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October 1998

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Subject:
From:
"Peroutka, Gregg W." <[log in to unmask]>
Reply To:
TechNet E-Mail Forum.
Date:
Wed, 28 Oct 1998 12:19:41 -0600
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Rick:

Like Jeff H, I also did ceramic circuits in a previous life.  My time was
spent at a defense contractor that fabricated ceramic substrates and
assembled ceramic modules for the military. Most substrates were
multi-layer, approximately 4"x5" or 5"x6" in size and .040-.060" thick.   I
concurr with Jeff about it being a robust product and process, but we
experienced some nuances that may/may not be relevant to your situation:

1--Thermal preheating of the substrate before any hand soldering was a must
to prevent thermal shock and micro-cracking.  We typically accomplished this
at workstations with embedded hot plates, custom fixturing, and good
technique.  If memory serves me right, I recall preheat temps in the
vicinity of 120-150 deg C.

2--All thermal exposures had rate-limits on heating and cooling.  This was
again necessary to prevent micro-cracking of the substrate with special
concern for small diameter internal radii or features in the substrate
outline.  In those days, laser heat from the substrate scribing/sizing
process would tend to concentrate too much in small features and produce
residual material stress. Thus thermal ramp rates had to be to be tightly
controlled so as not to induce latent cracking.

3--More solder was not necessarily better if you were using a sealing glass
layer.  Our studies back then found that smaller solder joints produced less
stress on the land and surrounding sealing glass layer of the substrate.
Even though the components and substrate CTE were typically matched, the
solder was influential in inducing micro-cracks around the land.   This was
especially true for LCCs.  Thus we migrated to leaner joints that typically
only rose about half-way up the castellation or other component terminal
face.

4--Related to the lean joints, our lands were adjusted somewhat longer to
provide an even lower wetting angle for the joint.

5--Substrates using a platinum-palladium-gold surface finish typically
required us to burnish it prior to processing for better wettability.
Again, may not be an issue any more due to materials, fluxes, and
application advances.

Depending upon the product scale you are working with, I think I can still
reach into the local medical companies here that use ceramic in their
pacemakers for a relevant contemporary resource.  Other companies like GE,
Texas Instruments, and Coors used to do ceramic circuits and might be
another avenue to information if you can somehow get connected to a willing
source.

> ----------
> From:         Jeff Hempton[SMTP:[log in to unmask]]
> Sent:         Tuesday, October 27, 1998 12:55 PM
> To:   [log in to unmask]
> Subject:      [TN] SMT Assembly on Ceramic substrate?
>
>      Rick,
>        I cut my teeth on this type of SMT assembly, many (we won't say how
>      many) moons ago. Ceramic is more fragile and a better heat sink then
>      typical FR4, so you may have to allow more time to ramp, time at
> peak,
>      and slower cool-down, to avoid cracking, especially if substrate
>      thickness is less then .030", and/or board is larger then one square
>      inch. The type of conductor used for the traces may be a concern also
>      (pt/pd/au? pd/ag? thickfilm vs. other?). Other then a few concerns
>      like this, it actually can be a very robust process. Please give more
>      info, or call me directly, and I'll be glad to answer any process
>      questions.
>
>      United Technology Electronic Controls
>      Jeff L. Hempton, Sr. SMD Engineer
>
>      Phone:  219-359-3514
> E-mail: [log in to unmask]
>
>
>
> ______________________________ Forward Header
> __________________________________
> Subject: [TN] SMT Assembly on Ceramic substrate?
> Author:  Rick Thompson <[log in to unmask]> at Internet
> Date:    10/27/98 9:07 AM
>
>
> Hi,
>
> One of our customers has asked us to look at assembling smt components on
> ceramic substrate for them.  This is a process that we have no experience
> with. If anyone can offer information regarding this process, things to
> watch for, etc. it would be greatly appreciated.
>
> TIA
>
>                 Rick Thompson
>                 Ventura Electronics Assembly
>                 2665A Park Center Dr.
>                 Simi Valley, CA 93065
>
>             [log in to unmask]
>
>                 (805) 584-9858 voice
>                 (805) 584-1529 fax
>
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