Makes sense. So it (corner bonding) would be applied to packages that are a bit bulky (=heavier than normal) and maybe don't have so many pins to absorb drop shock? Thanks Steve. Cheers........ Andy Kowalewski AdvantagePCB Pty Ltd +61 (2) 9499 4853 -----Original Message----- From: DesignerCouncil [mailto:[log in to unmask]] On Behalf Of Steve Gregory Sent: Thursday, 9 June 2011 09:06 To: [log in to unmask] Subject: Re: [DC] Underfill for chip scale packages Hi Andy, Corner bonding, not underfill. It helps with surviving drop shock without having to go through all the trouble of underfilling. Corner bonding is lots easier to do... Steve -----Original Message----- From: Andy Kowalewski Sent: Wednesday, June 08, 2011 6:53 PM To: [log in to unmask] Subject: [DC] Underfill for chip scale packages Just saw a web knock-down of the Barnes and Noble eBook reader. The larger Chip Scale Packages appear to have underfill applied to each corner, which has me intrigued. See http://www.techrepublic.com/photos/cracking-open-the-2011-barnes-noble-nook- e-book-reader-wi-fi/6243892?seq=35 <http://www.techrepublic.com/photos/cracking-open-the-2011-barnes-noble-nook -e-book-reader-wi-fi/6243892?seq=35&tag=content;thumbnail-view-selector> &tag=content;thumbnail-view-selector Does anyone know the criteria for this? Underfill is applied in flipchip assembly to prevent the silicon cracking because of the thermal mismatch in CTE between glass (3ppm/degree C) and pcb (FR4 at about 16ppm/degreeC). I guess the CSP might have a similar issue - no doubt the silicon chip inside the package also gets stressed as the package stresses, which implies that there isn't a lead frame to give compliance, or a FR4 laminate interposer like in bga packages that doesn't need stress relief. Cheers........ Andy Kowalewski AdvantagePCB Pty Ltd +61 (2) 9499 4853 ______________________________________________________________________ This email has been scanned by the MessageLabs Email Security System. For more information please contact helpdesk at x2960 or [log in to unmask] ______________________________________________________________________ ---------------------------------------------------------------------------- ----- DesignerCouncil Mail List provided as a free service by IPC using LISTSERV 16.0. To unsubscribe, send a message to [log in to unmask] with following text in the BODY (NOT the subject field): SIGNOFF DesignerCouncil. To temporarily stop/(restart) delivery of DesignerCouncil send: SET DesignerCouncil NOMAIL/(MAIL) For additional information, or contact Keach Sasamori at [log in to unmask] or 847-615-7100 ext.2815 ---------------------------------------------------------------------------- ----- ______________________________________________________________________ This email has been scanned by the MessageLabs Email Security System. For more information please contact helpdesk at x2960 or [log in to unmask] ______________________________________________________________________ ---------------------------------------------------------------------------- ----- DesignerCouncil Mail List provided as a free service by IPC using LISTSERV 16.0. To unsubscribe, send a message to [log in to unmask] with following text in the BODY (NOT the subject field): SIGNOFF DesignerCouncil. To temporarily stop/(restart) delivery of DesignerCouncil send: SET DesignerCouncil NOMAIL/(MAIL) For additional information, or contact Keach Sasamori at [log in to unmask] or 847-615-7100 ext.2815 ---------------------------------------------------------------------------- ----- ______________________________________________________________________ This email has been scanned by the MessageLabs Email Security System. For more information please contact helpdesk at x2960 or [log in to unmask] ______________________________________________________________________ --------------------------------------------------------------------------------- DesignerCouncil Mail List provided as a free service by IPC using LISTSERV 16.0. To unsubscribe, send a message to [log in to unmask] with following text in the BODY (NOT the subject field): SIGNOFF DesignerCouncil. To temporarily stop/(restart) delivery of DesignerCouncil send: SET DesignerCouncil NOMAIL/(MAIL) For additional information, or contact Keach Sasamori at [log in to unmask] or 847-615-7100 ext.2815 ---------------------------------------------------------------------------------