Phil,
Underfills that require solvent removal to cure will just take time for the underfill solvent to migrate out from under the package... A quick and dirty way to figure the cure time would be to check the cure time for a thick section of the underfill...
Try casting a block the thickness of the 1/2 the BGA with tape on the bottom... Then you can peel off the bottom tape in sections after certain durations, checking the bottom face if the material has sufficiently cured...
Oh... Merry Christmas...
Paul
Paul Edwards
Surface Art Engineering
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Phillip Bavaro
Sent: Wednesday, December 24, 2008 11:17 AM
To: [log in to unmask]
Subject: Re: [TN] Underfill, inhibition due to leftover activators in the flux residue
Thanks Wayne.
I will do a little experimentation to see if I can recreate the problem in
a lab environment.
When you misted the sample, were you talking about an underfilled BGA or
just raw underfill material?
Phil
At 12:43 PM 12/23/2008 -0500, Thayer, Wayne wrote:
>I have been in underfill "hell" numerous times.
>
>I still don't have a complete understanding of what makes it decide to not
>cure properly, but moisture can be a big problem, as far as some of the
>Henkel products go. We are getting better results with extended bake
>cycles to eliminate any moisture from the assembly. This might have
>something to do with your problem too: Send it through the oven a number
>of times, and each time it will be a bit drier.
>
>I use mostly RMA flux and solvent clean. I have mixed raw RMA flux
>directly with the underfills we use and they seem to cure OK. Only way I
>could get the uncured goo witnessed sometimes on the production line was
>to literaly mist it with water prior to attempting to cure.
>
>Good Luck!
>
>Wayne Thayer
>
>-----Original Message-----
>From: TechNet [mailto:[log in to unmask]] On Behalf Of Dwight Mattix
>Sent: Tuesday, December 23, 2008 11:46 AM
>To: [log in to unmask]
>Subject: Re: [TN] Underfill, inhibition due to leftover activators in the
>flux residue
>
>At 04:54 AM 12/23/2008, David D. Hillman wrote:
> >But - if you have a BGA that is sufficiently large and has significant
> >I/O, you are going to have some flux residue remaining under the
> >component.
>
>/heh no kidding.
>
>Phil,
>This under a 7xxx series MSM? Almost 700 pins on a .5mm or .4mm package?
>
>You're going to love the the 8xxx series. :-) lol!
>
>Merry Christmas,
>dw
>
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