A copper reduction method for a POFV process

Abstract

The application discloses a copper reduction method of a POFV process, and can reduce the thickness of copper and is not limited to the corner copper in the IPC specification, and solves the problem of difficult line etching caused by the copper thickness of the POFV process.

Description

TECHNICAL FIELD

[0001] The application relates to a copper reduction method of a POFV process and belongs to the field of PCB manufacturing. BACKGROUND

[0002] With the rapid development of electronic products, printed circuit boards are developing towards lightness, thinness, smallness, and the surface mounting and miniaturization of components are becoming more and more obvious, and the density of products is also increasing. In order to achieve good heat dissipation, many designs consider space utilization and adopt a hole-in-disc design, which requires the use of a POFV (plate over filled via) process.

[0003] The traditional POFV process needs to first drill a hole in the circuit board, then plate copper in the hole, then plug the hole with resin, then grind the plate with resin, remove the resin protruding from the plate surface, and then electroplate again, and then perform subsequent processes. Since the hole plugged with resin needs to be electroplated again, the copper thickness of the POFV process is very thick, and it is limited by the corner copper in the IPC specification. After the hole is plugged with resin, the copper reduction process cannot be effectively performed, the copper thickness cannot be reduced, and this causes difficulty in etching the circuit, making it impossible to design finer circuits and limiting the development of PCB circuit design. SUMMARY

[0004] The application provides a copper reduction method for a POFV process, which solves the problems disclosed in the background art.

[0005] To solve the above technical problems, the technical solution adopted by the application is as follows:

[0006] A copper reduction method for a POFV process, comprising:

[0007] Drilling a POFV hole in a circuit board that requires POFV;

[0008] Back drilling on the POFV hole to open a window in the original copper of the circuit board; wherein the depth of the window is less than the thickness of the original copper of the circuit board;

[0009] Plating a base copper on the surface of the circuit board after the windowing; wherein the base copper covers at least the inner wall of the POFV hole and the inner wall of the window;

[0010] Replating a layer of copper on the inner wall of the POFV hole and the inner wall of the window covered with the base copper, and plugging the POFV hole with resin;

[0011] Grinding the plate at the window to remove the resin protruding from the window and the copper protrusion formed by the re-plated copper;

[0012] Reducing the surface copper of the circuit board after the grinding, and grinding the resin protruding from the surface of the circuit board to flatten the surface of the circuit board;

[0013] The non-POFV hole does not need POFV when the circuit board is back-drilled;

[0014] The non-POFV hole is plated with copper, and the POFV hole is capped;

[0015] The circuit board after capping is pattern etched.

[0016] The original copper thickness remaining at the window is greater than 0.1 mil.

[0017] A white paper is used as a cover plate to back-drill by using a deep drilling machine table with a charge-coupled camera function, and a flat drill bit with a diameter less than a threshold value is used for back-drilling.

[0018] A layer of copper is plated on the inner wall of the POFV hole and the window by using image transfer.

[0019] Resin is inserted into the POFV hole by using a vacuum hole plugging method.

[0020] The thinning amount of the surface copper is determined according to the surface copper thickness before thinning and the corner copper thickness allowance of the slice, and the corner copper needs to be controlled to meet the requirements of IPC during thinning.

[0021] The present application has the following beneficial effects: the present application can reduce the thickness of copper, and is not limited to the corner copper in the IPC specification, and solves the problem of difficult circuit etching caused by the copper thickness of the POFV process. BRIEF DESCRIPTION OF DRAWINGS

[0022] Figure 1 A flowchart of the copper reduction method for the POFV process;

[0023] Figure 2 A schematic diagram of the circuit board after windowing;

[0024] Figure 3 A schematic diagram of the circuit board after plating with base copper;

[0025] Figure 4 A schematic diagram of the circuit board after plating with a layer of copper;

[0026] Figure 5 A schematic diagram of the circuit board after resin hole plugging;

[0027] Figure 6 A schematic diagram of the circuit board after flattening;

[0028] Figure 7 A schematic diagram of the circuit board after capping. EMBODIMENT

[0029] The present application will be further described below with reference to the accompanying drawings. The following examples are only used to more clearly illustrate the technical solutions of the present application, and cannot be used to limit the protection scope of the present application.

[0030] As shown in the figure, a copper reduction method of POFV process includes the following steps: Figure 1

[0031] Step 1, drill the POFV hole 2 of the circuit board which needs POFV.

[0032] Step 2, back drill on the POFV hole 2, and open the window 3 of the original copper of the circuit board; wherein the depth of the window 3 is less than the thickness of the original copper 1 of the circuit board.

[0033] Step 3, plate the base copper 4 on the surface of the circuit board after the window 3; wherein the base copper 4 covers at least the inner wall of the POFV hole 2 and the inner wall of the window 3.

[0034] Step 4, plate a layer of copper (5 in the figure) on the inner wall of the POFV hole 2 and the inner wall of the window 3 which are covered by the base copper 4, and plug the POFV hole 2 with the resin 7. Figure 4

[0035] Step 5, grind the plate at the window 3 to remove the resin 7 and the copper convex formed by the re-plated copper which protrude from the window 3.

[0036] Step 6, reduce the copper on the surface of the circuit board after the grinding process, and grind the resin 7 which protrude from the surface of the circuit board to flatten the surface of the circuit board.

[0037] Step 7, drill the non-POFV hole of the circuit board which does not need POFV.

[0038] Step 8, plate the copper on the non-POFV hole, and cap the POFV hole 2 with the cap 8.

[0039] Step 9, perform pattern etching on the circuit board after the cap 8.

[0040] As an embodiment of the present application, in the above method, the circuit board is a pressed multilayer board, and the specific copper reduction process can be as follows:

[0041] First, drill the POFV hole 2 of the circuit board which needs POFV, and further back drill on the POFV hole 2, that is, use the back drilling method to open the window 3 of the original copper 1 of the circuit board, see Figure 2 The back drilling does not completely remove the original copper 1, and a part of the original copper 1 needs to be reserved, which can effectively prompt the long-term reliability of the POFV hole 2. The specific back drilling depth can be controlled at 0.4±0.1 mil, and the thickness of the residual original copper 1 is greater than 0.1 mil.

[0042] ​​In back drilling, the deep drilling machine table with charged coupled camera function is operated to ensure the alignment accuracy, otherwise the drilling deviation will occur. Since the traditional aluminum cover plate will generate aluminum foil debris after back drilling, and the debris has high hardness and is difficult to clean, the white paper is used as the cover plate in the deep drilling machine table to perform the back drilling. Since the traditional drill bit with a drill tip angle will cause the uneven bottom of the back drilling hole, thereby affecting the judgment of the corner copper, and since the drilling depth is only 0.4 mil according to the process requirement of the present application, the drilling depth control accuracy is relatively high, and if the drill bit has a drill tip angle, the drill bit will be in advance conductive, thereby causing the drilling depth problem, therefore the flat head drill bit with a diameter less than the threshold value, i.e. the small diameter flat head drill bit is adopted.

[0043] After the windowing 3 is completed, a thin base copper 4 is plated on the surface of the circuit board, and the base copper 4 at least covers the inner wall of the POFV hole 2 and the inner wall of the windowing 3, see Figure 3 .

[0044] Further, the image transfer is adopted to plate a layer of copper on the inner wall of the POFV hole 2 and the inner wall of the windowing 3 which is covered by the base copper 4, see Figure 4 ; that is, through the image transfer, only the POFV hole 2 is developed, and then the dry film 6 is used to perform the hole copper plating, and after the hole copper plating is completed to meet the PCB product specification, the dry film 6 is removed by the degumming method.

[0045] After the dry film 6 is removed, the resin 7 is used to plug the hole on the whole surface of the board, and the vacuum plugging method is adopted to plug the POFV hole 2 with the resin 7, and after the resin 7 is filled, the position of the POFV hole 2 will have the protruding surface resin 7 and the copper protrusion formed by the copper plating, see Figure 5 .

[0046] The plate grinding treatment is performed on the windowing 3 to remove the resin 7 protruding from the windowing 3 and the copper protrusion formed by the copper plating, and after the removal is completed, the surface copper of the circuit board is removed. When the surface copper of the circuit board is removed, the thinning amount of the surface copper removal needs to be determined according to the thickness of the surface copper before the thinning and the thickness allowance of the corner copper of the slice, and the corner copper needs to be controlled to meet the IPC requirement during the thinning. After the surface copper is removed, the resin 7 protruding from the surface of the circuit board is ground to flatten the surface of the circuit board, see Figure 6 .

[0047] Further, the non-POFV hole which does not need to be drilled by the POFV of the circuit board is plated with copper, and the POFV hole 2 is capped with the cap 8, see Figure 7 ; Figure 7 In the formula, A is the thickness of the residual original copper 1, B is the thickness of the base copper, C is the thickness of the re-plated copper, D is the thickness of the corner copper, E is the thickness of the original copper after the surface copper is removed, F is the thickness of the cap, and G is the thickness of the surface copper before the etching, D=B+C, and G≈E+F.

[0048] The circuit board behind the cap 8 is subjected to pattern etching, and the subsequent normal process (i.e., other processes after the pattern etching in the POFV process) is continued, that is, the outer layer PAD of the POFV is etched by image transfer, and the hole cap process design in the new disc is finally realized.

[0049] In the specification defined by IPC, the corner copper does not include the original plate copper, and the original plate copper of the circuit board is partially reduced by back drilling on the POFV hole in the present application, so that the original plate copper not included in the corner copper can be effectively removed by back drilling. Since the back drilling only reduces the thickness of the original plate copper at the hole, the back drilling does not affect the thickness of the corner copper of the entire PCB. After the original plate copper of the circuit board is partially back drilled by the back drilling method, a step with height difference is formed at the hole (such as Figure 2 After the hole copper is electroplated, the electroplated copper is mainly increased at the height difference of the step, and this structure ensures that the hole has sufficient corner copper, and the thickness of the copper on the surface of the circuit board is not increased. In the traditional process, the hole is flat without the step, and the thickness of the surface copper will increase when the hole copper is electroplated. After the resin hole is blocked, a structure as shown in Figure 5 After the electroplated protrusions are ground, the thinning process is added in the present application, which further thins the copper thickness on the surface of the circuit board. At this time, due to the existence of the height difference step at the hole, the corner copper is very thick, and the thinning amount can be determined according to the thickness of the surface copper before thinning and the thickness of the corner copper at this time. The surface copper can be further reduced by thinning. Therefore, the thickness of the copper is reduced by the above steps, and the present application is not limited to the corner copper in the IPC specification.

[0050] The present application can reduce the surface copper of the circuit board in the POFV process by using the conventional equipment, and solve the problem of difficult etching of the circuit caused by the copper thickness in the POFV process.

[0051] The above is only the preferred embodiment of the present application, and it should be pointed out that for ordinary skilled persons in the art, some improvements and modifications can be made without departing from the technical principles of the present application, and these improvements and modifications should be regarded as the protection scope of the present application.

Claims

1. A method of copper reduction for a POFV process, characterized in that, The method comprises the following steps: POFV hole for POFV of circuit board; back drilling on the POFV hole to open a window on the original copper of the circuit board; wherein the depth of the window is less than the thickness of the original copper of the circuit board; plating a base copper on the surface of the circuit board after the window is opened; wherein the base copper covers at least the inner wall of the POFV hole and the inner wall of the window; plating a layer of copper on the inner wall of the POFV hole and the inner wall of the window covered by the base copper, and plugging the POFV hole with resin; grinding the surface of the circuit board at the window to remove the resin and the copper bump formed by the re-plated copper; descaling the circuit board after the grinding, and grinding the resin protruding from the surface of the circuit board to flatten the surface of the circuit board; non-POFV hole for POFV of the circuit board; plating copper on the non-POFV hole, and capping the POFV hole; pattern etching on the circuit board after capping.

2. The process for decoppering of POFV as claimed in claim 1 wherein, The thickness of the residual original copper at the window is greater than 0.1 mil.

3. The process for decoppering of POFV as claimed in claim 1 wherein, A deep drilling machine table with a charged coupled camera function is used to back drill with white paper as a cover plate, and a flat drill bit with a diameter less than a threshold value is used for back drilling.

4. The process for decoppering of POFV as claimed in claim 1 wherein, A layer of copper is re-plated on the inner wall of the POFV hole and the inner wall of the window covered by the base copper by image transfer.

5. The process for decoppering of POFV as claimed in claim 1 wherein, The resin is plugged into the POFV hole by vacuum hole plugging.

6. The process for decoppering of POFV as claimed in claim 1 wherein, The thinning amount of the descaling is determined according to the thickness of the surface copper before thinning and the corner copper thickness allowance of the slice, and the corner copper is controlled to meet the requirements of IPC during thinning.

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