Try it!!!! (Was - Re: One More PCB Dishwasher Question)

From: Bob Shannon <>
Date: Sat Dec 29 11:11:56 2001

I'm going to regret posting this, but...

TXCO's come from the factory with special caps you place over them while
they go through the soldering oven (modern boards don't get wave soldered anymore).

Failing to place these protective caps over the TXCO's when they go through the
wash cycle leads to a drifting oscillator that very often fails soon after its in
the field.

At Media 100 Inc, we make high-end video equipment, non-linear editors. We use
very fancy TXCO's, (+/-2 ppb) and they do not survive the wash cycle without very
special attention. ( I run the Test Engineering section at Media 100, and we have
learned these facts emperically, by collecting failure data for many years)

As the focus of the list is older machines, we need to keep things in mild like
paper roll caps, etc. Advising that running old boards through the dishwasher,
while sometimes safe, is not an absolutely safe thing to do.

I do agree that most often, semi-modern boards will survive the process, but there
are many components that will not. These components used to be much more common
than they are today. But as the discussion relates to this older technology, any
reccomendation to run the boards through a dishwasher should address the very real

How hot was the water? I don't know, its not something I can easily control. Is
is possible that the 'dishwashers' used for this function commercially have been
altered, and/or are connected to a lower temprature source of water? I do know
that dishes come out a bit too hot to handel unless you open the door and allow
them to cool.

I do know its a heck of a lot hotter than any bath, after all, there is a heater
element inside the dishwasher.

I'm not sure its a temprature issue, as some have assumed. A dishwasher may have
very powerful waterjets and a lot of vibration. The dammage may be mechanical,
possibly a bonding wire detachment.

But I'd like to point out once again that there are a good number of components
that will be dammaged by water. Some of these have been listed in posts here
already. If we accept that some components cannot be washed in this way, how can
anyone defend a blanket statement that using a dishwasher on a board will be safe
for that board?

Simply put, you cannot. Not unless you know eash and every component on that

All those tiny little pulse transfromers on your core memory sense amplifiers, do
you know those are able to withstand this treatment? Many are not fully
encapsulated, and would not be safe to treat this way. Some components (like
crystals, not oscillators, just quartz crystals) cannot even be soldered safely,
and are socketed for this reason. Is it s good idea to run these through your

Lastly, storage tempratures do not assume a condensing environment, much less
pressurized water jets at high tempratures, and high vibration levels. The safe
storage temprature specification does not really apply here. The inability of some
components to survive a water bath is.

So lets agree on this...

If your sure no components will be effected, go ahead and try your dishwasher. If
your not absolutely sure, or if replacement parts are hard to get, don't take the
risk, and use a little IPA and some elbow grease to clean your boards.
Received on Sat Dec 29 2001 - 11:11:56 GMT

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