Werner, As long as the solder bump is big enough to reach the pad when the chip is resting on the solder mask. Otherwise there may be some unsoldered joints. But what about for use with underfill? Does a deeper pocket (from a thicker solder mask) make it more likely that voids will develop, particularly if there is a narrower space between the chip and solder mask, which will help the underfill to wick more quickly? Ben -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of Werner Engelmaier /* Sent: Thursday, June 05, 2008 9:17 AM To: [log in to unmask] Subject: Re: [TN] Chip on Board and Solder Mask Hi Ben, The solder mask will automatically be thinner then the resulting joint height, because the CTE of the solder mask is greater than the CTE of the solder, and therefore wil shrink more on cooling from soldering temperatures. Having a soldermask under the component is agood thing, because it will increase the resulting joint height thereby increasing reliability. Werner Future workshops: Reliability Issues with Lead-Free Soldering Processes, June 17, London Interconnect Failures and Design for Reliability for PCB PTHs, June 17, London Solder Joint Reliability: Parts 1 through 4, July 17/18, Thal, Switzerland Pb-Free Soldering Processes-Survival, Quality, Reliability, August 18, Orlando Reliability Issues with Lead-Free Soldering Processes, September 22, Schaumburg Failure Mode and Root Cause Analyses Reliability (Fatigue, Brittle Fracture, ENIG), September 22, Schaumburg ************** Get trade secrets for amazing burgers. Watch "Cooking with Tyler Florence" on AOL Food. (http://food.aol.com/tyler-florence?video=4?& NCID=aolfod00030000000002) --------------------------------------------------- Technet Mail List provided as a service by IPC using LISTSERV 15.0 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 847-615-7100 ext.2815 ----------------------------------------------------- --------------------------------------------------- Technet Mail List provided as a service by IPC using LISTSERV 15.0 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 847-615-7100 ext.2815 -----------------------------------------------------