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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 10:52:16 -0800
Content-Type:
TEXT/plain
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TEXT/plain (139 lines)
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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