Hi David,
I must agree with you. We are about to embark on assembling a 16-layer, .062"
thick, VME card. That has been re-designed from a commercial card to a
"ruggedized" COTS card. The assembly has 17 BGA's, some are ceramic BGA's
with high-temp balls, and a few with eutectic balls...there are BGA's on both
sides of this board...none are "mirrored" though...and that's a good thing.
We've been having meetings on manufacturability issues with assembly (this is
not going to be easy), and the biggest thing that I've tried to stress, is
that it has to be built right from the beginning...rework should not be an
option.
But we have heard from our customer, that historically, 20% of the PowerPC
processors on this assembly have needed to be replaced (there's 4 of these on
the board). I don't know if the processors are dead, or if it because of a
manufacturing defect, but they say in the past, that's what the rework
percentage has been.
I'm absolutely freaking out about this!!! Especially when you see the density
of this board...
From my own personal point of view, I think COTS needs to be re-thought...too
many risks.
-Steve Gregory-
> I am appalled by these atttepmts to "repair" a board. The amount of damage
> and degradation done to the circuit
> poses a serious threat to the reliability, particularly for class 3
> operation.
>
> The concept of "repairable" finished SMT products is very misleading and
> potentaily dangerous.
> The ability to repair circuits is a legacy from the old Mil Spec days and
> have no business in todays processes!
> Smaller none repairable circuits must become the norm.
>
> David A. Douthit
> Manager
> LoCan LLC
>
>
> "Long, Thomas" wrote:
>
> > Yes Mike. I have done several with an Air-Vac. The best way is to make
> > sure you have solder above liquidus(use t-couple). I would target a
> > temp > 200 C for at least 30 seconds. Since the Parylene will still
> > have a good hold on the solder joints, you must shear through the joints
> > using a spatula. Once you get the hang of it, it is fairly simple and
> > straight forward. Like I said, I have taken off quite a few with no
> > problem on the pad side. Some clean up of course is required prior to
> > replacing a new part.
> >
> > Tom Long
> > ITT Avionics
> > Clifton, NJ
> >
> > -----Original Message-----
> > From: WEEKES, MICHAEL HS-SNS [mailto:[log in to unmask]]
> > Sent: Thursday, December 05, 2002 10:58 AM
> > To: [log in to unmask]
> > Subject: [TN] reworking paralyne (paraxylene) coated BGAs and uBGAs
> >
> > Hello fellow Technetters:
> >
> > Anyone have any experience removing paralyne (paraxylene) coated BGAs
> > and
> > uBGAs with conventional air vac DRS 24 type hot air equipment - I tried
> > conventional reflow profiles and it was very unsuccessful.
> >
> > [log in to unmask]
>
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