IPC-SM-840. This is used primarily for surface insulation resistance testing and solder mask testing. An electronic copy of IPC-SM-840, "Qualification and Performance of Permanent Solder Mask," is included with this Gerber format. The "A" Revision combines IPC-A-24 and IPC-A-25 comb patterns on a single-sided board. Find a current listing of board vendors carrying the IPC-B-25A board on the IPC...