Printing two and putting them one above another is unlikely to work well for anything with fine detail. The ink or toner needs to be in direct contact with the uv sensitive layer, unless you have a perfectly collimated uv source, which is unlikely.
I use ordinary A4 office paper, which seems to transmit about 30% of the uv hitting it, through a laserprinter. With my homebrew 196x uv led array that gives an exposure time of about 6 mins. It works very well indeed. As always with photographic developing, do a test strip to determine correct exposure time.
If this seems just too easy to be true, and it did slightly surprise me, put draughtsman's tracing paper (about 60% uv translucency) through a laserprinter. You might notice that I keep saying laserprinter.
Also, be aware that the chemistry you use for developing the image has a big effect on the contrast of the final image, and here contrast is our best friend. This is a 1-bit colour depth image - copper, or not copper, nothing in between. I get much better results using a silicate developer than plain sodium hydroxide - it's a higher contrast developer.
For a more in depth treatment of this, on much the same lines, I recommend anyone to read this:
Making PCBs
I have this page stored on my offline machine with the words THIS IS IT at the end of the folder name. The rest of his site is quite fun too.
I use ordinary A4 office paper, which seems to transmit about 30% of the uv hitting it, through a laserprinter. With my homebrew 196x uv led array that gives an exposure time of about 6 mins. It works very well indeed. As always with photographic developing, do a test strip to determine correct exposure time.
If this seems just too easy to be true, and it did slightly surprise me, put draughtsman's tracing paper (about 60% uv translucency) through a laserprinter. You might notice that I keep saying laserprinter.
Also, be aware that the chemistry you use for developing the image has a big effect on the contrast of the final image, and here contrast is our best friend. This is a 1-bit colour depth image - copper, or not copper, nothing in between. I get much better results using a silicate developer than plain sodium hydroxide - it's a higher contrast developer.
For a more in depth treatment of this, on much the same lines, I recommend anyone to read this:
Making PCBs
I have this page stored on my offline machine with the words THIS IS IT at the end of the folder name. The rest of his site is quite fun too.
Well it is in the link I gave above, here it is again:
Making PCBs
In case it's not working for you for some reason I'll quote the info, with apologies to Mike's Electric Stuff:
Take 200cc of "water glass", add 800cc of distilled water and stir. To this add 400g of sodium hydroxide (caustic soda).
Important safety precautions: The sodium hydroxide solid must NEVER be handled, use disposable gloves. When the sodium hydroxide dissolves in water it produces a great deal of heat so it must be added a little at a time and each portion allowed to dissolve before more is added. If the solution becomes very hot leave it to cool before adding more sodium hydroxide.
The solution is VERY caustic and it is particularly damaging to the eyes, use eye protection when making and handling it.
It also ruins clothing. Water glass is also known as "sodium silicate solution" and "egg preserver", It used in fire proofing fabrics, for waterproofing walls and making "chemical gardens". Caustic soda is used for clearing drains and available from any chemist. The solution cannot be made by dissolving solid sodium silicate.This solution will be the same strength as the concentrate, and so will need diluting - about 1 part concentrate to 4 to 8 parts water, depending on the photoresist used and temperature.
It does seem to be something available much more easily in Europe as a pcb product than in the US, though see later. The stuff that I use comes as a concentrate solution, no recipe attached, but warns that it contains NaOH and >5% silicates. Typical mealy mouthed euro-babble "safety" speak.
I don't understand the warning in the Mike's Electric Stuff recipe that it can't be made by dissolving sodium silicate in water - sodium silicate is water soluble, though there is a something of a family of related compounds, so some scope for confusion.
In the US, Web-tronics sell straight sodium silicate as pcb developer in tiny little 2oz bags.....:
Positive Developer
Read the MSDS sheet (the blurriest I've ever seen!) to find out what's actually in it:
http://www.web-tronics.com/pdf/POSDEV_MSDS.pdf
Sodium silicate, white powder, probably available from somewhere very close to you, very cheaply. Either the solid stuff, or "water glass". Add some NaOH, or don't add it. If you do do some home chemistry, I'd be glad to hear of your results.
Making PCBs
In case it's not working for you for some reason I'll quote the info, with apologies to Mike's Electric Stuff:
Take 200cc of "water glass", add 800cc of distilled water and stir. To this add 400g of sodium hydroxide (caustic soda).
Important safety precautions: The sodium hydroxide solid must NEVER be handled, use disposable gloves. When the sodium hydroxide dissolves in water it produces a great deal of heat so it must be added a little at a time and each portion allowed to dissolve before more is added. If the solution becomes very hot leave it to cool before adding more sodium hydroxide.
The solution is VERY caustic and it is particularly damaging to the eyes, use eye protection when making and handling it.
It also ruins clothing. Water glass is also known as "sodium silicate solution" and "egg preserver", It used in fire proofing fabrics, for waterproofing walls and making "chemical gardens". Caustic soda is used for clearing drains and available from any chemist. The solution cannot be made by dissolving solid sodium silicate.This solution will be the same strength as the concentrate, and so will need diluting - about 1 part concentrate to 4 to 8 parts water, depending on the photoresist used and temperature.
It does seem to be something available much more easily in Europe as a pcb product than in the US, though see later. The stuff that I use comes as a concentrate solution, no recipe attached, but warns that it contains NaOH and >5% silicates. Typical mealy mouthed euro-babble "safety" speak.
I don't understand the warning in the Mike's Electric Stuff recipe that it can't be made by dissolving sodium silicate in water - sodium silicate is water soluble, though there is a something of a family of related compounds, so some scope for confusion.
In the US, Web-tronics sell straight sodium silicate as pcb developer in tiny little 2oz bags.....:
Positive Developer
Read the MSDS sheet (the blurriest I've ever seen!) to find out what's actually in it:
http://www.web-tronics.com/pdf/POSDEV_MSDS.pdf
Sodium silicate, white powder, probably available from somewhere very close to you, very cheaply. Either the solid stuff, or "water glass". Add some NaOH, or don't add it. If you do do some home chemistry, I'd be glad to hear of your results.
If you possibly can, watch the pH, I think that it might well become much more corrosive as it becomes alkaline, ie its pH rises above 7. Corrosive both as in eats copper, and as in eats flesh.
If it isn't pokey enough to start with, maybe try adding a small amount of NaOH?
Haven't given much thought to the chemistry of this stuff's action on copper yet - hoping I can con someone else into working it all out for me!
If it isn't pokey enough to start with, maybe try adding a small amount of NaOH?
Haven't given much thought to the chemistry of this stuff's action on copper yet - hoping I can con someone else into working it all out for me!
I have used a product called Laserstar for several years in our proto lab at work. Never had a problem with even my first old laser printer almost 20 years ago.
Available here:
100062 - MEGA - LASERSTAR FILM, A4, 10 SHEETS | Farnell United Kingdom or here:
Mega-UK - Artwork Films
Developer for the more common positive resists these days is 14g of NaOH pr liter. I use standard caustic soda from the paint shop. Use at room temp or there abouts....... do not reuse, - discard after use.... it's cheap enough.....
There really is no need for any more or less strange additives. Use latex gloves if you feel for it. If the resist is somewhat old, out of date, a very light swipe with a cotton ball will help release the resist residues.
Available here:
100062 - MEGA - LASERSTAR FILM, A4, 10 SHEETS | Farnell United Kingdom or here:
Mega-UK - Artwork Films
Developer for the more common positive resists these days is 14g of NaOH pr liter. I use standard caustic soda from the paint shop. Use at room temp or there abouts....... do not reuse, - discard after use.... it's cheap enough.....
There really is no need for any more or less strange additives. Use latex gloves if you feel for it. If the resist is somewhat old, out of date, a very light swipe with a cotton ball will help release the resist residues.
Well, good to know it's there if you do have to use film for some reason, though happily I don't. Even at £5 per 10 sheets (direct from Mega) it costs about 100x plain paper, from Farnell, £12 per 10. I'll stick with the paper.
As for developers, NaOH works, I just find silicate better. I expect that having a good setup of bubble tanks etc reduces the need for high contrast developer with wide developing time latitude. The stuff I'm using is from Mega, via Rapid, though I should think I'll be buying it from ebay once Billy starts flogging off that sack full in his basement
Probably a rarity nowadays, but photographic developing tongs are useful and cheap for handling purposes, and don't make those men from forensic science, who still won't go away, ask even more awkward questions.....
As for developers, NaOH works, I just find silicate better. I expect that having a good setup of bubble tanks etc reduces the need for high contrast developer with wide developing time latitude. The stuff I'm using is from Mega, via Rapid, though I should think I'll be buying it from ebay once Billy starts flogging off that sack full in his basement
Probably a rarity nowadays, but photographic developing tongs are useful and cheap for handling purposes, and don't make those men from forensic science, who still won't go away, ask even more awkward questions.....
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To each his own, I say.. and I do certainly not feel offended...
I just don't see any reason to complicate things.... caustic soda is commonly available, and does the job, but using the recommended strength, developing is acceptably fast ( slow?) and well controlled. NaOH was also the recommended developer before some wise guys started another recipee at a much higher price.
And yes, - the Laserstar films are indeed quite expensive, but I've meade several boards with down to .025" (0.635mm) pin pitch with good results.
I just don't see any reason to complicate things.... caustic soda is commonly available, and does the job, but using the recommended strength, developing is acceptably fast ( slow?) and well controlled. NaOH was also the recommended developer before some wise guys started another recipee at a much higher price.
And yes, - the Laserstar films are indeed quite expensive, but I've meade several boards with down to .025" (0.635mm) pin pitch with good results.
To each his own, I say.. and I do certainly not feel offended...
I just don't see any reason to complicate things.... caustic soda is commonly available, and does the job, but using the recommended strength, developing is acceptably fast ( slow?) and well controlled. NaOH was also the recommended developer before some wise guys started another recipee at a much higher price.
And yes, - the Laserstar films are indeed quite expensive, but I've meade several boards with down to .025" (0.635mm) pin pitch with good results.
Well I'm with you on avoiding unnecessary complication, and I dislike the way in which the everyday useful is removed from shelves to be replaced by "special, better, purpose-made" items. Sad to say, even caustic soda (NaOH) is getting rarer in UK shops, being more and more supplanted by products that definitely contain it, but in unspecified amounts, and of course with a nice brand name, a slogan and a logo......rrrr!
Btw, trying to buy unadulterated acetone here these days is no laughing matter either.
Possibly the simplicity of my setup (darkroom trays, hand agitation) means I enjoy the latitude of silicate, where it just isn't an issue for you. Billy of course has the convenience of a sack full of silicate in his basement, and I'd be grateful if you didn't put him off too much before he's completed the exhaustive testing of the relative merits of silicate vs caustic developer which I'm trying to con him into.
As for the 25mil pin pitch, well just stop bragging!
Well, I can stilll buy caustic soda and regular acetone at the paint shop, but things that work for the few are indeed getting harder to find, all to protect those who seemingly work without brains....
As for the pin pitch, - it was just to show that Laserstar is a very good product for it's purpose, not bragging intended
OTOH- it looks and feels very much like the polyester drafting film we used with the Rotring pens back in the 70s..... the thaught has occured to me several times, but I've found no place to source that stuff, these days - at least locally...
As for the pin pitch, - it was just to show that Laserstar is a very good product for it's purpose, not bragging intended
OTOH- it looks and feels very much like the polyester drafting film we used with the Rotring pens back in the 70s..... the thaught has occured to me several times, but I've found no place to source that stuff, these days - at least locally...
Hi Simon
Well my bag of silicate did not work at all. I suppose it is something else I have. It is very transprent, very thick, and does nothing at all to pcbs you try to develop. it is called 'soda silicate' ...
So I got back to the usual NaOH.
I tried the paper isolation as you say, strange result: 4 to 5 mn has worse results than 5 to 6. after 6 becomes bad. from 2 to 4 is not enough.
I see that my boards have very poor enduction, with lots of lateral striping.
I wil now try semitranprent paper as you also mention.
At this point, the best result I got was with the usual mylar where I have to painfully redraw with a paint felt from Marabu.
Well my bag of silicate did not work at all. I suppose it is something else I have. It is very transprent, very thick, and does nothing at all to pcbs you try to develop. it is called 'soda silicate' ...
So I got back to the usual NaOH.
I tried the paper isolation as you say, strange result: 4 to 5 mn has worse results than 5 to 6. after 6 becomes bad. from 2 to 4 is not enough.
I see that my boards have very poor enduction, with lots of lateral striping.
I wil now try semitranprent paper as you also mention.
At this point, the best result I got was with the usual mylar where I have to painfully redraw with a paint felt from Marabu.
Hi Billy,
Sorry you've been finding my suggestions so useless, both the paper and the developer.....it works well for me, usually things work for other people and not for me!
Looks like AuroraB's suggestion of the LaserStar film might be the thing for you after all. Ok, yes, and NaOH, which I'm beginning to think is the thing doing the development in the ready made solution that I use, possibly with the silicate providing some sort of buffering action, though I know nothing of the chemistry of the UV photo-resist, so this isn't much more than an empty rearguard action on my part.
For entertainment value only, have a read of what this guy does to increase the UV transparency of plain paper for pcb masking purposes, it's almost obscene, but his uv unit looks a bit iffy too...
PCB Etching
I hope you soon get problem free pcb production sorted, sorry not to have been any help.
Sorry you've been finding my suggestions so useless, both the paper and the developer.....it works well for me, usually things work for other people and not for me!
Looks like AuroraB's suggestion of the LaserStar film might be the thing for you after all. Ok, yes, and NaOH, which I'm beginning to think is the thing doing the development in the ready made solution that I use, possibly with the silicate providing some sort of buffering action, though I know nothing of the chemistry of the UV photo-resist, so this isn't much more than an empty rearguard action on my part.
For entertainment value only, have a read of what this guy does to increase the UV transparency of plain paper for pcb masking purposes, it's almost obscene, but his uv unit looks a bit iffy too...
PCB Etching
I hope you soon get problem free pcb production sorted, sorry not to have been any help.
Hi Simon
Thanks for your info still. I will try on further since there is no magic there, only the proper way to do it nr not. It also seems that my boards are not of the best quality, surrently most of the problem comes from there too.
I ll ty also this oil paper as from your link.
Thanks for all.
Best regards
Billy
Thanks for your info still. I will try on further since there is no magic there, only the proper way to do it nr not. It also seems that my boards are not of the best quality, surrently most of the problem comes from there too.
I ll ty also this oil paper as from your link.
Thanks for all.
Best regards
Billy
Have you tried making a test strip ? - Cover parts of the layout with some thick paper or plastic. Start at fex 2 mins and move the cover in sections, increasing exposure by 1 min each move.
It may be that you don't get enough light through that setup you are using. Normal development time is appx 90 sec's +/- in regular NaOH concentration.
Prolonged development and /or developer solution too strong will cause jagged edges, and in general bad quality coverage of the resist.
Most prototype PCB light boxes uses 6-8 15W fluorescent tubes per side, with an exposure time of roughly 2.5- 3 min's......these tubes are usually called "actinious" tubes, specially for copy boxes. I know that black light tubes also work. The resist is sensitive to light in the region 3800-3900 nm wavelength... deep UV is the wrong wavelength, just for information ..
I too have used regular laser transparencies, two copies on top of each other, and that should give reasonable quality for a PCB without very thin lines.
Back in the early 90's, before laser printers became household items, the print quality of larger black sections was often so-so , - good edges but less than adequate toner fill in the middle, but I have not seen that probelm in the last decade or so.....
It may be that you don't get enough light through that setup you are using. Normal development time is appx 90 sec's +/- in regular NaOH concentration.
Prolonged development and /or developer solution too strong will cause jagged edges, and in general bad quality coverage of the resist.
Most prototype PCB light boxes uses 6-8 15W fluorescent tubes per side, with an exposure time of roughly 2.5- 3 min's......these tubes are usually called "actinious" tubes, specially for copy boxes. I know that black light tubes also work. The resist is sensitive to light in the region 3800-3900 nm wavelength... deep UV is the wrong wavelength, just for information ..
I too have used regular laser transparencies, two copies on top of each other, and that should give reasonable quality for a PCB without very thin lines.
Back in the early 90's, before laser printers became household items, the print quality of larger black sections was often so-so , - good edges but less than adequate toner fill in the middle, but I have not seen that probelm in the last decade or so.....
Honestly, the link to the guy soaking his paper masks in sunflower oil then leaving them to dry out for days was just for fun - please don't make me think there's someone else doing this! It's never going to be as translucent as tracing paper, which you should surely be able to buy in an Art Supplies shop.
AuroraB mentions UV sources, can I ask, what are you using for this? The test strip procedure that he mentions is very important - if you don't do it you're in the dark about what's happening.
There are a few variables at work here:
Photo-resist UV sensitivity spectrum
Resist not degraded through age, temperature, exposure
UV source spectrum
UV source intensity at working distance
-nb tubes brighter after warm-up, leds brighter kept cool
Transparency to UV of film / Opacity of toner
Exposure time
Developer concentration, temperature, agitation and time
Etchant concentration, temperature, agitation and time
Mostly these are things to check ok or be consistent with, the two key ones are exposure time and development time. You need to get them both right, you can't compensate for inadequate exposure with longer development or too much exposure with shorter.
I do this as follows: cut several narrow strips off a board, using a hacksaw. Tape strips of mask with modest size tracks on to the strips of board. Partially covering them with something opaque, like thick black paper, expose the strips in several sessions, revealing or concealing more of the board, so that you have a 'test strip' with multiple bands of progressively changing exposure times. Then develop these for different times, inspect them, then etch.
This might help determine what's going on, but it would be worth getting a fresh bit of board just to be sure of that being right.
AuroraB mentions UV sources, can I ask, what are you using for this? The test strip procedure that he mentions is very important - if you don't do it you're in the dark about what's happening.
There are a few variables at work here:
Photo-resist UV sensitivity spectrum
Resist not degraded through age, temperature, exposure
UV source spectrum
UV source intensity at working distance
-nb tubes brighter after warm-up, leds brighter kept cool
Transparency to UV of film / Opacity of toner
Exposure time
Developer concentration, temperature, agitation and time
Etchant concentration, temperature, agitation and time
Mostly these are things to check ok or be consistent with, the two key ones are exposure time and development time. You need to get them both right, you can't compensate for inadequate exposure with longer development or too much exposure with shorter.
I do this as follows: cut several narrow strips off a board, using a hacksaw. Tape strips of mask with modest size tracks on to the strips of board. Partially covering them with something opaque, like thick black paper, expose the strips in several sessions, revealing or concealing more of the board, so that you have a 'test strip' with multiple bands of progressively changing exposure times. Then develop these for different times, inspect them, then etch.
This might help determine what's going on, but it would be worth getting a fresh bit of board just to be sure of that being right.
Simon thanks, I have made a test strip all the way.
Ok tracing paper will probably play the trick better than sunflower oil ...
my UV source is a ready made device I purchased some time ago, UV tubes and leds, like the one AuroraB mentions.
I now think that the quality of my PCBs is probably the major problem, the test strip comes out showing big differences in thickness (?) or sensitivity, quite inconsistent. Plus shows some striping which will prevent any precision with thin tracks.
I'll go on trying by finding properly layered photoresist boards.
Ok tracing paper will probably play the trick better than sunflower oil ...
my UV source is a ready made device I purchased some time ago, UV tubes and leds, like the one AuroraB mentions.
I now think that the quality of my PCBs is probably the major problem, the test strip comes out showing big differences in thickness (?) or sensitivity, quite inconsistent. Plus shows some striping which will prevent any precision with thin tracks.
I'll go on trying by finding properly layered photoresist boards.
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