A method for improving tin bead residue in small holes of tin-spraying plate

Abstract

This invention discloses a method for improving solder ball residue in small holes of tin-plated circuit boards, addressing the contradiction between energy consumption and yield in existing air knife technologies. The method involves dividing the end face of the circuit board to be soldered into N parallel strip regions, each extending in the same direction as the air knife's soldering operation. The air knife has N adjustable pressure nozzles, each corresponding to one of the N strip regions. A scanning frame is used to scan the through-hole area ratio 'a' of each strip region along its extension direction. t The through-hole area ratio a t It is the ratio of the area S1 of the through-hole within the scanning frame to the area S0 of the scanning frame at time t; the pressure value of the corresponding air outlet is determined based on the maximum ratio of the through-hole areas in the strip region and the thickness of the circuit board. Its advantage is that the air outlet pressure can be locally adjusted as needed according to the through-hole distribution of the circuit board, thereby improving the yield without wasting energy.

Description

Technical Field

[0001] This invention relates to a method for improving solder ball residue in pinholes of tin-plated circuit boards. Background Technology

[0002] Tin plating is a common surface treatment process for circuit boards. Tin plating involves immersing the circuit board in molten tin-lead. Once a sufficient amount of tin-lead has adhered to the surface, hot air is used to pressurize and scrape away any excess. After the tin-lead cools, the soldered areas of the circuit board will have a layer of tin-lead of appropriate thickness. This is a general overview of the tin plating process.

[0003] The terminal component for hot air pressurization scraping tin and lead is generally an air knife. Existing air knives, such as... Figure 1 and Figure 2 As shown. The blade holder 10 has only one main air duct 17. The blade holder has an inner air duct 18 extending to both ends. The two outer sides of the bottom of the blade holder 10 are provided with air guide vanes 20. The lower ends of the two air guide vanes 20 are tightened towards the lower port of the inner air duct 18 but maintain a certain gap for pressurizing hot air.

[0004] Conventional circuit boards typically have holes of varying sizes, with significant differences in diameter between large and small holes. There are often holes as small as 0.2mm and holes larger than 4mm, a difference of up to 20 times or more. Small holes located near larger holes tend to have insufficient air pressure due to the greater hole's tendency to leak air. This ultimately prevents the solder balls inside the small holes from being blown out, resulting in defective components.

[0005] In existing air knife technology, the airflow rate in the horizontal direction is always fixed. To ensure that solder balls are blown out of all the small holes, the overall air pressure needs to be increased. However, there are not many areas on the entire circuit board that may require localized high pressure, which leads to additional power consumption. To maintain low power consumption, a certain yield must be sacrificed by discarding defective components blocked by solder balls in the later stages. Summary of the Invention

[0006] The purpose of this invention is to provide a method for improving solder ball residue in small holes of tin-plated boards, so as to solve the problems existing in the prior art.

[0007] The present invention describes a method for improving solder ball residue in small holes of a tin-plated board. The end face of the circuit board to be tinned is divided into N parallel strip regions. The extension direction of each strip region is the same as the moving direction of the air knife tinning operation. The air knife is provided with N air nozzles with adjustable pressure values. Each of the N air nozzles corresponds to one of the N strip regions. N is an integer greater than or equal to 3.

[0008] Using the scanning frame extending along the strip region, scan the through-hole area ratio 'a' of each strip region one by one. t The through-hole area ratio at It is the ratio of the area S1 of the through hole located within the scanning frame to the area S0 of the scanning frame at time t;

[0009] The pressure value of the corresponding air outlet is determined based on the maximum ratio of the through-hole area of ​​the strip region and the thickness of the circuit board.

[0010] The method for improving solder ball residue in small holes of tin-plated circuit boards described in this invention has the advantage of allowing for localized adjustment of the exhaust pressure based on the via distribution of the circuit board, thereby increasing the yield without wasting energy. The via distribution is determined by the via area ratio a. t reflect. Attached Figure Description

[0011] Figure 1 This is a schematic diagram of the air knife structure in the existing technology.

[0012] Figure 2 This is a schematic diagram of the cross-sectional structure of a wind knife in existing technology.

[0013] Figure 3 This is a schematic diagram illustrating the operation of the method described in this invention.

[0014] Figure 4 yes Figure 3 A magnified view of a portion of the image.

[0015] Figure 5 This is a schematic diagram of the scanning results of the through-hole area ratio of the first strip region in the embodiment.

[0016] Figure 6 This is a schematic diagram of the structure of the air knife described in this invention.

[0017] Figure 7 This is a schematic diagram of the cross-sectional structure of the air knife described in this invention.

[0018] Figure label:

[0019] 10-Knife holder, 11-Air supply duct, 12-Opening valve, 13-Air chamber, 17-Main air duct, 18-Inner air slot;

[0020] 20-Air guide vane;

[0021] 30 - Scan frame; 31-37 - First to seventh striped regions;

[0022] A - Initial position of the scan frame, B - Mid-position of the scan frame. Detailed Implementation

[0023] The standard width of a manufactured circuit board is typically 560mm. Therefore, considering both refined energy consumption adjustment and ease of control, dividing the circuit board into seven equal segments (N=7) is most suitable. Each segment should be 80mm wide. Figure 3 and Figure 4 As shown in the figure, the method for improving solder ball residue in small holes of a solder plating board according to the present invention is as follows: the circuit board to be processed is divided into seven parallel strip regions, corresponding to the seven air outlet positions of the air knife. The direction of the air knife's solder scraping operation is Y; the extension direction of the seven strip regions is also Y, and the parallel distribution direction is X; Z is the direction perpendicular to the solder scraping operation plane. The through-hole area ratio of the first strip region 31 is relatively large, while the spatial area of ​​the second strip region 32 and the third strip region 33 gradually decreases. For clarity of illustration, the through-holes of the fourth strip region 34 to the seventh strip region 37 are not shown, but they generally exist in actual production.

[0024] Using the scanning frame extending along the strip region, scan the through-hole area ratio 'a' of each strip region one by one. t The through-hole area ratio a t It is the ratio of the area S1 of the via within the scanning frame to the area S0 of the scanning frame at time t. In the prior art, circuit boards store various electronic parameters during the manufacturing process. These necessarily include the length, width, and thickness of the circuit board, as well as the diameter and specific location distribution of all vias on the board. Therefore, the scanning process can be pre-completed using software programs. Under the inventive concept disclosed in this invention, those skilled in the art can perform scanning operations based on common knowledge. The scanning frame is also a virtual scanning area in the software. The preferred size of the scanning frame is 80mm * 4mm; where 80mm is the length perpendicular to the direction of movement of the air knife soldering operation, and 4mm is the length parallel to the direction of movement of the air knife soldering operation.

[0025] The scanning process can begin with a stepless scan from point A in the first strip region 31 towards point B, recording the ratio of all through-hole areas a from time t0 to time T corresponding to the end of the strip region. t ,like Figure 5 As shown. The ratio of the through-hole area 'a' in this strip region is obtained. t The maximum value is then obtained. Then, the second strip region 32, the third strip region 33, and so on, are scanned sequentially in the same manner until the final seventh strip region 37 is completed. The ratio of the through-hole area 'a' of each strip region is obtained. t Maximum value.

[0026] Substitute the values ​​into the following formula to obtain the pressure value of the corresponding air outlet:

[0027] Pressure value = i + j * plate thickness + k * max(a) t );

[0028] Where, the constant i = 0.8370, and the unit is kg / cm³. 2 The constant j = 0.1392, unit: kg / cm³ 3The constant k = 8.6000, and the unit is kg / cm³. 2 The pressure value is measured in kg / cm². 2 .

[0029] In practical work, the common ratio of plate thickness to through-hole area is 'a'. t The maximum value mainly falls into the following categories:

[0030]

[0031] Excessive pressure at a single air vent may damage the circuit board, and it also depends on the output capacity of the external fan. Therefore, the maximum pressure at a single air vent should be controlled within 4 kg / cm². 2 This is quite suitable. However, as shown in the table above, even with the thickest circuit board, the output pressure of a single air outlet is still below 4 kg / cm² when it rarely reaches 30% of its maximum value. 2 Therefore, the formula provided in this invention is reasonable and feasible. A maximum value of 30% is an exception, with the most common values ​​being around 5% to 20%. Thus, cases exceeding 30% are rare and can be addressed using other methods.

[0032] To implement the method described in this invention, this invention also discloses a wind knife structure capable of implementing the method, such as... Figure 6 and Figure 7 As shown, the device includes a tool holder 10 and air guide vanes 20 located on both sides of the bottom of the tool holder 10. N air supply pipes 11 are arranged above the tool holder 10, and N air chambers 13 are located inside the tool holder 10. Each air supply pipe 11 is connected to the upper end of one of the air chambers 13. An opening valve 12 is provided at the end of each air supply pipe 11 near the air chamber 13. The air outlet at the lower end of the air chamber 13 extends through the bottom of the tool holder 10. The lower ends of the air guide vanes 20 on both sides are tapered towards the air outlet but maintain a certain gap for pressurizing hot air. The opening width of the air guide groove is 80mm to accommodate the width of each strip area.

[0033] The strip area with a larger maximum through-hole area ratio corresponds to a larger opening of valve 12 on the air knife, resulting in stronger airflow in that area. Conversely, the strip area with a smaller maximum through-hole area ratio corresponds to a smaller opening of valve 12 on the air knife, resulting in weaker airflow in that area. For example, the airflow corresponding to the first strip area 31 will be greater than that of the second strip area 32 and the third strip area 33. This ensures that the total airflow input to the air knife does not need to be at its maximum value, while still providing sufficient airflow to remove solder balls from the required areas. This allows for reasonable adjustment of energy consumption while maintaining a good yield.

[0034] For those skilled in the art, various other corresponding changes and modifications can be made based on the technical solutions and concepts described above, and all such changes and modifications should fall within the protection scope of the claims of this invention.

Claims

1. A method for improving solder bead residue in pinholes of a tin-plated board, characterized in that, The end face of the circuit board to be soldered is divided into N parallel strip regions. The extension direction of each strip region is the same as the moving direction of the air knife soldering operation. The air knife is equipped with N air nozzles with adjustable pressure values. Each of the N air nozzles corresponds to one of the N strip regions. N is an integer greater than or equal to 3. Using the scanning frame extending along the strip region, scan the through-hole area ratio 'a' of each strip region one by one. t The through-hole area ratio a t It is the ratio of the area S1 of the through hole located within the scanning frame to the area S0 of the scanning frame at time t; The pressure value of the corresponding air outlet is determined based on the maximum ratio of the through-hole area of ​​the strip region and the thickness of the circuit board.

2. The method for improving solder bead residue in pinholes of a tin-plated board according to claim 1, characterized in that, The formula for the pressure value is: Pressure value = i + j * plate thickness + k * max(a) t ); Where, the constant i = 0.8370, and the unit is kg / cm³. 2 The constant j = 0.1392, unit: kg / cm³ 3 The constant k = 8.6000, and the unit is kg / cm³. 2 The pressure value is measured in kg / cm². 2 .

3. The method for improving solder bead residue in pinholes of a tin-plated board according to claim 1, characterized in that, N＝7。 4. The method for improving solder bead residue in pinholes of a tin-plated board according to claim 1, characterized in that, The scanning frame has dimensions of 80mm*4mm; where 80mm is the length perpendicular to the direction of the air knife soldering operation, and 4mm is the length parallel to the direction of the air knife soldering operation.

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