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September 2001

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Subject:
From:
Bill Christoffel <[log in to unmask]>
Reply To:
TechNet E-Mail Forum.
Date:
Thu, 6 Sep 2001 14:32:48 -0500
Content-Type:
text/plain
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text/plain (203 lines)
Bruce thanks for the confirmation,  its always good to bounce
ideas/findings.  We are looking into plasma and a possible pre-bake.  Go
Technet !

Bill C.

-----Original Message-----
From: Misner, Bruce [mailto:[log in to unmask]]
Sent: Thursday, September 06, 2001 2:26 PM
To: [log in to unmask]
Subject: Re: [TN] Outgassing of LPI's and Legend Inks


Bill,

Well Done!!  Certainly seems like you found a smoking gun.  Maybe try to
fully outgass the material with a bake, then plasma clean (there are
places
you can have this done and recommend an appropriate plasma if you don't
have
in-house capability), before epoxy die attach.

Bruce

> ----------
> From:         Bill Christoffel[SMTP:[log in to unmask]]
> Reply To:     TechNet E-Mail Forum.
> Sent:         Thursday, September 06, 2001 3:05 PM
> To:   [log in to unmask]
> Subject:      Re: [TN] Outgassing of LPI's and Legend Inks
>
> 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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