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December 2002

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Subject:
From:
Karl Sauter <[log in to unmask]>
Reply To:
Karl Sauter <[log in to unmask]>
Date:
Fri, 20 Dec 2002 11:24:21 -0800
Content-Type:
TEXT/plain
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TEXT/plain (203 lines)
Mark,

Although moisture absorption is one of the factors affecting CAF resistance, I
am not aware of any testing that successfully isolated and was able to quantify
the effect of moisture absorption alone on the CAF resistance of Thermount
boards.

Regards,

  Karl Sauter, Staff Engineer
  VLSI/Advanced Component Engineering
  Sun Microsystems Inc.
  (650) 786-7663


> From: Mark Mazzoli <[log in to unmask]>
> To: "'Karl Sauter'" <[log in to unmask]>, [log in to unmask]
> Subject: RE: [TN] Thermount for Burn In boards
> Date: Fri, 20 Dec 2002 11:07:44 -0800
> MIME-Version: 1.0
>
> Thanks Karl,
>
> Any data compiled regarding moisture absorption insofar as how it affects
> the CAF for the Thermount boards?
>
> Mark
>
> -----Original Message-----
> From: Karl Sauter [mailto:[log in to unmask]]
> Sent: Friday, December 20, 2002 10:52 AM
> To: [log in to unmask]
> Subject: Re: [TN] Thermount for Burn In boards
>
>
> Mark,
>
> We have done some CAF testing with Thermount, epoxy resin version.  When the
> plated-through holes (PTHs) are oriented along the X or Y axis, then boards
> made
> with the Thermount laminate material (which have broken and random
> orientation
> of reinforcement fibers) showed significantly more resistance to CAF
> failures
> than standard FR-4 laminate materials.
>
> However, when PTHs are diagonally oriented the Thermount boards (epoxy resin
> version) showed slightly less resistance to CAF when compared with boards
> made
> using standard FR-4 laminate materials with X and Y oriented woven glass
> reinforcement.  In retrospect this seems understandable since the Thermount
> will
> have some fiber segments that do run in a diagonal direction.
>
> Since most boards (but perhaps not substrates) have the closest vias and
> other
> PTHs oriented in-line with the X or Y axis, then using the Thermount epoxy
> resin
> laminate material as an alternative in those cases should produce boards
> that
> are significantly more CAF resistant.
>
> Regards,
>
>   Karl Sauter, Staff Engineer (and Vice-Chair of IPC committee on CAF)
>   Sun Microsystems Inc.
>   (650) 786-7663
>
>
> > Date: Fri, 20 Dec 2002 09:46:10 -0800
> > From: Mark Mazzoli <[log in to unmask]>
> > Subject: Re: [TN] Thermount for Burn In boards
> > X-To: "TechNet E-Mail Forum." <[log in to unmask]>
> > To: [log in to unmask]
> >
> > Thanks for the info David.  I wasn't aware that CAF could form in that
> short
> > amount of time.  We've made numerous attempts to locate the actual shorts
> > but they don't show themselves.  Clearly, if we could find one it would
> make
> > decision making much easier.
> >
> > Thermount is billed as an anti CAF material due to the randomness of the
> > fiber.  Since it does not contain woven strands for channeling CAF, some
> > believe it to be resistant to that effect.  Our concern is its enthusiasm
> > for water absorption.  I can see how the absence of fiber "channels" would
> > inhibit filament growth but it seems like the accelerated water absorption
> > would create a fine growing environment for conductive incubation.
> >
> > Are you aware of the materials used in the IPC testing?
> >
> > -----Original Message-----
> > From: David Douthit [mailto:[log in to unmask]]
> > Sent: Friday, December 20, 2002 8:58 AM
> > To: TechNet E-Mail Forum.; Mark Mazzoli
> > Subject: Re: [TN] Thermount for Burn In boards
> >
> > Mark,
> >
> > Some round robin testing being done by the IPC committee on CAF indicates
> > that there is a "damage" ring around drilled holes/vias of up to .020
> > inches.
> > CAF will form there very quickly (hours!) in high >80% humidity and mild
> > temperatures (>5 degrees C and < 45 degrees C).
> > This damage area would most likely include edge routing and scoring.
> >
> >
> > You need to do some cross section work ups before you start "guessing"!
> >
> >
> > David A. Douthit
> > Manager
> > LoCan LLC
> >
> >
> > Mark Mazzoli wrote:
> >
> >
> >
> >
> > For those of you designing or building burn in boards, are any of you
> > building them on Thermount material?  One of our customers has shown an
> > interest in this material for their burn in boards and we're trying to
> > decide if that's a wise move or not.  Most of their boards use 0.8mm and
> > 0.5mm BGA's and have traditionally been built on Polyimide.  The problem
> is
> > that some percentage of them develop low voltage shorts in the field.
> Hole
> > to internal traces may be as low as 3 mils when drill wander and material
> > movement are at their worst but normally it's maintained at 6-mils or
> > better.  The boards are tested at 40 volts prior to shipping and all pass
> > but some number of them will develop the field problem.  CAF is suspected
> > but I'm not so sure.  The field failures develop in days or weeks rather
> > than months.  I suspect rather than CAF it may be due to the resin system
> > itself.  I understand that most Poly manufacturers use a common Poly resin
> > from Ciba and that it has been suspected of developing this low voltage
> > shorting issue (sulfur content I believe).
> >
> >
> > Anyone out there have any comments about the situation itself or comments
> > regarding Thermount (85RT and 55ST)?
> >
> >
> > Thanks,
> >
> >
> > Mark Mazzoli
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