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
> <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
>
> -- 
>
>
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