Method for eliminating overturning of vacuum reflow soldering chip

Abstract

The invention relates to a method for eliminating overturning of a vacuum reflow soldering chip, and belongs to the technical field of packaging and welding of a thick film hybrid circuit group. According to the method, the vacuumizing rate of a vacuumizing valve is mainly adjusted, and stepped vacuumizing is carried out in a backflow stage, namely, a small vacuumizing valve is adopted for vacuumizing for 3-10 seconds, heating is carried out for 3-5 seconds, and the process steps are repeated for 2-4 times, so that the vacuumizing rate is reduced, meanwhile, the continuous vacuumizing time is shortened in a stepped manner, the up-down amplitude of a chip is reduced, and chip overturning is eliminated. On the whole, the method is simple and convenient to operate, and has the characteristics of high reliability, high yield and low cost, and according to the chip assembly subjected to eutectic welding through the method and the steps, the welding yield is 100%, the welding void rate is within 5%, and the chip turnover rate is reduced from about 10% to below 0.01%.

Description

Technical Field

[0001] The invention relates to the technical field of thick film hybrid circuit assembly packaging welding, and in particular to a method for eliminating vacuum reflow soldering chip flipping. Background Art

[0002] The assembly packaging of thick film hybrid circuit power circuit includes multiple process steps, among which the welding between multiple IC chips, various resistors and capacitors and the film substrate is a key step. The traditional process method is that IC chips and various resistors and capacitors are all soldered with solder paste and then reflowed in a reflow oven. After reflow, the void rate of the chip is relatively high, generally 30% to 50%. When the product power is large, it is difficult to meet the heat dissipation requirements.

[0003] There are currently two main ways to improve the low voiding rate after chip welding. One is step temperature welding, where IC chips use solder sheet eutectic welding, and various resistors and capacitors use solder paste reflow or hot plate reflow. When IC chips use solder sheets for eutectic welding, a certain weight needs to be applied to the chip surface. The operation steps are complicated, and the weight can easily cause scratches on the surface of the tube core, affecting the product yield and processing efficiency. The second is to use vacuum reflow technology, that is, IC chips and various resistors and capacitors are all vacuum reflowed in a vacuum eutectic welding furnace or a vacuum reflow furnace after solder paste is applied. A vacuum environment is created by vacuuming during the circuit reflow stage, which prevents solder oxidation and improves the low voiding rate of the chip. However, due to the influence of the flux content in the solder paste, the rate and method of vacuuming, etc., during the vacuum reflow stage, the chip jumps up and down with a large amplitude, and the flux in the solder liquid vaporizes and expands violently, causing the chip to flip, affecting the efficiency of product processing.

[0004] After searching the existing patents, no content related to chip flipping in vacuum reflow technology was found. However, in the paper "Research on Defects of Vacuum Reflow Process of Power IC Chips" (Microelectronics, Vol. 49, No. 4, August 2019, author Yang Liangliang, Chen Rong, Qin Wenlong, Zhang Ying), the "chip flipping" was reduced by pre-evacuating in advance during the reflow heating stage and using grid solder paste printing to discharge the gas generated during the solder paste preheating and heating stages, and reducing the bubble pressure at the bottom of the chip. The present invention provides another method for eliminating chip flipping in vacuum reflow. Summary of the invention

[0005] The object of the present invention is to provide a vacuum reflow soldering method with low void rate and high yield rate using a vacuum eutectic soldering furnace, which can solve the problem of chip flipping during vacuum reflow soldering.

[0006] It adopts the following technical solutions: A method for eliminating vacuum reflow soldering chip flipping, comprising the following steps: 1. A method for eliminating chip flipping during vacuum reflow soldering, characterized by comprising the following steps: S1. Setting a solder paste printing tool, which includes a solder paste printing template with a certain thickness and opening size set according to the size and position of the circuit components to be soldered, and a soldering substrate positioning; S2. Adjust the vacuum pumping rate of the small vacuum pumping valve in the vacuum eutectic welding furnace so that the vacuum pumping rate of the small vacuum pumping valve is 20% to 30% of the full scale; S3, positioning the circuit to be processed in the solder paste printing tooling, debugging the solder paste printer, and printing the solder paste on the area to be soldered on the circuit surface; S4. After debugging the patch equipment, mount the corresponding components in a certain position and direction at the corresponding printed solder paste position according to the patch requirements; S5, placing the assembled circuit into the process chamber of the eutectic soldering furnace, closing the cover of the process chamber of the eutectic furnace, and then writing and saving the program, calling and running the program; Running the program has the following steps: S51, calling and running the program; S52, evacuating the process chamber and filling it with nitrogen in turn, and repeating this process twice; S53, empty the residual water in the cooling water pipe under the graphite plate in the eutectic welding furnace; S54, heating the process chamber of the quartz lamp in the vacuum eutectic furnace to a preheating temperature of 160°C, wherein the heating rate is 40±20°C / min; a gradient heating curve can be set according to the solder specifications; S55, the vacuum eutectic soldering furnace continues to heat to a soldering temperature of 220±5°C, wherein the heating rate is 60±10°C / min; S56, continue heating in a nitrogen environment and evacuate in a step-by-step manner, the heating temperature is maintained at 220±5°C, wherein the heating time is 3-5s, the small pumping valve is evacuated for 3-10s, and this is repeated 2-4 times; S57, the vacuum eutectic soldering furnace continues to heat and fill with nitrogen, wherein the heating temperature is 220±5°C and the heating time is 5 to 15 seconds, so that the solder can fully reflux in the nitrogen environment; S58, start the cooling circulation water, the vacuum eutectic soldering furnace starts to cool down, and the molten solder is cooled down in the nitrogen environment until it drops to a temperature that is convenient for handling; S59, end the program; S6. Open the process chamber cover and take out the chip assembly that has completed eutectic welding.

[0007] Furthermore, in step S4, solder resist needs to be applied to locations that are prone to tinning.

[0008] Furthermore, the positions that are prone to tinning include epoxy bonding positions and wire bonding positions.

[0009] Compared with the prior art, the present invention has the following beneficial effects: The present invention mainly adjusts the vacuuming rate of the vacuum valve and performs step-by-step vacuuming in the reflow stage. While reducing the vacuuming rate, the step-by-step vacuuming method is used to shorten the continuous vacuuming time, reduce the up and down amplitude of the chip, and eliminate "chip flipping". Overall, the operation is simple, and it has the characteristics of high reliability, high yield and low cost. The void rate can be controlled within 5%, and the chip flipping rate is reduced from about 10% to below 0.01%. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1 It is a structural schematic diagram corresponding to a method for eliminating vacuum reflow soldering chip flipping of the present invention; Figure 2 is a schematic diagram of a template for solder paste printing of the present invention; Figure 3 It is a schematic diagram of the circuit after the chip is mounted. DETAILED DESCRIPTION

[0011] To make the present invention more clear, a method for eliminating chip flipping during vacuum reflow soldering of the present invention is further described below in conjunction with the accompanying drawings. The specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0012] like Figure 1 As shown, a method for eliminating vacuum reflow soldering chip flipping includes the following steps: S1. Set up a solder paste printing tool, which includes a solder paste printing template 1, such as Figure 2 As shown, the solder paste printing template 1 is a steel plate with a certain thickness and opening size set according to the size and position of the circuit component 3 to be soldered, and the solder paste printing template 1 can form a detachable positioning match with the circuit 2 to be processed. Specifically, the positioning match between the two can be achieved through conventional methods such as positioning pin holes and positioning surfaces. As a conventional technology, it will not be repeated in this embodiment. Of course, in this step, the solder paste printing tooling is vacuum adsorbed and mechanically clamped according to different equipment.

[0013] S2. Manually adjust the adjustment knob of the small vacuum valve in the vacuum eutectic welding furnace to adjust the vacuum rate of the small vacuum valve so that the vacuum rate of the small vacuum valve is 20% to 30% of the full scale.

[0014] S3, positioning the circuit 2 to be processed in the solder paste printing tooling, debugging the solder paste printer, so that the positioning of the circuit to be processed, the solder paste printing position, angle, and thickness meet the requirements, and then printing the solder paste 4 on the circuit surface area. Here, the solder paste 4 used needs to be pre-treated, and the solder paste pre-treatment includes taking the solder paste from the refrigerator and returning it to temperature, and then using a solder paste mixer for stirring.

[0015] S4, debug the patch equipment, such as Figure 3 As shown in the figure, the corresponding components are mounted in a certain position and direction at the corresponding printed solder paste position according to the requirements of the patch. In this step, it should be noted that solder mask should be applied to the positions that are prone to tinning, such as epoxy bonding positions and lead bonding positions.

[0016] S5. Place the assembled circuit into the process chamber of the eutectic soldering furnace, close the cover of the process chamber of the eutectic furnace, and then write and save the program, call and run the program.

[0017] Here, running the program has the following steps: S51, calling and running the program; S52, vacuumize and fill the process chamber with nitrogen (purity ≥ 99.99%), repeat twice; S53, empty the residual water in the cooling water pipe under the graphite plate in the eutectic welding furnace; S54, heating the process chamber of the quartz lamp in the vacuum eutectic furnace to a preheating temperature of 160°C, wherein the heating rate is 40±20°C / min; a gradient heating curve can be set according to the solder specifications; S55, the vacuum eutectic soldering furnace continues to heat to a soldering temperature of 220±5°C, wherein the heating rate is 60±10°C / min; S56, continue heating and step-wise vacuuming in a nitrogen environment, the heating temperature is maintained at 220±5°C, wherein the heating time is 3-5s, the small vacuuming valve is used for vacuuming for 3-10s, and this is repeated 2-4 times; here, the opening and closing of the small vacuuming valve can be manually adjusted so that the vacuuming time in each cycle is 3-10s, so that a step-wise vacuuming rate curve can be formed in this step, which plays a similar buffering effect and reduces the amplitude of the up and down movement of the component; S57, the vacuum eutectic soldering furnace continues to heat and fill with nitrogen, wherein the heating temperature is 220±5°C and the heating time is 5 to 15 seconds, so that the solder can fully reflux in the nitrogen environment; S58, start the cooling circulation water, the vacuum eutectic soldering furnace starts to cool down, and the molten solder is cooled down in the nitrogen environment until it drops to a temperature that is convenient for handling; S59, end the program.

[0018] S6. Open the process chamber cover and take out the chip assembly that has completed eutectic welding.

[0019] The present invention mainly adjusts the vacuuming rate of the vacuuming valve and performs step-by-step vacuuming in the reflow stage (using a small vacuuming valve to vacuum for 3 to 10 seconds, heating for 3 to 5 seconds, and repeating the process steps 2 to 4 times). While reducing the vacuuming rate, the chip up and down amplitude is reduced by step-by-step reducing the continuous vacuuming time, eliminating the "chip flipping" and having nothing to do with the solder paste printing pattern. Overall, the operation is simple, the void rate is reduced, and the yield rate is high. The chip assembly eutectic soldered by the above method and steps has a soldering yield rate of 100% and a soldering void rate of less than 5%.

[0020] The above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the embodiments of the present invention. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the embodiments here. However, these obvious changes or modifications derived from the essential spirit of the present invention still fall within the scope of protection of the present invention.

Claims

1. A method for eliminating chip flipping during vacuum reflow soldering, characterized in that The following steps are involved: S1. Setting a solder paste printing tool, which includes a solder paste printing template with a certain thickness and opening size set according to the size and position of the circuit components to be soldered, and the solder paste printing template can form a detachable positioning match with the soldering substrate; S2. Adjust the vacuum pumping rate of the small vacuum pumping valve in the vacuum eutectic welding furnace so that the vacuum pumping rate of the small vacuum pumping valve is 20% to 30% of the full scale; S3, positioning the circuit to be processed in the solder paste printing tooling, debugging the solder paste printer, and printing the solder paste on the area to be soldered on the circuit surface; S4. After debugging the patch equipment, mount the corresponding components in a certain position and direction at the corresponding printed solder paste position according to the patch requirements; S5, placing the assembled circuit into the process chamber of the eutectic soldering furnace, closing the cover of the process chamber of the eutectic furnace, and then writing and saving the program, calling and running the program; Running the program has the following steps: S51, calling and running the program; S52, evacuating the process chamber and filling it with nitrogen in turn, and repeating this process twice; S53, empty the residual water in the cooling water pipe under the graphite plate in the eutectic welding furnace; S54, heating the process chamber of the quartz lamp in the vacuum eutectic furnace to a preheating temperature of 160°C, wherein the heating rate is 40±20°C / min; a gradient heating curve can be set according to the solder specifications; S55, the vacuum eutectic soldering furnace continues to heat to a soldering temperature of 220±5°C, wherein the heating rate is 60±10°C / min; S56, continue heating in a nitrogen environment and evacuate in a step-by-step manner, the heating temperature is maintained at 220±5°C, wherein the heating time is 3-5s, the small pumping valve is evacuated for 3-10s, and this is repeated 2-4 times; S57, the vacuum eutectic soldering furnace continues to heat and fill with nitrogen, wherein the heating temperature is 220±5°C and the heating time is 5 to 15 seconds, so that the solder can fully reflux in the nitrogen environment; S58, start the cooling circulation water, the vacuum eutectic soldering furnace starts to cool down, and the molten solder is cooled down in the nitrogen environment until it drops to a temperature that is convenient for handling; S59, end the program; S6. Open the process chamber cover and take out the chip assembly that has completed eutectic welding.

2. The method for eliminating chip flipping during vacuum reflow soldering according to claim 1, characterized in that: In step S4, solder resist needs to be applied to locations that are prone to tinning.

3. The method for eliminating chip flipping during vacuum reflow soldering according to claim 1, characterized in that: The positions that are prone to tinning include epoxy bonding positions and wire bonding positions.

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