This problem has been seen in pcb fabrication for years and years, and is known under several names, the most common of which is probably "mousebites." Unfortunately, I believe assembly also has a defect known by the same name. Anyway, the defect is not due to resist breakdown. Rather, during the copper plating process, bubbles attached to the edge of the dryfilm, preventing plating from occurring. When the boards come out of the copper tank and then progress to solder or tin plating, the traces resume plating and are protected during subsequent etching. I am sure that if the traces were cross sectioned, you would find that the copper was 1/2 ounce thick at the bottom of the pit, which is typically the starting thickness of the copper foil. What causes it? Too many small/micro-bubbles in the plating tank, poor cleaning prior to plating, substandard dryfilm developing... many people have suggested different failure modes. My vote is less than ideal developing followed by marginal preplate cleaning. Like beer in a glass, nucleation sites on the trace edges cause bubbles to form/gather at those locations. One of your pictures shows the regular spacing of the pits. This is sometimes a common observation and it can be seen that the pits repeat with depressions in the starting copper foil due to the laminate weave. Sometimes you will see that the pits all line up at the same place on trace after trace after trace, as the weave transverses a section of traces. In any case, the result is ugly. The copper is half thickness at the defect. Who knows whether or not it will affect the functionality of the product, since numerous designs have half ounce copper on inner signals. I would be more concerned if the board was high speed and impedance controlled. But that is not for me to decide, it is between the fabricator and the end-user. As a fabricator, our position is: spec or no spec, critical or not, we don't like ugly and would reject internally if we see this defect. But then again, I have never presumed to think that my business philosophy might represent an industry standard! At 11:33 AM 10/6/00 -0400, you wrote: >Hi Ya'll!! > >It's picture time again! Got some boards in at incoming inspection that are >really weird looking Go to: > >http://www.driveway.com/share?sid=e25a88c4.8e904&name=Pictures > >Look at Pits.jpg and Pits2.jpg...very, very strange! Never have seen >something like >this before...and it's only on the backside of the board? What could cause >this? > >Looking in the IPC-A-600F, it only talks about reductions in conductor width >of more than 20% (for class-2), but doesn't talk about reductions in >thickness by pits such as these...it's hard to tell if they've gone all the >way through the trace because the pits are filled with solder mask and you >can't see all the way down to the bottom of the pits. > >Common sense tells me that these boards are rejectable...am I right? > >-Steve Gregory- > >--------------------------------------------------------------------------- >------ >TechNet Mail List provided as a free service by IPC using LISTSERV 1.8d >To unsubscribe, send a message to [log in to unmask] with following text in >the BODY (NOT the subject field): SIGNOFF TECHNET >Please visit IPC web site (http://www.ipc.org/html/forum.htm) for additional >information, or contact Keach Sasamori at [log in to unmask] or 847-509-9700 >ext.5315 >--------------------------------------------------------------------------- >------ --------------------------------------------------------------------------------- TechNet Mail List provided as a free service by IPC using LISTSERV 1.8d To unsubscribe, send a message to [log in to unmask] with following text in the BODY (NOT the subject field): SIGNOFF TECHNET Please visit IPC web site (http://www.ipc.org/html/forum.htm) for additional information, or contact Keach Sasamori at [log in to unmask] or 847-509-9700 ext.5315 ---------------------------------------------------------------------------------