Hi Steve & All -

On the subject of used equipment - be extremely cautious.  A great deal of
the stuff sitting around moldering in warehouses will turn out to be
articles which have not had the best in maintenance, and may even be
suffering from a severe case of rot from previous usage.  These units can
generate small quanitities of HCl, which is removed by the acid stripper, if
the unit is properly maintained.  (I've seen quite a few that weren't.)  The
second issue, will obviously be the availabililty of repair/rebuild parts.
You may also find that these units have mechanical timers, which require a
fair amount of operator input to set-up and monitor.

Reflow fluid is only one issue, in the area of consumables.  The second is
the question of what containment media is used to prevent escape or major
loss of the reflow fluid.  In the days past, this was one of the freons
which has since gone out of production.  This freon blanket, was in turn
kept in place by a refrigeration or water cooling coil around the upper
third of the batch unit.  If you go forward with this effort, you will need
to be careful about the selection of a cover blanket media suitable for the
temperature of the refllow fluid.  Exhaust vent location and velocity also
needs to be set-up carefully - too high an airflow rate can siphon off the
cover blanket vapors, allowing loss of the primary fluid vapors.

We had a couple of experiences on a batch unit (using FC-70/FC-71), where
the temp controllers failed and ran the boil sump heaters wide open.  This
in turn overran the capability of the freon blanket to contain the reflow
vapors.  Fortunately, we had added some instrumentation around the units
upper lip and did a manual shut down without major problems.

I am not sure about the availability of solder pastes and fluxes for vapor
phase use.  This is another item which will need to be checked, since the
process is not in as high usage as it once was.

Regards - Kelly

-----Original Message-----
From: Stephen R. Gregory <[log in to unmask]>
To: [log in to unmask] <[log in to unmask]>
Date: Tuesday, March 21, 2000 7:47 PM
Subject: Re: [TN] Vapor Phase reflow chemicals and equipment..


>In a message dated 03/21/2000 6:46:27 PM Central Standard Time, Engelmaier
>writes:
>
>> Hi Steve,
>>  Downhole drilling electronics sees the most severe operational loading
of
>> any ellectronic assemblies. Design this stuff as robust as possible with
>the
>> least CTE-mismatch as possible, and be careful with the encapsulant
>material
>> chosen.
>>  Vapor phase soldering is a good idea; but, is there nothing between 253
>and
>> 215C?
>>  Good luck!
>>  Werner Engelmaier
>
>Hi Werner!
>
>Yeah, don't have tell me about how harsh an environment these boards will
>see, it's easy for anyone to imagine what these boards will go though. They
>go into a metal "tool" (about 9 boards per tool) that's about 8"-10" in
>diameter and about 10-feet long.
>
>The boards are very thin width-wise (less than 2-inches) and about a foot
>long. They are polyimide (I think) PCB's with a lot of copper in them. We
>don't control the designs, we're just gonna try and build them.
>
>After going back and looking at the Galden Fluids spec's, they do make a
>chemical that has a boiling point of 230 degrees C. I suppose with vapor
>phase you don't have to follow the standard guidelines for reflow profiling
>of hitting a peak of 20-30 degrees above liquidous of the alloy...that's
more
>for standard reflow equipment isn't it?
>
>With a chemical like the Galden HT230, I won't have to worry so much that
>there will be any temperature lags that one may see with convection or IR
>reflow....
>
>I'm still looking for equipment though...
>
>Thanks Werner!
>
>-Steve Gregory-
>
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