METHOD FOR FULL FILLING INTER-LAYER BLIND HOLE OF HDI RIGID-FLEX LAMINATE WITH COPPER

Abstract

A method for copper filling-up of blind vias in HDI rigid-flex PCB is provided which includes the steps of: 1) performing a copper reduction on a single side of a double sided copper-clad laminate; 2) drilling blind vias with inverted trapezoidal shape in a side of the double sided copper-clad laminate being copper reduced by laser; 3) cleaning via walls and the via bottoms of the blind vias to remove the residues left during the drilling process; 4) depositing metallic copper layers on surfaces of the via walls and the via bottoms of the blind vias; 5) filling the blind vias with copper after the blind vias being deposited by metallic copper layer. The copper filling-up of the blind vias in the HDI rigid-flex PCB is achieved, leading to decreased cost of equipment investment and improved production efficiency and benefits.

Claims

1. A method for copper filling-up of blind vias in HDI rigid-flex PCB, comprising the steps of: 1) performing a copper reduction on a single side of a double sided copper-clad laminate; 2) drilling blind vias with inverted trapezoidal shape in a side of the double sided copper-clad laminate being copper reduced by laser; 3) cleaning via walls and the via bottoms of the blind vias to remove the residues left during the drilling process; 4) depositing metallic copper layers on surfaces of the via walls and the via bottoms of the blind vias; and 5) filling the blind vias with copper after the blind vias being deposited by metallic copper layer, to achieve an interconnection between layers of the HDI rigid-flex PCB.

2. The method for copper filling-up of blind vias in HDI rigid-flex PCB according to claim 1, wherein in step 1), a dry film is coated on one side of the double sided copper-clad laminate, and the copper reduction on a single surface is performed on the other side without the dry film.

3. The method for copper filling-up of blind vias in HDI rigid-flex PCB according to claim 1, wherein in step 2), an UV laser is used for drilling.

4. The method for copper filling-up of blind vias in HDI rigid-flex PCB according to claim 1, wherein in step 2), in the blind vias, an upper via diameter A is larger than a lower via diameter B, and B

5. The method for copper filling-up of blind vias in HDI rigid-flex PCB according to claim 1, wherein in step 3), a wet adhesive-removing process is applied to clean the via walls and the via bottoms of the blind vias.

6. The method for copper filling-up of blind vias in HDI rigid-flex PCB according to claim 1, wherein in step 3), the via walls and via bottoms of the blind vias after cleaning have a roughness Ra of 500-1000 nm.

7. The method for copper filling-up of blind vias in HDI rigid-flex PCB according to claim 1, wherein in step 4), an electroless copper plating process is applied for depositing the metallic copper layers on surfaces of the via walls and the via bottoms of the blind vias.

8. The method for copper filling-up of blind vias in HDI rigid-flex PCB according to claim 1, wherein the metallic copper layer has a thickness of 0.2-1 m.

9. The method for copper filling-up of blind vias in HDI rigid-flex PCB according to claim 1, wherein in step 5), an electroplating process for blind via filling is applied to fill the blind vias with copper, and it is specifically performed by an electroplating with a current density of 10-16 ASF in 40-80 minutes, and copper filling-up on the filling agent line.

10. The method for copper filling-up of blind vias in HDI rigid-flex PCB according to claim 9, wherein in the electroplating process, an electroplating agent comprises 22020 g/L CuSO.sub.45H.sub.2O, 5010 g/L H.sub.2SO.sub.4, 5010 ppm chloride ion, 1.00.2 mL/L accelerator, 1.00.2 mL/L inhibitor and 1.00.2 mL/L leveler.

11. The method for copper filling-up of blind vias in HDI rigid-flex PCB according to claim 3, wherein in step 2), in the blind vias, an upper via diameter A is larger than a lower via diameter B, and B 0.6A.

12. The method for copper filling-up of blind vias in HDI rigid-flex PCB according to claim 5, wherein in step 3), the via walls and via bottoms of the blind vias after cleaning have a roughness Ra of 500-1000 nm.

13. The method for copper filling-up of blind vias in HDI rigid-flex PCB according to claim 7, wherein the metallic copper layer has a thickness of 0.2-1 m.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0031] FIG. 1 is a schematic diagram showing the drilled blind via in the HDI rigid-flex PCB of the present invention;

[0032] FIG. 2 is a structural diagram of the cross section of the HDI rigid-flex PCB prepared through the method of the present invention; wherein,

[0033] 1 interior layer of circuit;

[0034] 2 outer layer of blind vias;

[0035] 3 interior layer of PI;

[0036] 4 outer layer of copper plating;

[0037] 5 FR-4 (epoxy glass fabric laminated board).

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0038] The present invention will be further explained with reference to figures and embodiments.

[0039] In the following embodiments, the double sided copper-clad laminate is commercially available, the accelerator 3620A, inhibitor 3620S and leveler 3620L are produced by Shanghai SINYANG Semiconductor Materials Co., Ltd.

Embodiment 1

[0040] As shown in FIGS. 1 and 2, a method for copper filling-up of blind vias in HDI rigid-flex PCB is performed as following.

[0041] 1) A double sided copper-clad laminate is prepared, wherein copper coils having 18 m thickness on its upper and lower sides are comprised, and a substrate having thickness of 75 m is sandwiched therebetween. A dry film is coated on one side of the double sided copper-clad laminate, and a copper reduction on a single surface is applied to the other side without the dry film through horizontal copper reduction line, whereby the thickness of the copper coil after copper reduction is 7 m.

[0042] 2) Drilling data for the blind vias in HDI rigid-flex PCB are prepared through CAD software, and the vias are drilled in the side of the double sided copper-clad laminate being copper reduced, by applying UV laser drilling according to the drilling data; the formed blind via is inverted trapezoidal shaped, wherein A is the upper via diameter of the blind via, B is the lower via diameter of the blind via, and A>B0.6*A, as show in FIG. 1.

[0043] 3) The via wall and the via bottom of blind via in the HDI rigid-flex PCB are cleaned by wet adhesive-removing process, to remove the residual adhesive left during the drilling process; a certain roughness Ra between 500-1000 nm is formed in the via wall and the via bottom, for subsequent convenient chemical copper covering and deposition.

[0044] 4) The via wall and the via bottom of blind via in the HDI rigid-flex PCB are metallized by an electroless copper plating process including 30-second activation, 10-second microetching and 50-minute copper deposition, and therefore chemical copper layer of 0.2-1 m thickness is deposited on the via wall and via bottom of the blind via.

[0045] 5) An electroplating process for blind via filling is applied to fill the blind vias with copper after the blind vias being deposited by chemical copper, to achieve an interconnection between layers of the HDI rigid-flex PCB, wherein the electroplating process is specifically performed with a current density of 10-16 ASF in 40-80 minutes, and copper filling-up on the filling agent line; in this embodiment, the electroplating agent applied in the electroplating process comprises 200 g/L CuSO.sub.4.5H.sub.2O, 40 0gL H.sub.2SO.sub.4, 40 ppm chloride ion, 0.8 mL/L accelerator, 12 mL/L inhibitor and 12 mL/L leveler. The blind vias are filled up after the electroplating, and the circuit is flat.

Embodiment 2

[0046] This embodiment is basically the same as the embodiment 1, and they differ in that in step 5), the electroplating agent applied in the electroplating process comprises 220 g/L CuSO.sub.4.5H.sub.2O, 50 g/L H.sub.2SO.sub.4, 50 ppm chloride ion, 1.0 mL/L accelerator, 15 mL/L inhibitor and 15 mL/L leveler. The blind vias are filled up after the electroplating, and the circuit is flat.

Embodiment 3

[0047] This embodiment is basically the same as the embodiment 1, and they differ in that in step 5), the electroplating agent applied in the electroplating process comprises 240 g/L CuSO.sub.4.5H.sub.20, 60 g/L H.sub.2SO.sub.4, 60 ppm chloride ion, 1.2 mL/L accelerator, 18 mL/L inhibitor and 18 mL/L leveler. The blind vias are filled up after the electroplating, and the circuit is flat.

[0048] In the method for copper filling-up of blind vias in HDI rigid-flex PCB of the above embodiments, a copper reduction on a single surface is performed on one side of the double sided copper-clad laminate, blind vias are drilled thereon by laser before subsequent adhesive removing and copper deposition, and eventually an electroplating process for blind vias is applied to fill the blind vias with copper, whereby an interconnection between layers of the rigid-flex PCB is achieved, which saves the cost and time and improves the production efficiency and benefits.

[0049] The embodiment described hereinbefore is merely preferred embodiment of the present invention and not for purposes of any restrictions or limitations on the invention. It will be apparent that any non-substantive, obvious alterations or improvement by the technician of this technical field according to the present invention may be incorporated into ambit of claims of the present invention.