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Subject:
From:
Guy Ramsey <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Guy Ramsey <[log in to unmask]>
Date:
Fri, 22 Dec 2017 11:22:03 -0500
Content-Type:
text/plain
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text/plain (163 lines)
New facts please help if you can.

   - XRF showed 36uin of tin on the pads. (SAC305 solder)
   - The condition also appears on the package terminals but not as often.
   - The condition worsens after a second installation.
   - The locations that appear to be wetting the pad completely can be very
   fragile. I popped a nice little kiss shape of a pad. Mat finish on the
   board and bottom of the kiss.
   - I have photos of the condition appearing on SMD planes and SMD signal
   pads.
   - Some of the SM flaked off the signal pad exposing a ring of bare
   copper.  After reflow the copper and the nickel shared the same appearance.

I will send photos to Steve.

Thanks everyone.

On Thu, Dec 21, 2017 at 3:20 PM, George Wenger <[log in to unmask]>
wrote:

> Thanks for the info about flip chip packages using immersion tin.  That
> change must have happened after I retired and I'm glad I never had to deal
> with immersion tin BGAs because I really dislike that surface finish.
>
>
> -----Original Message-----
> From: TechNet [mailto:[log in to unmask]] On Behalf Of John Burke
> Sent: Thursday, December 21, 2017 3:10 PM
> To: [log in to unmask]
> Subject: Re: [TN] BGA pad non-wetting
>
>
>
>
>
>                 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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