In a message dated 7/27/04 9:37:01, [log in to unmask] writes: > Ofer, > As you have already seen from Brain, Jeff and others, there are varying > thoughts on this subject. > That said, here are mine. > Unused pads on inner layer can play an important part in the construction > and reliability of your PCBs. > I recommend removal of unused pads on low layer count, low Z axis CTE > materials to improve manufacturability at fab. > There will be longer drill life, less inner layer misregistration > possibilities, etc. > I adamantly refuse to allow removal of unused pads on high layer counts > and/or high Z axis CTE or mismatched CTE materials. > The reasons for this is pretty simple, first if the laminate material > stretches the copper barrel enough then the PTH barrel can actually end up longer > than the PCB is thick (very strange looking phenomena), also stretching of the > plated barrel can cause reliability issues due to cracking and subsequent > opens (read this as field failures). > Leaving at least a minimal annular ring on inner layer pads will aid in > supporting the PTH and reduce the likelihood of damage cause by PCB Z axis > expansion. > I think you will find most fabricators would prefer to see unused pads > removed as that will commonly improve manufacturability, where most reliability > types would prefer to see all pads remaining to improve barrel > anchoring/strength and integrity. > Talk to your fabricator and your quality guys to help reach the best > decision for your specific construction. > Remember communicate your issues and most of them will have an acceptable > solution. > Hope it helps, > FNK > Frank is right on the money. Regards, Werner Engelmaier Engelmaier Associates, L.C. Electronic Packaging, Interconnection and Reliability Consulting 7 Jasmine Run Ormond Beach, FL 32174 USA Phone: 386-437-8747, Fax: 386-437-8737, Cell: 386-316-5904 E-mail: [log in to unmask], Website: www.engelmaier.com --------------------------------------------------- Technet Mail List provided as a 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/contentpage.asp?Pageid=4.3.16 for additional information, or contact Keach Sasamori at [log in to unmask] or 847-509-9700 ext.5315 -----------------------------------------------------