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,  
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>>> dissemination, distribution or other disclosure of the contents  
>>> of this
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>>>
>>