What you drinking with that chili?   ;^)

At 05:15 PM 12/22/2008, Bev Christian wrote:
>That was supposed to be "to think". Too bad Spell Check doesn't 
>check that sort of thing.
>Bev
>
>----- Original Message -----
>From: TechNet <[log in to unmask]>
>To: [log in to unmask] <[log in to unmask]>
>Sent: Mon Dec 22 20:12:30 2008
>Subject: Re: [TN] Underfill, inhibition due to leftover activators 
>in the flux residue
>
>Phil,
>I have had more time outthink about this now.  A good chili on a winter
>night helps.  :)
>
>This could be really bad news. I have not heard of this before.  The good
>news is that the joints most at risk during thermal cycling and drop are the
>ones the farthest from the neutral point, which is where (neutral point) you
>are finding the phenomenon.  Even so, I am concerned.  Now I am wondering
>how many other combinations are doing this?
>Bev
>RIM
>
>-----Original Message-----
>From: TechNet [mailto:[log in to unmask]] On Behalf Of Phillip Bavaro
>Sent: Monday, December 22, 2008 6:02 PM
>To: [log in to unmask]
>Subject: [TN] Underfill, inhibition due to leftover activators in the flux
>residue
>
>I have made quite a few test samples and discovered that a certain
>underfill material will exhibit inhibited cure when it comes in contact
>with solderpaste flux residues at the center of a very dense BGA component.
>The rest of the underfill beneath the BGA will harden like normal.
>We don't clean nor plan on starting to clean our assemblies.
>DVT testing does not show any defects due to underfill adhesion.
>
>
>Background:
>We used a four up ABAB panel which goes through SMT twice.
>BGAs only passing through the oven once consistently show the problem.
>Two passes through the reflow oven (ABAB flip) and the problem goes away.
>This means that  half of our test samples still have soft material in the
>pocket at the center where the power ground pins are located.
>We measure peak temperature in this area and have found that raising the
>peak temperature helps quite a bit but does not eliminate the inhibition
>entirely.
>The manufacturers of the paste and the underfill acknowledge the issue but
>do not have a solution.
>
>Has anyone else run into similar compatibility issues with a paste and
>underfill?
>
>In the event that we cannot work out the root cause, and decide to make a
>change, I am trying to come up with a list of all the manufacturers of
>underfill.
>
>So far I have found 8 major underfill manufacturers but would appreciate
>knowing about more if there are any.
>
>3M
>Ablestik
>Epotek
>Henkel
>Hysol
>SP&S
>Sunstar
>Zymet
>
>Thanks in advance,
>
>Phil
>
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