You will see less post separation with a 3 point connection as the post if held in place during thermal expansion. The propensity for stresses to the post connection are related to the expansion coefficient of the package in the x, y and z axis. The CTE mismatch of the copper, glass and resin are major contributors to the stresses introduced to the package components during thermal cycling. The resins system will also shrink as the degree of cure is advanced slightly during thermal excursion, which propagates lateral stresses to the post connections as the pad is pulled from the barrel. The z axis expansion contributes to the separation by weakening the attachment. Excessive resin recession can be an indication of an under-cured package as the advancement of the cure increases. Jeffrey Bush Director, Quality Assurance and Technical Support VERMONT CIRCUITS INCORPORATED 76 Technology Drive - POB 1890 Brattleboro, Vermont 05302 Voice - 802.257.4571 ext 21 Fax - 802.257.0011 <http://www.vtcircuits.com/> -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of Rodney Miller Sent: Thursday, August 03, 2006 11:09 AM To: [log in to unmask] Subject: Re: [TN] Barrel to Laminate Adhesion loss So Anchoring barrel wall is not recommended on higher Tg/Td laminate systems due to Cu CTE... Could I get a copy of that White paper? I'm interested in the cause effect also... We have seen similare problems arise from trace/pad interface and fracturing. If what you say is good for Barrel, this may also have limits that are being exceeded. Our conventional wisdom is to teardrop or filet the interface from Annular ring to Trace, to help with the migration of a mechanical fracture. Will this logic still apply? LoHst and Confused... -----Original Message----- From: Werner Engelmaier [mailto:[log in to unmask]] Sent: Wednesday, August 02, 2006 5:23 PM Subject: Re: Barrel to Laminate Adhesion loss Hi Richard & All, Actually, the higher occurrances of hole wall separation and trace separation are not so much caused by more lateral stresses, but the different thermal and mechanical properties of SAC solders. To understand what is happening, one really needs to understand what the whole damage process causing hole wall separation [sometimes also called resin recession] and inner-layer separation [also called post separation or trace separation. (1) On heating the resin expands-because of the glass fiber reinforcement it is prevented to expand in x/y and thus expands in z at nearly 3-times its thermal expansion without the glass reinforcement]; there is an exception to this- the resin also tries to expand into the volume occupied by the PTH, and is of course, to some degree at least, prevented from doing so by the Cu barrel plating. Thin Cu plating and/or large separation between inner-layer land [serving as anchors] encourage larger bulging inwards of the Cu with plastic deformation of the Cu. (2) On cooling, the resin contracts to its former volume-if the Cu is plastically deformed to a significant degree, it cannot do so: the result=>hole wall separation, and near the surface in connection with land rotation inner-layer separation. (3) For SnPb solders the Solidus is 183C; thus, Solidus - Tg (183-170C)~13C. For SAC solders the solidus is 217C; thus, Solidus - Tg (217-170C)~47C. The consequence is that the delta-T after solder solidification is about 4-times larger for SAC-solders, over which the high above Tg-thermal contraction acts-and this also holds the Cu back to its former position: the result =>more hole wall separation, and inner-layer separation. Pretty straight-forward when you think about. Werner --------------------------------------------------- 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 847-615-7100 ext.2815 ----------------------------------------------------- --------------------------------------------------- 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 847-615-7100 ext.2815 ----------------------------------------------------- --------------------------------------------------- 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 847-615-7100 ext.2815 -----------------------------------------------------