Steve,

It appears the pad you are trying to solder to is oxidized nickel or a Ni-Sn intermetallic.  Do you know what the original surface finish was on the BGA?  My guess it was ENIG and although I've always hated the name for this type of failure it does appear as if you have "Black Pad"

George

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Steve Gregory
Sent: Thursday, December 21, 2017 2:40 PM
To: [log in to unmask]
Subject: [TN] BGA pad non-wetting

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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