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Subject:
From:
Gary Camac <[log in to unmask]>
Reply To:
TechNet E-Mail Forum.
Date:
Wed, 5 Apr 2000 13:48:50 -0500
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Joel,

I have found over the years that high velocity warm air will get a board pretty dry.  It
takes a lot of IR energy to vaporize all of the water off an assembly.  We are running an
older model Trieber (hey Ed) that starts its dryer section with a 10 HP driven Paxton
blower, followed by one 18" section of IR lamps (three above and three below), and then a
5 HP final air knife.  I know the temperature doesn't get above 180 F, because there is a
temperature sensor that shuts the system down at that temp.

I wouldn't want to say I'm bone dry at the exit, after all, bone dry in Florida isn't the
same as it is in say, Arizona.  However, if you tap the edge of one of our assemblies, you
won't see water appear.

On another point, you might well see failures at ICT if you test after coming right out of
the drier.  We have seen false failures at ICT when the parts (capacitors in particular)
have not been allowed to come towards ambient.  I suppose the limits of the ICT could
include allowances for the cap's temperature coefficient.  I'm not sure that we have ever
tried that approach.

Good Luck
Gary Camac

Joel Brock wrote:

> We are working on Continuous Flow.  However, we have a problem with wet PCBs.
> We would like to go directly from our Wave Washer to two Final Assembly steps
> and then over ICT.  We currently are evaluating an Electrovert Aquastorm 100
> Washer with four dry stations:
>
>     Dry Station # 1 - 15 hp Electrosonic Air Knives
>     Dry Station # 2 - 7.5 hp Electrosonic Air Knives
>     Dry Station # 3 - 7.5 hp Electrosonic Air Knives
>     Dry Station # 4 - 7.5 hp Standard Air Knives & IR Heat
>
> We still have problems with wet PCBs, especially connectors and tape.
>
> I have been told that IR Heat does nothing to dry out PCBs.  From those that I
> have talked to, it appears that "bone dry" PCBs comes from hot air only (around
> 200 F or higher), unless you bake (we prefer something inline).
>
> I have seen and tested PCBs in a TREK Vulcan Drying Tunnel (reaches 320 F, which
> we would not dream of going that high).  I have also been following leads on a
> custom Drying Tunnel that Technical Devices has built before, which takes their
> Washer Dry Stations and adds heating elements to the Air Knives (reaches around
> 200 F) in a stand alone inline unit.
>
> Does anyone know of any other options or have any advice?
>
> Thanks!
> Joel
>
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