Cheap & Cheerful DIY UV PCB Exposure Unit - UK Vintage Radio Repair and Restoration Discussion Forum

David G4EBT · 21st Dec 2014, 8:20 pm

In another thread 'Etching with Vinegar' the topic of UV techniques was touched upon, and rather than take that thread off-topic, I thought I'd start this one.

One of the biggest deterrents to DIY UV techniques is the cost of a UV exposure unit - an entry level no-frills 'hobby' unit consisting of two 8 Watt UV tubes with no timer is typically £100+. More sophisticated UV light boxes with a built-in timer, are upwards of £150.00. Clearly, this is out of the question for making the occasional PCB. For many years until the late 80s I used to make PCBs by painstakingly rubbing down PCB artwork transfers directly onto the copper. One drawback of that is that if you need more than one PCB of the same design, you have to go through the same rigmarole. In the late 80s I made a UV light box with a built-in timer and four 12 inch tubes, (which I still use today), which featured in EPE magazine.

However, with the widespread availability of high brightness 5mm UV LEDs of the right wavelength there's no need to go to the expense of UV tubes.

UV photo resist lacquer is sensitive to UV light in the 340nm to 420nm wave lengths. Traditional UV exposure units use mains powered UV tubes that emit UV light at a wavelength of around 350nm. A hundred 5mm high brightness (2000 MCP) UV LEDS with a Peak Wave Length (nm) of 395~400 - right in the middle of the desired spectrum - can be found from e-bay suppliers for $4.99 USD post free - that's a little over £3.00. Yes, 3p each! (From China of course - where else?).

A member of the EPE Chat Zone - Joe Farr - designed an excellent simple to make UV exposure unit using such UV LEDs in an array of 99 LEDs in nine rows of eleven, mounted on a piece of Strip-board, with 64 holes and 41 tracks. A larger unit could of course be built if desired, but that size should cater for most of the boards we're likely to want to produce. In addition to the LEDs and Strip-board, 33 limiting resistors are required, as outlined on Joe's website. The only other item needed is some 22 SWG solid tinned copper wire for links on the Strip-board.

The constructional details and description can be found at this link:

http://www.hobbyelectronics.net/con_...sure-unit.html

Some other interesting stuff on Joe's site too.

(The source of UV LEDs mentioned by Joe no longer exists, but other suppliers can be found by a google search for '100pcs Ultra Violet UV 5mm 2000mcd LED').

The basic unit could of course be refined by building it into a box with a lid etc if desired.

I hope Joe's design might prove useful to anyone who has thought about UV PCBs but has been put off by the high cost of the light box. Most other items needed for making UV boards are quite cheap. Personally, I don't buy pre-sensitised boards because if you under or over expose them, the thin coating of lacquer is either not fully developed, or just disappears, especially if the developer is just a little too strong. I prefer to spray a good layer of lacquer and leave it to harden off for a couple of days. If - as can happen at times - the board doesn't turn out as I'd like it, I just wipe it clean with meths, re-spray it and start again. (The UV lacquer I'm presently using has a use-by date of 1999 on the can, and is still good).

I understand why many prefer to get PCBs made professionally - making them on a DIY basis is a time-consuming process which can produce variable results, but I don't see it as a chore - if I did, I'd find another hobby!

UV isn't 'the only show in town' of course - in recent years there has been a lot of interest in the 'laser print/iron-on' technique, whereby the PCB artwork (in reverse of course!), is printed onto glossy paper torn from magazines, ironed onto the copper laminate, then soaked in hot water to leave just the laser toner on the PCB, ready for etching. It's not a technique I've tried, but I can see the attraction to anyone with a laser printer as it cuts of the need for UV lacquer, a light box and developer.

Ti Pwun · 21st Dec 2014, 9:08 pm

Had I not found my own 'sweet spot' for producing boards then I'm sure I would have explored the iro-on/magazine option - I've seen that done on YouTube with quite good results.

I do use the pre-prepared boards and acetate for taking a prototype off the breadboard but with the cost of professionally made boards now so cheap, if you're not in a mad rush, it's a good option. I've got them as good as tinning the traces and adding a nice solder mask but I'm still experimenting with silk screens using 120T mesh and emulsion. Once I get that sorted out properly I'll make everything myself and won't need to wait weeks for boards to get back to me.

I will probably revisit the spray on stuff at some point so I don't need to use pre-prepared boards but when I last did it I had too many problems. Operator error, no doubt, but I was obviously missing something at the time. Blotchy, blotchy and blotchy!

Edit: forgot to add - making your own UV box using LEDs is an interesting idea. I know an old scanner makes a nice UV box using tubes but LEDs would be a good alternative.

I also made a nice lightbox using a dead LCD monitor so I can examine my transparencies - very useful. The backlight was broken but a strip of 12v LEDs that you buy on a roll create a very nice even light when the various layers of the LCD are re-used.

For anyone who hasn't explored making their own PCBs, it really doesn't need to cost much money at all, does it?!

Wendymott · 21st Dec 2014, 11:31 pm

Hi David and TiPwun. I must admit I was fortunate to obtain my 3 M's UV light box, when the "old company" closed, it has 5 tubes, and a hinged lid with foam insert to hold the pcb onto the acetate. The tubes were getting a bit "tired" so I did try UV led lighting assy's ...I bought 9, and placed them in such a way as to diffuse the light. However I found that the exposure time was way longer than I wanted, thus I went back to the UV tubes, and bought new ones from my local electrical supplier.
I do like the LED array as in the article, but I cant see any exposure times, and I would need to make it a little larger. At present my exposure time is 45 seconds, with developer at 20 deg C...........As I said in the other thread, I always make a test exposure if making SMD pcb's.
I have also considered the "iron on" approach, but looking at the cost of the material.. its about £1 50 per sheet, and being a "Yorkshire" person........ "Ow much ??" when pre coated board is quite reasonable from CPC, if you get the "budget" board, I am sure that every one of the members has his own idea and method for making project boards, none of them right or wrong.......... just works best for you.

David G4EBT · 22nd Dec 2014, 12:09 am

Just to clarify, the 'iron on' technique using a laser printer (rather than the iron-on sheets that you can buy), is basically a no cost option. You simply use scrap gloss paper torn from magazines, and print the artwork on that, which you then iron onto the PCB. The toner adheres to the PCB to act as the resist when it's etched. (It doesn't matter that the page of scrap paper is covered with text or pictures because that's printers' ink and isn't ironed onto the board).

I don't have a laser printer and have no personal experience of the technique but there's a lot about it on the net and many claim to have achieved good results with it. For anyone who does have a laser printer, there's nothing to be lost from giving it a go.

Oldcodger · 22nd Dec 2014, 12:40 am

It's a method I'm about to try , once I get my semi retired laser printer back up and running. it's been sitting idle for some time and dust has gathered, so that now I get a set of black horizontal lines every two inches. I use Express PCB, and I notice that even with the lines ,the black output is not as dark as I'd like. However on an inkjet printout ,the black is very black, so I'm contemplating printing out on inkjet, scan into PC and print the scan on laser. Other alternative is to take inkjet print to a shop with a photo copier ,copy it and use that as my iron on copy. I've seen a few internet comments that most printer papers will work .

kellys_eye · 22nd Dec 2014, 1:47 am

I've used the backing paper from old CDROM label sheets as the carrier for laser printing. The print (on the shiney side of the paper) comes out very crisp and can you can brush it off with a fingertip if you're not careful.

Needless to say it transfers to copper board perfectly.

Oldcodger · 22nd Dec 2014, 10:43 pm

Two questions on that

Is it a problem either with the heat of the laser printer or iron ?
Does it go through laser printer without problems being so thin ?

Wendymott · 22nd Dec 2014, 10:44 pm

Hi David........ I obviously, as normal, got hold of the wrong end of the stick....sounds good to me... I will try it tomorrow...
Laser printers such as my Samsung are quite in expensive, it a Mono one.. ideal for this type of work..... my old HP was parallel port and my pc had no drivers for it..so it was "recycled"......... left it out for the scrap man..

Ti Pwun · 23rd Dec 2014, 7:23 am

Quote:

Originally Posted by Oldcodger

Is it a problem either with the heat of the laser printer or iron ?
Does it go through laser printer without problems being so thin ?

Plenty of examples on YouTube:

https://www.youtube.com/results?sear...iron+toner+pcb

I think the key thing to stop there being a problem with putting magazine pages through a laser printer is to cut the edge of the page, rather than leave a torn edge - I can imagine that causing a jamming problem.

But as I said, I haven't tried it that way myself. But if you watch some videos you'll see how others do it.

As for using the household iron... well, personally I would want to protect it with some brown paper.

Ti Pwun · 23rd Dec 2014, 7:40 am

I just watched an example video and the only thing I didn't like is the use of the Scotch Brite pads.

When I clean my boards I use Brasso and a soft cloth because it is much less abrasive and you don't get those awful scratches everywhere, which can result in minute gaps in the traces. Easily fixed, of course, but I don't want to take the chance of it happening, especially if the board is for someone else.

Wendymott · 23rd Dec 2014, 12:03 pm

I have also just looked at the video..... Interestin.. as "Steve Davis" would say...I am going into town to get some blank glossy paper............the problem with Youtube.. is you look at one thing.. that leads to another.. and whoops the morning as gone..

Ti Pwun · 23rd Dec 2014, 1:39 pm

Probably goes without saying but don't forget to flip the artwork!

Wendymott · 23rd Dec 2014, 10:26 pm

Yeah TiPwun.. I didn't find any Glossy white paper in town, so I will experiment with a glossy magazine cover..."Weekend" comes to mind.. haa haa...

Oldcodger · 24th Dec 2014, 1:05 am

Quote:

Originally Posted by Ti Pwun

I think the key thing to stop there being a problem with putting magazine pages through a laser printer is to cut the edge of the page, rather than leave a torn edge - I can imagine that causing a jamming problem.

But as I said, I haven't tried it that way myself. But if you watch some videos you'll see how others do it.

As for using the household iron... well, personally I would want to protect it with some brown paper.

I hope I'm not seen as being in confrontation but my question was in relation to the backing paper on CD ROM BACKING PAPER. To my mind the backing is "plastic y" and could could pose problems on a laser printer and again with heat from an iron.

Ti Pwun · 24th Dec 2014, 2:12 am

Not at all. I thought you were referring to David's post when you said 'It's a method I'm about to try , once I get my semi retired laser printer back up and running...' - not sure about CD 'backing paper' but I think it's just glossy paper as well. The only plasticy thing would be the toner, I would have thought.

julie_m · 24th Dec 2014, 2:44 am

The adhesive label backing paper must by definition be able to withstand the heat of the printer's fuser. All that is important, is for the toner to have a higher coefficient of adhesivity to the copper than the backing paper. It has quite a low melting point anyway -- lower than most people's hot taps, even; you can spot a photocopier repairer, because they always wash their hands with cold water first.

You could modify an old laser printer for no fusing by disconnecting the fuser element (so the toner won't be melted onto the paper), and shorting the thermistor terminals (so the printer doesn't think the fuser is faulty, go into a sulk and refuse to print).

Ti Pwun · 24th Dec 2014, 5:23 am

I'm confused now - 'adhesive backing paper'? I thought we were talking about the glossy case inserts. You certainly don't want to be putting anything adhesive through your laser printer, that's for sure...or under your iron - recipe for disaster.

The idea is that the toner is melted onto the glossy paper in reverse and then transferred to the board with the iron. Toner will favour a clean copper board over glossy paper. Soaking in water before peeling the paper off will prevent the toner from being pulled back off the board.

If the toner isn't heated onto the glossy paper to start with, I can't see how the process can work.

julie_m · 24th Dec 2014, 6:04 am

I think you're misunderstanding. We're talking about the backing paper from pre-cut, self-adhesive label sheets. It isn't adhesive itself -- it just has a smooth surface (and therefore a low coefficient of adhesivity), so the labels (which are adhesive, but the adhesive is in the middle of the sandwich, where the machinery of the printer is protected from it by the labels in front and the backing paper behind) come away from it cleanly.

When a print on such a surface is placed with the toner in contact with a copper-clad PCB and heated from behind with a steam iron, the toner melts and sticks to the copper in preference to the shiny paper.

David G4EBT · 24th Dec 2014, 9:32 am

Yes, the only reason for using glossy paper is that toner has poor adhesion to it, which is why non-photographic glossy paper is suggested. Obviously, laser photo paper is specifically intended so that laser toner does adhere to the paper, which makes it unsuitable for use in iron-on applications.

Never thought about adhesive label backing sheets, which should liberate the toner very readily. Nice bit of lateral thinking!

Don't know if anyone has viewed the youtube video of the yound girl (ten yr old?) using the technique for etching a brass brooch, which can be seen on the side-bar of the link in post 9 above. Certainly looks effective.

Ti Pwun · 24th Dec 2014, 9:32 am

Oh, that paper. Got you. I don't use those labels so I thought you both meant the glossy inserts.

That's what I said about temporary adhesion to the glossy paper and transfer from there via the iron to the board but if the printer doesn't heat the toner, won't it just fall off between 'printing' on the glossy paper and moving that paper to the board? Seems like it would - not something I've ever tried.

21st Dec 2014, 8:20 pm	#1
David G4EBT Dekatron Join Date: Feb 2003 Location: Cottingham, East Yorkshire, UK. Posts: 5,761	Cheap & Cheerful DIY UV PCB Exposure Unit In another thread 'Etching with Vinegar' the topic of UV techniques was touched upon, and rather than take that thread off-topic, I thought I'd start this one. One of the biggest deterrents to DIY UV techniques is the cost of a UV exposure unit - an entry level no-frills 'hobby' unit consisting of two 8 Watt UV tubes with no timer is typically £100+. More sophisticated UV light boxes with a built-in timer, are upwards of £150.00. Clearly, this is out of the question for making the occasional PCB. For many years until the late 80s I used to make PCBs by painstakingly rubbing down PCB artwork transfers directly onto the copper. One drawback of that is that if you need more than one PCB of the same design, you have to go through the same rigmarole. In the late 80s I made a UV light box with a built-in timer and four 12 inch tubes, (which I still use today), which featured in EPE magazine. However, with the widespread availability of high brightness 5mm UV LEDs of the right wavelength there's no need to go to the expense of UV tubes. UV photo resist lacquer is sensitive to UV light in the 340nm to 420nm wave lengths. Traditional UV exposure units use mains powered UV tubes that emit UV light at a wavelength of around 350nm. A hundred 5mm high brightness (2000 MCP) UV LEDS with a Peak Wave Length (nm) of 395~400 - right in the middle of the desired spectrum - can be found from e-bay suppliers for $4.99 USD post free - that's a little over £3.00. Yes, 3p each! (From China of course - where else?). A member of the EPE Chat Zone - Joe Farr - designed an excellent simple to make UV exposure unit using such UV LEDs in an array of 99 LEDs in nine rows of eleven, mounted on a piece of Strip-board, with 64 holes and 41 tracks. A larger unit could of course be built if desired, but that size should cater for most of the boards we're likely to want to produce. In addition to the LEDs and Strip-board, 33 limiting resistors are required, as outlined on Joe's website. The only other item needed is some 22 SWG solid tinned copper wire for links on the Strip-board. The constructional details and description can be found at this link: http://www.hobbyelectronics.net/con_...sure-unit.html Some other interesting stuff on Joe's site too. (The source of UV LEDs mentioned by Joe no longer exists, but other suppliers can be found by a google search for '100pcs Ultra Violet UV 5mm 2000mcd LED'). The basic unit could of course be refined by building it into a box with a lid etc if desired. I hope Joe's design might prove useful to anyone who has thought about UV PCBs but has been put off by the high cost of the light box. Most other items needed for making UV boards are quite cheap. Personally, I don't buy pre-sensitised boards because if you under or over expose them, the thin coating of lacquer is either not fully developed, or just disappears, especially if the developer is just a little too strong. I prefer to spray a good layer of lacquer and leave it to harden off for a couple of days. If - as can happen at times - the board doesn't turn out as I'd like it, I just wipe it clean with meths, re-spray it and start again. (The UV lacquer I'm presently using has a use-by date of 1999 on the can, and is still good). I understand why many prefer to get PCBs made professionally - making them on a DIY basis is a time-consuming process which can produce variable results, but I don't see it as a chore - if I did, I'd find another hobby! UV isn't 'the only show in town' of course - in recent years there has been a lot of interest in the 'laser print/iron-on' technique, whereby the PCB artwork (in reverse of course!), is printed onto glossy paper torn from magazines, ironed onto the copper laminate, then soaked in hot water to leave just the laser toner on the PCB, ready for etching. It's not a technique I've tried, but I can see the attraction to anyone with a laser printer as it cuts of the need for UV lacquer, a light box and developer. __________________ David. BVWS Member. G-QRP Club member 1339.

21st Dec 2014, 9:08 pm	#2
Ti Pwun Heptode Join Date: Aug 2013 Location: Bradford, West Yorkshire, UK. Posts: 888	Re: Cheap & Cheerful DIY UV PCB Exposure Unit Had I not found my own 'sweet spot' for producing boards then I'm sure I would have explored the iro-on/magazine option - I've seen that done on YouTube with quite good results. I do use the pre-prepared boards and acetate for taking a prototype off the breadboard but with the cost of professionally made boards now so cheap, if you're not in a mad rush, it's a good option. I've got them as good as tinning the traces and adding a nice solder mask but I'm still experimenting with silk screens using 120T mesh and emulsion. Once I get that sorted out properly I'll make everything myself and won't need to wait weeks for boards to get back to me. I will probably revisit the spray on stuff at some point so I don't need to use pre-prepared boards but when I last did it I had too many problems. Operator error, no doubt, but I was obviously missing something at the time. Blotchy, blotchy and blotchy! Edit: forgot to add - making your own UV box using LEDs is an interesting idea. I know an old scanner makes a nice UV box using tubes but LEDs would be a good alternative. I also made a nice lightbox using a dead LCD monitor so I can examine my transparencies - very useful. The backlight was broken but a strip of 12v LEDs that you buy on a roll create a very nice even light when the various layers of the LCD are re-used. For anyone who hasn't explored making their own PCBs, it really doesn't need to cost much money at all, does it?! Last edited by Ti Pwun; 21st Dec 2014 at 9:14 pm.

21st Dec 2014, 11:31 pm	#3
Wendymott Octode Join Date: Jun 2013 Location: Huddersfield, West Yorkshire, UK. Posts: 1,795	Re: Cheap & Cheerful DIY UV PCB Exposure Unit Hi David and TiPwun. I must admit I was fortunate to obtain my 3 M's UV light box, when the "old company" closed, it has 5 tubes, and a hinged lid with foam insert to hold the pcb onto the acetate. The tubes were getting a bit "tired" so I did try UV led lighting assy's ...I bought 9, and placed them in such a way as to diffuse the light. However I found that the exposure time was way longer than I wanted, thus I went back to the UV tubes, and bought new ones from my local electrical supplier. I do like the LED array as in the article, but I cant see any exposure times, and I would need to make it a little larger. At present my exposure time is 45 seconds, with developer at 20 deg C...........As I said in the other thread, I always make a test exposure if making SMD pcb's. I have also considered the "iron on" approach, but looking at the cost of the material.. its about £1 50 per sheet, and being a "Yorkshire" person........ "Ow much ??" when pre coated board is quite reasonable from CPC, if you get the "budget" board, I am sure that every one of the members has his own idea and method for making project boards, none of them right or wrong.......... just works best for you. __________________ Should get out more. Regards Wendy G8BZY

22nd Dec 2014, 12:09 am	#4
David G4EBT Dekatron Join Date: Feb 2003 Location: Cottingham, East Yorkshire, UK. Posts: 5,761	Re: Cheap & Cheerful DIY UV PCB Exposure Unit Just to clarify, the 'iron on' technique using a laser printer (rather than the iron-on sheets that you can buy), is basically a no cost option. You simply use scrap gloss paper torn from magazines, and print the artwork on that, which you then iron onto the PCB. The toner adheres to the PCB to act as the resist when it's etched. (It doesn't matter that the page of scrap paper is covered with text or pictures because that's printers' ink and isn't ironed onto the board). I don't have a laser printer and have no personal experience of the technique but there's a lot about it on the net and many claim to have achieved good results with it. For anyone who does have a laser printer, there's nothing to be lost from giving it a go. __________________ David. BVWS Member. G-QRP Club member 1339.

22nd Dec 2014, 12:40 am	#5
Oldcodger Nonode Join Date: Oct 2014 Location: West Midlands, UK. Posts: 2,181	Re: Cheap & Cheerful DIY UV PCB Exposure Unit It's a method I'm about to try , once I get my semi retired laser printer back up and running. it's been sitting idle for some time and dust has gathered, so that now I get a set of black horizontal lines every two inches. I use Express PCB, and I notice that even with the lines ,the black output is not as dark as I'd like. However on an inkjet printout ,the black is very black, so I'm contemplating printing out on inkjet, scan into PC and print the scan on laser. Other alternative is to take inkjet print to a shop with a photo copier ,copy it and use that as my iron on copy. I've seen a few internet comments that most printer papers will work .

22nd Dec 2014, 1:47 am	#6
kellys_eye Octode Join Date: Jan 2014 Location: Oban, Scotland, UK. Posts: 1,129	Re: Cheap & Cheerful DIY UV PCB Exposure Unit I've used the backing paper from old CDROM label sheets as the carrier for laser printing. The print (on the shiney side of the paper) comes out very crisp and can you can brush it off with a fingertip if you're not careful. Needless to say it transfers to copper board perfectly.

22nd Dec 2014, 10:43 pm	#7
Oldcodger Nonode Join Date: Oct 2014 Location: West Midlands, UK. Posts: 2,181	Re: Cheap & Cheerful DIY UV PCB Exposure Unit Two questions on that Is it a problem either with the heat of the laser printer or iron ? Does it go through laser printer without problems being so thin ?

22nd Dec 2014, 10:44 pm	#8
Wendymott Octode Join Date: Jun 2013 Location: Huddersfield, West Yorkshire, UK. Posts: 1,795	Re: Cheap & Cheerful DIY UV PCB Exposure Unit Hi David........ I obviously, as normal, got hold of the wrong end of the stick....sounds good to me... I will try it tomorrow... Laser printers such as my Samsung are quite in expensive, it a Mono one.. ideal for this type of work..... my old HP was parallel port and my pc had no drivers for it..so it was "recycled"......... left it out for the scrap man.. __________________ Should get out more. Regards Wendy G8BZY

23rd Dec 2014, 7:40 am	#10
Ti Pwun Heptode Join Date: Aug 2013 Location: Bradford, West Yorkshire, UK. Posts: 888	Re: Cheap & Cheerful DIY UV PCB Exposure Unit I just watched an example video and the only thing I didn't like is the use of the Scotch Brite pads. When I clean my boards I use Brasso and a soft cloth because it is much less abrasive and you don't get those awful scratches everywhere, which can result in minute gaps in the traces. Easily fixed, of course, but I don't want to take the chance of it happening, especially if the board is for someone else.

23rd Dec 2014, 12:03 pm	#11
Wendymott Octode Join Date: Jun 2013 Location: Huddersfield, West Yorkshire, UK. Posts: 1,795	Re: Cheap & Cheerful DIY UV PCB Exposure Unit I have also just looked at the video..... Interestin.. as "Steve Davis" would say...I am going into town to get some blank glossy paper............the problem with Youtube.. is you look at one thing.. that leads to another.. and whoops the morning as gone.. __________________ Should get out more. Regards Wendy G8BZY

23rd Dec 2014, 1:39 pm	#12
Ti Pwun Heptode Join Date: Aug 2013 Location: Bradford, West Yorkshire, UK. Posts: 888	Re: Cheap & Cheerful DIY UV PCB Exposure Unit Probably goes without saying but don't forget to flip the artwork!

23rd Dec 2014, 10:26 pm	#13
Wendymott Octode Join Date: Jun 2013 Location: Huddersfield, West Yorkshire, UK. Posts: 1,795	Re: Cheap & Cheerful DIY UV PCB Exposure Unit Yeah TiPwun.. I didn't find any Glossy white paper in town, so I will experiment with a glossy magazine cover..."Weekend" comes to mind.. haa haa... __________________ Should get out more. Regards Wendy G8BZY

24th Dec 2014, 2:12 am	#15
Ti Pwun Heptode Join Date: Aug 2013 Location: Bradford, West Yorkshire, UK. Posts: 888	Re: Cheap & Cheerful DIY UV PCB Exposure Unit Not at all. I thought you were referring to David's post when you said 'It's a method I'm about to try , once I get my semi retired laser printer back up and running...' - not sure about CD 'backing paper' but I think it's just glossy paper as well. The only plasticy thing would be the toner, I would have thought.

24th Dec 2014, 2:44 am	#16
julie_m Dekatron Join Date: May 2008 Location: Derby, UK. Posts: 7,735	Re: Cheap & Cheerful DIY UV PCB Exposure Unit The adhesive label backing paper must by definition be able to withstand the heat of the printer's fuser. All that is important, is for the toner to have a higher coefficient of adhesivity to the copper than the backing paper. It has quite a low melting point anyway -- lower than most people's hot taps, even; you can spot a photocopier repairer, because they always wash their hands with cold water first. You could modify an old laser printer for no fusing by disconnecting the fuser element (so the toner won't be melted onto the paper), and shorting the thermistor terminals (so the printer doesn't think the fuser is faulty, go into a sulk and refuse to print). __________________ If I have seen further than others, it is because I was standing on a pile of failed experiments.

24th Dec 2014, 5:23 am	#17
Ti Pwun Heptode Join Date: Aug 2013 Location: Bradford, West Yorkshire, UK. Posts: 888	Re: Cheap & Cheerful DIY UV PCB Exposure Unit I'm confused now - 'adhesive backing paper'? I thought we were talking about the glossy case inserts. You certainly don't want to be putting anything adhesive through your laser printer, that's for sure...or under your iron - recipe for disaster. The idea is that the toner is melted onto the glossy paper in reverse and then transferred to the board with the iron. Toner will favour a clean copper board over glossy paper. Soaking in water before peeling the paper off will prevent the toner from being pulled back off the board. If the toner isn't heated onto the glossy paper to start with, I can't see how the process can work.

24th Dec 2014, 6:04 am	#18
julie_m Dekatron Join Date: May 2008 Location: Derby, UK. Posts: 7,735	Re: Cheap & Cheerful DIY UV PCB Exposure Unit I think you're misunderstanding. We're talking about the backing paper from pre-cut, self-adhesive label sheets. It isn't adhesive itself -- it just has a smooth surface (and therefore a low coefficient of adhesivity), so the labels (which are adhesive, but the adhesive is in the middle of the sandwich, where the machinery of the printer is protected from it by the labels in front and the backing paper behind) come away from it cleanly. When a print on such a surface is placed with the toner in contact with a copper-clad PCB and heated from behind with a steam iron, the toner melts and sticks to the copper in preference to the shiny paper. __________________ If I have seen further than others, it is because I was standing on a pile of failed experiments.

24th Dec 2014, 9:32 am	#19
David G4EBT Dekatron Join Date: Feb 2003 Location: Cottingham, East Yorkshire, UK. Posts: 5,761	Re: Cheap & Cheerful DIY UV PCB Exposure Unit Yes, the only reason for using glossy paper is that toner has poor adhesion to it, which is why non-photographic glossy paper is suggested. Obviously, laser photo paper is specifically intended so that laser toner does adhere to the paper, which makes it unsuitable for use in iron-on applications. Never thought about adhesive label backing sheets, which should liberate the toner very readily. Nice bit of lateral thinking! Don't know if anyone has viewed the youtube video of the yound girl (ten yr old?) using the technique for etching a brass brooch, which can be seen on the side-bar of the link in post 9 above. Certainly looks effective. __________________ David. BVWS Member. G-QRP Club member 1339.