What is an Acid Trap in a PCB?

An acid trap is a section on the PCB that can accumulate corrosive chemicals when the PCB board is being cleaned with etching solutions to remove excess copper from the trace layout. The accumulated solution (acid) can corrode the copper traces on the PCB resulting in open or short circuits that can cause malfunctioning of the circuit board.

Acid is often trapped in copper traces that have sharp edges. One of the ways to minimize acid traps is to design copper traces that have tapered edges rather than sharp edges.

When an acid trap has been identified on a PCB, one of the solutions that can used to drain this acid is the addition of vias in the area. This will allow the accumulated acid to pass through the board without causing any damage.

Another way to avoid acid traps is to use photoactivated etchants in place of aggressive chemicals like ferric chloride and hydrochloric acid. Photoactivated Etchants become active when exposed to UV light. So during the etching process, when the unwanted copper needs to be removed from the traces the board is subjected to UV light so that the etchants can become active. Once the UV light is removed, even if the chemicals are tapped on the board, they do not become active as long as the PCB is not exposed to UV light.