Need some help with my etching process

[Plecto]

Hi. A friend of mine and I started etching recently. Some projects has been okay, but not all of them and definitely not those with small trace and gap sizes (which are required for smd stuff).

We print the circuit on magazine paper and cut a piece of copper clad board with the boards dimentions. We are very carefull not to touch the paper while doing this. We brush the board with some steel wool and then clean it with nail polish remover (without acetone). We then tape the paper to the board and holds a hot iron over it for about 5 minutes.

At the beginning we had a problem with about 1/3 of the toner not sticking to the board. We later figured that wobbling the iron back and forth carefully fixed that (figured that the iron isn't 100% flat and exposed some areas more than others). The problem now is that the toner some how moves so parts of the toner gets all smeared around. This usually happens with less than half the board (the rest of the board is absolutely perfect). I see videos of people moving the iron around like they are ironing clothes, but we keep the iron very steady with decent preasure so I have no idea how the toner gets spread around. I've also seen people in video guides that don't even use tape, we use tape on all four sides which makes it even stranger that the toner spreads.

The etching process is usually not a problem. Even though our nail polish remover doesn't contain acetone, it easly removes the toner. We are etching with HCL and hydrogen peroxide. We have followed a guide that said one part 30% HCL to two parts 3% hydrogen peroxide so we are following this to the letter. The guide said that the etchant would go from green to brown when it stopped working. When this happens we are supposed to add some more hydrogen peroxide to get more oxygen into the mix. Our etchant has never gotten brown, but the etching process is really slow! We usually add a little bit hydrogen peroxide and HCL for each time we etch (can go days in between) which seems to boost it up a little bit. I'm also unsure if it's any point moving the container around, not sure if that might add some more oxygen to it or not.

Anyone who could help us out with this?

 

[sky_123]

If the board doesn't begin properly, then it will end badly. You need to resolve the toner sticking issue, or find an alternate method. The alternative of pre-sensitized light-sensitive board works very well, with transparencies (i.e. print to a transparent sheet, expose to light then develop with sodium hydroxide or
otherwise). The board is already clean, just peel off the light-protective backing. Nothing much to go
wrong, as long as you have a very dense printed transparency (e.g. from a photocopier).
Regarding the etching, why not just use traditional ferric chloride? As long as it is warm, it is always effective.

 

[Plecto]

The plan was to etch with ferric chloride, but I have no idea of where to get it. It can't be shipped here (it will be stopped in customs) and it's extremely expensive to buy in my country. The only local places I've found it is at farmacies and the price is like 20 times that of an international website. I'm going to stick with HCL and hydrogen peroxide, after all it does work (just takes some time).

Using UV light instead of a hot iron sounds like a good idea, I've been reading a little about it. I guess I'm going to buy some of the equipment needed soon, but I would still like to know why my current method isn't working. I've seen loads of people getting quite nice results from using toner transfer.

 

[sky_123]

Maybe others have useful toner feedback (I've never used it). If you finally go the light-based method, it is close to what real PCB manufacture is like (they do photophotting rather than photocopying onto transparent sheet however). If you can find a company to photoplot for you, then you'll get incredible results (it can be expensive though). It's a shame there are no cheap photoplotters.
See **broken link removed**which has some brief prototyping
info - they printed on "inkjet film", presumably with an inkjet printer (I have only tried photocopying onto acetate, and photoplots).

 

[betwixt]

The UV system is VASTLY better and you can reuse the artwork over and over again.
I think the basic problem you have at the moment is the type of paper you are using. Bear in mind that toner is designed to stick once only and by re-heating it you are trying to make it jump from it's original surfece to a new one. I've tried it and had the same results as you, proper tranfer paper works far better but it is expensive.

Brian.

 

[Plecto]

I guess I could start focusing more on the UV system then. The plan is to make the UV exposure unit using an old scanner. One question I have is how much UV light should be in that thing? I'm looking at UV leds, but I'm not sure how many watts I shoudl be getting.

 

[sky_123]

You can make a UV table quite cheaply, just find an old scanner, it can serve as the enclosure. Then, obtain some UV tubes (e.g. those intended as spares for commercial UV systems). When I built something similar, I powered it from 12V using some transformer based supply (probably from an ancient fax machine, they used to have fluorescent tubes inside them). I only had 2 tubes, and it was
enough for very large PCBs. The thin scanner glass seemed to not cause any major issue to the UV.

 

[betwixt]

Use UV tubes, the UV LED wavelength is not suitable for PCBs and in any case you need uniform illumination over the board area. LEDs have lenses which narrow the beam too much.

I use two 8W UV tubes side-by-side about 4cm apart and it works perfectly for PCB up to about 180 x 100 mm. For bigger boards just add more tubes. You will need balast chokes and starters for the tubes but it will still work out much cheaper than LEDs.

Brian.

 

[Plecto]

Okay, I've just ordered a couple of UV bulbs from ebay. I don't know how strong these are so how do I know how long I should keep my board under the exposure? As far as I have seen, there won't be any visable change after the UV exposure, the visable change happens in the developing process. Also, does anyone know where to get these photo resist boards? I found some that cost 3.18usd for a 4 x 6" board, is this something I have to expect to pay?

 

[betwixt]

The price is about right but look for "PRP" spray paint. It's special photo sensitive paint in an aerosol so you can make your own boards. Handle it with care and remember that it has to be done in low light conditions. PRP isn't cheap but you can turn many plain copper boards into photo sensitive ones from one can.

I find the exposure time in my light box is about 3 minutes. You can *just* see the image after exposure but remember you have to work in fairly dark conditions, don't turn the room light on to look at it or the whole thing will disappear when in the developer! When you develop the board the image is very obvious, you should see bare copper where it is to be removed and a contrasting paint layer where it is protected. Look at pictures on my web site:
http://www.atv-projects.com/Making_PCBs.html where you can see the different stages of production.

Brian.

 

[stacksmith]

I've had really good results with heat-transferred laser toner. I find that you have to either spend $1.00 a sheet for the blue transfer sheets, or use old-school water-based mailing tape (I found a 4-inch-wide roll somewhere years ago, and it will last me a lifetime). It has a starch coating (I've read about people making their own), and dipped in water peels off very cleanly leaving a perfect resist layer.

BTW, HCl/peroxide etch is really fast if heated and properly balanced. I use an aquarium heater for my tank. See my instructable.

 

[rohitkhanna]

Hi. A friend of mine and I started etching recently. Some projects has been okay, but not all of them and definitely not those with small trace and gap sizes (which are required for smd stuff).

We print the circuit on magazine paper and cut a piece of copper clad board with the boards dimentions. We are very carefull not to touch the paper while doing this. We brush the board with some steel wool and then clean it with nail polish remover (without acetone). We then tape the paper to the board and holds a hot iron over it for about 5 minutes.

At the beginning we had a problem with about 1/3 of the toner not sticking to the board. We later figured that wobbling the iron back and forth carefully fixed that (figured that the iron isn't 100% flat and exposed some areas more than others). The problem now is that the toner some how moves so parts of the toner gets all smeared around. This usually happens with less than half the board (the rest of the board is absolutely perfect). I see videos of people moving the iron around like they are ironing clothes, but we keep the iron very steady with decent preasure so I have no idea how the toner gets spread around. I've also seen people in video guides that don't even use tape, we use tape on all four sides which makes it even stranger that the toner spreads.

The etching process is usually not a problem. Even though our nail polish remover doesn't contain acetone, it easly removes the toner. We are etching with HCL and hydrogen peroxide. We have followed a guide that said one part 30% HCL to two parts 3% hydrogen peroxide so we are following this to the letter. The guide said that the etchant would go from green to brown when it stopped working. When this happens we are supposed to add some more hydrogen peroxide to get more oxygen into the mix. Our etchant has never gotten brown, but the etching process is really slow! We usually add a little bit hydrogen peroxide and HCL for each time we etch (can go days in between) which seems to boost it up a little bit. I'm also unsure if it's any point moving the container around, not sure if that might add some more oxygen to it or not.

Anyone who could help us out with this?

#1 What type of printer are you using ? Inkjet & similar are wrong, laser with toner is right. Make sure you have the right type of printer, otherwise its no use. This might explain your "toner spread"

#2 What's the need to clean your board with "nail polish remover" ? There's no need - and you have no idea what chemicals are included here. I suggest simple soap/ water and some very very fine scrubs (soft steel wool works fine) to get the shine on the board. The idea of cleaning is to REMOVE any crap on the copper... not to ADD to the crap. This too might explain your "toner spread" and ALSO why 1/3 of your tracks are bad.

#3 wiggling the iron to ensure all places are covered is a good idea. However 5 minutes is way too long. Excellent transfers can be done with 1-2min max. Also - set the iron on MAX ( usually the cotton setting)

#4 I don't know how h2o2 + hcl works, since i always use fecl3. HOWEVER i have read about formulas using these for etching which claim success. Note that with fecl3, heating the solution speeds up the process considerably. Temps of 50 - 70 deg C have worked fine for me. Lower temps seems to exponentially prolong the process. Also, *mild* agitation ensures that fresh etchant always comes in contact with the copper for better/ quicker reactions. I don't think the movement/ agitation has anything to do with adding oxygen

#5 using photo paper is useful. Its the glossy side which is required ... and any magazine paper should be the shiny/ glossy type (e.g. front/ back covers; or maybe some pages with the ads on them), not the normal magazines pages. Unless its a really fancy magazine !!

#6 tape on even the entire length of one single side should be enough. As long as its enough to hold the paper steady against the board. Try using a few sheets of normal paper between the Iron and the sheet/board to prevent any sticking/ moving that might occur

hope something here was helpful. I HAVE etched many many boards down to 12mil width/8 mil space. Single tracks between 0.1" pads and 32 pin TQFP IC pads, so the method does work quite well.

However having SAID that, there are always a few "errors" on the toner-transfered board which need to be looked for carefully, and corrected using some suitable paint/ pen.
But with practise & proper care these could be down to just 2-3 in a dense board.

cheers!