Method and control structure for improving warping of asymmetric pressed circuit board

Abstract

The present invention proposes a control structure for improving the warping of an asymmetric pressed circuit board, comprising a first conductive layer, a first adhesive layer, an inner circuit board, a second adhesive layer, and a fourth conductive layer pressed in sequence, wherein the first conductive layer comprises a first molding area and a component welding area, the fourth conductive layer comprises a second molding area and a welding ink area, the first molding area is coated with solder resist ink, and the second molding area is covered with copper foil. Before the circuit board is formed, the present invention coats the molding area of ​​the surface that does not require solder resist ink with solder resist ink, and covers the molding area of ​​the surface that needs to be coated with solder resist ink with copper foil, and then mills off the molding area after drying the ink. Since the difference in ink content between the two surfaces is reduced before drying the ink, the stress difference between the two surfaces is reduced when the ink is dried, thereby solving the problem of warping caused by stress concentration on one surface.

Description

Technical Field

[0001] The invention relates to the field of production and manufacturing of circuit boards, and in particular to a control structure for improving warping of asymmetric pressed circuit boards, and a method for improving warping of asymmetric pressed circuit boards. Background Art

[0002] With the demand of application, electronic products have asymmetric designs. For example, the welding component area is not covered with ink, while the welding area on the other side is covered with ink. The asymmetric ink design makes the ink content difference on both sides of the circuit board exceed 100%. The ink covering the substrate will produce shrinkage stress during the curing process, causing the board to deform, and ultimately the warping rate of the finished circuit board exceeds 0.75%, which exceeds the standards stipulated in the industry, resulting in the scrapping of the board, increasing production costs and reducing production efficiency.

[0003] Generally speaking, to solve the problem of circuit board warping, a pressing process is usually added after the ink baking process to straighten the circuit board. However, although the circuit board can be straightened by pressing and baking, during the assembly process, the components and circuit boards need to be connected through high-temperature welding. Rapid cooling at high temperature can also cause the board to deform and cause the board to warp. Summary of the invention

[0004] In order to solve the above problems, the present invention proposes a control structure for improving the warping of an asymmetric pressed circuit board, and also proposes a method for improving the warping of an asymmetric pressed circuit board.

[0005] The main contents of the present invention are as follows:

[0006] A control structure for improving the warping of an asymmetric pressed circuit board comprises a first conductive layer, a first adhesive layer, an inner circuit board, a second adhesive layer and a fourth conductive layer which are pressed in sequence, wherein a component welding area and a first molding area are arranged on a side of the first conductive layer away from the first adhesive layer, and a welding ink area and a second molding area are arranged on a side of the fourth conductive layer away from the second adhesive layer, wherein the first molding area is arranged corresponding to the second molding area, the first molding area is covered with solder mask ink, and the second molding area is covered with copper foil.

[0007] Preferably, the ratio of the area of ​​the first molding area to the area of ​​the component welding area is 2:3; the ratio of the area of ​​the second molding area to the welding ink area is 2:3.

[0008] Preferably, the inner circuit board comprises a core board, a second conductive layer and a third conductive layer, wherein the second conductive layer is arranged between the core board and the first adhesive layer; and the third conductive layer is arranged between the core board and the second adhesive layer.

[0009] Preferably, the first adhesive layer and the second adhesive layer are prepregs.

[0010] Preferably, the thickness of the solder mask ink in the first molding area is 20-25 um; the thickness of the solder mask ink in the soldering ink area is 20-25 um.

[0011] The method for improving the warping of an asymmetric pressed circuit board comprises the following steps:

[0012] S1. Production of inner circuit board: A second conductive layer and a third conductive layer are produced on the upper and lower surfaces of the core board to obtain a double-sided copper-clad circuit board;

[0013] S2. Laminating in the order of the first conductive layer, the first adhesive layer, the inner circuit board, the second adhesive layer, and the fourth conductive layer; wherein the laminating pressure is 70-350 Psi, the laminating temperature is 140-205°C, and the laminating time is 5-115 min;

[0014] S3. The surface of the first conductive layer away from the first adhesive layer and the surface of the fourth conductive layer away from the second adhesive layer are treated to obtain the above-mentioned control structure for improving the warping of the asymmetric pressed circuit board;

[0015] S4, baking the control structure obtained in step S3 to dry the ink in the first molding area and the welding ink area;

[0016] S5. Surface treatment of the baked circuit board, using a milling cutter to mill off the first molding area and the second molding area;

[0017] S6. Conduct electrical testing and visual inspection on the semi-finished product obtained in step S5.

[0018] Preferably, step S3 includes the following sub-steps:

[0019] The surface of the first conductive layer away from the first adhesive layer is treated by dividing the surface into a first molding area and a component welding area, drilling, copper plating and etching the component welding area, and then coating the first molding area with solder mask ink;

[0020] The surface of the fourth conductive layer away from the second adhesive layer is treated by dividing the surface into a second molding area and a welding ink area, covering the second molding area with copper foil, and then coating the ink welding area with solder resist ink.

[0021] The beneficial effects of the present invention are as follows: The present invention proposes a control structure for improving the warping of an asymmetric pressed circuit board, wherein solder resist ink is coated on the molding area of ​​the surface that does not require solder resist ink before molding the circuit board, and copper foil is covered on the molding area of ​​the surface that needs to be coated with solder resist ink. The molding area is milled off after the ink is dried. Since the difference in ink content between the two surfaces is reduced before the ink is dried, the stress difference between the two surfaces is reduced when the ink is dried, thereby solving the problem of warping caused by stress concentration on one surface. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 It is a schematic diagram of the overall structure of the present invention;

[0023] Figure 2 is a plan view schematically showing the first conductive layer of the present invention;

[0024] Figure 3 FIG. 4 is a schematic plan view of the fourth conductive layer of the present invention. DETAILED DESCRIPTION

[0025] The technical solution protected by the present invention is described in detail below with reference to the accompanying drawings.

[0026] The present invention proposes a control structure for improving the warping of an asymmetric pressed circuit board. The control structure is an intermediate state for manufacturing an asymmetric pressed circuit board. In order to better understand the content of the present invention, the following will be combined with Figure 1 , Figure 2 and Figure 3 The method for improving the warping of an asymmetric pressed circuit board proposed by the present invention is explained, and the control structure is described during the explanation process.

[0027] First, the inner layer circuit board is manufactured: the second conductive layer 4 and the third conductive layer 5 are respectively manufactured on the upper and lower surfaces of the core board 3 to obtain a double-sided copper-clad circuit board; the specific manufacturing method can be manufactured according to the existing manufacturing process of the double-sided copper-clad board;

[0028] Next, the first conductive layer 1, the first adhesive layer 2, the inner circuit board, the second adhesive layer 6, and the fourth conductive layer 7 are pressed in the order of pressing pressure of 70-350 Psi, pressing temperature of 140-205°C, and pressing time of 5-115 min.

[0029] Wherein, the first adhesive layer 2 and the second adhesive layer 6 are both prepregs.

[0030] Then, the pressed structure is further processed to obtain a control structure for improving the warping of the asymmetric pressed circuit board. Figure 2 and Figure 3 ,like Figure 2As shown, the surface of the first conductive layer 1 away from the first adhesive layer 2 includes a first molding area 10 and a component welding area, the component welding area is drilled, copper plated and etched, and then the first molding area 10 is coated with solder mask ink;

[0031] like Figure 3 As shown, the surface of the fourth conductive layer 7 away from the second adhesive layer 6 includes a second molding area 70 and a welding ink area 71, the copper foil 9 is covered on the second molding area 70, and the ink welding area 71 is coated with solder mask ink, and the step of coating the ink welding area 71 with solder mask ink is performed after the second molding area 70 is covered with copper foil. The layout of the fourth conductive layer in the control structure can be obtained after printing and exposure by designing the screen for ink printing and the exposure film, that is, the second molding area is covered with copper foil, and the welding ink area is coated with welding ink.

[0032] In one embodiment, the thickness of the welding ink in the first molding area and the welding ink in the welding ink area is 20-25 um.

[0033] After obtaining the above control structure, the ink is dried, surface treated, molded, electrically tested and visually inspected to obtain the final molded product. The ink drying process is as follows: using a CMO-8WS Zhisheng oven, the baking temperature is selected to be 155°C, and the baking time is 70 minutes;

[0034] The surface treatment of the circuit board refers to: chemical gold plating is used on the surface of the circuit board, wherein the gold plating includes a nickel plating layer and a gold plating layer, and the thickness of the nickel layer is between 4 microns and 9 microns, and the thickness of the gold layer is between 0.05 microns and 0.15 microns, which enhances the anti-oxidation and wear resistance of the circuit board.

[0035] After processing the surface of the circuit board, a milling cutter is used to mill off the first molding area 10 and the second molding area 70. The first molding area 10 and the second molding area 70 are correspondingly arranged. Figure 2 As shown, the first molding area 10 is approximately semicircular and is located at both ends of the component welding area. Correspondingly, Figure 3 As shown, the second molding area 70 is also semicircular and is located at both ends of the welding ink area. In the thickness direction of the circuit board, the first molding area 10 and the second molding area 70 completely overlap; and the first molding area and the second molding area are milled off, that is, the areas corresponding to the first molding area and the second molding area on the first conductive layer, the first bonding layer, the inner layer circuit board, the second bonding layer and the fourth conductive layer are milled off, that is, the circuit board after molding, the areas corresponding to the first molding area and the second molding area are hollow structures.

[0036] Finally, the formed circuit board is subjected to electrical testing and visual inspection, and the warpage of the circuit board is measured. The method of the present invention can control the warpage to below 0.75%.

[0037] The above descriptions are merely embodiments of the present invention and are not intended to limit the patent scope of the present invention. Any equivalent structure or equivalent process transformation made using the contents of the present invention specification and drawings, or directly or indirectly applied in other related technical fields, are also included in the patent protection scope of the present invention.

Claims

1. Improve the control structure of warping of asymmetric pressed circuit boards, characterized in that: It comprises a first conductive layer, a first adhesive layer, an inner circuit board, a second adhesive layer and a fourth conductive layer which are pressed together in sequence, wherein a component welding area and a first molding area are arranged on a side of the first conductive layer away from the first adhesive layer, and a welding ink area and a second molding area are arranged on a side of the fourth conductive layer away from the second adhesive layer, wherein the first molding area is arranged correspondingly to the second molding area, the first molding area is covered with solder mask ink, and the second molding area is covered with copper foil; the component welding area is not covered with solder mask ink, and the welding ink area is covered with solder mask ink; The first forming area and the second forming area are areas that are milled off after the ink is dried.

2. The control structure for improving warping of asymmetric pressed circuit boards according to claim 1, characterized in that: The area ratio of the first molding area to the component welding area is 2:3; the area ratio of the second molding area to the welding ink area is 2:

3.

3. The control structure for improving warping of asymmetric pressed circuit boards according to claim 1, characterized in that: The inner circuit board includes a core board, a second conductive layer and a third conductive layer. The second conductive layer is arranged between the core board and the first adhesive layer; the third conductive layer is arranged between the core board and the second adhesive layer.

4. The control structure for improving warping of an asymmetric pressed circuit board according to any one of claims 1 to 3, characterized in that: The first adhesive layer and the second adhesive layer are prepregs.

5. The control structure for improving warping of an asymmetric pressed circuit board according to any one of claims 1 to 3, characterized in that: The thickness of the solder mask ink in the first molding area is 20-25 um; the thickness of the solder mask ink in the soldering ink area is 20-25 um.

6. A method for improving warping of an asymmetric pressed circuit board, characterized in that: The steps include: S1. Production of inner circuit board: A second conductive layer and a third conductive layer are produced on the upper and lower surfaces of the core board to obtain a double-sided copper-clad circuit board; S2. Laminating in the order of the first conductive layer, the first adhesive layer, the inner circuit board, the second adhesive layer, and the fourth conductive layer; wherein the laminating pressure is 70-350 Psi, the laminating temperature is 140-205°C, and the laminating time is 5-115 min; S3. The surface of the first conductive layer away from the first adhesive layer and the surface of the fourth conductive layer away from the second adhesive layer are treated to obtain a control structure for improving warping of an asymmetric pressed circuit board as claimed in any one of claims 1 to 5; S4, baking the control structure obtained in step S3 to dry the ink in the first molding area and the welding ink area; S5. The surface of the circuit board after baking is subjected to gold treatment, and the first molding area and the second molding area are milled out using a milling cutter; S6. Conduct electrical testing and visual inspection on the semi-finished product obtained in step S5.

7. The method for improving warping of an asymmetric pressed circuit board according to claim 6, characterized in that: Step S3 includes the following sub-steps: The surface of the first conductive layer away from the first adhesive layer is treated by dividing the surface into a first molding area and a component welding area, drilling, copper plating and etching the component welding area, and then coating the first molding area with solder mask ink; The surface of the fourth conductive layer away from the second adhesive layer is treated as follows: the surface is divided into a second molding area and a soldering ink area, the second molding area is covered with copper foil, and then the soldering ink area is coated with solder resist ink.

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