Hi Werner,
It is indeed a possibility.
With Technet’s help I’m off to collect the best evidence we can.

Thanks everyone, for the enormous help.  I will keep you posted.

Chris

From: Werner Engelmaier [mailto:[log in to unmask]]
Sent: Tuesday, November 23, 2010 12:20 PM
To: [log in to unmask]; Chris Mahanna
Subject: Re: [TN] ImSn finish, BGA solderability

Hi Chris,
All the advice about solderability issues is certainly valid; however, i wonder if it applies here. Looking at the 'no-wet' picture, I see no evidence of solder paste—maybe paste stenciling is the problem.
Werner



-----Original Message-----
From: Chris Mahanna <[log in to unmask]>
To: [log in to unmask]
Sent: Tue, Nov 23, 2010 10:00 am
Subject: [TN] ImSn finish, BGA solderability

Due to the holiday time crunch, I'm looking for some brainstorming on ImSn




solderability forensics.




I'm thinking that there may be some low hanging fruit that I'm missing because




we just have little experience with ImSn.








We've found random one-up Pb-free BGA balls not wetted to the lands.  Finish is




ImSn.  Basic question in my mind is Sn oxides, SnCu intermetallics, or misprint.




Representative bare boards passed J-STD-003 solderability with flying colors,




but it is a double sided SMT.  Haven't tried after reflow simulation yet.








Both the assemblies and representative bare boards are now naturally aged, so




SERA wouldn't quantify the problem as it existed.  Would it?








I've noted the coincidence of eggshell voids with the non-wet balls.  Doesn't




that imply some paste/flux?  Does it imply anything else?  Are the volatiles




more likely to form eggshells when they are burning through Sn oxides?








Here are some pics:








http://ipc-technet.groupsite.com/gallery/16789












Thanks!




Chris
























______________________________________________________________________




This email has been scanned by the MessageLabs Email Security System.




For more information please contact helpdesk at x2960 or [log in to unmask]<mailto:[log in to unmask]>




______________________________________________________________________








---------------------------------------------------




Technet Mail List provided as a service by IPC using LISTSERV 15.0




To unsubscribe, send a message to [log in to unmask]<mailto:[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]<mailto:[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]<mailto:[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]<mailto:[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] 
______________________________________________________________________