Hi Ioan! Yep, its falling off as we have had a couple of them stay in the
reflow oven for some additional "hot" time! A good friend and TechNet
lurker, Fritz Byle of Astronautics, made me a Excel program many years ago
that calculates & compares BGA weight to surface tension so I can usually
predict if I am going to have a problem. This BGA in question is one of
those that is "right on the edge of the cliff" in terms of holding on. We
have looked at reflow profile changes but I just can't convince the Laws of
Physics to temporarily go away for the BGA so I am working "Plan B" with
the temporary mask material until we can revise the assembly and move the
BGA to process side two.

Dave

On Tue, Dec 9, 2014 at 2:11 PM, Ioan TEMPEA <[log in to unmask]>
wrote:

> Hi Dave,
>
> Just out of curiosity, have you seen the BGA falling or you are just
> afraid it might?
>
> Because I have ran thousands of BGAs in second reflow (ceramic, metal top,
> name it), on bottom side, with absolutely no BGA loss. The balls would keep
> their collapsed aspect, even though they might be slightly stretched, but
> this is bound to improve compliance, hence long term reliability.
>
> Best regards,
>
> Ioan Tempea
> MDA Corporation
> >
> > -----Original Message-----
> > From: TechNet [mailto:[log in to unmask]] On Behalf Of David Hillman
> > Sent: Tuesday, December 09, 2014 8:42 AM
> > To: [log in to unmask]
> > Subject: [TN] BGA Reflow Issue
> >
> > Hi gang - looking for an adhesive suggestion. I have an assembly in
> > which a heavy BGA was accidently located on process side one (bottom)
> > so that when we reflow process side two (top) the BGA is doing its
> > best to fall off.
> > Unfortunately I can't reverse my process order for a couple of reasons
> > so I am looking for a temporary fix until I can get the assembly
> > revised. I was thinking of using some type of adhesive to temporarily
> > hold the BGA in place during reflow - tack down the corners sort of
> > action. Does anyone have any adhesive (ideally temporary, water
> > washable/removable) suggestions I can investigate?
> >
> > TIA
> >
> > Dave Hillman
> > Rockwell Collins
> > [log in to unmask]
>
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