Ingemar and Steve have provided good advice. In Gaby, Ingemar and Steve have provided good advice. Ingemar, Your vast experience with solder assembly and material issues still manages to amaze me. The only thing I would add is that Steve's idea of an inclusion in the solder paste may also be the cause. I've looked at the changing the brightness and contrast of the images and it does appear that at least on the small2.jpg the dark area does look like a fibrous inclusion that actually sticks out a short distance from the solder ball into the cross section potting compound. Regards, George George M. Wenger Andrew Wireless Solutions Senior Principal FMA / Reliability Engineer 40 Technology Drive, Warren, NJ 07059 (908) 546-4531 [Office] (732) 309-8964 [Mobile] [log in to unmask] -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of Inge Sent: Saturday, July 04, 2009 2:49 PM To: [log in to unmask] Subject: Re: [TN] Weird solder joints Gaby, solder joints are often expected to be perfect and according to the school book, but in the real world they are more or less imperfekt. Plus: good geomtry good wetting good surface formation no big dendrites no big voids good nickel barrier good grain structure Minus flux inclusions wich have not have time enough to withdraw to the surface. I think you have got a too dry paste. I've seen similar solder joints and we had no problems. If we had, some boards ought to show up after years of operation. I can't see any reason to panic, your solder joints are rather normal. Do this: take the polished crossection samples and put then in a jar with a flux remover. Place the jar in a water filled ultrasonic tank and let go for a minute. If the 'dark' streaks disappear, it's certainly flux. It's good for all to know how strong and longlasting solder joints can be despite numerous 'anomalies' as brother Creswick call them.I've tested solder joints with up to 50% voids...and they have been nearly as good as normal ones. Because the metallurgical properties have been good. Finally, judging solder joints from light microscope images demands a very experienced eye. If I were you , i.e. young and sweet and uncertain , I'd fine polish the samples, etch in a weak solution for a minute and have them placed in a SEM. Does not take many minutes to get a safer platform for determination. Inge ----- Original Message ----- From: "Gabriela" <[log in to unmask]> To: <[log in to unmask]> Sent: Saturday, July 04, 2009 9:54 AM Subject: [TN] Weird solder joints > Dear all, > By cross sectioning BGA solder joints on a failed assembly, I found that > the > suspected joints are not uniform and that they contain unusual separation > areas. > > I suspect mixed assembly and/or bad reflow profile. > > Steve was so kind and enabled me to send the links. > Please may I have your opinion? > http://stevezeva.homestead.com/files/small.jpg > > > > <http://stevezeva.homestead.com/files/small1.jpg> > http://stevezeva.homestead.com/files/small1.jpg > > > > <http://stevezeva.homestead.com/files/small2.jpg> > http://stevezeva.homestead.com/files/small2.jpg > > http://stevezeva.homestead.com/files/small3.jpg > > <http://stevezeva.homestead.com/files/small4.jpg> > http://stevezeva.homestead.com/files/small4.jpg > > > > > Gaby > > > --------------------------------------------------- > 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 ----------------------------------------------------- ------------------------------------------------------------------------------------------------ This message is for the designated recipient only and may contain privileged, proprietary, or otherwise private information. 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