We received this via fax at the IPC office and are forwarding to technet for comment. Can anyone help? Regards Dave Bergman, IPC Statement of Process Problem We are fabricating a 10 layer multilayer PWB with a 0.025" thick solid copper heatsink (12" x 18") in its center, with 5 layers on each side. This PWB has been previously fabricated using a conventional multilayer layup methodology with all layers assembled and then laminated in one package. We experienced a low yield rate. It was attributed to shorts caused by bubbles that formed within the drilled holes of the heatsink. We are currently experimenting with changing the production process to laminate the PWB in two stages - first completely fill the holes in the heatsink with prepreg, inspect and Second - layup the layers as usual. The heatsink undergoes pattern hole drilling, sanding and black oxide surface preparation treatment. The heatsink is assembled in the following package in the Multilayer Lamination Room: steel (12" x 18") lamination plate, aluminum sheet, 1 sheet tedlar release, 1 sheet each of 1080 prepreg, 2 sheets each of 106 prepreg, heatsink, 2 sheets each of 106 prepreg, 1 sheet each of 1080 prepreg, 1 sheet tedlar release, 1 aluminum sheet, steel lamination plate. The package undergoes lamination in a sealed vacuum "turkey" bag attached to a vacuum bag pulling 30" hg, in a Wabash single opening lamination press for 30 minutes at 375 deg. F & 4500# total force. Upon visual inspection, the heatsink/pregreg package exhibited bubbles in every drilled hole. It this the result of resin starvation in the holes? *************************************************************************** * TechNet mail list is provided as a service by IPC using SmartList v3.05 * *************************************************************************** * To unsubscribe from this list at any time, send a message to: * * [log in to unmask] with <subject: unsubscribe> and no text. * *************************************************************************** * If you are having a problem with the IPC TechNet forum please contact * * Dmitriy Sklyar at 847-509-9700 ext. 311 or email at [log in to unmask] * *************************************************************************** Ian Wylie Technical Systems Manager Exacta Circuits Ltd Printed Circuit Manufacturers Selkirk Scotland TD7 5EJ 00 44 1750 21601 Ext 3219 *************************************************************************** * TechNet mail list is provided as a service by IPC using SmartList v3.05 * *************************************************************************** * To unsubscribe from this list at any time, send a message to: * * [log in to unmask] with <subject: unsubscribe> and no text. * *************************************************************************** * If you are having a problem with the IPC TechNet forum please contact * * Dmitriy Sklyar at 847-509-9700 ext. 311 or email at [log in to unmask] * ***************************************************************************