Acid trap always occur on every PCB boards especially high density PCB's.This may result to a short circuit due to the un-etched copper.
Here are some rules to avoid this
1.minimize using trace connection less than 45deg vertex.
2.always remove those isolated plane island
3.minimize goup vias with a less spacing surrounded by traces
4.add some via holes to the area were your acid trap located so the chemical can escape thru the other side
But believe me as far as i know there is no such design that free from acid trap especially multilayer boards.There is no specs define for this.
Hope this can helps.