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'Kontakt Chemie Photopositiv: board coting & dust'
1998\10\30@125908 by Justin Crooks

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How about adding a little positive pressure to the plastic box.  Use one of
those dust mite filters and a small blower.  I used this in a
crystal-growing project in high school with good success.  To dry it,
you'll need a little circulation anyway.  It's not fancy, but it should
work for a home application.

>   It's me again ;). I am trying to use a Photopositive Photoresist by
> Kontakt Chemie to make a very small PIC board (stamp size) @home (well,
> almost). The leaflet says to keep the board away of dust for 24 hours.
> Whatever I do, the board collects dust like a magnet, even in a closed
> clean plastic box. I'm not going to set up an electronic grade clean room
> for this, so I'd like to have some input from others. I've thought of an
> ionizer air cleaner in the box (I have a module here).
>

1998\10\30@130123 by Paulo Soares

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I used this spray some 10 years ago and what I did was to cook it at 65C
(I think) for half an hour. The results where very acceptable dustwise.
The cooking was made in an electric cooker (those used for food with a
loop shaped resistance) and the temperature control was manual; I
switched it on and off according to an electronic thermometer (ah, ah)
that I made with an 1N4148 and a comparator that lighted a led when the
temperature was over 65C.
I did many boards this way (the things one does when we are young...).

Best Regards,
Paulo Soares

> {Original Message removed}

1998\10\30@155510 by Peter L. Peres

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Thanks Justin and Paolo,

 I'll try the positive pressure thing. Strange, I did read something
about surface charges building up on photoresist while drying. Wonder
where ?

Peter


'Kontakt Chemie Photopositiv: board coting & dust'
1998\11\03@104029 by Harri Suomalainen
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>  I'll try the positive pressure thing. Strange, I did read something
>about surface charges building up on photoresist while drying. Wonder
>where ?

Humm.. Never heard of that one. However, when spraying photoresist
through a small plastic nozzle it does get charged. (Static electricity)
I've always thought that is one definate reason why it attracts dust.

I think this problem is difficult to solve. Even spraying it inside
a box having slight over preassure and clean air is not simple to do,
however very possible with reasonable effort.

Cleaning the air inside the box is possible too with the aid of some
filters. You'd also need to pump in some clean air to get all vaporized
solvents out of there. And so on.

I'd just buy ready made boards with photoresist for high-quality boards.
For low-quality boards it is possible to spray them if you put them
into a *clean* container. Some errors will always occur so all dense
boards are definately out.



--
Harri Suomalainen     spam_OUThabaTakeThisOuTspamcc.hut.fi

We have phone numbers, why'd we need IP-numbers? - a person in a bus

1998\11\03@140312 by Peter L. Peres

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Thank you all who have answered,

 While it is true that it is better to but ready boards, this was a one
off, very small and on a board that needs so much machining that it is not
possible to do it with a precoated board.

 I have read about the surface charges in a semiconductor manufacturing
technology book. There is something about the solvent being polar or the
work of the solvent leaving the coating inducing charge just like the
spraying through the nozzle.

 What pisses me off is that I have used a REALLY clean box, that must
have had about 4 dust particles of eye-visible size in it when I closed it
with the board inside, and all 4 were on the board when I opened it a day
or so later.  Duh.

Peter

1998\11\03@220749 by Mark A Moss

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If you believe static to be attracting dust, use an ionizer.  They are
used in the clean room at work for just that purpose.  The type designed
to repel dust (the type used in clean rooms) may work better than the
type designed for ESD protection.

Mark Moss
Amateur Radio Operator, Technician, and General Tinkerer


On Tue, 3 Nov 1998 17:39:50 +0200 Harri Suomalainen <.....habaKILLspamspam@spam@CC.HUT.FI>
writes:
{Quote hidden}

Mark Moss
Amateur Radio Operator, Technician, and General Tinkerer

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1998\11\04@122400 by Peter L. Peres

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On Wed, 4 Nov 1998, Mark A Moss wrote:

> If you believe static to be attracting dust, use an ionizer.  They are
> used in the clean room at work for just that purpose.  The type designed
> to repel dust (the type used in clean rooms) may work better than the
> type designed for ESD protection.

The problem with an ionizer is oxygen + solvent vapor + corona discharge +
suitably closed box = big bang.

Peter

1998\11\05@034859 by Mark Willis

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Peter L. Peres wrote:
>
> On Wed, 4 Nov 1998, Mark A Moss wrote:
>
> > If you believe static to be attracting dust, use an ionizer.  They are
> > used in the clean room at work for just that purpose.  The type designed
> > to repel dust (the type used in clean rooms) may work better than the
> > type designed for ESD protection.
>
> The problem with an ionizer is oxygen + solvent vapor + corona discharge +
> suitably closed box = big bang.
>
> Peter

 Could you use the scheme used for tiny home-based clean glove boxes?

 Get a "Rainbow" vacuum cleaner, attach it to the box in a closed loop
scheme, with HEPA type filter;  After the vacuum cleaner should be an OK
place to put the ionizer, before the HEPA filter (with perhaps a
grounded grid just before the filter?) or something like that?

 One person does this with an old "printer silencer" box, and says that
the rainbox vacuum plus the filter does a really good job of getting the
inside of the box quite clean (He uses a clean air source to blow the
dust off anything he puts into the box, blowing it into the vacuum's air
intake.)  Really inexpensive (Except for the vacuum perhaps), he's
pretty happy with it.

 For a small box, you could try using "Canned Air", and a regular
vacuum, blow the box out, and get those last 4 specks out maybe (With
recirculating air through a filter of any sort, you'd be better off, it
sounds like.)

 Years ago, (back in the "Cold War" days) I joked with a friend about
using car engine air filters (Stacked atop each other) as air filters
for a fallout shelter - cheap, pretty robust, and nobody looks at you
strange if you buy a bunch of them <G>  I suspect that a car air filter
(even one of those lawnmower air filters with a foam pre-filter that you
soak with a dab of oil?) might be quite good for this job, too.  But
where to get the vacuum?  (And are they fine enough for YOUR dust? <G>)

 There's also some radio frequency air ionizer dealie (Can't remember
the brand name) that's "supposed to" work, but I don't know about it (Is
that what they use in clean rooms?  Or is that thing worthless?)

 Mark, .....mwillisKILLspamspam.....nwlink.com

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