

[0061] In a preferred embodiment, the rigid support 140 is made of a material with a coefficient of thermal expansion that matches that of the PCBA substrate to reduce thermal stress under high-temperature conditions. Exemplarily, FR-4 fiberglass board (coefficient of thermal expansion approximately 14-17 ppm / °C), ceramic board (coefficient of thermal expansion approximately 6-8 ppm / °C), or surface-insulated metal board (e.g., aluminum or copper substrate) can be used. For high-temperature scenarios in chip testing, ceramic or metal boards are preferred because they have higher flexural modulus and better thermal conductivity, providing both flexural strength and uniform heat dissipation. Specifically, the difference between the coefficient of thermal expansion of the rigid support 140 and that of the PCBA substrate is less than or equal to 5 ppm / °C.

[0062] In a preferred embodiment, the thickness (denoted by H) of the rigid support portion 140 is determined based on the target eutectic height after solder ball reflow. For example, for solder balls with a diameter of 0.45 mm, H is preferably 0.3-0.35 mm; for solder balls with a diameter of 0.6 mm, H is preferably 0.4-0.45 mm. In principle, the thickness H of the rigid support portion 140 needs to be approximately 0.1 mm less than the corresponding solder ball diameter to ensure consistent soldering height and stable signal transmission; the accuracy of the thickness H is controlled within ≤±0.02 mm.

[0063] In a preferred embodiment, the positions of a plurality of clearance holes 141 formed on the rigid support portion 140 should correspond one-to-one with the solder ball connection structure 130 (forming a solder ball array) disposed between the first printed circuit board assembly 110 and the second printed circuit board assembly 120. In principle, the diameter of the clearance hole 141 (denoted as D_hole) should be larger than the diameter of the solder ball (denoted as D_ball), with an allowable tolerance δ = D_hole - D_ball ≥ 0.1 mm. The gap between a single clearance hole 141 and a matching single solder ball is set to be not less than 0.1 mm, such that this gap is greater than the 0.1 mm tolerance range for ball grid array (BGA) stencil ball placement.

[0064] For example, such as Figure 3 As shown, positioning bosses 142 can also be arranged on the rigid support portion 140. Pre-positioning can prevent the solder balls from being scratched and damaged by the wall of the clearance hole 141. In addition, the inner wall of the clearance hole 141 is rounded to avoid damage to the solder balls, and a safe distance is left between the edge of the clearance hole 141 and the edge of the second pad 121 (for example, the safe distance is set to ≥0.05mm) to prevent solder creep from causing short circuits.

[0065] The positioning bosses 142 can be respectively disposed on the upper and lower surfaces of the rigid support portion 140, specifically in the form of cylinders or protruding columnar structures that mate with positioning holes. The positioning bosses 142 correspond to the positioning holes on the first printed circuit board assembly 110 or the second printed circuit board assembly 120, achieving precise alignment. The positioning bosses 142 and the clearance holes 141 are machined using the same reference surface during processing, ensuring that after the rigid support portion 140 is installed, the clearance holes 141 can be precisely aligned with the solder ball array positions on the first printed circuit board assembly 110 or the second printed circuit board assembly 120.

[0066] In a preferred embodiment, a support boss 143 is further provided within the array region of the clearance holes 141 of the rigid support portion 140, which can be disposed on the upper surface and / or lower surface of the rigid support portion 140. The specific structure can be as follows: Figure 3 The continuously distributed border-shaped protrusions 143a shown, or as... Figure 4 The discretely distributed micro-bump structure 143b is shown. The main function of the support boss 143 is to preferentially contact the PCBA and provide support when two opposing PCBAs undergo thermal warping, so as to keep the solder gaps in all areas of the PCBA board consistent.

[0067] Specifically, the structural relationship between the supporting boss 143 and the body (integral plate surface) of the rigid support 140 is as follows: the supporting boss 143 protrudes above the surface of the body, and the absolute height of the top of the supporting boss 143 (denoted by H_protrusion) = the thickness H of the body + the boss height h. The value range of the boss height h is 0.05mm ≤ h ≤ 0.10mm, preferably h = 0.05mm, 0.06mm, or 0.07mm. The discretely distributed micro-protrusion structure can be designed as an independent columnar structure located between several adjacent clearance holes 141; the continuously distributed frame-type protrusion structure can be designed as an integral frame structure that connects adjacent micro-protrusion structures longitudinally and / or laterally according to the spacing requirements.

[0068] Furthermore, the total surface area of ​​the support bosses 143 does not exceed 15% of the overall surface area of ​​the rigid support portion 140. When the first printed circuit board assembly 110 and the second printed circuit board assembly 120 are in a flat state and pressed together, the pressing force F is applied evenly by both to the surface of the rigid support portion 140. Since the surface area of ​​the rigid support portion 140 is much larger than the total area of ​​the support bosses 143 therein, according to the pressure formula P=F / A (A is the pressure-bearing area), more than 85% of the pressing force is borne by the large surface area of ​​the body, and the force distributed to each micro-bore will become extremely small (the force per square millimeter is only less than 1 / 6 of that on the body surface).

[0069] Meanwhile, the materials of the PCBA substrate (e.g., FR-4, thickness ≥ 0.8 mm) and the rigid support 140 themselves have a certain elastic modulus at the microscale (FR-4 elastic modulus is approximately 20-28 GPa). The 0.05 mm boss height h will be accommodated by a small elastic deformation of 0.02-0.03 mm during pressing. Therefore, in a flat state, the support boss 143 and the back of the PCBA are only in "just contact" or "micro-force contact" state, with the contact force < 5% of the total pressure, thus avoiding significant lifting effect or stress concentration.

[0070] When the first printed circuit board assembly 110 and the second printed circuit board assembly 120 undergo slight warping deformation due to heat or pressure (warping amount > 0.03 mm), the surface of the rigid support portion 140 separates from the back of the PCBA in the warped area (forming a suspension). At this time, the support boss 143, which was originally "just in contact," first contacts the warped back of the PCBA, providing local compensation support force and preventing the solder joints in this area from bearing additional tensile stress due to loss of support. The design of the support boss 143 realizes an adaptive support function of "not intervening when flat and triggering as needed when warped." Compared with the solution of simply using the remaining part of the rigid support portion 140 after drilling holes as a support, the point contact design of the micro-bump can generate stress during the soldering process, offsetting the warping deformation of the PCBA and ensuring contact flatness.

[0071] The supporting boss 143 and the rigid support portion 140 are integrally formed. For example, if the rigid support portion 140 is made of metal, it can be manufactured using a stamping and cold forging process; if it is made of FR-4 / resin-based composite material, it can be manufactured using a molding process; if it is made of ceramic, it can be manufactured using a dry pressing process. Those skilled in the art will understand that these processes are mature manufacturing processes in the field, with dimensional accuracy reaching ±0.02 mm.

[0072] In a preferred embodiment, the rigid support 140 has a coverage area in the direction parallel to the board surface of the first printed circuit board assembly 110 and the second printed circuit board assembly 120 that is not less than 45% to 75% (preferably 50% to 60%) of the smaller PCBA board surface area of ​​the first printed circuit board assembly 110 and the second printed circuit board assembly 120.

[0073] For example, for a 200mm × 300mm PCBA, the coverage area of ​​the rigid support 140 can be designed to be 45% of the smaller board area (approximately 27000mm²). 2 ), 60% (approximately 36000 mm) 2 ) or 75% (approximately 45000mm) 2 This provides sufficient continuous support stiffness, offering a spatial structural foundation for "continuous surface support" and "load bypass transfer." The coverage area can be adjusted within this range according to specific application scenarios and stiffness requirements; a larger area results in stronger anti-warping capabilities, and the design can balance the layout of avoidance holes and processing costs. Through the above material selection and structural design, the rigid support 140 in each embodiment of the present invention provides effective mechanical reinforcement for the entire ball-mounting and soldering device 100, particularly effectively solving the warping deformation problem of the chip testing PCBA under high temperature and high pressure conditions. The mechanism of this mechanical reinforcement mainly includes the following aspects:

[0074] First, continuous surface support replaces discrete point support. Traditional screw / support column solutions provide support only at a limited number of discrete points, and the PCBA area between these support points can still deform freely under thermal stress and mechanical forces. The rigid support portion 140 of this invention covers most of the area of ​​two PCBAs, providing continuous surface support, thereby increasing the bending stiffness of any PCBA from "PCBA's own stiffness" to "PCBA + rigid support portion 140 composite stiffness," significantly improving the overall bending stiffness.

[0075] Second, thermal expansion matching design. The thermal expansion coefficient of the material of the rigid support part 140 matches that of the PCBA substrate. Under high temperature environment, the two expand and contract approximately synchronously, without generating additional thermal stress.

[0076] Third, load bypass transmission. During chip testing, the pressure F from the external probe is transmitted through the path of the second printed circuit board assembly 120 --> support boss 143 --> rigid support 140 --> first printed circuit board assembly 110. The entire load path does not pass through the solder balls and solder joints, and the solder joints are protected from shear and tensile stress.

[0077] Fourth, it homogenizes temperature distribution. The rigid support part 140 made of metal also has good thermal conductivity, which can quickly and evenly conduct the heat generated by the heating element to the entire PCBA, avoiding non-uniform thermal deformation caused by local overheating.

[0078] In an optional embodiment, the ball-mounting and soldering apparatus 100 of the present invention further includes an underfill adhesive layer filling the gap between the first printed circuit board assembly 110 and the second printed circuit board assembly 120 and around the solder joints of the solder ball array. Exemplarily, the glass transition temperature (Tg) of the underfill adhesive layer is ≥120°C, preferably ≥150°C. The coefficient of thermal expansion of the underfill adhesive layer is ≤80ppm / °C, and the viscosity is 200-800cP. Preferably, a dedicated high-temperature underfill adhesive product with a high Tg (≥150°C) is used to adapt to chip testing conditions at 125°C.

[0079] See Figure 6 The diagram shows a process flow chart of the ball-mounting soldering method for printed circuit board assemblies according to the present invention.

[0080] The following embodiments of the present invention also provide a method for ball bonding between printed circuit board assemblies, utilizing the aforementioned rigid support portion 140 with an array of clearance holes 141 as a bonding gap control element. The main steps of this ball bonding method include:

[0081] Step S210: Provide the first printed circuit board assembly 110 and the second printed circuit board assembly 120.

[0082] Step S220: Solder balls are implanted on one of the first printed circuit board assembly 110 and the second printed circuit board assembly 120, and solder paste is applied to the other.

[0083] Specifically, after providing the first printed circuit board assembly 110 and the second printed circuit board assembly 120, solder balls are implanted on a plurality of second pads 121 of the second printed circuit board assembly 120 using a BGA ball-mounting process. This involves using a ball-mounting template to precisely place the solder balls on each second pad 121, and then using reflow soldering to initially fix the solder balls to the corresponding pad surfaces, forming a solder ball array. The solder ball material is preferably high-temperature solder SAC305 or SAC405, and the solder ball diameter ranges from 0.3 to 0.76 mm.

[0084] As mentioned above, the solder ball position is flexible, meaning the solder ball can be placed on the first printed circuit board assembly 110 or the second printed circuit board assembly 120, as long as the side with the solder ball faces between the two PCBAs. The choice can be made according to the actual equipment adaptation requirements.

[0085] Solder paste layers are applied to the first pad 111 of the first printed circuit board assembly 110 and the second pad 121 of the second printed circuit board assembly 120 using a stencil printing process. The solder paste thickness is preferably 0.1-0.15 mm.

[0086] Step S230: Provide a rigid support portion 140, on which a clearance hole 141 is provided, and place the rigid support portion 140 between the first printed circuit board assembly 110 and the second printed circuit board assembly 120, so that each solder ball in the solder ball connection structure 130 passes through the corresponding clearance hole 141.

[0087] Specifically, the rigid support 140 is positioned on the second printed circuit board assembly 120, so that each solder ball passes through its corresponding clearance hole 141. The rigid support 140 is precisely aligned with the second printed circuit board assembly 120 by a positioning structure (e.g., positioning boss 142).

[0088] In this step, the rigid support 140 is an independently prefabricated rigid plate-like component with an array of clearance holes 141. Its thickness H is equal to the preset solder gap. This rigid support 140 can limit the minimum distance between the first printed circuit board assembly 110 and the second printed circuit board assembly 120 during reflow soldering, preventing the two PCBAs from getting too close due to the surface tension after the solder paste melts. Furthermore, it ensures the consistency of the height of each solder joint after soldering; and during the finished product use stage, the rigid support 140 continuously bears external mechanical loads, minimizing the stress on each solder joint.

[0089] Step S240: Align and close the first printed circuit board assembly 110 and the second printed circuit board assembly 120 so that each solder ball contacts the corresponding solder paste layer.

[0090] The first printed circuit board assembly 110 and the second printed circuit board assembly 120 are precisely aligned using a positioning structure (e.g., positioning boss 142) on the rigid support 140, so that the solder ball array is further aligned one by one with the first pad 111 of the first printed circuit board assembly 110. Then the two PCBAs are joined together so that the surface of the solder balls contacts the solder paste layer on the first pad 111.

[0091] Step S250: Perform reflow soldering. During the soldering process, the thickness of the rigid support 140 limits the minimum distance between the first printed circuit board assembly 110 and the second printed circuit board assembly 120, so that the height of each solder joint remains consistent.

[0092] Specifically, the assembled components are fed into a reflow oven and reflow soldered according to a preset temperature profile. The peak temperature for reflow soldering is set based on the solder ball alloy composition, typically between 240-270°C. During reflow soldering, the solder balls and solder paste layer melt and bond together to form solder joints, which electrically and mechanically connect the first pad 111 and the second pad 121. The rigid support portion 140 provides rigid support throughout the reflow soldering process to maintain the consistency of the solder joint height.

[0093] Optional step: bottom fill.

[0094] For applications such as chip testing that require long-term high-temperature aging and repeated mechanical impact, after reflow soldering, a high-Tg underfill adhesive is injected along the edges of the two PCBAs. This fills the gaps between the two PCBAs and the area around the solder joints through capillary action, and then is heated to cure, forming the underfill adhesive layer. The selection of the underfill adhesive has already been explained in the design section of the rigid support 140 above, and will not be repeated here.

[0095] In a preferred embodiment, the process flow for the bottom filling adhesive layer is as follows:

[0096] (1) Preheating: Heat the two PCBAs to 80-120℃ and keep them for 5-10 minutes to reduce the viscosity of the adhesive and remove moisture.

[0097] (2) Dispensing: Use an automatic dispensing machine to apply bottom filler glue along the edges of the two PCBAs. The dispensing path is selected according to the shape of the two PCBAs, such as I-shaped, L-shaped or U-shaped. After dispensing, the glue enters the heating zone within 5-10 seconds.

[0098] (3) Capillary flow: The glue is automatically drawn into the gap between the two PCBAs under capillary action. The process lasts for 3-10 minutes. The filling is complete when the glue flows out from the opposite edge.

[0099] (4) Heating and curing: Place in a hot air circulating oven for curing. The standard conditions are 150℃ for 5-10 minutes. For heat-sensitive devices, the curing conditions can be adjusted to 120℃ for 10-15 minutes. The oven temperature should be uniformly controlled within ±3℃.

[0100] (5) Cooling: Allow to cool naturally to room temperature.

[0101] Tests have shown that after filling the bottom with adhesive, the thermal cycle life of the solder ball array can be increased by about 16 times, and its drop impact resistance can be increased by 3-5 times.

[0102] After the welding is completed in steps S210-S250, the finished PCBA assembly is subjected to X-ray inspection and electrical testing to confirm the welding quality.

[0103] X-ray inspection:

[0104] Two-dimensional X-ray inspection equipment is used to perform transmission imaging on finished PCBA components to detect defects such as solder ball voids, bridging, misalignment, and cold solder joints. The solder ball void rate is calculated using the following formula: Void rate = Void area / Solder ball area × 100%. The judgment standard refers to IPC-A-610: Chip testing equipment belongs to high-performance application scenarios and must meet Level 3 requirements. Any degree of bridging and pillow effect is considered a defect.

[0105] Inspection sampling plan: 100% full inspection of the first piece; 5-10 pieces per batch for small batches; 3-5 pieces per batch for large batches.

[0106] Electrical testing:

[0107] Use a flying probe tester or a dedicated test fixture to perform continuity tests to confirm the absence of open or short circuits. Then perform a contact resistance test (four-point Kelvin test). The contact resistance should be ≤20mΩ, and the difference between each solder ball should be ≤±5mΩ.

[0108] All X-ray inspection images and electrical test data are archived and stored, and an inspection record file is established for each finished PCBA component to achieve quality traceability.

[0109] In some embodiments, the ball bonding apparatus 100 for inter-printed circuit board assemblies of the present invention is not limited to the specific embodiments described above, and can be adapted or improved according to actual application scenarios.

[0110] For example, regarding the location of the solder ball array: as mentioned above, the solder balls can be placed on the first printed circuit board assembly 110 or the second printed circuit board assembly 120, only requiring that the side with the solder balls faces the gap between the two PCBAs. Currently, due to existing equipment adaptation requirements, the solder balls are placed on the second PCBA.

[0111] For example, regarding the arrangement of the soldering areas (a plurality of first solder pads 111 and a plurality of second solder pads 121): the arrangement of the soldering areas (e.g., single row / multiple rows, long strip / segmented, etc.) directly affects the thickness of the rigid support 140, and also affects process parameters such as soldering power. Therefore, the specific structural design of the rigid support 140, especially the size and layout design of the clearance holes 141 and the support bosses 143, will be adjusted according to the PCBA board model and the changes in soldering form / process. This invention provides specific embodiments for BGA ball soldering scenarios, which can cover the soldering needs of various different connection structures such as chip stacking, and also support scenarios such as irregularly shaped PCBA boards and irregularly arranged soldering areas.

[0112] See Figure 7 The diagram illustrates the overall structure of a PCBA ball-mounting and soldering device 100', another example. The rigid support portion 140' is provided with an array of rectangular clearance holes 141 corresponding to the ball array configuration of the first pad 111' and the second pad 121'.

[0113] For example, regarding practical application scenarios: the ball bonding device 100 and method (process) provided in the various embodiments of the present invention can meet the conversion requirements of existing equipment to adapt to new specification chips, and are used to reduce the height in the Z-axis direction and replace the original connector solution.

[0114] In one practical application, the first printed circuit board assembly 110 can be a power board, and the second printed circuit board assembly 120 can be a load board (e.g., a test machine load board). After placing the chip on the load board, it is pressed down with a probe. The ball bonding device 100 of the present invention can be used in high-frequency connection scenarios of test machine load boards, effectively reducing high-frequency signal transmission loss.

[0115] The ball-mounting soldering apparatus and soldering method for printed circuit board assemblies provided in the embodiments of the present invention have at least one or a portion of the following advantages:

[0116] (1) By setting a rigid support with clearance holes between the first PCBA and the second PCBA, the relative position and distance between the two PCBAs are limited by the thickness of the rigid support. During the welding process, the welding gap is controlled to ensure that the height of each solder joint is consistent. During the finished product use stage, the external mechanical load is borne so that the solder joints are free from stress to the maximum extent. Thus, the functions of electrical interconnection, gap control, mechanical bearing and anti-warping support are integrated.

[0117] (2) By setting a first pad on the first PCBA and a second pad on the second PCBA, and welding a solder ball array between the two, the pad positions correspond one-to-one, thus realizing reliable electrical interconnection between the two PCBAs;

[0118] (3) By opening clearance holes on the rigid support part that correspond one-to-one with the solder ball array, each solder ball passes through the corresponding clearance hole, which not only ensures the electrical connection function of the solder ball, but also avoids the interference of the rigid support part on the solder ball.

[0119] (4) By setting the diameter of the clearance hole of the rigid support to be greater than the diameter of the solder ball and the difference to be not less than 0.1mm, and leaving a safe distance between the edge of the clearance hole and the edge of the solder pad, and the inner wall of the clearance hole is a rounded corner structure, the short circuit caused by solder crawling and the hole wall damage to the solder ball are effectively avoided.

[0120] (5) The rigid support has a coverage area of ​​not less than 60% of the area of ​​the smaller of the two PCBA boards in the direction parallel to the PCBA board surface, providing continuous surface support, so that the bending stiffness of the PCBA is improved from the PCBA's own stiffness to "PCBA + rigid support composite stiffness", and the overall bending stiffness is significantly improved.

[0121] (6) By setting the matching relationship between the thickness of the rigid support and the diameter of the solder ball: 0.45mm solder ball corresponds to a thickness of 0.3-0.35mm, 0.6mm solder ball corresponds to a thickness of 0.4-0.45mm, and the thickness accuracy is controlled within ±0.02mm to ensure the consistency of the welding gap and the stability of signal transmission;

[0122] (7) By setting a support boss on the surface of the rigid support part and setting the height to 0.05-0.10mm, the total surface area does not exceed 15% of the surface area of ​​the rigid support part body. When the PCBA is flat, the pressing force is borne by the surface of the rigid support part body. When the PCBA is warped, the support boss contacts the warped area to provide local support, thus realizing the adaptive support function of "not intervening when flat and triggering as needed when warped".

[0123] (8) By setting the support boss as a discrete micro-bump structure, the support is provided in the form of point contact. In the flat state, it only maintains "just contact" or "micro-force contact" with the PCBA. The majority of the pressing force is borne by the large area of ​​the rigid support, which effectively avoids stress concentration and lifting effect.

[0124] (9) By setting the support bosses as a continuously distributed frame-type protrusion structure, the adjacent micro-protrusions are connected longitudinally and / or laterally, which enhances the structural lateral connection stiffness and stability of the rigid support in the adjacent clearance hole area.

[0125] (10) By setting a positioning structure on the rigid support, the precise alignment between it and the PCBA is achieved, ensuring the precise alignment of the solder ball and the clearance hole, and the solder pad and the solder ball, and avoiding the solder ball being scratched and damaged by the hole wall;

[0126] (11) By filling the gap between two PCBAs and around the solder joints with bottom filler glue, the thermal fatigue resistance of the solder joints can be improved, the thermal cycle life can be increased by about 16 times, and the drop impact resistance can be increased by 3-5 times.

[0127] (12) The ball-mounting and soldering method of the present invention, through the process of ball-mounting --> paste printing --> installation of rigid support --> alignment and closing --> reflow soldering, the thickness of the rigid support limits the minimum distance between the two PCBAs during the reflow soldering process, so that the height of each solder joint is consistent. The peak temperature of reflow soldering is 240-270℃, and all interconnections are completed in one reflow soldering, without the need for an additional screw-locking process.

[0128] (13) The rigid support part uses a material with a thermal expansion coefficient that matches that of the PCBA substrate. Under high temperature conditions, the two expand and contract synchronously without generating additional thermal stress; and the metal rigid support part also functions as a heat distribution plate, which can eliminate local hot spots.

[0129] (14) In addition to the welding process, X-ray inspection and electrical testing (contact resistance test) were also carried out to ensure the reliability and traceability of the welding quality.

[0130] While some embodiments of the present general inventive concept have been shown and described, those skilled in the art will understand that changes may be made to these embodiments without departing from the principles and spirit of the present general inventive concept, the scope of which is defined by the claims and their equivalents.

Claims

1. A ball-mounting and soldering apparatus for inter-printed circuit board assemblies, characterized in that, The ball-planting welding device includes: First printed circuit board assembly; The second printed circuit board assembly is disposed opposite to the first printed circuit board assembly; A solder ball connection structure is disposed between the first printed circuit board assembly and the second printed circuit board assembly, and the solder ball connection structure is used to connect the first printed circuit board assembly and the second printed circuit board assembly after soldering; A rigid support portion is disposed between the first printed circuit board assembly and the second printed circuit board assembly. The rigid support portion includes a first surface and a second surface facing away from each other, and a plurality of support bosses disposed on the first surface and / or the second surface. The first surface faces the first printed circuit board assembly, and the second surface faces the second printed circuit board assembly. The rigid support portion has clearance holes that pass through the first surface and the second surface. At least a portion of the solder ball connection structure passes through the clearance holes. The support bosses are respectively located between adjacent clearance holes. The rigid support portion abuts against the first printed circuit board assembly and the second printed circuit board assembly respectively.

2. The ball-planting welding device according to claim 1, characterized in that, When the support boss is provided on the first surface and the warping deformation of the first printed circuit board assembly toward the rigid support is greater than or equal to the height of the top surface of the support boss protruding from the first surface, the warped area of ​​the first printed circuit board assembly abuts against the first surface. And / or, When the support boss is provided on the second surface, and the deformation of the second printed circuit board assembly warping toward the rigid support is greater than or equal to the height of the top surface of the support boss protruding from the second surface, the warped area of ​​the second printed circuit board assembly abuts against the second surface.

3. The ball-planting welding device according to claim 1, characterized in that, The solder ball connection structure includes a first pad disposed on the first printed circuit board assembly, a second pad disposed on the second printed circuit board assembly, and an array of solder balls soldered between the first pad and the second pad. The positions of the first pad and the second pad correspond one-to-one. The solder ball array includes multiple solder balls. The clearance holes correspond one-to-one with the solder balls, and the solder balls pass through the corresponding clearance holes.

4. The ball-planting welding device according to claim 3, characterized in that, The thickness of the rigid support portion satisfies the following condition: When the diameter of the solder ball is 0.45 mm, the thickness of the rigid support is 0.3-0.35 mm; and / or, When the diameter of the solder ball is 0.6 mm, the thickness of the rigid support is 0.4-0.45 mm; and / or, The thickness tolerance of the rigid support is ±0.02mm.

5. The ball-planting welding apparatus according to claim 3, characterized in that, The diameter of the clearance hole is larger than the diameter of the solder ball, and the difference between their diameters is greater than or equal to 0.1 mm; and / or, A safety distance is maintained between the edge of the clearance hole and the edge of the first pad and / or the second pad, the safety distance being greater than or equal to 0.05 mm; and / or, The inner wall of the clearance hole has a rounded corner structure.

6. The ball-planting welding apparatus according to claim 3, characterized in that, In the direction parallel to the board surface of the first printed circuit board assembly and the second printed circuit board assembly, the coverage area of ​​the rigid support is greater than or equal to 45% to 75% of the smaller board surface area of ​​the first printed circuit board assembly and the second printed circuit board assembly.

7. The ball-planting welding apparatus according to any one of claims 1-6, characterized in that, A support boss is provided on the first surface and / or the second surface, wherein the support boss is a micro-protrusion structure protruding from the body surface of the rigid support portion; and / or, The height of the support boss is in the range of 0.05-0.10mm, and the total surface area of ​​the support boss is less than or equal to 15% of the body surface area of ​​the rigid support.

8. The ball-planting welding apparatus according to claim 7, characterized in that, The supporting boss is a discretely distributed micro-protrusion structure or a continuously distributed frame-type protrusion structure, and the supporting boss and the body of the rigid support are integrally formed.

9. The ball-planting welding apparatus according to claim 7, characterized in that, The rigid support is further provided with a positioning structure, which is aligned with the positioning holes on the first printed circuit board assembly and / or the second printed circuit board assembly.

10. The ball-planting welding apparatus according to claim 1, characterized in that, The ball-mounting and soldering apparatus further includes a bottom filler adhesive layer, which fills the gap between the first printed circuit board assembly and the second printed circuit board assembly and around the solder joints. The glass transition temperature of the bottom filler adhesive layer is greater than or equal to 120°C.

11. A method for ball bonding between printed circuit board assemblies, the ball bonding method being used in the ball bonding apparatus according to any one of claims 1-10, characterized in that, The ball-planting welding method includes the following steps: Provide a first printed circuit board assembly and a second printed circuit board assembly; Solder balls are implanted on one of the first printed circuit board assembly and the second printed circuit board assembly, and solder paste is applied to the other. A rigid support portion is provided, and a clearance hole is provided on the rigid support portion. The rigid support portion is disposed between the first printed circuit board assembly and the second printed circuit board assembly, so that the solder ball passes through the clearance hole. The first printed circuit board assembly and the second printed circuit board assembly are aligned and joined together, so that each solder ball contacts the corresponding solder paste layer. During reflow soldering, the thickness of the rigid support portion limits the minimum spacing between the first printed circuit board assembly and the second printed circuit board assembly, ensuring that the height of each solder joint remains consistent.

12. The ball-planting welding method according to claim 11, characterized in that, The peak temperature of the reflow soldering is 240-270℃; The rigid support is made of FR-4 fiberglass board, ceramic board, or surface-insulated metal board, and the difference between the thermal expansion coefficient of the rigid support and the thermal expansion coefficient of the substrate of the printed circuit board assembly is less than or equal to 5 ppm / ℃.

13. The ball-planting welding method according to claim 11, characterized in that, After reflow soldering is completed, the ball-mounting method further includes: Underfill adhesive is injected along the edges of the first and second printed circuit board assemblies, filling the gaps between them and the area around the solder joints through capillary action, and then cured by heat. The bottom filler has a glass transition temperature greater than or equal to 120°C, a coefficient of thermal expansion less than or equal to 80ppm / °C, and a viscosity of 200-800cP.

14. The ball-planting welding method according to claim 11, characterized in that, The ball-planting welding method also includes a testing step: X-ray inspection equipment is used to perform transmission imaging on the finished printed circuit board assembly after welding to detect solder joint defects. Use a flying probe tester or test fixture to perform continuity and contact resistance tests.

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