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 <[log in to unmask]>
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
>> <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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>