Yes it is the PCB side.
And for the record a lot of BGA substrates are now using immersion tin as a finish where the package is a flip chip as opposed to wire bonded.
Best regards,
John BurkeEngineering FellowSanDisk |a Western Digital brand951 SanDisk Drive, Milpitas, CA 95035T: + 1 (408 597 1423)| M: + 1 (408 518 1496)[log in to unmask]
Sent from my iPad Pro
On Thu, Dec 21, 2017 at 12:04 PM -0800, "George Wenger" <[log in to unmask]> wrote:
Steve,
I just went back and re-read your initial post and looked at the pictures again. I originally thought we were looking at the pads on the BGA but now I think we're looking at the pads on your PCBA. If they are the pads on the PCBA then my suggestion is to look at a new non-soldered PCBA and let us know if the pads look like gold or tin. If they look like gold you have an ENIG Black Pad problem if they look like tin then you have an oxidized Cu-Sn IMC. The real problem in either case there really isn't a reasonable fix. The only think I would try is to use a very aggressive flux and try to pre-tin the pads with solder and then clean off the flux residue and go back through your normal repair process.
George
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of George Wenger
Sent: Thursday, December 21, 2017 2:58 PM
To: [log in to unmask]
Subject: Re: [TN] BGA pad non-wetting
Steve,
I totally agree with John. My first thought was that the pad looked like thin immersion tin where the IMC came to the surface an oxidized in which case solder will not stick to the pad. But I don't know of any BGA where they use Immersion tin so I still suspect you have an ENIG Bad Pad issue.
George
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of John Burke
Sent: Thursday, December 21, 2017 2:51 PM
To: [log in to unmask]
Subject: Re: [TN] BGA pad non-wetting
Assuming it’s not ENIG???
If not ENIG I would suspect immersion tin where the intermetallic has come to the surface.
If an ENIG problem or an immersion Tin problem it is not realistically recoverable without impacting the assembly with some serious reliability issues.
Sent from my iPhone
> On Dec 21, 2017, at 11:39 AM, 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
>
> --
>
>
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