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June 2009

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Subject:
From:
"Stadem, Richard D." <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Stadem, Richard D.
Date:
Thu, 4 Jun 2009 10:40:33 -0500
Content-Type:
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Hi, Edward
As was proven in a lawsuit last week in which I was the expert witness,
the general underfill process itself is in the public domain, but a
certain amount of process development is required to get to the right
material, the optimum cure schedule, the optimum dispense rate and board
temperature/material temperature when dispensed, etc., to ensure that
you have the best possible process for your particular application or
product. You are going down the right path in developing a process,
which is to first gather as much information as you can. The second is
to secure samples and develop a plan for the process. The third step is
trying the different materials and carrying out the plan and testing to
get results (data). Once you have optimized and qualified the process
you document it.
Some applications are much more difficult than others. The results are
manifest during qualification as shown by the increase in cycles before
failure (or lack thereof). So when you are developing your underfill
process you want to qualify and validate the results with some type of
thermal cycling, using the guidelines in Werner's article. Your finished
and documented process IS proprietary material (intellectual property),
and should be protected.

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Whittaker, Dewey
(EHCOE)
Sent: Thursday, June 04, 2009 10:00 AM
To: [log in to unmask]
Subject: Re: [TN] When not to underfill

Guidelines in of themselves are merely the under fill of the great belly
of knowledge that is Technet.
Dewey 

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Edward Rios
Sent: Thursday, June 04, 2009 7:50 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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