A control method for lead-free tin spraying of circuit board

Abstract

The present invention provides a control method for lead-free tin spraying of a circuit board, which specifically comprises: MI, drilling, copper deposition, circuit, electrical diagram, AOI, solder resist and tin spraying; in the MI stage, if the circuit board has an outer copper skin, it is necessary to set the outer copper skin spacing of the circuit board to be greater than or equal to 0.25mm; in the tin spraying stage, it is necessary to control the copper content in the tin furnace to be below 0.6%; when the copper content is greater than 0.6%, the tin furnace is subjected to copper removal treatment; the tin immersion time is 7 to 10 seconds; and the problems of solder resist blistering and delamination are solved.

Description

Technical Field

[0001] The invention relates to a control method for lead-free tin spraying on a circuit board. Background Art

[0002] As a common surface treatment process for circuit boards, tin spraying has the advantages of low cost and good solderability. However, there is a type of circuit board, which is characterized by a thicker board thickness, generally reaching more than 3.2mm, and a hole diameter of 0.4-0.8mm. Due to the thicker board thickness, the temperature of the tin in the hole is lower than the temperature of the board surface, resulting in tin blocking the hole during tin spraying. Generally, 0.4-0.8mm small holes are prone to tin blocking when the board thickness is more than 3.2mm. Therefore, when tin spraying, a higher tin furnace temperature and longer tin immersion time are required than for boards of ordinary thickness. Other problems will arise during tin spraying: blistering and oil loss of solder mask at the edge of the copper skin, delamination and explosion of the board, and other problems.

[0003] The existing technology mainly uses other surface treatment processes instead of tin spraying for boards above 3.2MM, such as OSP and nickel-gold immersion (or lead-based tin spraying, which is less used due to environmental protection issues), etc., but the solderability and reliability of OSP are not as good as tin spraying, and the cost of nickel-gold immersion is relatively high. Another method is to improve the problem of tin bead blocking the hole by significantly extending the tin immersion time or spraying the tin twice, but significantly extending the tin immersion time or spraying the tin twice will cause problems such as board delamination, solder mask blistering and insufficient hole copper. Summary of the invention

[0004] The technical problem to be solved by the present invention is to provide a control method for lead-free tin spraying of a circuit board and solve the problem of solder mask blistering and delamination.

[0005] The present invention is implemented as follows: a control method for lead-free tin spraying of a circuit board, specifically including: MI, drilling, copper deposition, circuit, diagram, AOI, solder resist and tin spraying;

[0006] In the MI stage, if the circuit board has an outer copper layer, the outer copper layer spacing of the circuit board needs to be set to be greater than or equal to 0.25mm;

[0007] During the tin spraying stage, the copper content in the tin furnace needs to be controlled below 0.6%; when the copper content is greater than 0.6%, the tin furnace is subjected to copper removal treatment; the tin immersion time is 7 to 10 seconds.

[0008] Furthermore, before tin spraying, if the circuit board is larger than 18*24in, the milling operation is performed until the circuit board is smaller than or equal to 18*24in; otherwise, the milling operation is not performed.

[0009] Furthermore, the temperature of the tin furnace is 270 to 275°C.

[0010] Furthermore, if no characters are needed after the solder mask is completed, the curing operation is directly carried out, and tin spraying is carried out within two hours; if it exceeds two hours, the board is baked before tin spraying; the baking temperature is set to 150°C, the time is 30 to 60 minutes, and after the baking, tin spraying is carried out within two hours. If it exceeds two hours, the board needs to be baked again;

[0011] If characterization is required after completing the solder mask, curing operation should be carried out after the characterization, and tin spraying should be carried out within two hours; if it exceeds two hours, the board should be baked before tin spraying; the baking temperature is set to 150℃, the time is 30 to 60 minutes, and after the baking, tin spraying should be carried out within two hours. If it exceeds two hours, the board needs to be baked again.

[0012] The invention has the following advantages: the problem of tin plugging holes is solved at a lower temperature and in a shorter time, thereby also solving the problems of blistering and oil loss of solder mask at the edge of copper skin, delamination and explosion of plate materials, etc. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] The present invention will be further described below in conjunction with embodiments with reference to the accompanying drawings.

[0014] Figure 1 The present invention is a flow chart of a control method for lead-free tin-spraying of a circuit board.

[0015] Figure 2 The present invention is a schematic diagram of the thickness spacing of the middle and outer copper layers in a control method for lead-free tin spraying of a circuit board. DETAILED DESCRIPTION

[0016] The invention discloses a control method for lead-free tin spraying of a circuit board, which solves the problem of tin blocking holes at a relatively low temperature and in a relatively short time, thereby also solving the problems of blistering and oil loss of solder resist at the edge of the copper sheet, delamination and explosion of the plate, and can produce tin spraying plates with a plate thickness of 3.2-5.0 mm and a hole diameter of 0.4-0.8 mm.

[0017] The present invention can solve the following problems by appropriately extending the tinning time on the basis of optimizing the tinning process and parameters:

[0018] 1: In order to solve the problem of solder mask blistering, the design requirements are clarified. The distance between the copper skins of 1OZ copper thick plates is more than 0.25mm. At the same time, it is stipulated that the residence time after tin spraying and baking the plate should be within 2 hours.

[0019] 2: Hole blocking and stratification problems caused by tin beads in the holes: Before spraying tin, the large panels are milled into small panels. At the same time, the tin furnace is treated to remove copper before spraying thick panels to reduce the copper content. The tin immersion time is appropriately extended from the conventional 2-5S to 7-10S. If the time is too short, the holes will be blocked by tin beads, and if it is too long, problems such as solder mask blistering and stratification will occur.

[0020] like Figure 1As shown, the present invention provides a control method for lead-free tin spraying of a circuit board, which specifically includes: MI, drilling, copper deposition, circuit, electrical diagram, AOI, solder mask and tin spraying;

[0021] like Figure 2 As shown, in the MI stage, if the circuit board has an outer copper layer, it is necessary to set the outer copper layer spacing of the circuit board to be greater than or equal to 0.25mm; if the circuit board does not have an outer copper layer, this step is not required; the thicker the board thickness and the smaller the outer copper layer spacing, the more serious the solder mask blistering phenomenon. By setting the outer copper layer spacing of 0.25mm, the solder mask blistering phenomenon is greatly reduced;

[0022] During the tin spraying stage, the copper content in the tin furnace needs to be controlled below 0.6%; when the copper content is greater than 0.6%, the tin furnace is subjected to copper removal treatment; the tinning time is 7 to 10 seconds, and the temperature of the tin furnace is 270 to 275°C. If the copper content is high, the tin furnace needs to be copper removed. High copper content will lead to poor fluidity of tin. In addition, the higher the copper content, the higher its melting point, the higher the required temperature, and the longer the time;

[0023] Before tin spraying, if the circuit board is larger than 18*24in, the milling operation is performed until the circuit board is less than or equal to 18*24in; otherwise, the milling operation is not performed; the milling operation will not affect the production efficiency, from drilling to solder mask, the large production panel is maintained, and when tin spraying, the large panel is milled into small panels according to the size requirements of tin spraying, so that the tin furnace temperature required for the small panel is lower and the required tin immersion time is shorter, the board is heated more evenly, the occurrence of delamination and explosion can be reduced, and the defect of tin beads blocking the holes in the local holes will not occur. At the same time, due to the lower temperature and shorter immersion time, the copper bite amount is also reduced by 1-2UM, ensuring the hole copper thickness;

[0024] If no characters are needed after solder mask is completed, the curing operation can be directly carried out, and tin spraying can be carried out within two hours; if it exceeds two hours, the board should be baked before tin spraying; the baking temperature is set to 150℃, the time is 30 to 60 minutes, and after baking the board, tin spraying can be carried out within two hours. If it exceeds two hours, the board needs to be baked again;

[0025] If characterization is required after completing the solder mask, curing operation should be carried out after the characterization, and tin spraying should be carried out within two hours; if it exceeds two hours, the board should be baked before tin spraying; the baking temperature is set to 150℃, the time is 30 to 60 minutes, and after the baking, tin spraying should be carried out within two hours. If it exceeds two hours, the board needs to be baked again.

[0026] Although the specific implementation modes of the present invention are described above, those skilled in the art should understand that the specific implementation modes described are only illustrative and are not intended to limit the scope of the present invention. Equivalent modifications and changes made by those skilled in the art in accordance with the spirit of the present invention should be included in the scope of protection of the claims of the present invention.

Claims

1. A control method for lead-free tin spraying of a circuit board, characterized in that: Specifically include: MI, drilling, copper deposition, circuit, electrical diagram, AOI, solder mask and tin spraying; In the MI stage, if the circuit board has an outer copper layer, the outer copper layer spacing of the circuit board needs to be set to be greater than or equal to 0.25mm; During the tin spraying stage, the copper content in the tin furnace needs to be controlled below 0.6%; when the copper content is greater than 0.6%, the tin furnace is subjected to copper removal treatment; the tinning time is 7 to 10 seconds; Before tinning, if the circuit board is larger than 18*24in, milling operation is performed until the circuit board is less than or equal to 18*24in; If not, the milling operation will not be performed; If no character is needed after solder mask is completed, the curing operation can be carried out directly, and tin spraying can be carried out within two hours; If it exceeds two hours, bake the board before tin spraying; set the baking temperature to 150℃ for 30 to 60 minutes, and spray tin within two hours after baking. If it exceeds two hours, bake the board again; If characters are required after solder mask is completed, curing operation should be carried out after characters are completed, and tin spraying should be carried out within two hours; If it exceeds two hours, bake the board before spraying tin; set the baking temperature to 150℃ for 30 to 60 minutes, and spray tin within two hours after baking the board. If it exceeds two hours, bake the board again.

2. A control method for lead-free tin-spraying of a circuit board according to claim 1, characterized in that: The temperature of the tin furnace is 270 to 275°C.

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