Hello to All, I asked this with thoughts unrelated to BGA's. We have selective wave solder process on some assemblies with pth connectors. As we move to leadfree, we review our processes and practices and have thought to change to soldermask defined pads for PbFree selective solder of pth conectors. I was reviewing a document about this and reading my technet email at the same time, so the possibility of a problem with soldermask defined pads alarmed me. Does a soldermask defined pad reduce solder joint cycles-to-failure in a pth, selective wave scenario? Thanks again, -Chris Werner Engelmaier /* <[log in to unmask] To OM> [log in to unmask] Sent by: TechNet cc <[log in to unmask]> Subject Re: [TN] fractured SJs due to 09/17/2009 02:48 soldermask compression PM Please respond to TechNet E-Mail Forum <[log in to unmask]> ; Please respond to [log in to unmask] M Indeed, it is. Werner -----Original Message----- From: Stadem, Richard D. <[log in to unmask]> To: [log in to unmask]; [log in to unmask] Sent: Thu, Sep 17, 2009 2:36 pm Subject: RE: [TN] fractured SJs due to soldermask compression Thanks, Werner. I think I understand this a little better. If the soldermask-defined pad does not allow the solder to flow down around the sides of the pad, but rather induces a stress riser where the BGA solderball meets the top of the pad, the stress is focused at the point where the solder contacts the pad, at the top of the pad. Therefore it is easier for the crack to form as opposed to a solder ball that is "anchored" with the pad fully embedded inside the solder ball. So the CTE-induced stresses are not from the mask, but the CTE delta between the BGA package and the substrate. Being that this stress riser is circumferential around the point where the solder makes contact with the pad, the initiation point and the direction of the crack propagation can be anywhere and go in any direction. Is that correct? -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of Werner Engelmaier /* Sent: Thursday, September 17, 2009 1:22 PM To: [log in to unmask] Subject: Re: [TN] fractured SJs due to soldermask compression Hi Dean, Let us be clear about this. If you have soldermask-defined pads (SMDs), what results is solder joints with geometries defined by that solder mask. These geometries cause st ress concentrations which typically will cause cycles-to-failure to be cut by about half. It has nothing to do with CTE expansion and contraction of the solder mask—unless, you do solder mask repair after assembly (!?) and the solder mask fills the space between component and PCB. Werner -----Original Message----- From: Stadem, Richard D. <[log in to unmask]> To: [log in to unmask]; [log in to unmask] Sent: Thu, Sep 17, 2009 1:49 pm Subject: RE: [TN] fractured SJs due to soldermask compression Werner, What I am trying to say is that issues of ground plane configuration will probably not lead to a reliability issue directly, unless they cause issues during reflow of the BGA. But if the ground pour is done using soldermask-defined pads, the soldermask-defined pads can lead to premature failure of the SJ. My understanding (gained from a direct question I asked you in your class) was that the soldermask can constrict the solder during CTE expansion and contraction. Did I not understand you correctly? -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of Werner Engelmaier /* Sent: Thursday, September 17, 2009 12:32 PM To: [log in to unmask] Subject: Re: [TN] fractured SJs due to soldermask compression Hi Chris, First, never heard of "fractured SJs due to soldermask c ompression during cyclic operation"—solder mask is much too soft and too thin; now, if you talk encapsulants that is a different story. Second, "all of the other issues pale in the face of fractured SJs due to soldermask compression during cyclic operation"—even if it were an issue, a failure is a failure is a failure—'nough said. Werner -----Original Message----- From: Chris Ball <[log in to unmask]> To: [log in to unmask] Sent: Thu, Sep 17, 2009 1:07 pm Subject: [TN] fractured SJs due to soldermask compression Hello, Starting a new branch here. "All of the other issues pale in the face of fractured SJs due to soldermask compression during cyclic operation." Is this concern specifically for BGAs, or the same for any soldermask defined pad, even including selectively waved through-hole (PbFree)? Thanks, -Chris This e-mail message is intended only for the use of the intended recipient(s). The information contained therein may be confidential or privileged, and its disclosure or reproduction is strictly prohibited. If you are not the intended recipient, please return it immediately to its sender at the above address and destroy it. --------------------------------------------------- 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 temporarily20halt or (re-start) delivery of Technet send e-mail to Listse [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 previ ous 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 ----------------------------------------------------- --------------------------------------------------- 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=2 0site 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 ----------------------------------------------------- This e-mail message is intended only for the use of the intended recipient(s). The information contained therein may be confidential or privileged, and its disclosure or reproduction is strictly prohibited. If you are not the intended recipient, please return it immediately to its sender at the above address and destroy it.