Ed,
I didn't write earlier as, to use Dave Hillman's phrasing, I was
fighting alligators.
As Werner says, there are positive uses for it and many cases where it
is irrelevant. I would like to point out there are cases where it can
be detrimental. The only case that I can remember of solder joint
failure during thermal cycling in the last 5 years was where an
underfill with good drop characteristics but crappy thermal cycling
characteristics was chosen for a trial. The results after thermal
cycling were a disaster. You really, really need to match underfill
characteristics to your situation - use environment of your product,
CTE, modulus of elasticity, etc.
I will post the draft for pass fail/criteria for discussion in a few
minutes.
Bev
RIM
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Edward Rios
Sent: Thursday, June 04, 2009 10:50 AM
To: [log in to unmask]
Subject: Re: [TN] When not to underfill
Thanks Werner. Yes, your column was very helpful. Sounds like my
question may be a bit naive and that I am trying to simplify things too
much. I was searching for an IPC guideline or to at least start a
discussion on the subject, but maybe this is a proprietary area. Fellow
TechNetters: is that the case?
Have a great day,
Ed
Werner Engelmaier /* wrote:
> Hi Ed,
> Underfill makes solder attachments sufficiently reliable in cases
where without it solder joint failures would occur prematurely for the
application in question. As work by Motorola [see my reliability column
Engelmaier, W., "Reliability Improvement with Underfill," Global SMT &
Packaging, Vol. 6, No. 3, March 2006, pp. 66-67] has shown, not all
underfills are of equal benefit and that increases of up to 6x are
achievable in praxis.
> If the reliability without the underfill is sufficient-because of
small component size, high solder joint stand-off, built-in component
compliancy [Tessera patents], small CTE-mismatch, small delta-T, then
there is no need for underfills.
> Werner
>
>
>
>
>
>
>
> -----Original Message-----
> From: Edward Rios <[log in to unmask]>
> To: [log in to unmask]
> Sent: Wed, 3 Jun 2009 5:45 pm
> Subject: [TN] When not to underfill
>
>
>
>
>
>
>
>
>
> Hi TechNet,
>
>
> OK I'll admit it, I'm fairly new to the field of solder joint
> reliability. ;) Therefore, the recent thread about underfill
inspection
> criteria prompted me to do additional reading on the subject. It seems
> like there is consensus on the positive effect of underfilling on BGA
> solder joint reliability. On the other hand, are there cases where
> underfill doesn't have a significant impact? Maybe in smaller BGA
> components?
>
>
> Thanks,
>
>
> Ed Rios
>
>
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