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This Instructable is to accompany a demonstration to be given to Ipswich (UK) Makerspace in May 2014, but might be of interest to any would-be PCB producers, particularly based in the UK (due to the sourcing of materials).

It is a 'photographic' system, using pre-sensitised boards (4" x 6" at £2-40 including VAT and delivery) and a laser printer for the printing of the PCB layout image. The final results are suitable for very fine PCB tracks.

The total cost, from scratch, for all the tools and equipment is less than £25. This then sets up the whole process, enabling boards to be produced for the cost of the pre-sensitised boards themselves.

This Instructable covers the purchase of the UV light source, the chemicals, and the pre-sensitised PCB. It then details the 'calibration' of the exposure time, the developing and the etching. It does not cover the software needed to produce the PCB layout.

Step 1: Order the Tools and Chemicals

If starting from scratch, you need to order a few things for delivery.

1) Buy a UV Nail Curing Lamp. The one I bought cost £10.47 inclusive from Ebay (free delivery). If you look at the photograph of mine, you can see dozens of vendors selling the same one. It was advertised as "36W UV Lamp Light Gel Curing Nail Dryer + 4 x 9W Blubs". I removed the sliding bottom, and did not bother using it.

2) Get some good quality tracing paper. Many people online suggest alternatives, so be prepared to experiment, I'm sure there are many different options. In the past, I have purchase some 'special' PCB tracing paper called 'Laserstar PCB Printing Film', it was brilliant, but too expensive for my current situation. This time, I went to my local art shop (Hussey Knights Ltd. Bramford Rd, Ipswich, Suffolk, UK IP1 4AS Phone: 01473 461603) and bought an A4 pad of their 112gsm tracing paper 'Gateway natural tracing paper pads 112 gsm'. You get 30 sheets, which I cut into A5 size, because all of my PCBs are smaller than A5! This paper cost £6.50p inclusive of VAT. I intended buying 90gsm paper which I'm sure would be great, but they also had this thicker paper in stock. The idea is that tracing paper passes UV easily; thick tracing paper has a very smooth surface which reproduces fine detail really well; thick paper does not crinkle; thick paper is very dimensionally-stable as it passes through the laser printer.

3) Get some pre-sensitised PCB. I use single-sided, economy board. I have had great success with economy boards from Rapid Electronics, but this time I went to CPC (www.cpc.co.uk) because they do not charge delivery, even for a tiny order. I ordered 'Economy PCB Board 4"x6" PC00348' at £2.49 inc VAT. This board has a layer of photo-sensitive etch-resist already laid onto it. It has a layer of black tape stuck over the resist, to keep the light away. This layer has to be removed, just before exposing to the UV light source.

4) Developer for the board. I ordered 'Developer Powder for 1L PC00034' at £2.09 inc VAT from CPC. I only make small boards, so I split the powder into 4 and only mix up a quarter of the powder (to make 0.25L of developer solution). The dilution varies, but I use 50g for 1 litre (the strongest recommended dilution). I add 12.5g of powder to 0.25L of water in a bottle. The developer has a shelf-life of 3 to 4 weeks.

5) Etching chemical. I prefer Sodium Persulphate to Ferric Chloride, but either are fine. Sodium Persulphate is a clear liquid, so you can watch the progress of the etching, and remove the board as soon as it is complete. The Ferric Chloride is opaque, and you have to keep lifting the board out to check it. Both chemicals come as a powder/crystals. When mixing, it is vital that you add the powder to the water, not the water to the powder (the latter can boil the tiny quantity of water and throw some REALLY nasty boiling acid in your face). To make the working solution, I add 100g of Sodium Persulphate powder to 0.5L of tap water. I bought 0.5kg of Sodium Persulphate from ebay a couple of years ago and mix up 0.5L of solution as necessary. The solution is supposed to have a shelf-life of 6 to 8 weeks, but I am currently using solution which I mixed up 2 years ago - it seems fine and still etches well. If I were buying it now, I would probably add it to my CPC order as 'KEMO ELECTRONIC ETCHANT, 100G PC01608' at £2.75 inc VAT.

These goods total £24.30p (including VAT and delivery) and set you up for years of PCB manufacture!

Step 2: Safety

I'm very careful using the chemicals. In particular the Sodium Persulphate (and Ferric chloride) is a very nasty acid.

Goggles and rubber gloves are recommended.

Young people, should not handle these chemicals without adult supervision.

I am old and do not have children in my house. If I did, then I would be doubly-careful with my working practices. As it is, I follow these rules:

  • I always label the solutions carefully. Sometimes, I use old carbonated drink bottles to store solutions (which is not good practice), but they are fully labelled and kept in our basement.
  • I always add the powders to the water, not the reverse.
  • I have a special set of plastic containers for these chemicals and do not use our kitchen ones.
  • I flush waste solutions down the outside drain with copious quantities of water.
  • I work on layers of newspaper - drops of liquid invariably end up around the containers - newspaper absorbs them really well.

Step 3: Gather Other, Supporting, Materials

Other equipment is needed.

  • An exposure frame (mine is a piece of glass from an old picture frame and a matching piece of plywood, with some rubber bands).
  • Some plastic containers to act as chemical baths.
  • A timer capable of measuring seconds.
  • The PCB layout you want to produce - preferably laser-printed on tracing paper.

Step 4: Calibrate the Etching Time

With a new set-up, you need to find out the best exposure time. This should only need doing once (in theory).

A strip of PCB is placed under the PCB printout (black toner should be in contact with the photo-sensitive layer of the board) and the glass is held firmly down to clamp everything.

An opaque card (or similar) is placed on top of the assembly, leaving a small exposed area of PCB. The lamp is placed on top and switched on for one minute. Then the strip of opaque card is moved to expose a new strip of PCB and the lamp switched on for another one-minute interval. At this stage, the first exposed area has had a total of two minutes of UV light, and the second area has had one minute of exposure. This process is repeated, slowly building up a set of PCB areas, each with a different, known, exposure time.

I did 8 PCB areas, each 1cm wide.

The resulting board is developed by immersing it in the developer (for 60 seconds or so, depending on the temperature of the developer) and then rinsed under tap water. I agitate the board continually during the development. The developer should be permitted to finish its job - you do not need to 'judge' when it is right to remove the board, you cannot really over-develop unless you leave it in for 20 or 30 times the optimum time.

The used developer is returned to the stock bottle for future use (it has a shelf-life of 3 to 4 weeks).

You can immediately judge the best exposure time by looking carefully at the image which is left. Some will be very thin (too much exposure) some will be too dark (not enough exposure). You can also etch the board and see the effect of the different exposure times on the finished product.

Surprisingly, the exposure time I required was short (1 to 2 minutes). The lamps must be pretty powerful.

I should probably repeat the process using 20 second intervals, to get a more precise estimate of the best exposure time.

Step 5: Etching

Once developed and rinsed, the board is immersed in a bath of etchant and agitated continuously. The board seems to generate tiny bubbles which, I assume, would inhibit the action of the etchant. Sometimes, the bubbles are persistent, and I extract the board completely for a couple of seconds; this clears them off.

The etching process is very slow when it is cold. I always place the container of etchant, complete with the PCB, in a bigger container and pour boiling water into the outer container, to act as a hot water-bath. This rapidly raises the temperature of the etchant and brings the etching time down dramatically (eg to 5-6 minutes).

It is pretty obvious when the etching is nearing the end of the process, because the board matrix (ie white fibreglass) starts showing through (firstly at the edges of the PCB).

Once everything necessary is etched away (including the tiny drill hole marks), the board is flushed under tap-water.

In fact, the board can be removed, rinsed, inspected and put back into the etchant as often as needed. I find inspecting the PCB with a very bright light underneath the board (and hence shining through the board matrix) highlights any unwanted copper bridges, etc.

The etching solution is returned to its stock bottle for future use.

Cellulose thinner (aka acetone or nail-polish remover) is used to remove the photo-resist layer from the copper.

<p>What is the watt rating of the UV bulb inside the lamp? I have the same type of lamp but in mine even after 10 minutes the photoresist is barely exposed.</p>
<p>I would also like to know the ans to that question?</p>
Nice ible.<br>A working solution.<br>Pretty fast etching, as described.<br>Thank you!
<p>Nice job indeed. BTW, if you guys need real PCB prototyping, here is a company www.syspcb.com FYR.</p>
it isn't all that hard to pull the copper from the solution using say aluminium
ferric chloride isn't an acid? the hcl used to make the solution is however
very cool (or hot) idea with the hot water to warm the merchant! will try this. :)<br>thanks!
<p>Interesting topic and useful</p>
<p>Thanks for an excellent instructable, a great way to produce really professional boards at a budget price!</p><p> I shall be using your method in the future. I particularly like the use of tracing paper to print the resist mask:-)</p><p>If I may make one observation, I have doubts about the wisdom of disposing of the used chemicals in the drains.... All this stuff ends up either in a watercourse where it will be poisonous or in a water treatment plant where it may not be removed and so could contaminate drinking water supplies.</p><p>All the best to you,</p><p>Steve.</p>
<p>He might be 'on to something' using the tracing paper. I have tried clear transparency 'film'..but it's made of plastic. Even on the darkest setting my laser printer does not print a good 'solid' on the transparency. The laser printer toner powder is mostly plastic which is heated and 'pressed' into the paper. But, since the toner is plastic and the transparency is plastic, maybe the toner powder will not 'melt' into the plastic. This could be the problem. Tomorrow...will get tracing paper and give it a try!</p>
<p>I'm sure you are right about the disposal of the Sodium Persulphate - the best explanation I have seen of its use and disposal as an etchant is here:</p><p><a href="http://frgmnt.org/tag/sodium-persulfate/" rel="nofollow">http://frgmnt.org/tag/sodium-persulfate/</a></p><p>In reality, the day-to-day disposal of the chemical when you are etching is virtually zero. I have not done any serious disposal in 2 or more years, because the solution's shelf life is very long (from my experience). My 0.5 litre stock is still going strong! Admittedly I only produce a few small PCBs a year. After I have returned the contents of the etching bath to the stock bottle, I rinse out the plastic container at an outside tap and these few drops (literally) do go down the drain. I'm guessing that this is OK in reality (especially as I believe copper sulphate is routinely used to clear tree roots from sewer pipes!).</p><p>I think copper ions will disrupt the operation of septic tanks, so this should certainly be avoided.</p><p>The disposal advice in the link above is obviously the way to go.</p><p>Many thanks for the helpful comment.</p><p>Best wishes</p>
<p>I can second that. Copper ions are harmful to almost all biological live. Please dispose of the used solution as chemical waste in your nearest facility. Also it should be clear, that if you dump etachant down the drain, you will etch all copper and iron plumbings from the inside. Not very nice... ;)</p>
<p>Thanks for the Instructable. Great idea. I just ordered one the the 'curing' units on eBay. $16.85 free shipping. Seems to be a Chinese company with USA shipping location. </p><p>Removing the two 'side' UV lamps and saving them for replacements is a great suggestion. </p>
<p>I always use an ordinary 20 Watts compact fluorescent lamp - expose the PCB from about 8 cm distance for 8 minutes and the results are great.</p><p>Since the fluorescent lamp seems to produce enough UV light, there is no need for specialized UV lights.</p>
<p>I'm sure you are right. I think all fluorescent lights have mercury vapour inside which produces a strong emission at the UV wavelength of 365nm. The powder coating on the inside of the tube absorbs the UV and re-emits it in the visible part of the spectrum. Obviously, a thin coating does not do a 100% job of absorbing the UV, and I guess that is what you are relying on. Brilliant! (The 'black' lights are the same, except they have a coating which is transparent to the desired wavelengths of UV).</p><p>I'm amazed that for &pound;10 I can buy the whole unit - I couldn't begin to make it for a similar price!!!</p>
<p>Great 'ible, and very well presented, must try this method a.s.a. </p><p>Just bought my wife a UV lamp just like yours, maybe, just maybe I'll ......... no, maybe not, I'll just send for another one.</p><p>BTW I'm not far from you, about 56 miles I would guess, what a small world this is.</p><p>Don't know how you get away with doing these things in the kitchen though.</p><p>Best regards</p>
<p>Hmm, I manage to get away with it! I have a shallow cardboard box in my workshop with some old plastic ice cream containers in it. They house the two bottles of liquids, and various tupperware-type containers. I sneak the cardboard box into the kitchen, lay out a whole newspaper on the worktop and do the business in a half-hour or so. I rapidly put everything back in the cardboard box and beat a retreat! Never leave a mess, is the key!</p><p>Best wishes</p>
<p>I wish I had your courage, I really do. I'm sure there's a camera up in our kitchen (there I go again saying 'our kitchen') somewhere but I can't find it.</p><p>Joking aside, I've got a new 12' x 9' shed and I've filled it up with lots and lots of useful 'stuff', but I'm sure I could find the space to have a go at this little project.</p><p>Thanks again for a great 'ible.</p><p>Best wishes from G.Y.</p>
<p>A nicely documented Instructable. I was going to suggest using a metasilicate based etch resist developer as I assumed your powder was Sodium Hydroxide. However, it seems that it is a metasilicate. I use the same nail lamp with just the two centre bulbs and it works well. </p><p>Two more things I can really recommend for professional PCBs is a tinning solution (e.g. Mega sell some that's available at CPC) and a solder mask. I can't recommend dry film soldermask enough. You'll need a laminator in addition to the UV lamp but it makes all the difference. Instructable here: <a href="https://www.instructables.com/id/Dry-Film-Solder-Mask/" rel="nofollow">https://www.instructables.com/id/Dry-Film-Solder-Ma...</a></p><p>I'm in the UK, so if you have a laminator then drop me a message and I'll mail you some to try out.</p>
<p>I've never tried a soldermask. With very fine boards it can be tricky hand-soldering the very tiny pads which are in close proximity to tracks. It is easy to get bridges if you are not careful. Your instructable looks really interesting. So is the blog. I'll look out for a laminator!</p><p>My biggest concern is the quality of my laser-printed PCB masks for the copper side. The 'solid' blacks are anything but solid when viewed through a magnifying loupe; despite this, the PCBs are good - I just think that this 'basic' weakness removes all the error-margin from the following steps. (I have two HP laser printers both have similar marginal black results!). Any thoughts, what do you use for your masks (what paper, what printer, any 'special' printer settings)?</p><p>Best wishes </p>
<p>That solder mask Instructable isn't mine - just one I found useful.<br><br>I found the mask easier to expose and develop than the etch resist. Only needed about 45s and developed well.<br><br>I get great results with a Canon MG5250 inkjet printer on some old transparencies, especially if I specify T-shirt paper when printing. It creates a nice thick layer of ink and also mirrors automatically. Generally inkjet printers seem better than lasers for photo exposure work.</p>
<p>Oh, I forgot Ziploc vacuum bags to press the transparency down against the PCB. I blogged about all this stuff here if you're interested: http://0xfred.wordpress.com/2014/02/28/further-pcb-improvements/</p>
<p>Wow. I'm always impressed with how one can create technological objects with relatively simple household tools...</p>
Yep. A source of UV light packaged so perfectly for PCB manufacture is a real gift. The wavelength of the UV light from the bulbs is 365nm, which again is perfectly matched to that required for the resist layer on the PCBs.<br><br>I left all four bulbs in the unit, however, I think I will probably remove the two bulbs on the sides and keep them as spares. UV light coming from the side does not really help (and could undercut the resist - not very likely). Removing these two bulbs would also lengthen the exposure time, which would not be a bad thing as it is so short (60s - 90s) at the moment.<br><br>Thanks for your comment. Best wishes
<p>agree!</p>

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