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'[OT] PCB exposure unit'
1999\04\25@232945 by Eric Oliver

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Hi,

I've been slowly researching what I'll need to build decent PCBs at home.
I found some plans for an etchant tank on the Net but I can't find any
decent info on building an exposure unit.

I already have a wooden box roughly 24" square with a lid, all of it lined
with 1/4" reflective insulation that I built for brewing beer.  I thought
this box would be ideal but I'm not sure what type of UV lights I need, how
many I should use, how far from the PCB they should be, best way of
supporting the PCB above the lights, how long the PCB should be exposed,
etc., etc.

I would appreciate any guidance from those that have been there and done
that ..


Thanks,
Eric

1999\04\26@042651 by Benjamin Petersen

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part 0 3414 bytes
I were undergoing the same problems as you 2 month ago.. I'll tell you what I did...

1. I bought a BlackLight tube ($30) + armature ($10)..
2. First I bought some technical drawing paper, for $15 and was laser printing the PCB on to that but the Black toner wasn't good enough. Not even in I was printing it twice.. (bad bad boy). Then I was printing on a transparent with a HP inkjet. I think the quality was okay the first time (I think) but I gave it an other ink exposure. Remember to (if you can) set the printer options to transparent, this will use more ink, but I can assure you that you will be pleased with the result. I don't know if it matters, but I turned off the night while exposing the pcb to uv. I gave it a doses of 7 minutes, (on each side since I was making a double sided pcb). If you are doing a double side you can print each side on a transparent and tape them together in the corners. Then you will get a very precise result (very important since say 0.2-0.3 mm is a lot on the other side. Remember to print page two in mirror, then flip the page so that the ink touches the pcb. In this case no light will go between. Even if you don't think it means anything, I can tell you that it does. But only if you are routing with small lines (say 1 mm)... But do it anyway if you can.. Again if the pcb is double, remove the black protection paper from both sides of the pcb. Slide the pcb in between the two (taped in the corners) transparent. Tape (use clear tape) the pcb to the lower transparent from the inside and only in the corners of the pcb. Only use as little tape as possible, but enough so you can flip the whole part without movement of the pcb. I was using euro-sized pcbs. I places the blacklight on two times two (that's 10 cm together) phone books on a table and placed the tube on it (so it would lit down on the table) then I placed the transparent (with the pcb inside) on the table. On top of the transparent I placed a piece of glass (you should use plexi-glass (plastic) because it doesn't reflect as much) just to help pressing the transparent towards the pcb. Turn on the UV lamp and set your timer to 7 minuts (remember to start :). BRRRRRRING... Flip the transparent (if needed) and repeat.
3. To develop/etcher the pcb, I to it the hard core and speedy way (and VERY toxic) I use... (I'll tell you if you ask). But it only take about 2 minutes.... Do it outside !!!!

There are a few things you can do to make a good result besides using the uv stuff... You can get something called Toner transfer system. It's like a piece of paper that you laser print on and iron it onto the pcb. I have never used, but I am sure that if I had the chance it  would have saved me step one and two... It's not that cheap, but then again.... Please mail me if I can help you with something.. I am sure that other people are doing different than me but this works best for me. If your laser printer prints VERY black you can use something called UTOPLEX (UTOPLEX 889 I think) it's not completely transparent but that's actually ok... To see if whatever method is working for you hold the transparent/utoplex against a window if any light goes trough the black part so will the uv... Small holes are accepted (at least I do).


Benjamin Petersen
Mark Product A/S
Maglebjergvej 11
DK-2800 Lyngby
Phone (+45) 45 93 98 80 ext. 50
Fax (+45) 45 93 18 11
E-mail spam_OUTbenjaminTakeThisOuTspammark-info.com



1999\04\26@071245 by Pavel Korensky

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Hello,

>I already have a wooden box roughly 24" square with a lid, all of it lined
>with 1/4" reflective insulation that I built for brewing beer.  I thought
>this box would be ideal but I'm not sure what type of UV lights I need, how
>many I should use, how far from the PCB they should be, best way of
>supporting the PCB above the lights, how long the PCB should be exposed,
>etc., etc.

The box I build myself is approx. 30x20 cm, high is around 10 cm. Mine is
constructed from aluminium "L" profiles and plywood. But it is really not
important.
I simply bought the UV lights and starters from RS Electronic (http://www.rs.co.uk
or similar). For mounting of light tubes, starters and transformer, I used
the plastic fixtures from old neon lights.
I am using 4 UV tubes with approx. 5 cm space between them. PCB is approx.
5 cm above lights and I expose it 4-5 minutes. The exposition time needs
some experiments. AFAIK, not all PCB materials are the same.
As a timer, I am using small compact unit with PIC16F84,LED display,
buttons and relay, which is built in this box.

Best regards

PavelK

**************************************************************************
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* DATOR3 LAN Services spol. s r.o.ÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊ *
* Styblova 13, 140 00, Prague 4, Czech Republic      ÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊ *
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**************************************************************************

1999\04\26@091709 by Lawrence Lile

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Kepro  .....keproKILLspamspam@spam@worldnet.att.net   1-800-325-3878  will sell you anything you
need to make PCBs, from a UV lamp (which you need bad) to photosensetized
boards in single quantities, to a Lanier Photoplotter ($10,000) and complete
plated thru hole system ($25,000) .  They have a great pamphlet titled "how
to make printed circuit boards" that goes step by step on how to use thier
simplest equipment.

My PCB setup includes a UV exposure frame (in the print shop next door)  A
plastic bucket, inside it a deep plastic tray that holds a gallon of ferric
chloride.  I heat it all with a hair dryer to about 40 C, and bubble air
through the etch tank with an air compressor, some aquarium tubing, and a
length of fiberglass tube that lets the bubbles out.  It will etch a board
in five minutes flat with fresh etchant.  It is all homemade, and I use it
to make really professional prototypes.

For quick runs I plot negative gerbers onto clear mylar with a laser
printer.  For exact physical sizes I send a gerber file out to a house and
have it photoplotted for a nominal fee.

If you want to discuss this topic more, let's take it offline - many folks
on the List are kind of bored with it.  (Not me!)

-- Lawrence

{Original Message removed}

1999\04\26@120732 by Stuart Meier

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Eric

I ended up buying a commercial one, and I think you will get replies to
this. However the PIClist archive does have threads in it about this. Now,
Ive just searched for a URL, and dammit I can't find one. Isuggest you
private email Mark Willis who will I am sure direct you

OTH, can you direct me where you found stuff on etchant tanks?
I just use an old icecream tub sitting in ahot water bath...

Stuart Meier
{Original Message removed}

1999\04\26@135802 by Nick Taylor

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Stuart Meier wrote:
<snip>
> OTH, can you direct me where you found stuff on etchant tanks?
> I just use an old icecream tub sitting in ahot water bath...

Stuart:

Jim Fong has a nice etchant tank and instructions on:
   http://www.hooked.net/~jfong/etchant.html

- - - Nick - - -

1999\04\26@150441 by Gabriel Gonzalez

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Here you will find all you need to know:

http://www.thinktink.com/


Gabriel


-----Original Message-----
From: Eric Oliver <ericspamKILLspamKEDCOENT.COM>
To: .....PICLISTKILLspamspam.....MITVMA.MIT.EDU <EraseMEPICLISTspam_OUTspamTakeThisOuTMITVMA.MIT.EDU>
Date: Sunday, April 25, 1999 10:24 PM
Subject: [OT] PCB exposure unit


{Quote hidden}

1999\04\26@171901 by Eric Oliver

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Stuart,

This link that Nick Taylor gave is the same one I was referring to :

http://www.hooked.net/~jfong/etchant.html

Eric

1999\04\26@184650 by Tony Nixon

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Nick Taylor wrote:
>
> Jim Fong has a nice etchant tank and instructions on:
>     http://www.hooked.net/~jfong/etchant.html

Why bother with a setup like that.

My method is about as simple as you can get and it uses no power, works
just as fast, if not faster, and does not smear fine artwork. Costs
peanuts too.

See http://www.picnpoke.com/projects/pcb.html

--
Best regards

Tony

PicNPoke - Multimedia 16F84 Beginners PIC Tools.

http://www.picnpoke.com
Email picnpokespamspam_OUTcdi.com.au

1999\04\27@002024 by Graeme Smith

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On this same topic....

I have been wondering, if it would be possible to get a UV exposure
system going on my Logical Devices Eprom Eraser....

The idea I came up with was to do something to increase the
coverage of the light by putting some sort of reflecter behind the bulb.
I noticed that placement of the chips was important to recover from
that pesky "configuration bit not blank" message, which suggests that
the buff box, does not have even coverage for reflective rays.

I have been assured that the UV eraser bulbs tend to be the wrong
frequency for Photo-etching, but it seems likely that I could change
the bulb, or have both bulbs in the same case, and simply switch back and
forth on a toggle switch.

This would mean that I could expose card sized circuit boards for the cost
of the bulb, and circuitry to connect it. I thought of using Aluminum Foil
as the difuser/reflecter, but I am unsure about its reflective
frequencies.

A freind suggested that it would be much better at UV, than silver, which
for some reason, he figures is transparent at those frequencies.

Anyways, does anyone see any reason why I COULDN't rebuild my current box
into a combinatoin exposure system?

                               GREY

GRAEME SMITH                         email: @spam@grysmithKILLspamspamfreenet.edmonton.ab.ca
YMCA Edmonton

Address has changed with little warning!
(I moved across the hall! :) )

Email will remain constant... at least for now.

1999\04\27@042844 by Benjamin Petersen

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part 0 378 bytes
On this same topic....

I have been assured that the UV eraser bulbs tend to be the wrong
frequency for Photo-etching, .............

Anyways, does anyone see any reason why I COULDN't rebuild my current box
into a combinatoin exposure system?

I had an UV eraser, and even if PCB was exposed only for 30 sec, it was to much.
...So I use BlackLight.

Regards
Benjamin Petersen

1999\04\27@043920 by Benjamin Petersen

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Why bother with a setup like that.

My method is about as simple as you can get and it uses no power, works
just as fast, if not faster, and does not smear fine artwork. Costs
peanuts too.

See http://www.picnpoke.com/projects/pcb.html

It might just be me but I think Ferric Chloride sucks...

Regards
Benjamin Petersen


1999\04\27@044541 by Michael Rigby-Jones

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{Quote hidden}

If over-exposure is a serious problem, maybe you could put a piece of smoked
perspex between the tube and the PCB to attenuate the light?

Regards

Mike Rigby-Jones

1999\04\27@064411 by Leo van Loon

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Both UV and blacklight tubes are wrong. Use Philips colour 05 or Osram
colour 70. Tubes at 3 cm, 1 min exposure and you get a perfect PCB.

Use cupric chloride/hydrogen peroxide/hydrochloric acid as etchant. Clean,
stable, infinite life, cause you can regenerate it time after time.

Leo van Loon
SBB simpeltronics
Netherlands
tel +31 (0481) 450034
fax+31 (0481) 450051
mail spamBeGonesbb.simpeltronspamBeGonespamtip.nl
url http://www.sbb-simpeltronics.nl
SBB simpeltronics ontwikkelt technische projecten voor basisschool en
basisvorming.
SBB simpeltronics develops technical projects for children in primary and
secondary education.



{Quote hidden}

1999\04\27@070711 by Benjamin Petersen

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>Use cupric chloride/hydrogen peroxide/hydrochloric acid as etchant. Clean,
>stable, infinite life, cause you can regenerate it time after time.

Regards
 Benjamin

1999\04\27@085548 by Julian Fine

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Use the Greatest souce of ultra violet the SUN.
With positive 20 only 1 to 2 minutes in the sun is all you need unless you
stay in some place where you dont have much sunlight then experiment with
exposure times.

By the way this only works during daylight hours ( HeHe)

************* Julian Fine ***********
********** TakeThisOuTjulianEraseMEspamspam_OUTfine.co.za ********
******* http://www.fine.co.za *******
** http://www.eagle-wireless.co.za **

1999\04\27@092555 by Benjamin Petersen

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> Use the Greatest souce of ultra violet the SUN.
> With positive 20 only 1 to 2 minutes in the sun is all you
> need unless you
> stay in some place where you dont have much sunlight then
> experiment with
> exposure times.

Is positive 20 a spray ?

Regards
Benjamin Petersen

1999\04\27@132454 by Julian Fine

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Hi
>Is positive 20 a spray ?
>
>Regards
>Benjamin Petersen
>

Yes it is I think They spell it positiv 20 and it should be available at
most electronic shops.

************* Julian Fine ***********
********** RemoveMEjulianspamTakeThisOuTfine.co.za ********
******* http://www.fine.co.za *******
** http://www.eagle-wireless.co.za **

1999\04\27@191512 by mkinga

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I could talk for hours on my experience of building PCB's over the last 5 years
or so, but the basics are :-

For tubes, find a company who sells commercial units and buy spare tubes from th
em, you'll also need fluorescent starters and a ballast suitable for the
tubes. My unit uses two 8 watt tubes, the PCB is supported by a glass sheet abou
t 3 cm above the tubes.

Exposure time can vary depending on resist type and age (and to an extent tube a
ge), if you can, make a test strip and expose at 1 minute intervals to
determine the optimum time. (as a rough guide I usually have to expose a board f
or 3 to 5 minutes).

If your hoping for particularly fine track widths, place the artwork PRINT SIDE
DOWN onto the PCB this minimises light leakage through the film, also make
sure the board and artwork are pressed down firmly onto the glass (on my unit th
ere's some foam rubber on the lid for this). Ensure that the glass is
clean.

For REALLY good results, print the artwork at 200% scale (or as large as you can
manage, but make a note of the scaling factor), then take the artwork to
a printers and get them to accurately photo reduce it onto film, this produces a
very dense black artwork with any "roughness" smoothed out by the
reduction process. Note though, this can be expensive so I only use it for "spec
ials"

For etching I no longer use ferric chloride (horrible stuff). I use a white powd
er which on the container says it's "Sodium Persulphate/Sodium
Bisulphate", it has to be used hot and takes longer, but because of this produce
s less under-etch of tracks, so again finer track widths can be produced.

I actually find the most difficult part of making PCB's is accurate and fast dri
lling, so I put a small CCD video camera module under my drill stand with
the lens adjusted to focus it close up, with the board placed on the drill stand
upside down, I can view the magnified pads on a monitor and drill them
very accurately with a cross hair on the monitor.

As all this isn't strictly PIC related, if you've got any further questions feel
free to EMail me.

Martin.

1999\04\28@004703 by kypros.vassiliou

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Graeme Smith wrote:
{Quote hidden}

Hi,
For the exposure of my PCBs I do use a self made exposure unit consist
of the following:
2 fluorescent tubes (non UV but the standard one) 1,5 feet long encolsed
in a white (painted) wooden box which is size so it can accommodate the
lambs and their control gear (starter,chock etc.). The box has about
15cm hight and on top there is a 4mm thick glass.
The exposure time depends on the thickness of the photosensitive spray
but my standart time (by experience) is between 8 and 10 minutes.
There is no need for pure UV light since the photoresist is sensitive to
visible light (around blue light).
The advantage of the long exposure time, the system takes, is that 1 or
2 minutes of overexposure it is not critical.

Regards
Kypros

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