Hi Don, You write: >Before you hit the slopes - two last questions. >In point #2, do you mean exactly what is written: that the non-functional >pads reduce the possibility of hole wall separation? Or do you mean that >the presence of additional anchors reduces the propagation or magnitude >of separation when it occurs? >How does the presence of additional pads reduce the possibility of inner >layer separation? My understanding is that the adhesion of b-stage to >c-stage is greater than the adhesion of polymer to copper. A: I mean that the non-functional pads prevent the occurrance, not the propagation or magnitude, of hole wall separation. You need to understand what the mechanism causing hole wall separation is. Hole wall separation has little to do with adhesion. Hole wall separation is caused by the PCB resin expanding towards the hole center during heating. The higher the resin content (prepreg layer has mor than the laminate layer) the more this expansion. The larger the drilled hole diameter, the thinner the plated copper barrel, the longer the compressed cylinder (PCB thickness), the fewer cylinder reinforcement ribs (read: functional and non-functional lands), the easier the expanding resin is capable of buckling the PTH hole wall inwards. Too much inwards movement will cause plastic deformation of the copper cylinder. Thus, on cooling the resin returns to its former volume and position; so will the PTH wall if the copper barrel is only elastically deformed. However, if the copper barrel is only plastically deformed, it will stay where it is--voila, you have hole wall separation. --------------------------------------------------------------------------------- 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 To temporarily halt delivery of Technet send e-mail to [log in to unmask]: SET Technet NOMAIL To receive ONE mailing per day of all the posts: send e-mail to [log in to unmask]: SET Technet Digest Search previous postings at: www.ipc.org > On-Line Resources & Databases > E-mail Archives 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 ---------------------------------------------------------------------------------