Sourcing a UV Exposure Box for PCB Development.

0. Introduction
1. What's For Sale?
2. Ultraviolet exposure unit with timer 202E
3. Ultraviolet exposure unit with timer 202E - Starter Kit
4. UV tubes available on eBay
5. Flight case style enclosures
6. Minimum parts required
7. Conclusion
8. More
9. Developer Crystals - Rapid 34-0395
10. Immerse Tin Crystals - Rapid 34-0775
11. Copper Etchant - Rapid 87-0722
12. Chemical Storage Requirements
13. Processing Tray Areas cm'3

0. Introduction
I wish to start developing PCBs using the Photoresist and UV Development method.  In the past I have used a Dalo pen and drawn everything out, using ferric cloride to etch the copper off.  I would like to design more complex circuits on a PC and print to transparancies.

The immiediate requirement is to source a UV Development box.  There are two options; Build One; Buy One.  When considering building one the light output has to be in the range of 400nM.  There is absolutely no point in approaching DIY outlets as they have haven't a clue what you're talking about (I've been out hunting today).  Blacklight dark UV tubes for making your white t-shirt glow are NOT suitable.

UV LEDs have been suggested as a possibility.  These would need to be of a high candle output documented to be in the region of 5000-7000mcd, these can only be economically sourced from Hong Kong.  There is a documented concern that UV LEDs placed in a grid fashion will result in exposure hot spots on the resulting PCBs.  The projects are documented on the net, yet there are no examples of the PCBs which have been produced.  This is a natural concern despite excitement in using such devices.  It would be brilliant to have a compact UV light box.

1. What's For Sale?
There are very few UV boxes out there.  The most basic are about 120 all in, ranging to 1000's for double sided vaccum models.

There are very many UV tubes for sale on eBay.  UV LEDs are also available.

2. Ultraviolet exposure unit with timer 202E
This is sold by Rapid for 115.68 (98.39+VAT) item number 34-0700.  It is also sold by Maplin for 105.14 (inc. VAT) item number YA36P.  It uses a 6-minute mechanical timer.  It uses two 8W 12" (304mm) tubes, 15" maybe??.  The exposure area is 240 x 165mm (9.5 x 9.5").  The overall unit dimensions are 438 x 184 x 102mm (17 x 7 x 4").

3. Ultraviolet exposure unit with timer 202E - Starter Kit
This is available from Rapid for 129.54 (110.25+VAT) item number 34-0690.  It includes a number of accessories making a saving of about 20 if bought seperately.  It is Kit B.

These accessories are;

     Rapid    Quantity  Description                     Unit     Sub    (inc.VAT)
     -----    --------  -----------                     ----     ---    ---------

    34-0796     (1)     Artwork Drafting Pack           4.95   4.95
                (6)     Assorted Sheet Transfer         -----
    34-0105     (3)     100 x 160mm SS Photo PCB        2.49   7.47
    34-0115     (1)     203 x 114mm SS Photo PCB        3.49   3.49
    34-0295     (1)     Polifix Block                   1.95   1.95
    34-0745     (1)     Polypropylene Chemical Tray     -----
    34-0395     (2)     Developer Crystals              0.79   1.58
    34-0385     (1)     Seno GS Etching Kit             8.95   8.95
                                                               28.39    (33.36)

    34-0700     (1)     UV Exposure Unit - 202E                98.39   (115.68)
                                                              126.78   (148.97)

A saving of some 20 is made as predicted.  When offset against the standalone cost of a 202E, the above items are provided for an imaginary cost of some 10.

4. UV tubes available on eBay
A wide range of UV tubes are available.  Most are marketed for use with Fly Killer devices and for curing Acrylic Nails in beauty salons.

4W 6" (152mm) straight tubes;

9W 6" (152mm) nail curing double tubes;

25W 9" (229mm) U tubes;

22W 8" (203mm) Circular tubes;

5. Flight case style enclosures
It would be intended to fit a self build unit into a small flight case.  These are relatively expensive to buy.  I have a small case here which is 283 x 235 x 90 (11" x 9" x 3.5") external dimensions, it was purchased for 9.99 and contains a hobby drill.  It seems that to obtain the smaller flight cases it is economically easier to buy something else and to use it's presentation case, thus discarding it's contents.  Makeup boxes, hairdryers, all sorts of low priced items come in perfectly adequate aluminium flight cases.

My full size budget flight case which can be bought for 11 in a local DIY store has external dimensions of; 464 x 328 x 150mm (18 x 13 x 6").  It is made as cheaply as possible yet you could not achieve that level of build yourself without significant outlay.

6. Minimum parts required
This is assuming use of a full size budget flight case, with basic ON/OFF operation;

              Quantity  Description                     Unit     Sub    (inc.VAT)
              --------  -----------                     ----     ---    ---------

                (1)     Flight case                    11.00  11.00
                (4)     12" UV tubes                    5.00  20.00
                (4)     Starters                        1.00   4.00
                (2)     Ballasts                        7.50  15.00
                (1)     Rocker ON/OFF Switch            1.00   1.00
                (1)     IEC 3-pin socket                2.00   2.00
                (1)     4mm Cut glass (local)           5.00   5.00
                (1)     Other unknowns (fixings etc.)  20.00  20.00
                (1)     Travelling costs               15.00  15.00
                                                               93.00    (NA)

The above does not take into consideration PCBs, developer etc.  It appears cost effective to buy the UV 202E kit from Rapid for an approximate 35 extra.  The above also does not take into account stress and rushing about.  I could have the kit on this coming Tuesday after the Easter bank holiday weekend.         

7. Conclusion
It will be more practical and straightforward to buy the complete kit for 129.54 (110.25+VAT) item number 34-0690, from Rapid.  At this early stage in my experiences with UV development it makes sense to buy a prepared kit with instructions where it is all there for you from the moment go.

Having spoken to my Mother who knows everything her comment is, "You're just like your bloody Grandfather, you'd lick a farthing out of a turd."  In other words, buy the kit.

8. More
RD WIDE MOUTH BOTTLE 250ML (HD) (RE)            14-2014    (2)       0.42      0.42
RD WIDE MOUTH BOTTLE 100ML (HD) (RE)            14-2012    (2)       0.40      0.40
PHOTOETCH PCB SS 100 X 160 (RC)                 34-0105    (3)       2.49      7.47
PHOTOETCH PCB DS 100 X 160 (RC)                 34-0125    (1)       2.95      2.95
POLIFIX BLOCK (RE)                              34-0295    (1)       1.95      1.95
JETSTAR A4 10 SHEET PACK (RE)                   39-0780    (1)       5.50      5.50
GREEN FILL LAB THERM -10/110 (150MM)(RE)        85-2652    (1)       0.95      0.95
IMMERSE TIN CRYSTALS (RE)                       34-0775    (1)      12.65     12.65
DEVELOPER CRYSTALS (RE)                         34-0395    (2)       0.79      0.79

9. Developer Crystals - Rapid 34-0395
"Fotoboard (1) and FPC 16 (1) - Mix the powder with hot tap water (50'C) until all the crystals have disolved at the rate of 50g per litre.  Allow solution to cool down and use between 20'C - 25'C.

Fotoboard (1) and FPC 16 (1) - If the above concentrations are used the resist will develop very quickly.  Do not over-develop.  Normally no more than 30 seconds is needed when the board should be rinsed immiediately.  Above concentrations can also be reduced by up to a half for longer developing time therefore greater safety margins.  However reducing developer strength may result in the solution having a short working life.

* Available either in dry crystalline form, sufficient to produce 500ml solution (1 litre when used with Fotoboard 2), or as 1 litre of concentrate, to make 10 litres of working solution (20 litres when used with Fotoboard 2)
* Developer gives a long tank life and fast developing time
* The shelf life of the solution is considerably greater than the crystalline form and should be kept in undiluted form in an airtight container
* Safe to use: contains no sodium hydroxide
* Suitable for use in our tanks 34-0764 and 34-0765"

My crystals we have here are sufficiant to make 1 litre of solution for use with the Fotoboard 2 which we are using.  The weight of a single packet is 25 grams.  Disolve in hot water at a temperature of 50'C, allow to return to room temperature;

        Weight  Fotoboard (1)   Fotoboard (2)
        ------  -------------   -------------
         25g    ....500ml....   ...1000ml....
         12.5g  ....250ml....   ....500ml....
         10g    ....200ml....   ....400ml....
          7.5g  ....150ml....   ....300ml....
          5g    ....100ml....   ....200ml....

10. Immerse Tin Crystals - Rapid 34-0775
"90 grams makes 1 litre - Fill the container containing the powder with hot tap water (50'C).  Replace the top and shake thoroughly to ensure all the powder has dissolved.  Allow solution to cool down to room temperature when it will be ready for use.  Thoroughly scrub clean then rinse copper surface.  Immerse board in solution for 15-30 mins.  Remove and wash thoroughly firstly in cold water then hot.  Finally dry with tissues or paper towels.  Mixed solution should be stored in an airtight container or PCB processing tank with a lid.

* Powder is mixed with warm 50C water, allowed to cool and used at room temperature
* No heated tanks are required
* Low operating temperature allows very small tin molecules to be deposited, giving a very smooth and hard surface
* The longer the board is left immersed, the thicker the deposit
* 1.5 to 2.0 microns in 30 minutes and 4.5 microns in up to 2 hours
* Solution will last up to six months, unmixed powder has unlimited shelf life
* Available in 90g (1 litre) or 450g (5 litres) packs
* Sufficient to cover 0.6m or 2.7m of boards"

We need to make up only the solution that is required.  We have 90 grams of crystals.  A 90 gram container costs 13.28 inclusive;

        Weight    Solution       Cost
        ------  -------------   ------
         90g    ...1000ml....   13.28
         45g    ....500ml....    6.64
         22.5g  ....250ml....    3.32
         11.5g  ....125ml....    1.66
         10g    ....110ml....    1.48
          5g    .....55ml....    0.74
          4.5g  .....50ml....    0.66

11. Copper Etchant - Rapid 87-0722
"Disolve the crystals in 250ml of warm water in a plastic or glass vessel, or in an etching tank.  Stir to dissolve and agitate flow of solution over board being etched.  Solution can be re-used and as it becomes weaker heating will increase it's life.  Contents are sufficient for a total amount of 500ml (1 pint) of solution.

* Provides reasonably safe etchant when combined with warm water
* Supplied in 250g bags"

This is a 250g pack sufficiant to make 500ml of solution.  Disolve 250g of crystals in 250ml of warm water.

        Weight  Water  Solution
        ------  -----  --------
         250g   250ml    500ml    
         125g   125ml    250ml
          50g    50ml    100ml

12. Chemical Storage Requirements
The Immerse Tin Crystals will require..  One 250ml bottle for the solution.  One 100ml container for the remaining crystals.

The Copper Etchant will require..  One 250ml bottle for the solution.  One 250ml container for the remaining crystals.

The Developer will require..  One 250ml bottle for the solution.  The remainer of crystals to be stored in original packaging.

An accurate measuring jug is now required.

13. Processing Tray Areas cm'3
My issue with so many of the processing trays is that they're just so big.  If you're working with a small 3 x 4" PCB then alot of the solution will be wasted.  This examines how much solution is required for a particular area of tray.  Most liquids are metric based 1ml = 1g.  A litre of liquid will generally weigh 1Kg and displace an area of 1000cm'2.  A processing tray is 25 x 30 x 5cm.
        Width   Length   CM'2     Depth    CM'3      ml
        -----   -----   ------    -----   ------    -----
         10cm    10cm   100cm'2    3cm    300cm'3   300ml
          8cm    11cm    88cm'2    2cm    176cm'3   176ml
          8cm    11cm    88cm'2    3cm    264cm'3   264ml
         25cm    30cm   750cm'2    5cm   3750cm'3   3.75l

The largest board we can work with (due to software limitations) is 3 x 4' (7.62 x 10.16cm).  Ideally a processing tray would have a flat interior base.