[log in to unmask] asked:

>I have attended a few training sessions and vapor phase reflow has been
>discussed, but how much is this process used in production these days?
>Isn't the convection reflow process better, more cost efficient, etc.?
>Inquiring minds wish to know?

Makes a good foil to throw in for a minute to dazzle the audience.

It _is_ a "good process" in that it will provide consistent results and it
can heat a lot of work fairly quickly. The work cannot heat past the fluid
boiling point, so the max temp is restricted.

There are unique advantages - some "tank" type VP systems are gigantic, and
you simply lower the work (like an entire assembly the size of your desk)
into the vapor zone, wait a few seconds, and pull it back out.

Trouble is, the heating is very rapid. The fluid (typically a
perfluorinated FC) is boiled to a vapor, then when the work enters the
chamber, it condenses on the work, then drips back to the boiling liquid at
the bottom of the chamber. The phase change transfers the heat pretty
evenly to any surface contacting the vapor.

Some VP furnaces have two vapor zones (one with a lower boiling fluid), or
some other type of pre-heating to reduce the thermal shock to the work.

It is difficult to get the type of "profile" with VP which IR or convection
furnaces can provide. Typically, the conveyor rate is much slower, as the
vapor zone is pretty short.

The fluids are _very_ expensive, and there is some drag-out or unwanted
evaporation in most systems.

To answer your question, it seems to me that most of the industry has gone
away from it in favor of the convection furnace. I'd say cost, some
environmental concerns (greenhouse effect), ability to "profile", and
throughput are the main reasons.


regards,

Jerry Cupples - [log in to unmask]
Interphase Corporation
13800 Senlac Dr.
Dallas TX 75234
(214) 654-5150
(214) 654-5500 FAX


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