Electronic – Are acid traps real? (2014)

acid-trapdfmdrcpcb-fabrication

Some people online say that acute angles in trace routing will cause these problems:

  • "Acid Trap" – PCB etchant gets stuck in the corner, and eats away too much, causing open circuit
  • "Peelable" – Narrow strip of photoresist falls off the board before or while the etchant is applied, causing too much etching and thus open circuit

Some people online say these are real problems, others say they are old wives' tales. Are they real or not? Or are they only real if you use a low-cost fab house that might use older processes?

Please avoid answers like "ask your fab house". I'm looking to learn in general, not just get one design out the door.

Best Answer

In order to combat acid traps, underetching of thick copper layers and other such problems with traditional thermally activated etchants, a lot of board houses have switched to photoactivated etchants. These etchants are much more active under the influence of light than just by themselves, which means you can get cleaner edges on thick copper layers. Also, etchant trapped in sharp corners in the design doesn't eat away at the sides nearly as much as it would with traditional methods.