Solder paste jet printing detection threshold value method based on SPI (Serial Peripheral Interface)

Abstract

The invention relates to an SPI (Serial Peripheral Interface)-based solder paste jet printing threshold detection method, which comprises the following steps of: designing a scheme and preparing a sample piece, and determining a packaging form of a device to be detected; secondly, relevant data of the steel screen printing technology are collected through SPI detection equipment; then, through formula equivalent conversion, solder paste jet printing related target parameters are calculated; then solder paste jet printing process parameters of different packaging devices are obtained through a series of mathematical analysis calculation and experimental research; and finally, a solder paste jet printing SPI detection threshold value is obtained, and the SPI detection threshold value is verified, popularized and applied. The method for detecting the threshold value is suitable for obtaining the optimal jet printing process parameters of different packaging devices, the detection precision and the accuracy rate are greatly improved when the quality of the jet-printed solder paste is detected, and furthermore, the detection result conforms to the actual situation.

Description

Technical Field

[0001] The invention relates to the technical field of surface mounting of circuit components, and in particular to a solder paste spray printing detection threshold method based on SPI. Background Art

[0002] As a new type of solder paste coating technology without steel mesh, the existing solder paste printing technology has practical value in the production of military electronic products with its convenience and flexibility. The solder paste printing technology is a non-contact solder paste coating technology, which has the advantages of no pressure during the spraying process, strong precision control and high material utilization rate. In addition, different printing process parameters can be selected according to the pad, which solves the coating quality problem caused by the mixed coating of components with different pad sizes from the coating form.

[0003] However, due to the different coating methods between solder paste printing technology and traditional steel screen printing technology, there is a huge difference in the morphology of the solder joints formed by coating, which has a great impact on the detection of solder paste coating results. When the SPI detection specifications of traditional steel screen printing are used to detect the quality of printed solder paste, the false alarm rate and missed alarm rate increase significantly, and the detection results are very different from the actual situation. Currently, there is no SPI detection equipment specifically used to detect the quality of solder paste printing on the market, so how to optimize the traditional SPI detection threshold to meet the new solder paste printing technology is particularly important. Summary of the invention

[0004] In order to solve the above technical problems, the present invention provides a solder paste printing detection threshold method based on SPI. In the solder paste quality detection process for printing, the detection threshold method obtains a detection result with greatly improved accuracy and precision compared with the previous process method, and comprises the following steps:

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

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

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

[0008]

[0009] The target volume ratio of solder paste printing (Vtarget) is calculated to be 114.91%, where Vreference is the average volume ratio of the stencil printing solder paste obtained in step S2, which is 109.81%; q1 is the metal component ratio of the printed solder paste, which is 90%; q2 is the metal component ratio of the printed solder paste, which is 86%;

[0010] Step S4: mathematically analyze and calculate to obtain the solder paste printing process parameters of different packaged devices; perform printing operations with different printing process parameters, collect printing volume ratio data through SPI after printing, and obtain a fitting curve and a fitting formula; calculate the theoretical preset volume ratio of printing (Vtheoretical preset) through the fitting formula; round the theoretical preset volume ratio to form an actual preset volume ratio (Vactual preset);

[0011] The actual preset volume ratio is used for printing operation to obtain the actual volume ratio (Vactual); finally, the actual volume ratio (Vactual) is compared with the target volume ratio (Vtarget) of solder paste printing, and the actual preset volume ratio (Vactual preset) is adjusted. After adjustment, the printing operation is performed again until the adjusted actual volume ratio (Vactual) is close to the target volume ratio (Vtarget) of solder paste printing, and finally the preset volume ratio (Vfinal preset) of solder paste printing is obtained;

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

[0013] Step S6: SPI detection threshold verification; applying 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 sample with a flatness of ≤0.05 mm, selecting the packaging form of the resistor and capacitor to be verified, designing a PCB board with a material of FR-4 and a thickness of 1.6 mm to 2.0 mm, and formulating solder paste printing process parameters.

[0015] In one embodiment of the present invention, the solder paste is a spray-printed solder paste model of Sn63Pb37, and the diameter of the metal particles is in the range of 15 to 25 μm; and a solder paste spray printer is selected, and the spray diameter range of the equipment is 0.33 to 0.52 mm, and the spray height is 1000 μm.

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

[0017] In one embodiment of the present invention, in step S2, a solder paste printer is used to print a steel mesh of a specified thickness. After printing, the amount of solder paste printed is detected by an SPI detection device to collect 2500 sets of solder paste thickness, area ratio (actual solder paste area / PCB pad area), and volume ratio (actual solder paste volume / (PCB pad area×steel mesh thickness)).

[0018] In one embodiment of the present invention, in step S5, a repeatability test is performed using a preset volume ratio (Vfinal preset) of solder paste printing to obtain the mean and standard deviation of the printing thickness, area ratio, and volume ratio.

[0019] The above technical solution of the present invention has the following advantages compared with the prior art: the detection threshold method described in the present invention is suitable for obtaining the optimal printing process parameters for different packaging devices. When detecting the quality of printed solder paste, the detection precision and accuracy are greatly improved, and further, the detection results are consistent with the actual situation. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] In order to make the contents of the present invention more clearly understood, the present invention is further described in detail below based on specific embodiments of the present invention in conjunction with the accompanying drawings.

[0021] Figure 1 It is a process flow diagram of the SPI-based solder paste printing detection threshold method of the present invention;

[0022] Figure 2 Schematic diagram of a PCB board containing resistor and capacitor components in the present invention;

[0023] Figure 3 It is a group of fitting curves and fitting formula diagrams corresponding to the preset volume ratios and actual volume ratios of different packaged devices in the present invention. DETAILED DESCRIPTION

[0024] like Figure 1 As shown, this embodiment provides a solder paste printing detection threshold method based on SPI. In the solder paste quality detection process for printing, the detection threshold method obtains a detection result with greatly improved accuracy and precision compared with the previous process method, and includes the following steps:

[0025] Scheme design and sample preparation;

[0026] Design a sample with a flatness of ≤0.05mm, and the sample material is aluminum alloy. Select the package form of the device to be verified. The device package list is shown in Table 1, with a total of 10 different package types of resistors and capacitors. Design a PCB board with a material of FR-4 and a thickness of 1.6mm to 2.0mm. The PCB pad size is designed as follows Figure 2 The surface treatment process is lead tin spraying.

[0027] Formulate solder paste printing process parameters, select the solder paste model Sn63Pb37, and the metal particle diameter range is 15-25μm. And the solder paste printer, the equipment's printing diameter range is 0.33-0.52mm, and the printing height is 1000μm. The printing process parameters are the preset area ratio and the preset volume ratio. The printing process parameters are as follows:

[0028] Device Package List

[0029]

[0030] Printing process parameters

[0031]

[0032] SPI testing equipment collects data related to stencil printing technology;

[0033] A solder paste printer was used to print a 0.12 mm thick steel mesh on an aluminum alloy sample. After printing, the amount of solder paste printed was tested by SPI testing equipment, and 2500 sets of solder paste thickness, area ratio (actual solder paste area / PCB pad area), volume ratio (actual solder paste volume / (PCB pad area×stencil thickness)) and other related data were collected. The average solder paste printing thickness was 116.63 μm, the average area ratio was 112.91%, and the average volume ratio was 109.81%.

[0034] Calculate the target parameters related to solder paste printing through equivalent conversion of formula;

[0035] In order to compare the amount of solder paste sprayed and printed, the solder paste volume ratio is used as a reference. According to the equivalent conversion formula (1), the target volume ratio of solder paste spraying (Vtarget) is calculated to be 114.91%.

[0036]

[0037] Among them, V 参考 The average volume ratio of the stencil printing solder paste obtained in step S12 is 109.81%;

[0038] Q1 is the metal content of solder paste for printing, which is 90%;

[0039] Q2 is the metal content of solder paste for printing, which is 86%.

[0040] Through mathematical analysis and calculation, the solder paste printing process parameters of different packaging devices are obtained;

[0041] According to the solder paste printing process parameters designed in step S1, the printing operation with different printing process parameters is completed. After printing, the printing volume ratio data is collected through SPI to obtain the fitting curve and fitting formula of the relationship between the preset printing volume ratio (V preset) and the actual volume ratio (V actual), such as Figure 3. By fitting the formula, the theoretical preset volume ratio (Vtheoretical preset) of the printing is calculated when the target volume ratio (Vtarget) of the printing is 114.91%. The theoretical preset volume ratio is rounded to form the actual preset volume ratio (Vactual preset). The actual preset volume ratio is used to perform the printing operation again to obtain the actual volume ratio (Vactual). Finally, the actual volume ratio (Vactual) is compared with the target volume ratio (Vtarget) of solder paste printing. If there is a difference, the actual preset volume ratio (Vactual preset) is adjusted, and the printing operation is performed again after adjustment until the adjusted actual volume ratio (Vactual) is close to the target volume ratio (Vtarget) of solder paste printing, and finally the preset volume ratio (Vfinal preset) of solder paste printing is obtained.

[0042] Setting the preset volume ratio for printing of different packaged devices

[0043]

[0044] Get the solder paste printing SPI detection threshold;

[0045] A repeatability test was conducted using a preset volume ratio (V final preset) for solder paste printing, and the mean and standard deviation of the printing thickness, area ratio, and volume ratio were obtained, as shown in the following table. It can be seen that the mean thickness is around 150μm, the mean area ratio is around 90%, and the mean volume ratio is around 115%, so the detection thickness, area ratio, and volume ratio parameters corresponding to SPI are determined to be 150μm, 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 printing morphology will be affected by many factors such as temperature, humidity, solder paste type, solder paste viscosity, pad design, and PCB flatness. Therefore, when formulating the SPI detection threshold, in addition to considering the standard deviation, it is also necessary to adjust the detection threshold range based on actual products and production experience. After comprehensive consideration, the SPI detection threshold parameter results are as follows:

[0046] Mean and standard deviation of printing thickness, area ratio and volume ratio of different packaged devices

[0047]

[0048]

[0049] SPI detection threshold parameters for different packaged devices

[0050]

[0051] Verification and promotion of SPI detection threshold;

[0052] The obtained optimal printing process parameters (V final preset) and SPI detection threshold are promoted and applied in actual products.

[0053] The detection threshold method described in this embodiment solves the problem that when the SPI detection specification of traditional steel screen printing is used to detect the quality of printed solder paste, the false alarm rate and the missed alarm rate increase significantly, and the detection result is very different from the actual situation.

[0054] Obviously, the above embodiments are merely examples for clear explanation and are not intended to limit the implementation methods. 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 implementation methods here. The obvious changes or modifications derived from these are still within the protection scope of the invention.

Claims

1. A solder paste printing detection threshold method based on SPI. In the solder paste quality detection process for printing, the detection threshold method obtains a detection result with a significantly improved accuracy and precision compared with the previous process method, characterized in that: The steps include: Step S1: Scheme design and sample preparation; Step S2: The SPI detection equipment collects data related to the steel screen printing technology; Step S3: Equivalent conversion, calculate the target parameters related to solder paste printing; use the solder paste volume ratio as a reference, according to the formula: The target volume ratio of solder paste printing (Vtarget) is calculated to be 114.91%, where Vreference is the average volume ratio of the stencil printing solder paste obtained in step S2, which is 109.81%; q1 is the metal component ratio of the printed solder paste, which is 90%; q2 is the metal component ratio of the printed solder paste, which is 86%; 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, collect printing volume ratio data through SPI after printing, and obtain fitting curves and fitting formulas; The theoretical preset volume ratio of printing (Vtheoretical preset) is calculated by fitting formula; the theoretical preset volume ratio is rounded to form the actual preset volume ratio (Vactual preset); The actual preset volume ratio is used for printing operation to obtain the actual volume ratio (Vactual); finally, the actual volume ratio (Vactual) is compared with the target volume ratio (Vtarget) of solder paste printing, and the actual preset volume ratio (Vactual preset) is adjusted. After adjustment, the printing operation is performed again until the adjusted actual volume ratio (Vactual) is close to the target volume ratio (Vtarget) of solder paste printing, and finally the preset volume ratio (Vfinal preset) of solder paste printing is obtained; Step S5: obtaining a solder paste printing SPI detection threshold; Step S6: SPI detection threshold verification; applying the obtained optimal printing process parameters and SPI detection threshold in the actual product process.

2. The detection threshold method according to claim 1, characterized in that: Step S1 includes designing a sample with a flatness of ≤0.05 mm, selecting the packaging form of the resistor and capacitor to be verified, designing a PCB board with a material of FR-4 and a thickness of 1.6 mm to 2.0 mm, and formulating solder paste printing process parameters.

3. The detection threshold method according to claim 2, characterized in that: The solder paste is a spray-printed solder paste model of Sn63Pb37, with a metal particle diameter range of 15 to 25 μm; and a solder paste spray printer is selected, the spray diameter range of the equipment is 0.33 to 0.52 mm, and the spray height is 1000 μm.

4. The detection threshold method according to claim 2, characterized in that: The resistors and capacitors to be verified include 10 different package types, namely 0402, 0603, 0805, 1206, 1210, 1812, 2220, 3528, 6032, and 7343.

5. The detection threshold method according to claim 1, characterized in that: In step S2, a solder paste printer is used to print a steel screen of a specified thickness. After printing, the amount of solder paste printed is tested by an SPI testing device to collect 2500 sets of solder paste thickness, area ratio, and volume ratio.

6. The detection threshold method according to claim 1, characterized in that: In step S5, a repeatability test is performed using a preset volume ratio (Vfinal preset) of solder paste printing to obtain the mean and standard deviation of the printing thickness, area ratio, and volume ratio.

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