Preparation method for forming welding pin of copper stand column

Abstract

The invention discloses a preparation method for forming a welding pin of a copper stand column, and the method comprises the following steps: designing a through hole bonding pad which is disposed on a circuit board and comprises a front bonding pad and a pin forming surface bonding pad, the diameter of the front bonding pad is larger than that of a welding contact surface of the copper stand column, and the diameter of the pin forming surface bonding pad is smaller than that of the front bonding pad; the diameter of the pin forming surface bonding pad is larger than that of the front surface bonding pad; the openings of the steel mesh are in one-to-one correspondence with the through hole pads, the openings of the steel mesh are larger than the front pads in size, and the thickness of the steel mesh is calculated according to the sizes of the through hole pads and the copper columns; covering the steel mesh on the circuit board with the through hole bonding pad, smearing a solder on the surface of the circuit board, and feeding the circuit board smeared with the solder into a preheating area, a heating area, a constant temperature area and a cooling area of a reflow oven; and hot air backflow heating is conducted on the welding flux, the hot air backflow heating technology is controlled, and a pin welding forming face is formed. The pin filling amount of the copper stand column is increased, and the yield of the forming angle and height of the welding face of the pin is increased.

Description

Technical Field

[0001] The invention relates to the technical field of electronic equipment welding, and in particular to a preparation method for forming a copper column welding pin. Background Art

[0002] At present, conventional through-hole reflow soldering is generally used to solder plug-in devices, and metal devices are rarely soldered. The traditional through-hole reflow method has a relatively wide process window and the characteristics of free solder filling after reflow. Therefore, it is impossible to ensure the forming state of the soldering pins. Manual repair of solder joints is often required, and the soldering yield is difficult to control.

[0003] In order to solve the problem of difficult-to-control welding yield, the existing technology mainly designs the external dimensions of the copper pillars welded on the printed circuit board, and increases the contact area of ​​the solder by modifying the front contact surface of the copper pillar welding, using the bottom concave surface to increase the contact area of ​​the solder, and by increasing the solder on the front contact surface of the welding, the total contact area of ​​the IMC metal alloy layer after welding is increased, thereby improving the overall strength and improving the welding quality. However, although this method can partially improve the quality of the solder joints, it is necessary to customize the copper pillars in batch production, and the copper pillars that have been designed and processed do not have universal adaptability, so they do not have the role of promotion and use. In the field of automotive electronics, the copper pillar welding on the power board is generally the main method, but it uses laser welding. By using a laser beam of a certain energy to heat the flux, the copper pillar and the copper material welding surface are melted together to form a welding surface. This laser welding method can only solve the problem of single-sided welding, and when welding the circuit board, laser welding has a very obvious local heating effect, which easily causes the pad to expand due to heat, causing welding quality problems. Summary of the invention

[0004] Purpose of the invention: The purpose of the present invention is to provide a preparation method for forming copper column welding pins, by improving the structural dimensions of the through-hole pad and the steel mesh, combined with the hot air reflow process control in the reflow furnace, the pin filling amount of the copper column is increased, the yield rate of the forming angle and height of the pin welding surface is improved, the solder joint rework and repair time is greatly reduced, and the production cost is saved.

[0005] Technical solution: To achieve the above purpose, the present invention discloses a preparation method for forming a copper column welding pin, comprising the following steps:

[0006] Designing a through-hole pad, wherein the through-hole pad is arranged on the circuit board, the through-hole pad comprises a front pad and a pin forming surface pad, the front pad diameter M is larger than the copper column welding contact surface diameter L, and the pin forming surface pad diameter N is larger than the front pad diameter M;

[0007] The opening of the steel mesh corresponds to the through-hole pad one by one, where the opening of the steel mesh is larger than the front pad size, and the thickness of the steel mesh is calculated according to the size of the through-hole pad and the copper column;

[0008] Cover the steel mesh on the circuit board with through-hole pads, apply solder to the surface of the circuit board, and send the circuit board with solder applied to the preheating zone, heating zone, constant temperature zone and cooling zone of the reflow oven; perform hot air reflow heating on the solder, reduce the heating air volume on the top of the circuit board during the furnace process, and increase the heating air volume on the bottom of the circuit board so that the heating air volume on the bottom is higher than the heating air volume on the top; measure the temperature of the front pad and the temperature of the pad on the pin forming surface, control the temperature difference ΔT between the front pad and the pad on the pin forming surface, and keep the furnace time required by the reflow oven to less than 10s, and increase the conveying speed of the circuit board to quickly pass through the cooling zone so that the liquid phase state of the solder alloy is maintained within 1 to 3s to form a pin welding forming surface.

[0009] Optionally, the difference between the front pad diameter M and the copper column welding contact surface diameter L ranges from 0.1 to 0.5 mm.

[0010] Optionally, the difference between the diameter N of the lead forming surface pad and the diameter M of the front surface pad is in the range of 0.2 to 1 mm.

[0011] Optionally, the difference between the opening of the steel mesh and the size of the front pad is 0.1 to 0.15 mm.

[0012] Optionally, the calculation formula for the steel mesh thickness h is:

[0013] h=2H(D 2 -d 2 ) / M 2 +ε

[0014] Where H is the thickness of the circuit board, D is the opening diameter of the through-hole pad, d is the diameter of the copper column in the through-hole pad opening, M is the front pad diameter, and ε is the correction constant.

[0015] Optionally, the correction constant ε has a value range of 0 to 0.127 mm.

[0016] Optionally, the steel mesh is a stepped steel mesh.

[0017] Optionally, the bottom heating air volume is 30% to 45% higher than the top heating air volume.

[0018] Optionally, the temperature difference ΔT ranges from 5 to 15°C.

[0019] Optionally, the conveying speed of the circuit board is 150 to 240 mm / s.

[0020] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages: the present invention controls the filling volume of solder by designing the size of the steel mesh, performs an epitaxial design of the steel mesh size by the size of the front pad, adjusts and optimizes the thickness of the steel mesh, and ensures that the solder volume after printing can fully fill the copper column welding surface and the through-hole gap, and form a welding surface; the steel mesh thickness calculated in the present invention can ensure that the solder volume can just meet the filling requirements; the present invention controls the thermal conduction efficiency of the copper column and the solder volume by improving the structural dimensions of the through-hole pad and the steel mesh, and combining the hot air reflow process control in the reflow furnace, so that after the printed solder volume is fully melted, it fills the gap between the copper column pin and the through-hole, ensuring that a good intermetallic alloy layer and pin shape are finally formed; the present invention can effectively improve the yield and reliability of copper column welding forming. The pin filling volume of the copper column of the present invention is increased by nearly 30%, and the yield of the welding surface forming angle and height of the pin reaches 100%, which greatly reduces the solder joint rework and repair time and saves production costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is a schematic diagram of the welding principle of the copper column in the present invention. DETAILED DESCRIPTION

[0022] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0023] It should be understood that the present invention can be implemented in different forms and should not be construed as being limited to the embodiments set forth herein. On the contrary, providing these embodiments will make the disclosure thorough and complete and fully convey the scope of the present invention to those skilled in the art. In the accompanying drawings, the sizes and relative sizes of the components may be exaggerated for clarity. The same reference numerals throughout represent the same components.

[0024] The present invention is mainly applied to positions on through holes of circuit boards where copper posts need to be welded. The use of the present invention can greatly improve the pass rate and reliability of copper post welding pin forming.

[0025] like Figure 1 As shown, the present invention discloses a method for preparing a copper column welding pin forming, comprising the following steps:

[0026] A through-hole pad is designed, wherein the through-hole pad is arranged on a circuit board 1, and the through-hole pad includes a front pad 2 and a pin forming pad 3, wherein the diameter M of the front pad is larger than the diameter L of the welding contact surface of the copper column 4, and the difference range is 0.1 to 0.5 mm; the diameter N of the pin forming pad is larger than the diameter M of the front pad, and the difference range is 0.2 to 1 mm. The present invention increases the area of ​​the pin forming surface after the through-hole reflow, improves the heat conduction efficiency of the hot air, ensures that the solder is spread as soon as possible on the pin forming contact surface, and avoids the solder falling, which leads to insufficient solder filling in the through-hole.

[0027] The opening of the steel mesh corresponds to the through-hole pad one by one, where the opening of the steel mesh is 0.1 to 0.15 mm larger than the front pad size. The calculation formula for the thickness h of the steel mesh is:

[0028] h=2H(D 2 -d 2 ) / M 2 +ε

[0029] Wherein H is the thickness of the circuit board, D is the opening diameter of the through-hole pad, d is the diameter of the copper column in the opening of the through-hole pad, M is the diameter of the front pad, ε is a correction constant, and the value range of ε is 0 to 0.127 mm; when the solder is insufficient, the steel mesh can use a step steel mesh, which can further make up for the volume of the solder, increase the printing amount of the solder on the front pad below the copper column, and ensure that the solder to be welded is sufficient and sufficient. The present invention controls the filling volume of the solder by designing the size of the steel mesh, and performs an extension design of the steel mesh size by the size of the front pad, adjusts and optimizes the thickness of the steel mesh, and ensures that the volume of the printed solder can fully fill the copper column welding surface and the through-hole gap, and form a welding surface; the thickness of the steel mesh calculated in the present invention can ensure that the volume of the solder can just meet the filling requirements.

[0030] The solder may be a solder with a metal component, for example, the volume proportion of the metal component in the solder is about 50%, and a conventional Pb63Sn37 solder may be used.

[0031] Cover the steel mesh on the circuit board with through-hole pads, apply solder to the surface of the circuit board, and send the solder-coated circuit board into the preheating zone, heating zone, constant temperature zone and cooling zone of the reflow oven; perform hot air reflow heating on the solder, reduce the heating air volume on the top of the circuit board during the furnace process, and increase the heating air volume on the bottom of the circuit board, so that the heating air volume at the bottom is 30% to 45% higher than the heating air volume at the top. The hot air volume can be adjusted through the threshold of the corresponding fan inverter; the time of the preheating zone and the heating zone can be increased to ensure the auxiliary The flux is fully activated and volatilized; the temperature of the front pad and the pin forming pad is measured, and the temperature difference ΔT between the front pad and the pin forming pad is controlled, and the temperature difference ΔT ranges from 5 to 15°C; and the furnace time required by the reflow furnace is maintained at less than 10s, and the required furnace temperature refers to the furnace temperature above 183°C, and the circuit board transmission speed is increased to 150 to 240mm / s, and the circuit board passes through the cooling zone quickly, so that the liquid phase state of the solder alloy is maintained within 1 to 3s to form a pin welding forming surface. The present invention reduces the air supply volume of the front pad and increases the air supply volume of the pin forming surface, utilizes the metal heat conduction effect of the copper column, melts the solder by heating the bottom pin, and controls the temperature difference ΔT between the front pad and the pin forming surface pad; under the reverse action of the liquid metal surface tension and the cooling air of the reflow furnace, the gravity of the molten solder is balanced, and in the cooling zone of the reflow furnace, a larger pin forming surface pad is utilized to perform rapid heat dissipation cooling to form a pin welding forming surface 5, thereby ensuring the forming angle and height of the pin welding surface.

[0032] The present invention improves the structural dimensions of the through-hole pad and the steel mesh, and combines the hot air reflow process control in the reflow furnace to control the thermal conduction efficiency of the copper column and the solder volume, so that after the printed solder volume is fully melted, it fills the gap between the copper column pin and the through hole, ensuring that a good intermetallic alloy layer and pin shape are finally formed. The present invention can effectively improve the yield and reliability of copper column welding forming. The pin filling amount of the copper column of the present invention is increased by nearly 30%, and the yield of the welding surface forming angle and height of the pin reaches 100%, which greatly reduces the rework and repair time of the solder joint and saves production costs.

[0033] Example 1

[0034] The present invention discloses a preparation method for forming a copper column welding pin, comprising the following steps:

[0035] A hole is opened on a circuit board 1 with a thickness of 1.2mm, and a through-hole pad is designed on the hole with an aperture of 0.85mm. The through-hole pad includes a front pad 2 and a pin forming pad 3. The diameter L of the soldering contact surface of the copper column 4 is 2.4mm. The diameter d of the copper column in the through-hole pad opening is 0.8mm. The diameter M of the front pad is larger than the diameter L of the soldering contact surface of the copper column 4, with a difference of 0.1mm. The diameter N of the pin forming pad is larger than the diameter M of the front pad, with a difference of 0.5mm. The opening of the steel mesh corresponds to the through-hole pad one by one, where the opening of the steel mesh is 0.1mm larger than the size of the front pad. The steel mesh thickness correction constant ε is 0.068mm.

[0036] The solder used is conventional Pb63Sn37 type solder.

[0037] Cover the steel mesh on the circuit board with through-hole pads, apply solder to the surface of the circuit board, and send the solder-coated circuit board into the preheating zone, heating zone, constant temperature zone and cooling zone of the reflow furnace; heat the solder with hot air reflow, reduce the heating air volume on the top of the circuit board during the furnace process, and increase the heating air volume on the bottom of the circuit board, so that the bottom heating air volume is 30% higher than the top heating air volume; measure the temperature of the front pad and the temperature of the pin forming surface pad, control the temperature difference ΔT between the front pad and the pin forming surface pad, and the temperature difference ΔT range is between 5°C; and keep the reflow furnace temperature above 183°C for 9s, and increase the circuit board conveying speed, the conveying speed is 150mm / s, and quickly pass through the cooling zone, so that the liquid phase state of the solder alloy is maintained within 3s to form the pin welding forming surface. The pin filling amount of the copper column in this embodiment is increased by nearly 30%, and the yield rate of the forming angle and height of the pin welding surface reaches 100%, which greatly reduces the rework and repair time of the solder joint and saves production costs.

[0038] Example 2

[0039] Embodiment 2 is the same as Embodiment 1, except that: the front pad diameter M is larger than the copper column 4 welding contact surface diameter L, the difference is 0.3mm; the pin forming surface pad diameter N is larger than the front pad diameter M, the difference is 0.8mm; the opening of the steel mesh is 0.12mm larger than the front pad size, the correction constant ε of the steel mesh thickness is 0.055mm, the bottom heating air volume is 40% higher than the top heating air volume, the reflow furnace temperature is maintained at above 183°C for 8s, and the solder alloy liquid phase state is maintained within 2s. The pin filling amount of the copper column in this embodiment is increased by nearly 30%, and the yield rate of the soldering surface forming angle and height of the pin reaches 100%, which greatly reduces the solder joint rework and repair time and saves production costs.

[0040] Example 3

[0041] Embodiment 3 is the same as Embodiment 1, except that: the front pad diameter M is larger than the copper column 4 welding contact surface diameter L, the difference is 0.5mm; the pin forming surface pad diameter N is larger than the front pad diameter M, the difference is 1mm; the opening of the steel mesh is 0.15mm larger than the front pad size, the correction constant ε of the steel mesh thickness is 0.028mm, the bottom heating air volume is 45% higher than the top heating air volume, the reflow furnace temperature is maintained at above 183°C for 7s, and the solder alloy liquid phase state is maintained within 1s. The pin filling amount of the copper column in this embodiment is increased by nearly 30%, and the yield rate of the pin welding surface forming angle and height reaches 100%, which greatly reduces the solder joint rework and repair time and saves production costs.

Claims

1. A method for preparing copper column welding pin forming, characterized in that: The steps include: Designing a through-hole pad, wherein the through-hole pad is arranged on the circuit board, the through-hole pad comprises a front pad and a pin forming surface pad, the front pad diameter M is larger than the copper column welding contact surface diameter L, and the pin forming surface pad diameter N is larger than the front pad diameter M; The opening of the steel mesh corresponds to the through-hole pad one by one, where the opening of the steel mesh is larger than the front pad size, and the thickness of the steel mesh is calculated according to the size of the through-hole pad and the copper column; Cover the steel mesh on the circuit board with through-hole pads, apply solder to the surface of the circuit board, and send the circuit board with solder applied to the preheating zone, heating zone, constant temperature zone and cooling zone of the reflow oven; perform hot air reflow heating on the solder, reduce the heating air volume on the top of the circuit board during the furnace process, and increase the heating air volume on the bottom of the circuit board so that the heating air volume on the bottom is higher than the heating air volume on the top; measure the temperature of the front pad and the temperature of the pad on the pin forming surface, control the temperature difference ΔT between the front pad and the pad on the pin forming surface, and keep the furnace time required by the reflow oven to less than 10s, and increase the conveying speed of the circuit board to quickly pass through the cooling zone so that the liquid phase state of the solder alloy is maintained within 1 to 3s to form a pin welding forming surface.

2. A method for preparing a copper column welding lead forming according to claim 1, characterized in that: The difference between the front pad diameter M and the copper column welding contact surface diameter L is in the range of 0.1 to 0.5 mm.

3. The method for preparing a copper column welding lead forming according to claim 1, characterized in that: The difference between the diameter N of the lead forming surface pad and the diameter M of the front surface pad is in the range of 0.2 to 1 mm.

4. The method for preparing a copper column welding lead forming according to claim 1, characterized in that: The difference between the opening of the steel mesh and the size of the front pad is 0.1 to 0.15 mm.

5. The method for preparing a copper column welding lead forming according to claim 1, characterized in that: The calculation formula of the steel mesh thickness h is: h=2H(D 2 -d 2 ) / M 2 +ε Where H is the thickness of the circuit board, D is the opening diameter of the through-hole pad, d is the diameter of the copper column in the through-hole pad opening, M is the front pad diameter, and ε is the correction constant.

6. A method for preparing copper column welding lead forming according to claim 5, characterized in that: The correction constant ε has a value range of 0 to 0.127 mm.

7. The method for preparing a copper column welding lead forming according to claim 1, characterized in that: The steel mesh is a stepped steel mesh.

8. The method for preparing a copper column welding lead forming according to claim 1, characterized in that: The bottom heating air volume is 30% to 45% higher than the top heating air volume.

9. The method for preparing a copper column welding lead forming according to claim 1, characterized in that: The temperature difference ΔT ranges from 5 to 15°C.

10. The method for preparing a copper column welding lead forming according to claim 1, characterized in that: The conveying speed of the circuit board is 150-240 mm / s.

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