Never Assume !!! However in this case, Yes we are seeing a dramatic
drop off in bond pull strengths and interfacial failure modes. Our tests
we performed with controls on board lots, epoxy lot (down to syringe
level) and all epoxy stamping done on same machine, same run etc.
As a follow on we ran some down and dirty "wettability" tests using
glass slides and measuring contact angle vs. oven atmosphere (loaded/not
loaded), definitely a difference when boards with previously cured
legend ink on them we in the oven. I think we found the source, now how
to eliminate it ?
Bill C.
-----Original Message-----
From: Misner, Bruce [mailto:[log in to unmask]]
Sent: Thursday, September 06, 2001 1:46 PM
To: [log in to unmask]
Subject: Re: [TN] Outgassing of LPI's and Legend Inks
Bill,
My experience with the type ovens you describe have shown them to do an
excellent job of exhausting outgassed material and precluding redeposit
on a
board or substrate surface. If it is outgassing, I would tend to believe
that you would see a difference in wire bond pull strengths as well.
Especially when comparing before/after accelerated bakes. Is this the
case?
Please forgive me, but are you absolutely sure the same lot and even
same
syringe/application of epoxy was used on both board types?
Bruce Misner
> ----------
> From: Bill Christoffel[SMTP:[log in to unmask]]
> Reply To: TechNet E-Mail Forum.
> Sent: Thursday, September 06, 2001 9:03 AM
> To: [log in to unmask]
> Subject: [TN] Outgassing of LPI's and Legend Inks
>
> Technetters,
>
> We are experiencing what appears to be the result of some type of
> outgassing of white legend ink.
> Details: Board design uses a white legend ink as an overcoat.
> Subsequent processing includes die attach (COB) using electrically
> conductive epoxy. Testing shows that the die attach epoxy strength
(die
> shear) is greatly reduced on boards that use the white legend ink. I
do
> not believe this to be a surface contaminant issue since the epoxy
> failure mode is cohesive. Epoxy cure temperature is 150C in a air
> circulating oven with a high exhaust rate. Questions - Is outgassing
> of legend inks and LPI's a probable cause? Is any information
> available regarding this ?
>
> Bill C.
>
>
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