Jeff,
Another material to consider would be Polyimide Glass which has a Tg
between 220 and 260C depending upon the grade of material selected.

Fine line/fine pitch should be OK if the temperatures do not change a
great deal.  If the temperature changes such that you get many cycles
then the coefficient of thermal expansion may be a problem.  You never
mentioned whether you were going to use plastic or ceramic components.
Your choice of laminate material may have to be based on the component
types you choose.  Tear dropping all via pads is a good idea especially
if you are using fine lines

Standard eutectic solder should be fine for this application.  We use it
all the time for these types of temperatures.  The primary thing you
need to be concerned with is the effect of wide changes in temperature
on the solder joint life due to thermal expansion.  If you are in a
stable, but hot environment then, then the thermal cycles will not be a
big problem.

Conformal coating materials should be evaluated at your temperature for
durability.  Some coatings may breakdown if exposed to high temperatures
for to long.  For instance polyurethane may start to harden, crack, and
discolor if exposed to high temperatures for to long.  Silicone coating
my stand up better but may provide problems when doing any rework
(assuming rework is a concern).

Bill Dieffenbacher
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Lockheed Martin Control Systems
600 Main St.  Rm R52F
Johnson City, NY  13790
Tel:   (607)770-2961
Fax:   (607)770-2056
Email:  [log in to unmask]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~


> ----------
> From:         McGlaughlin, Jeffrey A[SMTP:[log in to unmask]]
> Reply To:     DesignerCouncil E-Mail Forum.;McGlaughlin, Jeffrey A
> Sent:         Monday, February 16, 1998 1:25 PM
> To:   [log in to unmask]
> Subject:      [DC] High Temperature Environment
>
> To All -
>
> I am currently working on the design of a PWB that must continuously
> function (read as IPC-D-275 class 3) at ambient temperatures as high
> as
> 105 degrees C.  I am seeking input as to design criteria for this
> environment.
>
> The items I have already identified include:
>
> 200 degree C Tg FR-4/Gtek base material
> Conformal leaded parts where ever available
> No fine line / fine pitch design
> Teardrop at all drilled pads including vias
>
> My primary question is should we be using a "NO LEAD" finish and
> solder
> for these boards?
> Is there any thing I have overlooked?
>
> TIA
> Jeffrey McGlaughlin
> [log in to unmask]
> Battelle Memorial Institute
> Columbus Ohio
>
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