Background Theory > PCB Design > Plating of PCB Holes and the Copper Balance

The process of plating holes in a printed circuit board (PCB) is crucial for creating plated-through holes (PTH), which are used to electrically and mechanically connect different layers of the PCB. Plating adds a layer of copper to the walls of the drilled holes, allowing electrical current to pass through.

The plating process typically involves several steps:

Desmear and Etch

As discussed earlier, the drilled holes are first cleaned (desmeared) and etched to provide a clean, rough surface for good plating adhesion.

Copper Seed Layer Deposition

A thin layer of copper is chemically deposited onto the hole walls. This serves as a "seed" layer for the subsequent electroplating process.

Electroplating

The PCB is immersed in an electroplating bath, which contains a solution of copper ions. An electric current is passed through the bath, causing the copper ions to deposit onto the seed layer and form a thicker layer of copper.

Electroless Nickel/Immersion Gold (ENIG) or Other Surface Finish

To protect the copper from oxidation and improve solderability, a surface finish such as ENIG, HASL (Hot Air Solder Leveling), or OSP (Organic Solderability Preservatives) might be applied.

It's crucial to maintain a balance of copper across the PCB during the plating process. Copper imbalance can lead to issues like warping or bowing of the PCB due to different rates of thermal expansion and contraction. Copper imbalance can also lead to uneven plating, where some areas of the PCB (including some holes) might have more or less plating than others.

To achieve copper balance, PCB designers aim to evenly distribute copper across the PCB's surface and throughout its layers. This may involve adding copper pours or thieving patterns in areas without active circuitry. It's also important for the PCB manufacturer to carefully control their plating process to ensure even and consistent plating thickness.

Failure to maintain copper balance can lead to issues with the PCB's mechanical stability and electrical performance, so it's a crucial consideration in PCB design and manufacturing.