New facts please help if you can. - XRF showed 36uin of tin on the pads. (SAC305 solder) - The condition also appears on the package terminals but not as often. - The condition worsens after a second installation. - The locations that appear to be wetting the pad completely can be very fragile. I popped a nice little kiss shape of a pad. Mat finish on the board and bottom of the kiss. - I have photos of the condition appearing on SMD planes and SMD signal pads. - Some of the SM flaked off the signal pad exposing a ring of bare copper. After reflow the copper and the nickel shared the same appearance. I will send photos to Steve. Thanks everyone. On Thu, Dec 21, 2017 at 3:20 PM, George Wenger <[log in to unmask]> wrote: > Thanks for the info about flip chip packages using immersion tin. That > change must have happened after I retired and I'm glad I never had to deal > with immersion tin BGAs because I really dislike that surface finish. > > > -----Original Message----- > From: TechNet [mailto:[log in to unmask]] On Behalf Of John Burke > Sent: Thursday, December 21, 2017 3:10 PM > To: [log in to unmask] > Subject: Re: [TN] BGA pad non-wetting > > > > > > Yes it is the PCB side. > And for the record a lot of BGA substrates are now using immersion tin as > a finish where the package is a flip chip as opposed to wire bonded. > Best regards, > John BurkeEngineering FellowSanDisk |a Western Digital brand951 SanDisk > Drive, Milpitas, CA 95035T: + 1 (408 597 1423)| M: + 1 (408 518 1496) > [log in to unmask] > > > > Sent from my iPad Pro > > > > > > On Thu, Dec 21, 2017 at 12:04 PM -0800, "George Wenger" < > [log in to unmask]> wrote: > > > > > > > > > > > Steve, > > I just went back and re-read your initial post and looked at the pictures > again. I originally thought we were looking at the pads on the BGA but now > I think we're looking at the pads on your PCBA. If they are the pads on > the PCBA then my suggestion is to look at a new non-soldered PCBA and let > us know if the pads look like gold or tin. If they look like gold you have > an ENIG Black Pad problem if they look like tin then you have an oxidized > Cu-Sn IMC. The real problem in either case there really isn't a reasonable > fix. The only think I would try is to use a very aggressive flux and try > to pre-tin the pads with solder and then clean off the flux residue and go > back through your normal repair process. > > George > > -----Original Message----- > From: TechNet [mailto:[log in to unmask]] On Behalf Of George Wenger > Sent: Thursday, December 21, 2017 2:58 PM > To: [log in to unmask] > Subject: Re: [TN] BGA pad non-wetting > > Steve, > > I totally agree with John. My first thought was that the pad looked > like thin immersion tin where the IMC came to the surface an oxidized in > which case solder will not stick to the pad. But I don't know of any BGA > where they use Immersion tin so I still suspect you have an ENIG Bad Pad > issue. > > George > > -----Original Message----- > From: TechNet [mailto:[log in to unmask]] On Behalf Of John Burke > Sent: Thursday, December 21, 2017 2:51 PM > To: [log in to unmask] > Subject: Re: [TN] BGA pad non-wetting > > Assuming it’s not ENIG??? > > If not ENIG I would suspect immersion tin where the intermetallic has come > to the surface. > > If an ENIG problem or an immersion Tin problem it is not realistically > recoverable without impacting the assembly with some serious reliability > issues. > > Sent from my iPhone > > > On Dec 21, 2017, at 11:39 AM, Steve Gregory wrote: > > > > Hi all, > > > > I've been asked to post this to the Technet by a dear friend: > > > > *We installed this little processor. At test we identified opens on > > the device. When we removed it we saw a number of pads that were matte > > gray with no evidence of solder adhered to the pad. * *We attempted to > > bump the pads with solder, they did not wet easily. In some cases we > > had to scrape through the matte finish to a shiny metal. > > But, we did get all the pads to appear wetted.* > > > > *We cleaned the site well and then fluxed the bumps with a tacky flux > > ROLO designed for POP, placed the BGA and reflowed it on a rework > > station.* > > > > *The assembly failed test with similar result, opens under the > > processor.* > > > > *The attached photo shows that the bump process only appeared to wet > > the pads. The condition returned when we removed the BGA second > > time.* > > > > * http://stevezeva.homestead.com/2017-12-21_11.21.17.jpg > > * > > > > *Have you seen this before? Is there any recovery? This assembly is > > worth about $45K. * > > > > Thanks, > > > > Steve > > > > -- > > Steve Gregory > > Kimco Design and Manufacturing > > Process Engineer > > (208) 322-0500 Ext. -3133 > > > > -- > > > > > > This email and any attachments are only for use by the intended > > recipient(s) and may contain legally privileged, confidential, > > proprietary or otherwise private information. Any unauthorized use, > > reproduction, dissemination, distribution or other disclosure of the > > contents of this e-mail or its attachments is strictly prohibited. If > > you have received this email in error, please notify the sender > > immediately and delete the original. >