08-03-2012, 08:16 PM
You can indeed paint tracks and dunk it in ferric chloride, but since you asked Joe, for what it’s worth here are my own comments on using UV techniques based on experience gained over many years using a home-made UV light box with four 12” 8W tubes and a built-in timer.
I'm not suggesting that anyone wade through this diatribe, but it might be useful for reference. (No numpties on this forum BTW - only class acts! Kwality!!) Nor am I saying that my ways are the right ways, I’m just saying what works for me, and sharing my experiences with others, which I hope may be of interest. (You can expose a PCB to UV simply by rays from the sun by placing the PCB and mask on a window sill or in a greenhouse, but it takes much longer).
Back in the 1970s before we had computers and home printers, and before I made a UV light box, as most of the projects I made were from magazine articles I used to take a photocopy of the artwork, sellotape it over a piece of blank PCB, then centre punch through the paper to mark the PCB at all the points where components were to be fitted. I then removed the paper and used it a pattern to ‘join the dots’ on the PCB using rub down transfers directly onto the PCB. I then etched the PCB in ferric chloride, then drilled all the holes. You must not drill any holes until after the board is etched or the etchant will start to etch away copper around the holes and will also impregnate the holes with etchant which risks corroding wires of components that are later fitted in the holes and soldered to the PCB, however well you think you’ve cleaned the board after etching. Occasionally I’d design my own PCBs on paper then use rub down transfers to copy that design onto plain PCB, the after etching, drill the holes. This rub-down transfer technique was time consuming and if you wanted another board, you had to repeat the process. I never found ‘Dalo’ pens a success – the board always ended up threadbare and offensive to the eye.
To make PCBs using UV techniques, admittedly there are some setup costs but by far and away the most expensive has been a UV box. The splendid UV LED design I mentioned earlier in this thread overcomes that problem – what’s not to like about a UV exposure unit for under a tenner?
Basically, the UV technique is to place a mask of the artwork for the PCB layout on a sheet of glass above the UV tubes, place the PCB on the mask held tight to the mask, then expose the PCB to UV light for several minutes. All of the areas of lacquer which aren’t obscured by the layout on the mask will – when the PCB is placed in developer, dissolve off the PCB leaving the layout. The exposure period isn’t critical but can only be found by trial and error. For my set-up, it usually takes about five minutes. The way to ascertain the correct exposure time is to use a test piece of coated PCB say five inches long, with four inches covered and exposed for one minute, then two inches exposed, then three inches, two inches and finally one inch, all at one minute intervals. The strip of PCB is then placed in developer to see which period of time has correctly exposed the lacquer to UV. EG, if all of the lacquer which has been exposed longer than two minutes dissolves, then three minutes will be adequate, but if the only area that dissolves in the developer is that which has been exposed for five minutes, then with that UV exposure unit and the lacquer that you’ve used, it will take five minutes – maybe longer for a large PCB. You don’t actually see any visible signs on the PCB at the end of the exposure – it’s only at the developing stage that the design become visible. (Hopefully!).
Making a mask:
I’m not adept at designing my own PCB layouts - I generally scan magazine artwork or designs from websites, then clean it up in Photoshop to improve track densities if need be. Often, the layout looks fine until it is enlarged and examined, when it is sometimes full of holes due to the limitations of the printing, and there’s no point in starting off with a layout that will look threadbare under UV light, so I make the threadbare areas opaque. Occasionally, I use Photoshop or MS Paint programs to modify the layout to suit my needs. For example, the PCB layout for the ESR meter project that I made has been much modified by me over time from the original layout.
I use an ink-jet printer to print the mask onto good quality universal inkjet transparency film. The type I use has an RRP of £69.00 for 50 A4 sheets but I get it from a reputable source for £14.52p with free P&P (about 29p a sheet). The print is dense and dries quite quickly. (I do a test print first on plain paper).
Q-Connect KF26074 Universal Inkjet transparency film. Clear, A4, OHP film suitable for use in inkjet printers. Features include: excellent ink reception, good drying times and coating on one side.
http://www.amazon.co.uk/INKJET-CLEAR-PRI...B000KJO7BO
£14.52 Delivered FREE in the UK
(RRP £69.00!)
The ink has excellent density on the film, but to make sure, I always print off two identical copies of the artwork onto one sheet, then sellotape them together to improve the density. It’s probably not necessary, but you might as well do it, or you end up throwing the rest of the sheet away anyway! You need to make sure that the slightly rougher side is face down in the paper feed tray of your printer, so when it comes into the printer it’s the right way up on which the ink will appear.
I usually print two layouts onto one acetate sheet, then cut them apart and tape together one behind the other to make sure the layout is nice and opaque, but one alone is generally fine. Printers do vary greatly in the quality of the mask that results. (I had an HP printer that made excellent masks with very dense black lines, but it gave up the ghost. I recently replaced it with an Epson Stylus SX535WD which in mediocre whatever setting it’s on).
PCB material:
I’ve long since abandoned using pre-sensitised boards, which are expensive and leave you with lots of useless offcuts (albeit they can be used for test exposures). The lacquer coating is thin, and I’ve found that exposure duration can be critical, as can the strength of the developer. Too weak and it doesn’t develop - just a little too strong and the design disappears before your eyes, leaving you with a plain PCB. All in all, a bit hit and miss.
I prefer to use spray-on lacquer, which must be applied in as dust-free an atmosphere as possible. I do mine in the greenhouse and quickly cover the PCB with a plastic box before any dust has chance to settle. I do it on a level surface – just a couple of quick flashes across the board to get a nice coating. (I make sure I’m not wearing a woolly jumper which would liberate dust onto the board). I leave it overnight in a warm place to harden off - usually in a desk drawer. The next stage is the UV exposure which I’ve mentioned above, followed by developing.
Developing:
I don’t buy developer from the usual sources, (EG Maplin, from whom it currently costs £8.99 for 250G - enough to make 2.5 L of developer). Instead, I buy laboratory grade sodium metasilicate pentahydrate in 1kG packs for £10.56 + £6.99 P&P at this e-bay link(or I could get it from Maplin and pay £36 for the same amount):
http://cgi.ebay.co.uk/1Kg-Sodium-Metasil...upplies_ET&hash=item359fddaa26
I save the developer in a bottle to use again. It lasts a few weeks, but becomes so opaque that you can’t see the PCB at the bottom of the container. I use a shallow plastic container about 30 cms long and 20cms wide so I can see the board through the developer, and rock the container gently back and forth. You start to see the dissolved lacquer floating off the surface which starts to happen after perhaps 30 seconds or so.
I start with a weak solution, using less than the recommended amount of crystals dissolved in warm water and if the exposed lacquer doesn’t float off after two or three minutes, I add a few more crystals until it starts to work. It should take two or three minutes, gently rocking the plastic tray back and forth before there are any signs of the lacquer coming off. As soon as the exposed lacquer has all gone, I quickly rinse the board in clear water as there’s a risk that the design will be dissolved away if left in developer any longer.
If there are any mishaps, you can clean off the board with meths, then repeat the process, spraying it again with UV lacquer. Little is lost apart from time, and as it’s just a hobby, times isn’t a major consideration. The solution can be used several times and lasts for a few weeks. 0.5L is plenty – I save it in a clearly marked plastic container.
Caustic soda as a developer?
In the past, I’ve used caustic soda, (sodium hydroxide - NaOH) as a developer, which is cheap and plentiful. (EG £2.45 for 500g from the well-known High St Chemists). It’s also sold for use as a drain cleaner. It is a strongly alkaline compound, used in the manufacture of chemicals and soaps and in petroleum refining. It must be used with extreme caution.
I’ve found it difficult to get the concentration right. You need to add just a few teaspoonfuls of crystals in a Litre of warm water to make a very weak solution, and dip your finger and thumb into this very dilute concentration to see if it feels soapy when you rub your finger and thumb together. If so, it’s strong enough. I’m not recommending this – caustic soda is nasty stuff and sensible precautions should always be exercised when using chemicals.
Etching the board:
I’ve abandoned using ghastly ferric chloride. It’s only merit is that it’s fairly cheap and lasts quite a long time in solution. Instead, I use Sodium Persulphate clear PCB etchant. This is a much cleaner effective alternative to ferric chloride and has a 6 – 8 minute etch time at 45C – 50C. (above 50C it loses its strength). The bath life is a maximum of 4 – 6 weeks depending on use and operating temperature. Unlike ferric chloride, it leaves no residue – the solution turns pale blue in use. I warm it up with an aquarium heater and thermometer, but you can stand the plastic etchant container in a washing up bowl of boiling water to warm up the etchant. You can use it cold – it just takes longer to work. As the PCB etches, the liquid turns light blue. You can use it several times over. I use an aquarium heater to warm it up, and an aquarium air stone about 4” long, with a small aquarium air pump, placed in the bottom of a plastic cereal container to ‘bubble’ the solution to speed up the etching process, but you don’t have to.
The product is supplied as a fine crystalline white powder and instructions for use are printed on the bottle label. A 500 gram HDPE bottle of Sodium Persulphate copper etchant will make up to 2.5 litres of etching solution. You can buy it from Maplin for £19.99 a 1 kG tub, but I get mine in 500G plastic bottles from a reputable hobby chemicals source at less than half that price - £3.50 for 500g plus P&P at cost, £2.24. That’s £7.00 for 1kG, almost a third of the price of Maplin.
http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&item=270746775207&ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1439.l2649
You can buy UV positive photo resist lacquer, tinning solution and other PCB materials from ESR Electronics, at Cullercoats who I find to be an excellent firm to deal with. The link to their PCB products is here:
http://www.esr.co.uk/electronics/products/frame_pcb.htm
A lot of experimentation is called for to get right what seems to work for you. Don't be discouraged - we're not putting rockets into space (well I'm not!) - we're just hobbyists!
(I don't have any connection with any of the suppliers mentioned above, or indeed, any commercial interest whatsoever, except as a customer).
To speed up the etching process, I use a 5” long aquarium airstone, which are very cheap, and a small aquarium air pump. I use a plastic cereal container as an etchant bath.
Drilling the board.
I don’t bother with tungsten carbide drills – I only use cheap HSS drills in a small PCB drill and drill stand, with a homebrew drill speed controller. For most holes for resistors, caps, IC sockets etc, I use 0.8mm, for some diodes - 1N400x series, 1 mm, and for Veropins, 1.2mm. I discard the drills after a couple of boards as they tend to wander when they get blunt and leave a burr. (0.8mm HSS drills can be had for ten for under £5.00. For those who only possess a normal pillar drill, you can get 0.8mm drills with a 2.34mm shank at a higher price).
I’ve attached a pic of my low budget etching tank, which consists of a cereal container from Poundland, an aquarium airstone (another pound), and an aquarium air pump for about a tenner. The digital infra red thermometer was on offer at Maplin for about £15.00 but is now listed at £39 (cheaper ones on internet, so no surprises there then). Not essential, but handy for checking the temperature of the etchant and knowing when to switch off the heater. I can’t recall how much the acquarium heater cost as I’ve had it for years, but here’s one for a tenner:
http://www.amazon.co.uk/100W-Aquarium-Fi..._7?ie=UTF8&qid=1331233965&sr=8-7
I hope these notes of interest and may provide a few useful pointers.
In closing, I should add that I do all this messy tedious stuff as a hobby and for enjoyment, but as can be appreciated, it's labour intensive and often you can buy ready made PCBs for magazine projects quite cheaply, or if a batch of PCBs are needed, can get them made at keen prices, so the cost-benefit case for DIY PCBs isn't a strong one.
I often make things I don't need on a whim, like why would I need a precision 10 Volt Voltage Reference? I can't sensibly answer that rhetorical question, but I'm making one, if only out of curiosity. I've just tarted up the EPE magazine artwork to make the mask, and have now etched and built the PCB. I've attached a copy of the mask to give an idea of what it looks like. (I could have bought the PCB from EPE for just £7.77).
David
I'm not suggesting that anyone wade through this diatribe, but it might be useful for reference. (No numpties on this forum BTW - only class acts! Kwality!!) Nor am I saying that my ways are the right ways, I’m just saying what works for me, and sharing my experiences with others, which I hope may be of interest. (You can expose a PCB to UV simply by rays from the sun by placing the PCB and mask on a window sill or in a greenhouse, but it takes much longer).
Back in the 1970s before we had computers and home printers, and before I made a UV light box, as most of the projects I made were from magazine articles I used to take a photocopy of the artwork, sellotape it over a piece of blank PCB, then centre punch through the paper to mark the PCB at all the points where components were to be fitted. I then removed the paper and used it a pattern to ‘join the dots’ on the PCB using rub down transfers directly onto the PCB. I then etched the PCB in ferric chloride, then drilled all the holes. You must not drill any holes until after the board is etched or the etchant will start to etch away copper around the holes and will also impregnate the holes with etchant which risks corroding wires of components that are later fitted in the holes and soldered to the PCB, however well you think you’ve cleaned the board after etching. Occasionally I’d design my own PCBs on paper then use rub down transfers to copy that design onto plain PCB, the after etching, drill the holes. This rub-down transfer technique was time consuming and if you wanted another board, you had to repeat the process. I never found ‘Dalo’ pens a success – the board always ended up threadbare and offensive to the eye.
To make PCBs using UV techniques, admittedly there are some setup costs but by far and away the most expensive has been a UV box. The splendid UV LED design I mentioned earlier in this thread overcomes that problem – what’s not to like about a UV exposure unit for under a tenner?
Basically, the UV technique is to place a mask of the artwork for the PCB layout on a sheet of glass above the UV tubes, place the PCB on the mask held tight to the mask, then expose the PCB to UV light for several minutes. All of the areas of lacquer which aren’t obscured by the layout on the mask will – when the PCB is placed in developer, dissolve off the PCB leaving the layout. The exposure period isn’t critical but can only be found by trial and error. For my set-up, it usually takes about five minutes. The way to ascertain the correct exposure time is to use a test piece of coated PCB say five inches long, with four inches covered and exposed for one minute, then two inches exposed, then three inches, two inches and finally one inch, all at one minute intervals. The strip of PCB is then placed in developer to see which period of time has correctly exposed the lacquer to UV. EG, if all of the lacquer which has been exposed longer than two minutes dissolves, then three minutes will be adequate, but if the only area that dissolves in the developer is that which has been exposed for five minutes, then with that UV exposure unit and the lacquer that you’ve used, it will take five minutes – maybe longer for a large PCB. You don’t actually see any visible signs on the PCB at the end of the exposure – it’s only at the developing stage that the design become visible. (Hopefully!).
Making a mask:
I’m not adept at designing my own PCB layouts - I generally scan magazine artwork or designs from websites, then clean it up in Photoshop to improve track densities if need be. Often, the layout looks fine until it is enlarged and examined, when it is sometimes full of holes due to the limitations of the printing, and there’s no point in starting off with a layout that will look threadbare under UV light, so I make the threadbare areas opaque. Occasionally, I use Photoshop or MS Paint programs to modify the layout to suit my needs. For example, the PCB layout for the ESR meter project that I made has been much modified by me over time from the original layout.
I use an ink-jet printer to print the mask onto good quality universal inkjet transparency film. The type I use has an RRP of £69.00 for 50 A4 sheets but I get it from a reputable source for £14.52p with free P&P (about 29p a sheet). The print is dense and dries quite quickly. (I do a test print first on plain paper).
Q-Connect KF26074 Universal Inkjet transparency film. Clear, A4, OHP film suitable for use in inkjet printers. Features include: excellent ink reception, good drying times and coating on one side.
http://www.amazon.co.uk/INKJET-CLEAR-PRI...B000KJO7BO
£14.52 Delivered FREE in the UK
(RRP £69.00!)
The ink has excellent density on the film, but to make sure, I always print off two identical copies of the artwork onto one sheet, then sellotape them together to improve the density. It’s probably not necessary, but you might as well do it, or you end up throwing the rest of the sheet away anyway! You need to make sure that the slightly rougher side is face down in the paper feed tray of your printer, so when it comes into the printer it’s the right way up on which the ink will appear.
I usually print two layouts onto one acetate sheet, then cut them apart and tape together one behind the other to make sure the layout is nice and opaque, but one alone is generally fine. Printers do vary greatly in the quality of the mask that results. (I had an HP printer that made excellent masks with very dense black lines, but it gave up the ghost. I recently replaced it with an Epson Stylus SX535WD which in mediocre whatever setting it’s on).
PCB material:
I’ve long since abandoned using pre-sensitised boards, which are expensive and leave you with lots of useless offcuts (albeit they can be used for test exposures). The lacquer coating is thin, and I’ve found that exposure duration can be critical, as can the strength of the developer. Too weak and it doesn’t develop - just a little too strong and the design disappears before your eyes, leaving you with a plain PCB. All in all, a bit hit and miss.
I prefer to use spray-on lacquer, which must be applied in as dust-free an atmosphere as possible. I do mine in the greenhouse and quickly cover the PCB with a plastic box before any dust has chance to settle. I do it on a level surface – just a couple of quick flashes across the board to get a nice coating. (I make sure I’m not wearing a woolly jumper which would liberate dust onto the board). I leave it overnight in a warm place to harden off - usually in a desk drawer. The next stage is the UV exposure which I’ve mentioned above, followed by developing.
Developing:
I don’t buy developer from the usual sources, (EG Maplin, from whom it currently costs £8.99 for 250G - enough to make 2.5 L of developer). Instead, I buy laboratory grade sodium metasilicate pentahydrate in 1kG packs for £10.56 + £6.99 P&P at this e-bay link(or I could get it from Maplin and pay £36 for the same amount):
http://cgi.ebay.co.uk/1Kg-Sodium-Metasil...upplies_ET&hash=item359fddaa26
I save the developer in a bottle to use again. It lasts a few weeks, but becomes so opaque that you can’t see the PCB at the bottom of the container. I use a shallow plastic container about 30 cms long and 20cms wide so I can see the board through the developer, and rock the container gently back and forth. You start to see the dissolved lacquer floating off the surface which starts to happen after perhaps 30 seconds or so.
I start with a weak solution, using less than the recommended amount of crystals dissolved in warm water and if the exposed lacquer doesn’t float off after two or three minutes, I add a few more crystals until it starts to work. It should take two or three minutes, gently rocking the plastic tray back and forth before there are any signs of the lacquer coming off. As soon as the exposed lacquer has all gone, I quickly rinse the board in clear water as there’s a risk that the design will be dissolved away if left in developer any longer.
If there are any mishaps, you can clean off the board with meths, then repeat the process, spraying it again with UV lacquer. Little is lost apart from time, and as it’s just a hobby, times isn’t a major consideration. The solution can be used several times and lasts for a few weeks. 0.5L is plenty – I save it in a clearly marked plastic container.
Caustic soda as a developer?
In the past, I’ve used caustic soda, (sodium hydroxide - NaOH) as a developer, which is cheap and plentiful. (EG £2.45 for 500g from the well-known High St Chemists). It’s also sold for use as a drain cleaner. It is a strongly alkaline compound, used in the manufacture of chemicals and soaps and in petroleum refining. It must be used with extreme caution.
I’ve found it difficult to get the concentration right. You need to add just a few teaspoonfuls of crystals in a Litre of warm water to make a very weak solution, and dip your finger and thumb into this very dilute concentration to see if it feels soapy when you rub your finger and thumb together. If so, it’s strong enough. I’m not recommending this – caustic soda is nasty stuff and sensible precautions should always be exercised when using chemicals.
Etching the board:
I’ve abandoned using ghastly ferric chloride. It’s only merit is that it’s fairly cheap and lasts quite a long time in solution. Instead, I use Sodium Persulphate clear PCB etchant. This is a much cleaner effective alternative to ferric chloride and has a 6 – 8 minute etch time at 45C – 50C. (above 50C it loses its strength). The bath life is a maximum of 4 – 6 weeks depending on use and operating temperature. Unlike ferric chloride, it leaves no residue – the solution turns pale blue in use. I warm it up with an aquarium heater and thermometer, but you can stand the plastic etchant container in a washing up bowl of boiling water to warm up the etchant. You can use it cold – it just takes longer to work. As the PCB etches, the liquid turns light blue. You can use it several times over. I use an aquarium heater to warm it up, and an aquarium air stone about 4” long, with a small aquarium air pump, placed in the bottom of a plastic cereal container to ‘bubble’ the solution to speed up the etching process, but you don’t have to.
The product is supplied as a fine crystalline white powder and instructions for use are printed on the bottle label. A 500 gram HDPE bottle of Sodium Persulphate copper etchant will make up to 2.5 litres of etching solution. You can buy it from Maplin for £19.99 a 1 kG tub, but I get mine in 500G plastic bottles from a reputable hobby chemicals source at less than half that price - £3.50 for 500g plus P&P at cost, £2.24. That’s £7.00 for 1kG, almost a third of the price of Maplin.
http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&item=270746775207&ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1439.l2649
You can buy UV positive photo resist lacquer, tinning solution and other PCB materials from ESR Electronics, at Cullercoats who I find to be an excellent firm to deal with. The link to their PCB products is here:
http://www.esr.co.uk/electronics/products/frame_pcb.htm
A lot of experimentation is called for to get right what seems to work for you. Don't be discouraged - we're not putting rockets into space (well I'm not!) - we're just hobbyists!
(I don't have any connection with any of the suppliers mentioned above, or indeed, any commercial interest whatsoever, except as a customer).
To speed up the etching process, I use a 5” long aquarium airstone, which are very cheap, and a small aquarium air pump. I use a plastic cereal container as an etchant bath.
Drilling the board.
I don’t bother with tungsten carbide drills – I only use cheap HSS drills in a small PCB drill and drill stand, with a homebrew drill speed controller. For most holes for resistors, caps, IC sockets etc, I use 0.8mm, for some diodes - 1N400x series, 1 mm, and for Veropins, 1.2mm. I discard the drills after a couple of boards as they tend to wander when they get blunt and leave a burr. (0.8mm HSS drills can be had for ten for under £5.00. For those who only possess a normal pillar drill, you can get 0.8mm drills with a 2.34mm shank at a higher price).
I’ve attached a pic of my low budget etching tank, which consists of a cereal container from Poundland, an aquarium airstone (another pound), and an aquarium air pump for about a tenner. The digital infra red thermometer was on offer at Maplin for about £15.00 but is now listed at £39 (cheaper ones on internet, so no surprises there then). Not essential, but handy for checking the temperature of the etchant and knowing when to switch off the heater. I can’t recall how much the acquarium heater cost as I’ve had it for years, but here’s one for a tenner:
http://www.amazon.co.uk/100W-Aquarium-Fi..._7?ie=UTF8&qid=1331233965&sr=8-7
I hope these notes of interest and may provide a few useful pointers.
In closing, I should add that I do all this messy tedious stuff as a hobby and for enjoyment, but as can be appreciated, it's labour intensive and often you can buy ready made PCBs for magazine projects quite cheaply, or if a batch of PCBs are needed, can get them made at keen prices, so the cost-benefit case for DIY PCBs isn't a strong one.
I often make things I don't need on a whim, like why would I need a precision 10 Volt Voltage Reference? I can't sensibly answer that rhetorical question, but I'm making one, if only out of curiosity. I've just tarted up the EPE magazine artwork to make the mask, and have now etched and built the PCB. I've attached a copy of the mask to give an idea of what it looks like. (I could have bought the PCB from EPE for just £7.77).
David
Regards, David.
BVWS Member.
G-QRP Club Member 1339.
'I'm in my own little world, but I'm happy, and they know me here'
BVWS Member.
G-QRP Club Member 1339.
'I'm in my own little world, but I'm happy, and they know me here'
