Hi Peter, What I am saying is, that "barrel cracking is now the more common problem in small-diameter holes, that the "non-functional pad" issue has fallen off in importance and that n-f pads do not contribute to barrel cracking." Small-diameter holes are more prone to barrel cracking, which is caused by the z-axis expansion of the resin. Thin, non-uniform and low-ductility Cu plating, as well as high resin content and low Tg, and of course PCB thickness and Tmax all contribute to the possibility of barrel cracking. The presence of n-f lands replaces some of the resin, which has some but not a significant positive effect. Larger diameter holes are more prone to inner-layer [post] separation. Thin Cu plating, as well as high resin content and low Tg, and of course PCB thickness and Tmax all contribute to the possibility of ILS; further bad or thin Cu foil as well as low quality wet processing also are an issue. The absence of n-f lands increases resin recession, but not necessarily ILS. >How then to support hole plating and prevent its deformation through resin recession and/or >hole pull-away? ****You got it backwards--barrel hole wall is deformed during resin expansion; when the resin cools and returns to its initial volume, the plastically deformed Cu cannot follow and 'resin recession' or 'hole pull-away' results. >Or are these defects not significant in purely interconnect via holes? **** 'Resin recession' or 'hole pull-away' are not real reliability issues either for vias or PTHs. >Is removal of n-f pads to prevent barrels cracking better than keeping them to give support >to the barrel plating? ****As I said, n-f pads do not significantly affect barrel cracking one way or the other. If processing problems are not an issue, I would keep the n-f pads, however. >Do you know what, if any, correlation there is between plating thickness, >hole diameter, aspect ratio, number of layers and the point where barrel >cracking becomes more prevalent and hole pull-away/resin recession becomes >less significant? ****Aspect ratio is a 'red flag' indicator, not a real parameter. However, for barrel cracking the correlation between plating thickness, hole diameter, PCB thickness, resin Tg and T-excursion exists and has been modeled. For ILS the correlation is qualitative, but not quanitative. I had hoped to deal with some of these issues in workshops in Singapore, which because of the SARS issue I had to postpone. Werner Engelmaier Engelmaier Associates, L.C. Electronic Packaging, Interconnection and Reliability Consulting 7 Jasmine Run Ormond Beach, FL 32174 USA Phone: 904-437-8747, Fax: 904-437-8737 E-mail: [log in to unmask], Website: www.engelmaier.com --------------------------------------------------- Technet Mail List provided as a free service by IPC using LISTSERV 1.8e 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 or (re-start) delivery of Technet send e-mail to [log in to unmask]: SET Technet NOMAIL or (MAIL) To receive ONE mailing per day of all the posts: send e-mail to [log in to unmask]: SET Technet Digest Search the archives of previous posts at: http://listserv.ipc.org/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 -----------------------------------------------------