Paul

There are two questions to consider here:
1. the quality of the components (it is not unknown for unsealed
components to be supplied, in place of sealed ones -- with all due
respect, purchasing guys are often unaware of the difference and they
see that there are physically identical units available at 5 cents less,
each. This is a constant problem with pots and, if the supplier
guarantees that they are designed to withstand cleaning, then it must be
taken up with him. If he doesn't, then change the supplier.)
2. the cleaning process (it is useful to know that it is better to have
each stage about 5°C hotter than the previous one, to create an
environment where the air in the component expands throughout the
process. It has been found that a very small drop in temperature can
sometimes contract the air sufficiently that water is drawn in, past the
O-ring. Also, make sure that wash chemicals, such as saponifiers, are
compatible with the O-ring material.)

Brian

Paul Truit wrote:
>
> I wanted to hear how fellow Technet people are processing surface mount
> potentiometers.
>
> I have experienced some field failures recently in this area.  Water has
> leaked into a "Sealed" potentiometer.  When power is applied an
> alternate circuit grows inside the pot causing the part to fail.
>
> We are processing this part using an OA solder paste through a normal
> pick and place operation.  Reflow profile takes this through a normal
> reflow curve Max. Peak temperature of 195-205 degrees C with a Ramp rate
> of 2-2.5 Degrees C.  We then add on a few through hole parts through
> progressive assembly then  wave solder and clean the assembly.
>
> We are utilizing an Electrovert Aquastorm 100.  We process the boards
> through at 4 feet per minute.  Water temperature is 145 degrees F.
>
> We have been cleaning boards (and potentiometers) for over eight years
> with never a problem.  This one has sure surprised me.  Just wondering
> if anyone else has had any experience with this and what they have done
> to fix this other than hand soldering the pot on in final.
>
> --
> Paul Truit, Mfg. Eng.
> RBB Systems, Inc.
> 4265C E. Lincolnway
> Wooster, OH  44691
> Ph. (330) 567-2906 ext 514
> Fax (330) 263-5324
> Email: [log in to unmask]
>
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