Looks like it's also cracked across the ball-to-device interface too. Both interfaces failed at the same time? -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of John Burke Sent: Monday, June 15, 2009 10:29 AM To: [log in to unmask] Subject: Re: [TN] Corner ball pad cratering Isn't that joint cracked straight through the intermetallic interface? John Burke (408) 515 4992 -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of Steve Gregory Sent: Monday, June 15, 2009 6:15 AM To: [log in to unmask] Subject: Re: [TN] Corner ball pad cratering Morning Genny and everyone! Hope you all had a good weekend! It was HOT here! Genny, I have the last picture you sent on Friday posted, it's here: http://stevezeva.homestead.com/files/darker_100x.jpg I saw something here Saturday afternoon that I think might cause cratering, I don't know though. So I took a picture of it. What do you think? http://stevezeva.homestead.com/files/Pad_Craterer.jpg Steve -----Original Message----- From: Genny Gibbard [mailto:[log in to unmask]] Sent: Friday, June 12, 2009 4:53 PM To: TechNet E-Mail Forum Cc: Steve Gregory Subject: RE: [TN] Corner ball pad cratering OK, I may be premature in discounting that that there is possible improvement to be made in the reflow profile. I will add it to the list to check. The board is still in the proto-type/NPI phase, it is encountering far more handling than it will once design settles down. Lots of installation and removal from the chassis, etc, for modifications. The board is large with high layer count, but not overly thick, the affected IC is large, and there are mechanically mounted shields on areas adjacent to the IC. This particular board passed all tests with flying colours, including tests over temperature, until it came to the final system verification check, and then it started failing. The cross-section only revealed cratering on the corner balls, unfortunately some of the corner balls are more critical than strictly redundant pwr/gnd type connections. So it may have possibly started in reflow, but didn't propagate to a failure point until the end of the process. Or it may have been completely induced by mechanical means, due to all the extra handling and flexing of the board. We do not currently have a cross-section from early in the process to compare. The success already mentioned with corner bonding (by Amol and in the article link below), encourages me to look in that direction for improvement, along with reviewing reflow profiles. One last pic - less bright. I believe this shows a good joint (immersion Ag, leadfree ball). Please correct me if I'm wrong. Steve, if I could impose one more time...for Monday morning. Thanks for all the discussion. Genny -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of Werner Engelmaier /* Sent: June 12, 2009 1:07 PM To: [log in to unmask] Subject: Re: [TN] Corner ball pad cratering Hi Genny, When you say: "We believe the cause is mechanical, not thermal"-what do you mean by that? Where would these mechanical stresses come from? Werner -----Original Message----- From: Genny To: [log in to unmask] Sent: Fri, 12 Jun 2009 12:12 pm Subject: Re: [TN] Corner ball pad cratering As always, Steve, you are a wealth of information. That article is perfect, thank you. This seems to mirror what Amol said about doing a 1/4 of the length. This article said to do an L shaped bead 2-6 balls along each corner side. Here are some photos to post. Would you oblige? BGA is 40mm per side. PCB is ~1 ft sq. A little bigger than what is found in the typical blackberry, I think... Ball pitch is 1.27mm. We believe the cause is mechanical, not thermal. Thanks everyone. Genny -----Original Message----- From: Steve Gregory [mailto:[log in to unmask]] Sent: June 12, 2009 6:35 AM To: TechNet E-Mail Forum; Genny Gibbard Subject: RE: [TN] Corner ball pad cratering Morning Genny, Since you said you were going to look at corner bonding, here is a really good article (if you haven't seen it already) that Michael Kochanowski from Intel and Brian Toleno from Henkel did about it: http://www.trafalgar2.com/documents/Technical_Articles/6.09-kochanowski. pdf Steve -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of Genny Gibbard Sent: Thursday, June 11, 2009 3:10 PM To: [log in to unmask] Subject: [TN] C orner ball pad cratering Hello all, If you have identified a BGA with corner ball pad cratering, what would be your suggestions to correct this condition? Our thoughts: 1. We plan to evaluate our handling processes to reduce/remove excessive flex/strain occurring around this part 2. We plan to evaluate corner bonding or underfilling for the BGA. Which do you feel would be the best direction to go? Do you have other suggestions? Thanks in advance for all your help Genny --------------------------------------------------- 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 ----------------------------------------------------- --------------------------------------------------- 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 -----------------------------------------------------