agree, it could be something silly as gas bubble present during the etch process for oxide removal (if just a quick dip). oxide some time is anti-wetting and form bubble easy on surface without aggitation... On Dec 21, 2017, at 4:34 PM, John Burke wrote: > > > > > If you achieved tin copper intermetallic the only way to > “uniformly separate” it would be with a shock test. > Besides the surface appearance is not uniform from what I can see > some of those pads exhibit partially solderable surfaces from a > purely visual examination. > > > > > Sent from my iPad Pro > > > > > > > On Thu, Dec 21, 2017 at 1:31 PM -0800, "Guy Ramsey" > <[log in to unmask]> wrote: > > > > > > > > > > > Thanks for the thoughtful response. One of the other MEs here is > thinking > that this is a normal appearance, that the SAC305 solder uniformly > separated from the intermetallic when we reflowed and pulled the BGA. > > I wish this was the case but it seems unlikely. Isn't the affinity > of the > bulk solder to the intermetallic higher than its surface tension? > > On Thu, Dec 21, 2017 at 4:26 PM, Yuan-chia Joyce Koo > wrote: > >> Steve, your friend might need cross section and see if UBM is done >> correctly, besides, the solder mask looks extra thick for a device... >> didn't look like std BT substrate... cross section of good vs >> after reflow >> one might give you some clue what is wrong... the color of the >> pad look >> like poor adhesion of the nickel layer... it might be poorly done >> either >> possiviation layer prior to balling (either ImAg, ImAu or ImTin), or >> missing etchant step (or pH adjustment not done properly) prior to >> last >> immersion plating step...IMHO. >> On Dec 21, 2017, at 2:39 PM, 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. >>> >>