Jason et al

For my twopennorth, may I submit the following for consideration.

With the advent of BGA and other "difficult" components, it becomes
necessary to apply temperature excursions that may be 20 to 30 degrees C
 say 70 to 85 F ) over the alloy eutectic - whatever alloy that may be. The
reason being due to the thermal efficiencies of "assemblies" that include
such components and the need to ensure that eutectic is achieved on the
solder spheres (I hate the term solder balls as it has other connotations -
get out of the gutter!) located in the centre of the component.

The particular benefit of vapour phase, or "condensation soldering" using
its newest guise, or "anaerobic soldering" to be more correct, is that you
will achieve far more uniform and controlled soldering over the entire
assembly surfaces.

The Heat Transfer Fluids (HTFs) are available with various boiling points
and, as Brian has already pointed out, the physics are such that you cannot
(greatly) "overboil" them. We actually have 200C - 215C - 230C - 250C and
260C materials so they do exist but perhaps not readily within the US.

These HTFs are very expensive so it becomes extremely important, both from
the environmental and financial standpoint, to contain them as far as
possible. Systems do exist that minimise their loss by the use of a sealed
chamber which is emptied under partial vacuum.

Their particular advantage really "kicks-in" when you talk lead-free.
Because the eutectic of these alloys are mostly greater than tin-lead (tin,
copper silver is 224C), it becomes clear that these "difficult" components
may well be exposed to temperatures of around 260C by conventional means of
soldering; whereas with condensation soldering, they are limited to less
than 230C giving a deltaT of around 6C instead of 30C.

These NEW systems can be either batch or in-line via a discontinuous
process.

Regards,
Graham Naisbitt

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WEB: http://www.concoat.co.uk

CONCOAT Ltd
Alasan House, Albany Park
CAMBERLEY GU15 2PL UK

Tel: +44 (0) 1276 691100  Fax: +44 (0) 1276 691227
----- Original Message -----
From: Jason Gregory <[log in to unmask]>
To: <[log in to unmask]>
Sent: Wednesday, March 01, 2000 1:53 PM
Subject: [TN] vapor phase reflow


> Hello techies!
>
> I am looking for anyone who has performed any qualifications on the
advantages/disadvantages of vapor phase reflow. Particularly dealing with
higher temp alloys. Is it the way to go? Is convection better? Who are the
major manufacturers? Are silicon castments to keep the bottomside components
from falling off mandatory? Any replies are GREATLY appreciated.
>
> Jason Gregory
> Production Manager
> Electrospec
> (713)784-4900
> (713)784-1194 fax
>
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