Assembly method for preventing thermal mismatch of device

Abstract

The invention discloses an assembly method for preventing thermal mismatch of a device. The assembly method comprises the following steps: carrying out modification treatment on the surface of a welding surface of the device; carrying out modification treatment on the surface of the printed board bonding pad; performing solder paste printing processing on a central bonding pad and a target pin bonding pad of the printed board; correspondingly placing the welding surface of the device and a printed board bonding pad, and realizing interconnection between the device and the printed board through reflow soldering; welding the residual pins of the device and the residual bonding pads of the printed board to complete fixation of the residual pins of the device and the residual bonding pads of the printed board; and reinforcing the part between the device and the printed board. Through modification treatment, rasterization steel mesh printing, step-by-step welding and corner reinforcing design on the surface of the device and a printed board bonding pad, stress concentration caused by mismatching of thermal expansion coefficients of the device and the printed board can be effectively relieved, welding spot cracks and failure risks are reduced, and therefore the installation reliability of the device in the long-term application process is improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of printed board and device assembly, and particularly relates to an assembly method for preventing device thermal mismatch. BACKGROUND

[0002] The packaging material of a device gradually develops from early plastic packaging to ceramic material packaging and then to silicon-based material packaging. Compared with a plastic packaged device, the ceramic packaging has great improvement in reliability, air tightness and heat dissipation, and the thermal expansion coefficient of the ceramic packaging is generally 2.5-8.5 ppm / ℃ according to the difference of ceramic composition. The silicon-based packaging meets the needs of high-speed computing, bandwidth expansion, multi-functional integration and extreme miniaturization, and the thermal expansion coefficient of the silicon-based packaging is generally 2.6 ppm / ℃, which is the development direction of future device packaging. However, in the subsequent assembly process, most of the devices are soldered to a printed board, and the mainstream material of the printed board is FR-4, and the thermal expansion coefficient of the printed board is generally 14-18 ppm / ℃. In the existing device assembly process, a direct reflow soldering method is usually used to realize soldering and fixation of the device and the printed board. However, in the case of mismatch of the thermal expansion coefficients, a large residual stress is formed at the soldering point in a single soldering process, and the soldering point is prone to failure in the subsequent use process. The tethered balloon radar is commonly used for monitoring the "low, slow and small" aircraft represented by the unmanned aerial vehicle, and early warning of various "black flight" and "random flight" phenomena. Since the radar works in a vibrating environment, the cracking of the soldering point caused by the above thermal mismatch often occurs, resulting in failure of the radar. SUMMARY

[0003] The present application aims to at least solve one of the problems in the related art. To this end, one object of the present application is to provide an assembly method for preventing device thermal mismatch, which can effectively alleviate the stress concentration caused by the mismatch of the thermal expansion coefficients of the device and the printed board, reduce the risk of soldering point cracking and failure, and improve the assembly reliability of the device in the long-term application process.

[0004] In a first aspect, the present application provides an assembly method for preventing device thermal mismatch, and the method comprises the following steps:

[0005] S1: performing modification treatment on the surface of the device soldering surface, so that the plating thickness of the device soldering surface reaches a preset value;

[0006] S2: performing modification treatment on the surface of the printed board pad;

[0007] S3: performing tin paste printing treatment on the center pad and the target pin pad of the printed board;

[0008] S4: placing the device soldering surface and the printed board pad correspondingly, and realizing interconnection of the device and the printed board through reflow soldering;

[0009] S5: welding the remaining pins of the device and the remaining pads of the printed board, and fixing the remaining pins of the device and the remaining pads of the printed board;

[0010] S6: reinforcing the device and the printed board.

[0011] Preferably, the surface of the device welding surface is modified by the magnetron sputtering method in step S1, and a tin-lead alloy is plated on the device welding surface, and the thickness of the plating layer on the device welding surface is 1 um.

[0012] Preferably, the parameters of the magnetron sputtering method are: the sputtering power is more than 2 kW, the sputtering time is more than 30 min, and the vacuum degree is 10 -3 Pa order of magnitude.

[0013] Preferably, the surface of the printed board pad is modified by the manual tin soldering method in step S2, the temperature of the soldering iron is 260-300℃, and the printed board is baked for 2-4 hours before tin soldering, and the temperature is 100-120℃.

[0014] Preferably, the center pad and the target pin pad of the printed board are printed with tin paste by the SMT steel mesh in step S3, the SMT steel mesh is uniformly provided with a plurality of groups of grids of the same size at the position corresponding to the center pad of the printed board, the interval width between adjacent grids is 3-5 thousandths of the width of the center pad, and the SMT steel mesh is provided with a hole corresponding to the position of the target pin pad. The target pin pad is a preset number of pin pads at the center position of each group of edges.

[0015] Preferably, the tin paste is subjected to temperature recovery and stirring treatment before being printed in step S3, and the target pin pad is two pin pads at the center position of each group of edges.

[0016] Preferably, the furnace temperature of the reflow soldering in step S4 is set to be the actual temperature of the printed board plus 30-40℃.

[0017] Preferably, the remaining pins of the device and the remaining pads of the printed board are welded by a manual soldering iron in step S5, the temperature of the soldering iron is set to be 280-300℃, the single-point welding time is not more than 3s, a pointed soldering iron is used, and the preheating temperature of the printed board is 70-80℃.

[0018] Preferably, two-component DG-3 epoxy glue is applied to reinforce the four vertices of the device in step S6, the ratio of the epoxy glue is 1.5-3, the dispensing height is greater than half of the body height, and the temperature of the printed board is preheated to 70-80℃ when dispensing.

[0019] In the second aspect, the present application provides an electronic device applying any one of the above-mentioned device heat mismatch prevention assembly methods.

[0020] The beneficial effects of the present application are:

[0021] The application forms a tin-lead alloy plating layer on the device welding surface by using a magnetron sputtering method, which firstly improves the device surface welding reliability, enables the low thermal expansion coefficient device to better realize initial interconnection with the printed board, and thus reduces the risk of virtual welding and cracking caused by poor interface bonding;

[0022] Secondly, the printed board pad surface is subjected to manual tin-bushing modification treatment, and is subjected to baking treatment before tin-bushing, which effectively improves the welding performance of the pad, avoids the bulging problem caused by local heating, and enables the printed board and the device to form uniform and stable welding points when welded, and further improves the interconnection reliability;

[0023] In addition, the application introduces a grid structure in the steel mesh design, uniformly opens a grid at the center pad position and limits the grid interval width, reasonably controls the distribution and amount of solder paste; and only holes are opened at the center position of each side on the pin pad to realize positioning, so that only part of the welding points are fixed first during reflow soldering, which ensures the positioning accuracy of the device and avoids the residual stress concentration caused by large-area welding;

[0024] Further, the application adopts a step-by-step welding process, first completes the interconnection of the center pad and part of the positioning pin by reflow soldering, and then completes the fixation of the remaining pins by manual repair welding, so that the thermal stress can be gradually released, and the failure risk of the welding points in the vibration environment is significantly reduced;

[0025] Finally, the device is reinforced by point-coating two-component epoxy glue at the four corners, which not only enhances the mechanical bonding strength between the device and the printed board, but also effectively suppresses the problems of device loosening and welding point cracking caused by external environmental vibration or temperature fluctuation, and improves the long-term reliability of the device assembly as a whole. BRIEF DESCRIPTION OF DRAWINGS

[0026] In the drawings:

[0027] Figure 1 A flow chart of an assembly method for preventing device thermal mismatch is proposed in the application;

[0028] Figure 2 a is a device diagram to be assembled in the embodiment proposed in the application, Figure 2 b is a printed board diagram to be assembled in the embodiment proposed in the application;

[0029] Figure 3 An effect diagram of the device welding surface modification in the embodiment proposed in the application;

[0030] Figure 4 A steel mesh design diagram in the embodiment proposed in the application;

[0031] Figure 5a is the effect diagram of the conventional assembly method, Figure 5 b is the effect diagram of the assembly method proposed by the present application. DETAILED DESCRIPTION

[0032] Reference Figure 1 An assembly method for preventing thermal mismatch of devices, the method steps are as follows:

[0033] S1: modifying the surface of the device soldering surface so that the thickness of the plating layer on the surface of the device soldering surface reaches a preset value;

[0034] Specifically, the surface of the device soldering surface is modified by a magnetron sputtering method, a tin-lead alloy is plated on the device soldering surface, the thickness of the plating layer on the surface of the device soldering surface is 1 um, and the parameters of the magnetron sputtering method are: sputtering power is more than 2kW, sputtering time is more than 30min, and vacuum degree is 10 -3 Pa order of magnitude.

[0035] Obviously, based on the above: the magnetron sputtering method can form a uniform and dense metal plating layer on the device soldering surface. First, the modification process improves the wettability of the surface of the low thermal expansion coefficient device such as ceramic or silicon, so that it can be fully combined with the solder in the subsequent soldering process, thereby avoiding false welding and soldering caused by poor interface bonding. Second, the tin-lead alloy plating layer has good ductility and thermal conductivity, which can effectively buffer the concentration of thermal stress and mechanical stress under the conditions of thermal cycle and external mechanical vibration, and reduce the risk of cracking of the solder joint during use. In addition, the plating layer can also improve the oxidation resistance of the device soldering surface, ensure the stability of the soldering interface in the subsequent process, and thus improve the reliability and long-term service life of the overall solder joint interconnection.

[0036] S2: modifying the surface of the printed board pad;

[0037] Specifically, the surface of the printed board pad is modified by a manual tin soldering method, the temperature of the soldering iron is 260-300℃, and the printed board is baked for 2-4 hours before tin soldering, and the temperature is 100-120℃.

[0038] Obviously, based on the above: first, the tin treatment makes the original solder pad surface covered by a fresh tin layer, removing the oxide film or contaminated layer on the surface of the solder pad, thereby significantly improving the wettability and bonding force between the solder pad and the solder. Second, the baking process before tinning can drive away the moisture inside the printed board and around the solder pad, avoiding the gas generated by heating or local bulging, ensuring the uniform and stable formation of the solder joint during welding. In addition, by properly controlling the temperature of the iron within the range of 260-300℃, the tin layer of the solder pad can be uniformly formed, which not only ensures good welding performance, but also avoids the solder pad falling off or the printed board being damaged caused by high temperature. Through the above treatment, the printed board solder pad can exhibit better wettability and solderability in the subsequent solder paste printing and welding process, thereby improving the reliability of the entire device assembly.

[0039] S3: printing tin paste on the center pad and the target pin pad of the printed board;

[0040] Specifically, the SMT steel mesh is used to print tin paste on the center pad and the target pin pad of the printed board. The SMT steel mesh is uniformly provided with a plurality of groups of grids of the same size at the position corresponding to the center pad of the printed board, and the interval width between adjacent grids is 0.003-0.005 of the width of the center pad. The SMT steel mesh is provided with a hole at the position corresponding to the target pin pad, and the target pin pad is provided with a preset number of pin pads at the center position of each side.

[0041] Obviously, based on the above: first, the grid design of the center pad effectively controls the amount of solder paste, which not only ensures reliable welding between the center pad and the device bottom, but also avoids virtual welding, voids or bridging caused by excessive solder, thereby improving the solder joint formation quality. Second, only two pins at the center position of each side of the target pin pad are selected as positioning points, so that the device can be accurately fixed at the predetermined position during reflow soldering, and the remaining pins without solder paste printing remain in a free state, which helps to reduce the residual stress concentration caused by the mismatch of thermal expansion coefficients during the initial welding. In addition, the temperature and stirring treatment of the tin paste before printing can restore the flowability and printing performance of the tin paste, avoid defects caused by poor tin paste state, and ensure uniform and stable transfer of the solder paste at the steel mesh hole. Through the implementation of this step, not only can the center pad and part of the pins realize reliable interconnection during reflow soldering, but also can provide accurate positioning and stable basis for subsequent step-by-step repair welding, thereby improving the reliability of the overall assembly process.

[0042] S4: placing the device welding surface and the printed board pad correspondingly to realize the interconnection of the device and the printed board by reflow soldering;

[0043] Specifically, the furnace temperature of the reflow soldering is set to the actual temperature of the printed board plus 30-40℃.

[0044] Clearly, based on the above: First, reflow soldering allows for simultaneous metallurgical bonding between the device's bottom pads and some target pins and the printed circuit board (PCB) pads, enabling rapid and uniform initial interconnection and ensuring stable device positioning on the PCB. Second, setting the furnace temperature to 30-40°C above the PCB's actual temperature avoids incomplete solder paste melting due to insufficient heating, preventing cold solder joints and preventing pad warping, device damage, or excessive residual stress caused by excessively high temperatures, thus achieving effective control of the process window. Furthermore, this step-by-step soldering method ensures that only the central pads and some positioning pins are soldered during reflow soldering, while the remaining pins remain free. This effectively buffers stress concentration caused by thermal expansion mismatch between the device and the PCB, reducing the risk of solder joint cracking or failure during subsequent use. This step not only achieves initial interconnection and precise positioning of the device and PCB but also provides a reliable foundation for subsequent resoldering processes, improving overall solder joint quality and assembly reliability.

[0045] S5: Solder the remaining pins of the device and the remaining pads on the printed circuit board to complete the fixation of the remaining pins of the device and the remaining pads on the printed circuit board;

[0046] Specifically, the remaining pins of the device and the remaining pads on the printed circuit board are soldered manually with a soldering iron. The soldering iron temperature is set to 280-300℃, the single-point soldering time does not exceed 3 seconds, a pointed soldering iron is used, and the preheating temperature of the printed circuit board is 70-80℃.

[0047] Clearly, based on the above: First, performing resoldering in stages avoids all pins being stressed simultaneously during reflow soldering, allowing the remaining pins to bond firmly to the pads one by one during manual soldering. This reduces stress concentration during the overall soldering process and improves the stability of the solder joints. Second, strictly controlling the soldering iron temperature and single-point soldering time prevents pad detachment, pin damage, or excessive solder diffusion due to overheating, ensuring uniform solder joint morphology and a strong connection. Furthermore, preheating the printed circuit board to 70-80°C helps reduce the temperature difference between the device and the printed circuit board during soldering, avoiding thermal shock effects, and also makes it easier for the solder to wet and spread, improving the quality of the solder joint formation. By implementing this step, while achieving complete interconnection between all pins and pads, residual stress from previous processes can be further released and dispersed, significantly improving the reliability and failure resistance of the solder joints during long-term use.

[0048] S6: Reinforce the connection between the device and the printed circuit board.

[0049] Specifically, apply two-component DG-3 epoxy adhesive to the four vertices of the device for reinforcement. The epoxy adhesive ratio is 1.5-3, and the dispensing height is greater than half the height of the device body. The printed circuit board temperature is preheated to 70-80℃ during dispensing.

[0050] Clearly, based on the above: First, the four-corner dispensing method can form a stable mechanical support structure on the outside of the device, creating multi-point constraints between the device and the printed circuit board, thereby effectively suppressing device loosening or warping caused by external vibration or thermal expansion stress. Second, a reasonable epoxy adhesive ratio ensures the curing strength and toughness of the adhesive, providing reliable mechanical bonding and buffering thermal stress to a certain extent, avoiding additional damage to the solder joints due to excessively hard or brittle adhesive. Furthermore, dispensing the adhesive to more than half the height of the device body significantly improves the support strength between the device body and the printed circuit board, ensuring device stability during long-term service and in complex environments. Dispensing under preheating conditions helps the epoxy adhesive cure quickly and prevents it from flowing into the bottom of the chip, thus ensuring normal device operation and extending the lifespan of the solder joints. Through this step, the overall assembly structure is further enhanced in terms of mechanical strength and environmental adaptability, thereby significantly improving the long-term reliability of the device-printed circuit board interconnection.

[0051] As another embodiment of this application, this embodiment proposes an electronic device that applies any of the above-described assembly methods for preventing thermal mismatch of devices.

[0052] To more clearly illustrate the implementation plan and its effects, we will use the attached diagram as an example:

[0053] like Figure 2 As shown in Figure a, the device to be assembled is packaged in ceramic, and has multiple sets of pins around its perimeter. Figure 2 As shown in b, the printed circuit board material to be assembled is the common FR4 material.

[0054] Tin-lead plating was applied to the surfaces of gold-plated components to improve the reliability of subsequent soldering. The surface modification method chosen was surface sputtering of a tin-lead thin film, with a tin-lead alloy used as the sputtering target in magnetron sputtering. The sputtering power was 3kW, the sputtering time was 60 minutes, and the vacuum degree was 4*10⁻⁶. -3 Pa, the tin-lead plating thickness is approximately 1 μm, such as Figure 3 As shown, Figure 3 The effect of surface modification on the surface to be welded.

[0055] The surface of the printed circuit board (PCB) pads is modified. The PCB pads are initially gold-plated, and then re-tinned to improve solderability. A manual soldering iron is used for tinning at 280℃. Before tinning, the PCB needs to be baked for 2-4 hours at 100-120℃ to prevent single-point heating and bulging during tinning.

[0056] like Figure 4As shown, the stencil aperture design is as follows: two pads are selected at the center of each of the four sides of the device pins for apertures; the pads at other positions are left unapproved to avoid excessive solder paste on the pads during printing. The bottom pads have normal apertures, but a 3x3 grid pattern is added with rib widths of 0.25-0.3mm to reduce solder paste volume. The stencil described above is used for solder paste printing. The solder paste is warmed for 30 minutes before printing and stirred at 1200 rpm for approximately 3-5 minutes.

[0057] The automatic printing machine is set with the following parameters: 50° angle between the squeegee and the printed circuit board, printing speed of 30 mm / s, and squeegee pressure of 2.5 N / s, to complete the solder paste printing. Surface-modified components are then machine-mounted onto the printed circuit board with the solder paste. After printing, the quality of the solder paste printing on the pads is checked, requiring no collapse or burrs.

[0058] The peak temperature for reflow soldering is 250℃, held for 10-20 seconds, and above 183℃, held for 70 seconds. The chain speed is 900 mm / s.

[0059] After the soldering is completed and cooled to room temperature, use a manual soldering iron to solder the other pins of the device to the printed circuit board. Set the soldering iron temperature to 280-300℃, and the soldering time for a single point should not exceed 3 seconds. Use a pointed soldering iron and preheat the printed circuit board to 70-80℃.

[0060] After successful self-inspection and electrical testing following soldering, apply two-component DG-3 epoxy adhesive to the four vertices of the device body for reinforcement. The epoxy adhesive ratio should be between 1.5 and 3. The dispensing height must be greater than half the height of the device body. Ensure the printed circuit board is preheated to 70-80℃ during dispensing to facilitate rapid curing of the DG-3 epoxy adhesive and prevent it from flowing under the chip. Avoid contact with the chip under DG-3 epoxy adhesive during use, as the adhesive expansion due to temperature can cause stress on the chip and premature solder joint failure. Figure 5 Figure b shows the result after assembly using this method. Figure 5 "a" represents the effect after assembly using the conventional method. After assembly using the conventional method, the pins and the body are soldered together, resulting in poor solder adhesion on the pins. After assembly using this method, the pins are completely encased in solder.

Claims

1. An assembly method for preventing thermal mismatch of devices, characterized in that, The method steps are as follows: S1: Modify the surface of the device's welding surface to make the coating thickness on the device's welding surface reach the preset value; S2: Modify the surface of the printed circuit board pads; S3: Print solder paste onto the center pads and target pin pads of the printed circuit board; S4: Align the component soldering surface with the printed circuit board pads and perform reflow soldering to achieve interconnection between the component and the printed circuit board; S5: Solder the remaining pins of the device and the remaining pads on the printed circuit board to complete the fixation of the remaining pins of the device and the remaining pads on the printed circuit board; S6: Reinforce the connection between the device and the printed circuit board.

2. The assembly method for preventing thermal mismatch of devices according to claim 1, characterized in that: In step S1, the surface of the device soldering surface is modified by magnetron sputtering, and a tin-lead alloy is plated on the device soldering surface with a coating thickness of 1 μm.

3. The assembly method for preventing thermal mismatch of devices according to claim 2, characterized in that: The parameters for magnetron sputtering are: sputtering power above 2kW, sputtering time above 30min, and vacuum level of 10. -3 Pa level.

4. The assembly method for preventing thermal mismatch of devices according to claim 1, characterized in that: In step S2, the surface of the printed circuit board pads is modified by manual soldering with an electric soldering iron. The soldering iron temperature is 260-300℃, and the printed circuit board is baked for 2-4 hours before soldering at a temperature of 100-120℃.

5. The assembly method for preventing thermal mismatch of devices according to claim 1, characterized in that: In step S3, an SMT stencil is used to print solder paste on the center pad and target pin pad of the printed circuit board. The SMT stencil is evenly opened with multiple sets of grids of the same size at the position of the center pad of the printed circuit board. The spacing between adjacent grids is 3-5 per thousand of the width of the center pad. The SMT stencil is opened with holes at the position of the target pin pad. The target pin pad is a preset number of pin pads at the center position of each set of edges.

6. The assembly method for preventing thermal mismatch of devices according to claim 5, characterized in that: In step S3, the solder paste is warmed and stirred before printing. The target pin pads are the two pin pads at the center of each group of edges.

7. The assembly method for preventing thermal mismatch of devices according to claim 1, characterized in that: In step S4, the reflow oven temperature is set to the actual temperature of the printed circuit board plus 30-40°C.

8. The assembly method for preventing thermal mismatch of devices according to claim 1, characterized in that: In step S5, the remaining pins of the device and the remaining pads of the printed circuit board are manually soldered with a soldering iron. The soldering iron temperature is set to 280-300℃, the single-point soldering time does not exceed 3s, a pointed soldering iron is used, and the preheating temperature of the printed circuit board is 70-80℃.

9. The assembly method for preventing thermal mismatch of devices according to claim 1, characterized in that: In step S6, two-component DG-3 epoxy adhesive is applied to the four vertices of the device for reinforcement. The epoxy adhesive ratio is 1.5-3, and the dispensing height is greater than half the height of the device body. The printed circuit board temperature is preheated to 70-80℃ during dispensing.

10. An electronic device, characterized in that: The assembly method for preventing thermal mismatch of devices as described in any one of claims 1-9 is applied.

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