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'PCB Exposure Time.'
1998\05\11@055843 by Clewer,Brian

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Hi all,

I made a UV exposure unit for producing PCB's at the weekend.  It
consists of 2   8watt tubes inside an old PC case.  I have a photo
sensitive PCB held behind a glass plate about 1 and a half to two inches
above the tubes.  The tubes are brand new and are replacements for the
normal unit you can buy in the shops.

My question is 'how long would be a reasonable time for exposure' ,
because I tried this out last night with an exposure time of one minute
and when I was developing it in sodium hydroxide, it appeared to work at
first but it then took all the photo sensitive layer off.

Any help is appreciated,

Thanks,
Brian.

1998\05\11@061309 by Anders Eliasson

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I use a similar arangement with two tubes, but they are about 8 inches from
the board, and exposure time is about 5-6 minutes.

The concentration of the sodium hydroxide is also quite important...
I have found that about 5 grams in half a litre of water is about right.
You'll just have to experiment a bit to see what suites your equipment.

Cheers
Anders



At 10:52 1998-05-11 PDT, you wrote:
{Quote hidden}

1998\05\11@063002 by Keith Howell

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Clewer,Brian wrote:
>
> Hi all,
> I have a photo sensitive PCB held behind a glass plate

> it appeared to work at first but it then took all the
> photo sensitive layer off.

Errm, ordinary glass absorbs UV. The glass in UV EPROMs
is fused quartz (which doesn't).

Perhaps your glass plate is absorbing UV, hence the
uniformity of your etching.

Is your resist UV-softened or hardened?
This will dictate whether your symptoms are caused by
too much or too little UV.

1998\05\11@074021 by alex_holden

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Clewer,Brian wrote:
> I made a UV exposure unit for producing PCB's at the weekend.  It
> consists of 2   8watt tubes inside an old PC case.  I have a photo
> sensitive PCB held behind a glass plate about 1 and a half to two inches
> above the tubes.  The tubes are brand new and are replacements for the
> normal unit you can buy in the shops.
>
> My question is 'how long would be a reasonable time for exposure' ,
> because I tried this out last night with an exposure time of one minute
> and when I was developing it in sodium hydroxide, it appeared to work at
> first but it then took all the photo sensitive layer off.

Try more like two minutes exposure, and don't develop it for as long.
Your developer may also be too strong. Don't heat the developer either
(though it does help to heat the etchant a little, especially if you
don't have a bubble etch bath).

--
--------------- Linux- the choice of a GNU generation. --------------
: Alex Holden (M1CJD)- Caver, Programmer, Land Rover nut, Radio Ham :
---------- http://www.geocities.com/CapeCanaveral/Lab/1532/ ---------

1998\05\11@103210 by wwl

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On Mon, 11 May 1998 06:13:09 -0400, you wrote:

>I use a similar arangement with two tubes, but they are about 8 inches from
>the board, and exposure time is about 5-6 minutes.
This time is about right for various laminates and UV units
>The concentration of the sodium hydroxide is also quite important...
>I have found that about 5 grams in half a litre of water is about right.
>You'll just have to experiment a bit to see what suites your equipment.
Forget sodium hydroxide - it's utterly dreadful stuff for developing
PCBs - apart from it's causticity, it's very sensitive to both
temperature and concentration, and  made-up solution doesn't last
long.

I use a silicate based developer from Mega electronics (UK) - it comes
as a liquid concentrate. I normally make it up stronger than they
recommend (4 to 5 parts water to 1 part developer instead of 9:1) -
boards develop very cleanly in about 5 seconds, but most importantly,
it is VERY HARD to over-develop (i.e. strip) - you can leave a PCB in
'5 second' strength solution for as minute with no visible damage, so
variations in concentration/temp/different resists are very unlikely
to over-develop a PCB. Made-up solution lasts until it 'wears out' -
i.e. indefinite shelf life, and you can then just top up with
concentrate.
Mega electronics are on (+44)1233 893900, fax 893894 I don't know if
they have any outlets outside the UK. They do everything you'll ever
need for PCB making Order code for 1 litre concentrate is 600-010,
cost UKP 9.50 (96/7 catalogue)- this will last the avarage hobbyist a
lifetime.
Also available from Rapid Electronics(+44)206 751166 fax 751188 Email
spam_OUTsalesTakeThisOuTspamrapidelec.co.uk, order code  34-0790

For resist stripping I use methanol - drip a thin film onto the PCB,
wait 10 seconds and wipe off with a paper towel.
    ____                                                           ____
  _/ L_/  Mike Harrison / White Wing Logic / .....wwlKILLspamspam@spam@netcomuk.co.uk  _/ L_/
_/ W_/  Hardware & Software design / PCB Design / Consultancy  _/ W_/
/_W_/  Industrial / Computer Peripherals / Hazardous Area      /_W_/

1998\05\11@115522 by Peter L. Peres

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 You want a small film representing some of the features you want,
repeated a few times.

 A suitable film can be generated with a computer, with a postage stamp
sized design containing most features you are interested in reproducing,
repeated on a strip. 5 copies are enough, with each copy about 20x20 mm^2.

 Place a strip of sensitized board in the machine, put the film on it,
and use an opaque plate to cover all but one of the designs. Expose 1
minute, then move the opaque plate to have 2 designs exposed. Expose
another minute. The next exposure is 1 minute etc. The last exposure of 1
minute is without any cover.

 When you finish this, your strip will have the 1st design exposed 5
minutes, the 2nd 4 etc. Develop the board and inspect the designs with a
magnifying glass. Pick the best one. It helps if you draw squares on the
board before you start, and number them 1..5 with a felt tip pen
(indelible waterproof black). Each square should contain a copy of the
test pattern. Of course you can do it in the computer (but some brain-dead
board drawing programs won't let you). The lines and numbers will survive
the exposure and developing.

 You may have to move the lamps farther away. This will increase pattern
sharpness. Exposure times under 1 minute are critical on operator
precision with such equipment (do you use a timer ?).

 Develop the board according to the photo-resist's
manufacturer's indications, and keep an eye on the temperature and
concentration of the developer.

hope this helps,

Peter

1998\05\12@005631 by Leon Heller

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In message <35573B63@tarkus>, "Clewer,Brian"
<Brian.ClewerspamKILLspamTELEMATICS.COM> writes
>Hi all,
>
>I made a UV exposure unit for producing PCB's at the weekend.  It
>consists of 2   8watt tubes inside an old PC case.  I have a photo
>sensitive PCB held behind a glass plate about 1 and a half to two inches
>above the tubes.  The tubes are brand new and are replacements for the
>normal unit you can buy in the shops.
>
>My question is 'how long would be a reasonable time for exposure' ,
>because I tried this out last night with an exposure time of one minute
>and when I was developing it in sodium hydroxide, it appeared to work at
>first but it then took all the photo sensitive layer off.

You need to experiment - there are lots of variables, such as the
distance of the PCB from the tubes, the strength of the developer,
temperature, etc. I use perspex rather than glass in my UV exposure unit
(a modified cardboard box), and use a 6 min. exposure for a
transparency, and 7 min. for a print on tracing paper. Sodium
metasilicate has a lot more latitude than NaOH, when developing the
resist. I heat the developed PCB in the oven on a low setting to harden
the resist, prior to etching. I often use spray-on resist - if I cock
things up I just strip off the resist and try again.

Leon
--
Leon Heller: .....leonKILLspamspam.....lfheller.demon.co.uk http://www.lfheller.demon.co.uk
Amateur Radio Callsign G1HSM    Tel: +44 (0) 118 947 1424
See http://www.lfheller.demon.co.uk/dds.htm for details of my AD9850
DDS system. See " "/diy_dsp.htm for a simple DIY DSP ADSP-2104 system.

1998\05\12@074241 by Leo van Loon

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Dear Leon,

You are definitively using the wrong type of tubes. Short wavelength UV,
used for erasing EPROM's is not suitable for photosensitive PCB's.
Use for photosensitive PCB's tubes with the (Philips) color 05, with long
wavelength UV glass plates are no problem. With a distance of 2 cm of the
tubes to the PCB exposure time is 1-2 minutes, dependant of the transparency
of the masks. expose as long as possible, dependant of the density of he
print of the mask. I use calque drawing paper printed with a Deskjet 870
printer, and expose 90 seconds for optimum result.
Never use the concentration of the developer to shorten exposure time. Bad
PCB's will be the result.
Developing time must be about three minutes, a 1% sodium hydroxide solution,
always fresh made will work in most cases.

Look at http://www.thinktink.com for excellent information.

Leo van Loon
EraseMEsbb.simpeltronicsspam_OUTspamTakeThisOuTtip.nl

-----Oorspronkelijk bericht-----
Van: Leon Heller <leonspamspam_OUTLFHELLER.DEMON.CO.UK>
Aan: @spam@PICLISTKILLspamspamMITVMA.MIT.EDU <KILLspamPICLISTKILLspamspamMITVMA.MIT.EDU>
Datum: dinsdag 12 mei 1998 7:00
Onderwerp: Re: PCB Exposure Time.


{Quote hidden}

1998\05\14@213801 by scoll

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On 11-May-98, Clewer,Brian wrote:
>Hi all,

>I made a UV exposure unit for producing PCB's at the weekend.  It
>consists of 2   8watt tubes inside an old PC case.  I have a photo
>sensitive PCB held behind a glass plate about 1 and a half to two inches
>above the tubes.  The tubes are brand new and are replacements for the
>normal unit you can buy in the shops.

>My question is 'how long would be a reasonable time for exposure' ,
>because I tried this out last night with an exposure time of one minute
>and when I was developing it in sodium hydroxide, it appeared to work at
>first but it then took all the photo sensitive layer off.

>Any help is appreciated,

>Thanks,
>Brian.

I have built something similar and I normally use about 5-6 mins and develop
untill photo layer goes except where tracks are.


Steve

1998\05\14@213801 by scoll

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On 11-May-98, Clewer,Brian wrote:
>Hi all,

>I made a UV exposure unit for producing PCB's at the weekend.  It
>consists of 2   8watt tubes inside an old PC case.  I have a photo
>sensitive PCB held behind a glass plate about 1 and a half to two inches
>above the tubes.  The tubes are brand new and are replacements for the
>normal unit you can buy in the shops.

>My question is 'how long would be a reasonable time for exposure' ,
>because I tried this out last night with an exposure time of one minute
>and when I was developing it in sodium hydroxide, it appeared to work at
>first but it then took all the photo sensitive layer off.

>Any help is appreciated,

>Thanks,
>Brian.

I have built something similar and I normally use about 5-6 mins and develop
untill photo layer goes except where tracks are.


Steve

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