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PCB Plating Process | Multi-layer PCB Manufacturing Process - 06

by: Aug 08,2022 943 Views 0 Comments Posted in PCB Manufacturing Information

PCB Manufacturing


The hole walls after drilling are composed of non-conductive epoxy resin and fiberglass board. In order to connect circuits between different layers, it is necessary to metalize the hole walls through an autocatalytic redox reaction, which deposits a coat of copper on the non-conductive substrate, namely electroless copper deposition. The quality of metallized holes directly affects the electrical performance and reliability.

Pre-treatment

Before the process of electroless copper plating, the board must be cleaned,which mainly includes the steps of deburring, alkaline degreasing, desmear, and micro-etching. Deburring is to remove the residues produced during drilling process and improve the structure of hole walls, thereby enhancing its binding force. Then alkaline solution is used to remove impurities such as oil, fingerprints and oxides from the surface of the board.

Next, desmear process uses Potassium permanganate to etch the epoxy resin on the surface of the hole walls to increase the absorptive capacity of hole walls for activation solution.

Finally, the micro-etching step is carried out to remove the oxides on the surface of the board and increase the roughness of the surface. This step can ensure good adhesion between the subsequent copper layer and the copper at the bottom of the substrate so as to avoid delamination in the panel plating.

Activation

The cleaned board should first be pre-impregnated before activation to prevent the water attached to the surface of the board from changing the PH value of the activation solution, thus affecting the activation effect or even causing delamination.

During the activation process, the board is immersed into the activation tank to deposit a thin coat of colloidal palladium on the surface of the board and into the hole walls to ensure the electroless copper can be plated evenly over all surfaces.

Electroless Copper Plating

After the processes above, the board is immersed into the copper fluid and creates a redox reaction. The surface of the board will form a layer of 20-40 micro inches of chemical copper, so that the insulated hole walls can produce electrical conductivity to connect inter-layer circuits.

Panel Plating

In order to prevent the thin coat of copper in the hole from being oxidized and micro-etched before the pattern plating, the copper on the surface and inside the holes need to be thickened to 5-8 micron through electroplating.

 

Check 01 02 03 04 05 for previous process.

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