Rudolph,
I agree with George Wenger that what you are probably experiencing is a
"double reflow" induced fracture at the nickel/solder interface. If you look
at the traces coming off the part in that area, you see that the pad that is
failing is the only one without a via nearby. I think what is happening is
that vias are providing sufficient heat transfer during wave solder so that
all the balls except for the one with the lengthy trace goes through
liquidous. The pad with the long trace is now experiencing all the stresses
in that area (the rest of the pads are melted) and since it is near to
eutectic it is not very strong to begin with. The solder joint fractures in
a clean break at the weakest point, right at the nickel interface. The paper
George references does a good job documenting this phenomena. Preventing the
solder joints from melting (the Kapton tape suggestion) will keep the joint
from fracturing. Other possible resolutions is putting a via next to that
pad so it heats similar to the others, or reduce the temperature of the
solder pot if that is possible. We tend to run our wave solder as low as
possible to reduce the chances of experiencing this issue. This is not to
state that reduced pot temperatures will eliminate the problem, but it is
one method utilized to minimize risk.
Thanks,
Robert Furrow
Printed Wiring Board Engineer
Strategic Supply Global Account Manager
Supply Chain Networks
Lucent Technologies
978-960-3224 [log in to unmask]
> -----Original Message-----
> From: Rudolph Yu [SMTP:[log in to unmask]]
> Sent: Wednesday, March 28, 2001 8:58 PM
> To: [log in to unmask]
> Subject: [TN] BGA crack- major headache wi/pic
>
> I have taken some pic for the problem I mentioned in last email.
> The board is a single sided board, with wave soldering.
> I hope the Technet will accept this email with the zip file attacted to
> it.
>
> Thanks for the supports you guys had been giving me in this.
>
> Rudolph
>
>
>
> ------Original Message------
> From: Werner Engelmaier <[log in to unmask]>
> To: [log in to unmask]
> Sent: March 28, 2001 8:24:08 PM GMT
> Subject: Re: [TN] BGA crack- major headache
>
>
> Hi Rudolph,
> I think you have too complex a situation to get a proper diagnosis to your
> problem via the TechNet forum.
> We need to see a good picture(s) showing the failure mode, we need to see
> details of the BGA construction as well as the PCB, and also get some idea
> of
> any testing (ESS, burn-in) you have performed on your product prior to
> shipping. Further, the use conditions are critical.
>
> Werner Engelmaier
> Engelmaier Associates, L.C.
> Electronic Packaging, Interconnection and Reliability Consulting
> 7 Jasmine Run
> Ormond Beach, FL 32174 USA
> Phone: 386-437-8747, Fax: 386-437-8737
> E-mail: [log in to unmask], Website: www.engelmaier.com
>
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