Are the dots delam or prepreg dryness? Perhaps you have forced most of the resin away from the BV's and when you heat them up you get a measles pattern. I get a picture in my head of the vias standing taller than the surrounding board and plunging the resin to the side. This may not be a true failure. Can you have a micro section run to see if there is an actual void. Gfranck wrote: > Technetters, > > We have a lot of a 12 layer PWB made from a High Tg Epoxy material, some 75 mil thick overall. The board has 3 sequential laminations, and four drill operations to get the three Blind vias (BV) and thru holes in the board. The BVs from > layer 1 - 10 terminations are visible thru the material from the Layer 12 side. During the assembly prebake process the tops of these little BVs delaminate. A patteren of little white dots which closely matchs the 1-10 BV drill pattern > emerges. I believe the BV drill size was 10 mil > > Boards are 20 months old. Assemblier was aware of the age of the boards, and the delamination occured during the pre-bake process, and thermal profile set up. > > Would anyone want to discuss why a BV would be more prone to delamination than the rest of the board? > > *** Warning: the follow contains sarcasm.*** > *** For those unable or unwilling to understand sarcasm, please read no further.*** > > Current corrective action proposals: > 1) Don't assembly old PWBs. > 2) Add a ground plane between layer 11 and 12 to prevent the layer 10BV terminations (and delaminations) to be visible from the outside of the board. > 3) Blame the PWB supplier, and get them to replace the boards. > 4) Willing to entertain other options. > > Thanks, > > George Franck > > ############################################################## > TechNet Mail List provided as a free service by IPC using LISTSERV 1.8c > ############################################################## > To subscribe/unsubscribe, send a message to [log in to unmask] with following text in > the body: > To subscribe: SUBSCRIBE TECHNET <your full name> > To unsubscribe: SIGNOFF TECHNET > ############################################################## > Please visit IPC web site (http://www.ipc.org/html/forum.htm) for additional > information. > If you need assistance - 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 1.8c ############################################################## To subscribe/unsubscribe, send a message to [log in to unmask] with following text in the body: To subscribe: SUBSCRIBE TECHNET <your full name> To unsubscribe: SIGNOFF TECHNET ############################################################## Please visit IPC web site (http://www.ipc.org/html/forum.htm) for additional information. If you need assistance - contact Keach Sasamori at [log in to unmask] or 847-509-9700 ext.5315 ##############################################################