A method for obtaining a detection threshold of SPI-based solder paste jet printing

Abstract

The present application relates to a kind of based on SPI's tin paste jet printing detection threshold acquisition method, comprising the following steps: scheme design and sample preparation are needed, the device package form that needs to be detected is clear;Secondly, the relevant data of steel screen printing technology are collected by SPI detection equipment;Then, the target parameter of tin paste jet printing is calculated by formula equivalent transformation;Then again through a series of mathematical analysis and calculation and experimental research, obtain the tin paste jet printing process parameters of different packaging devices;Finally, the SPI detection threshold of tin paste jet printing is obtained, and SPI detection threshold verification and popularization and application.The detection threshold acquisition method of the present application is suitable for obtaining the optimal jet printing process parameters of different packaging devices, when detecting the quality of tin paste jet printing, the detection precision and accuracy are greatly improved, further, the detection result is consistent with the actual situation.

Description

TECHNICAL FIELD

[0001] The present application relates to the surface mounting technology field of circuit components, in particular to a SPI-based solder paste jet printing detection threshold value acquisition method. BACKGROUND

[0002] The existing solder paste jet printing technology is a new solder paste coating technology without steel mesh, and it has practical value in the production of military electronic products due to its convenience and flexibility. The solder paste jet printing technology is a non-contact solder paste coating technology, which has the advantages of no pressure generated during the spraying process, strong precision control, high material utilization rate, etc., and can select different jet printing process parameters according to the pads, thereby solving the coating quality problems caused by the mixed coating of different pad size components.

[0003] However, due to the difference between the solder paste jet printing technology and the traditional steel mesh printing technology, there is a great gap in the appearance of the solder joints formed by coating, which greatly affects the detection of the solder paste coating result. When using the traditional SPI detection specification of steel mesh printing to detect the quality of jet printing solder paste, the false positive rate and the false negative rate are significantly increased, and the detection result is greatly different from the actual situation. At present, there is no SPI detection equipment specially used for detecting the quality of solder paste jet printing on the market, so how to optimize the traditional SPI detection threshold value to meet the new type of solder paste jet printing technology is particularly important. SUMMARY

[0004] To solve the above technical problems, a SPI-based solder paste jet printing detection threshold value acquisition method is provided, which is used in the solder paste jet printing quality detection process to improve the accuracy and precision of the detection result, and includes the following steps:

[0005] Step S1: scheme design and sample preparation;

[0006] Step S2: the SPI detection equipment collects data related to the steel mesh printing technology;

[0007] Step S3: equivalent conversion, calculate the target parameters related to the solder paste jet printing; use the solder paste volume ratio as a reference, and calculate the target volume ratio of the solder paste jet printing according to the formula:

[0008]

[0009] The target volume ratio of the solder paste jet printing is 114.91%, wherein the steel mesh printing solder paste volume ratio is 109.81%, the printing solder paste metal component ratio is 90%, and the jet printing solder paste metal component ratio is 86%.

[0010] ​​​​Step S4: Mathematical analysis and calculation to obtain solder paste printing process parameters for different packaged devices; perform printing operations with different printing process parameters, and collect printing volume ratio data via SPI after printing to obtain fitting curves and fitting formulas; calculate the theoretical preset printing volume ratio using the fitting formulas. The theoretical preset volume ratio is rounded down to form the actual preset volume ratio. );

[0011] The actual volume ratio is obtained by performing the printing operation using the actual preset volume ratio. Finally, compare the actual volume ratio ( ) and solder paste printing target volume ratio ( ), for the actual preset volume ratio ( Adjustments were made, and the printing process was repeated until the adjusted actual volume ratio was achieved. Approaching the target volume ratio of solder paste printing ( ), and finally the preset volume ratio for solder paste printing was obtained ( );

[0012] Step S5: Obtain the SPI detection threshold for solder paste printing;

[0013] Step S6: SPI detection threshold verification; apply the obtained optimal printing process parameters and SPI detection threshold in the actual product process.

[0014] In one embodiment of the present invention, step S1 includes designing a template with a flatness of ≤0.05mm, selecting the packaging form of the resistor-capacitor device to be verified, designing a PCB board with FR-4 material and a thickness of 1.6mm~2.0mm, and formulating solder paste printing process parameters.

[0015] In one embodiment of the present invention, the solder paste is Sn63Pb37, with a metal particle diameter ranging from 15 to 25 μm; and a solder paste inkjet printer is used, with an inkjet diameter ranging from 0.33 to 0.52 mm and an inkjet height of 1000 μm.

[0016] In one embodiment of the present invention, the resistor-capacitor device to be verified includes 10 different package types, namely 0402, 0603, 0805, 1206, 1210, 1812, 2220, 3528, 6032, and 7343.

[0017] In an embodiment of the present application, in step S2, a stencil printer is used for printing the steel mesh with a specified thickness, and after printing, the amount of tin paste printing is detected by an SPI detection device, and 2500 groups of tin paste thickness, area ratio (actual tin paste area / PCB pad area), and volume ratio (actual tin paste volume / (PCB pad area*stencil thickness)) are collected.

[0018] In an embodiment of the present application, in step S5, a tin paste jet printing is performed with a preset volume ratio (V1) to obtain the mean value and standard deviation of the jet printing thickness, area ratio, and volume ratio.

[0019] The above technical solution of the present application has the following advantages compared with the prior art: The detection threshold acquisition method of the present application is suitable for obtaining optimal jet printing process parameters for different packaged devices, and when detecting the quality of the jet printed tin paste, the detection accuracy and accuracy are greatly improved, and further, the detection result is consistent with the actual situation. BRIEF DESCRIPTION OF DRAWINGS

[0020] In order to make the content of the present application more easily understood, the present application will be further described in detail below according to specific embodiments of the present application and in conjunction with the accompanying drawings.

[0021] Figure 1 is a process flow diagram of the SPI-based tin paste jet printing detection threshold acquisition method of the present application;

[0022] Figure 2 is a schematic diagram of a PCB containing a resistor-capacitor device in the present application;

[0023] Figure 3 is a group of fitting curves and fitting formulas corresponding to the preset volume ratio and the actual volume ratio of different packaged devices in the present application. DETAILED DESCRIPTION

[0024] As shown in Figure 1 , the present embodiment provides an SPI-based tin paste jet printing detection threshold acquisition method, which greatly improves the accuracy and precision of the detection result compared with the previous process method in the tin paste quality detection process of jet printing, including the following steps:

[0025] Design and sample preparation;

[0026] A sample plate with a flatness of ≤0.05mm is designed, and the sample plate material is aluminum alloy. The packaging form of the device to be verified is selected, and the device packaging list is shown in Table 1, a total of 10 different types of resistor-capacitors. A PCB with a material of FR-4 and a thickness of 1.6mm~2.0mm is designed, and the PCB pad size design is shown in Figure 2 , and the surface treatment process is lead-free tin spraying.​

[0027] The tin paste jet printing process parameters are formulated, the tin paste model selected for jet printing is Sn63Pb37, the metal particle diameter range is 15-25 μm. The jet printing diameter range of the tin paste jet printing machine, equipment is 0.33-0.52 mm, and the jet printing height is 1000 μm. The jet printing process parameters are preset area ratio, preset volume ratio, and the jet printing process parameters are as follows:

[0028] Device packaging list

[0029]

[0030] Jet printing process parameters

[0031] The SPI detection equipment collects steel mesh printing technology related data;

[0032] The tin paste printer is used to perform 0.12 mm thickness steel mesh printing on an aluminum alloy sample plate. After printing, the tin paste printing amount is detected by the SPI detection equipment, and 2500 groups of tin paste thickness, area ratio (tin paste actual area / PCB pad area), volume ratio (tin paste actual volume / (PCB pad area x steel mesh thickness)) and other related data are collected. The tin paste printing thickness average is 116.63 μm, the area ratio average is 112.91%, and the volume ratio average is 109.81%.

[0033] Through equivalent transformation formula, the tin paste jet printing related target parameters are calculated;

[0034] In order to facilitate the comparison of the tin paste amount of jet printing and printing, the tin paste volume ratio is used as a reference, and according to the equivalent transformation formula (1), the tin paste jet printing target volume ratio (V) is calculated as 114.91%.

[0035] Formula (1)

[0036] Among them, The steel mesh printed tin paste volume ratio obtained in step S12 is 109.81%;

[0037] The tin paste metal component ratio for printing is 90%;

[0038] The tin paste metal component ratio for jet printing is 86%.

[0039] Through mathematical analysis and calculation, different packaging device tin paste jet printing process parameters are obtained;

[0040] ​According to the solder paste jet printing process parameters designed in step S1, different jet printing process parameters are completed, and after jet printing, the volume ratio data of the jet printing body is collected through SPI to obtain the fitting curve and fitting formula of the relationship between the preset volume ratio ( ) and the actual volume ratio ( ), such as Figure 3 . Through the fitting formula, the theoretical preset volume ratio ( ) is calculated when the jet printing target volume ratio ( ) is 114.91%. The theoretical preset volume ratio is rounded to form the actual preset volume ratio ( ). The actual preset volume ratio is used for jet printing again, and the actual volume ratio ( ) is obtained. Finally, the actual volume ratio ( ) and the solder paste jet printing target volume ratio ( ) are compared. If there is a difference, the actual preset volume ratio ( ) is adjusted, and after adjustment, the jet printing operation is performed again until the adjusted actual volume ratio ( ) is close to the solder paste jet printing target volume ratio ( ), and finally the solder paste jet printing preset volume ratio ( ) is obtained.

[0041] Different packaging device jet printing preset volume ratio setting

[0042] Obtain the SPI detection threshold of solder paste jet printing;

[0043] Repeat the test using the solder paste jet printing preset volume ratio ( ), and obtain the mean and standard deviation of the jet printing thickness, area ratio, and volume ratio, as shown in the following table. It can be seen that the thickness mean is about 150 μm, the area ratio mean is about 90%, and the volume ratio mean is about 115%, so the corresponding detection thickness, area ratio, and volume ratio parameters of SPI are 150 μm, 90%, and 115%. For the upper and lower control lines of the SPI detection parameters, we consider using ±3σ as the key control line, but in the actual production process, the solder joint jet printing appearance will be affected by many factors such as temperature, humidity, solder paste type, solder paste viscosity, pad design, PCB flatness, etc. Therefore, when setting the SPI detection threshold, in addition to considering the standard deviation, the detection threshold range also needs to be adjusted according to the actual product and production experience, and the SPI detection threshold parameter results are as follows:

[0044] Different packaging device jet printing thickness, area ratio, and volume ratio mean and standard deviation

[0045]

[0046] SPI detection threshold parameters for different packaged devices

[0047] SPI detection threshold verification and promotion application;

[0048] The obtained optimal inkjet printing process parameters ( The detection thresholds for SPI are being promoted and applied in actual products.

[0049] The detection threshold acquisition method described in this embodiment solves the problem that when using the traditional SPI detection specification printed by stencil to detect the quality of inkjet solder paste, the false alarm rate and false negative rate are significantly increased, and the detection results differ greatly from the actual situation.

[0050] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A method for obtaining a detection threshold for solder paste printing based on SPI, wherein in the quality inspection process of solder paste printing, the detection threshold acquisition method is used to improve the accuracy and precision of the inspection results, characterized in that, It comprises the following steps: Step S1: scheme design and sample preparation; Step S2: SPI detection device collects steel mesh printing technology related data; It uses a solder paste printer to print a specified thickness of steel mesh, and after printing, the SPI detection device detects the amount of solder paste printing, collects 2500 groups of solder paste thickness, area ratio, volume ratio; Step S3: equivalent conversion, calculate the target parameters of solder paste jet printing; using the volume ratio of solder paste as a reference, according to the formula: The target volume ratio of the solder paste is calculated is 114.91%, wherein is the average of the steel mesh printing solder paste volume ratio obtained in step S2, and is 109.81%; is the proportion of the metal component of the solder paste for printing, and is 90%; is the proportion of the metal component of the solder paste for printing, and is 86%; Step S4: mathematical analysis and calculation, obtain different packaging device solder paste jet printing process parameters; perform jet printing operations with different jet printing process parameters, and after jet printing, collect the volume ratio data of the jet printing body by SPI, and obtain the fitting curve and fitting formula; Theoretical preset volume ratio is calculated by fitting formula ; rounding the theoretical preset volume ratio to form actual preset volume ratio ; The actual preset volume ratio is used for the inkjet printing operation to obtain an actual volume ratio ; finally, the actual volume ratio is compared with a target volume ratio of the solder paste inkjet printing , the actual preset volume ratio is adjusted, the inkjet printing operation is performed again after the adjustment, until the adjusted actual volume ratio approaches the target volume ratio of the solder paste inkjet printing , and finally a preset volume ratio of the solder paste inkjet printing is obtained ; Step S5: Obtain the SPI detection threshold of the tin paste jet printing; specifically, a preset volume ratio of the tin paste jet printing is adopted Repetitive tests are conducted to obtain the mean value and standard deviation of the jet printing thickness, area ratio and volume ratio. Step S6: SPI detection threshold verification; the optimal jet printing process parameters and SPI detection threshold obtained are used in actual product processes.

2. The method of claim 1, wherein: In step S1, a sample plate with a flatness of ≤0.05mm is designed, the packaging form of the capacitor device to be verified is selected, and a PCB board with FR-4 material and a thickness of 1.6mm~2.0mm is designed, and the solder paste jet printing process parameters are formulated.

3. The method of claim 2, wherein: The solder paste is selected from a solder paste model Sn63Pb37, and the metal particle diameter range is 15~25μm; and a solder paste jet printer is selected, and the jet printing diameter range of the equipment is 0.33~0.52mm, and the jet printing height is 1000μm.

4. The method of claim 2, wherein: The capacitor device to be verified includes 10 different packaging types of capacitors, which are 0402, 0603, 0805, 1206, 1210, 1812, 2220, 3528, 6032 and 7343.

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