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Cheshiretaurus

How to make photo etched parts at home

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Making photo etched parts at home

Many years ago I was a young apprentice in a small electronics company, one of my tasks was making printed circuit boards (PCBs) for prototypes and one off’s. Making PE parts is a very similar process, so I gave it a go. When I made PCBs the boards were pre-coated and we used ferric chloride as an etchant, I’m going to show you how to make a double sided PE using dry film resist. You will need to invest in some bits and bobs to help you along, nearly everything is on good old ebay, the rest you can get in Tesco, ASDA etc, and don’t forget to pick up some wooden or plastic stirrers from Mc Donald’s and the like. I won’t write a long list now of things you need I’ll leave that to the end and get straight to the interesting bits, You may not get success first time but keep practising, I had many fails at various stages getting this right so i'll share what I know.

but first this :-

Making photo etched parts uses some hazardous chemicals and as such safety steps should be taken in the form of protective clothing, gloves, goggles etc. The chemicals are corrosive to skin as well as to brass so should be immediately washed off with plenty of water if contact with skin occurs, medical attention may be required as well. By continuing to read this article you must accept that YOU are responsible for your own safety and should read all labels and safety data sheets available.

Nuff said, lets get on with it.

Artwork

The artwork was printed on over head projector (OHP) film for inkjets this film has a rough and a smooth side. The rough side is the printing side. We are going to use negative resist film so when you create your artwork white is where you want brass and black is where it is to be etched away. You will notice the ‘sprue gates’ are only on the rear art work this is so they get etched away from one side only and become half the thickness off the surrounding brass. Start off by creating your artwork without the gates so the parts are ‘floating’ with no attachment to the surrounding frame, save this file call it ‘front’ or something now make a copy of that file and call it ‘rear’. Open the rear file into your editing software and draw the ‘gates’ in.

You now have 2 files front and rear. Print your files using your printers best settings, on mine I have selected Print quality high, Use black ink only, darkness max, contrast max, high resolution paper. If your software can print alignment/crop marks, use them! If not add some crosshairs to your art work but they must be the same on both files so check for this before you create the second file.

The two artworks are shown here, top is the front with the floating parts bottom is the rear with the 'sprue gates' (to be printed mirror image)

Fold lines should be on the inside of the fold and twice the thickness of the brass.

9428203547_4e57f776da_o.jpg

Printing preference page

9428787290_b62cb24ca3_o.jpg

manual ajustment pop up page

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Because I’m from up north and a bit tight, to save on OHP film print off one of your artworks on plain paper first, now you can cut out a bit of OHP film appropriate to the size of your artwork to include the alignment marks, tape this to the paper over where it is to print and put it back through the printer, same again with the other file. Print the rear one as a mirror image and let them dry for an hour or so.

I’ve tried using laser printers for the artwork but the blacks aren't as deep, I find the inkjet better.

We have 2 artworks, the rear one should be turned upside onto a white surface or light box if you have one. Cut the top art work out so it just includes the alignment marks but make sure it smaller than the bottom one. Now carefully align the two together on top of each other with printed sides on the outside, this is where your alignment mark come into use, use a magnifying glass if necessary. When you are satisfied that you cannot get aligned any better put a piece of tape across one edge to form a hinge and make sure it doesn't move as you do so.

We now have our art work prepared, did you make that second check that is defiantly aligned? If it has moved peel off the tape and do it again, super accuracy is required here if your PE is going to be of any use.

Cut out a piece of brass just bigger than the artwork with scissors and give it a clean with Acetone, IPA or other solvent. I'm going to use a 0.005" or 0.125mm gauge sheet

9401201204_dee64735fd_h.jpg

Applying the resist

The resist is a negative resist so the bits that get exposed to UV cure and harden while the unexposed bits stay weak, the resist should be stored in the dark and away from sunlight. It should also be kept away from sunlight and bright lights while your work with it until it has been developed.

Switch the laminator on.

Cut out two pieces of resist just larger than the brass, the resist is in between 2 protective sheets you need to remove one before applying to the brass. Take one piece and with two bits of tape on either side of one corner pull them apart, one of the protective sheets should come away, you might find it takes a couple of goes to get this.

Put your brass on something flat that will be easy to turn around as you work, a hotel room key is ideal for this, make sure there is no dust or anything and put a big blob of water on it.

Take your piece of resist, find the side without the protective layer (it’s the side that feels sticky if you touch it on the edge, don’t touch the bit that’s going on the brass) and gently offer this side to the brass, when it touches the water, the water will grab it, gently lower it on and let it settle. Check there are no air bubbles trapped, if there are just lift the resist a little and gently give the bubble a little persuasion to depart. You might need a little more water before lowering the resist down again. When you’re happy that there is nothing there except a thin layer of water give the centre of the sheet a small press just to tack it into place and stop it slipping, then with a tissue or soft cloth work the water out from the centre don’t press hard just yet, if you do it will tack that bit onto the brass making it harder to remove should you find an air bubble. Once you are happy that you have ALL the water out with NO air or water bubbles trapped smooth the resist down with a bit of pressure.

Take a piece of paper and fold it in half, gently lift the brass off using a scalpel blade to break the adhesion and place it in your folded paper. The paper acts as a carrier to go through the laminator if you put the brass through naked it will get bent and damaged, also as its small it might get lost in there, with all the electrical hazards you might expect with a loose bit of metal rattling inside an electrical appliance.

Once though the laminator, open up the paper, the resist will be stuck to the brass except where there is air or water trapped, you did get it all out didn’t you? The overlap will also be stuck to the paper so take your scalpel and cut the brass sheet free.

Do the same for the other side.

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Exposure

You need a UV light source, ebay has some ladies gel nail curing lights for £10-15, they come with four bulbs two above and one on each side, you only want the light going straight down through the artwork onto the brass so leave the side bulbs out and put them some ware safe, these are now your spares.

You need two sheets of glass, I found two cheap 4”x6” photo frames the ones that are just glass and wooden back in Tesco for 50p each kept the glass a threw the rest away.

Make sure they are clean, now slip your brass between the two artworks making sure you are happy with the positioning then sandwich this between the sheets of glass and clip together with bulldog clips. A quick check that the brass is still in the right place, no foreign objects obscuring things and the handles of the clips are not in the way.

-Optional- You get a slightly sharper image if you remove the protective sheets at this stage however you run the risk of the resist getting stuck to the artwork if this happens you will need to strip the resist off the brass and start again. This is why the artwork has been prepared printed side out. If you get the resist on the artwork IPA or acetone may get it off (only clean the non-printed side) but you could end up having to print a new artwork.

Expose this to UV light, I have a bit of cardboard clipped to the side not being exposed, this is just to stop light spilling round to the rear so you can remain in control of how much exposure takes place. Once exposed turn over, swap the card to the other side and expose the other side.

Timing, getting the timing tight is critical, too short and your resist is not suitably hardened, to long and you start to expose the bits you shouldn't, remember the artwork is actually translucent the black bits don’t block the light completely they just attenuate it.

I have found 45 seconds per side seems to be the optimum timing, this will all depend on how dark your black is, how strong the light is, how close the bulb is, how old the bulb is. 45 second is for my setup yours may differ, some experimenting maybe required.

Once done your brass should have the image on it with the exposed bits turning darker blue.

Edit - You can use sunlight to expose but be careful as this is an unknown and variable quantity so you could end up over exposing it.

9398435821_fb0adcbbc5_h.jpg

Developing

As I said earlier exposure to UV light hardens the resist leaving the unexposed areas soft and dissolvable in the ‘developing’ fluid.

The fluid we are going to use is a sodium hydroxide solution. Sodium hydroxide is caustic soda sold as household drain cleaner. We need to make a 5% solution of this. I’m going to make 50ml of the stuff.

1ml of water weighs 1 gram so 5% of 50g is 2.5g. you need to make enough to submerge the brass in your container, find out how much you need either in volume (ml) or measure the weight of the water (g) and multiply this figure by 0.05 e.g. 50g x 0.05 = 2.5g. This is how much caustic soda you need to weigh out. Dissolve this in your measured amount of warm water. You’ve now made your developing fluid. Be careful, this is corrosive and will cause chemical burns.

I warm the fluid up by leaving the it in the airing cupboard where it is 38°c, Remove the protective layers from your brass with tape on the corner, once the protection is removed avoid putting the brass flat down on any surface, if you do the unexposed bits may well stick to it and you will be back to stripping and starting again. Dunk you brass in the fluid for 2-3 min to dissolve the unexposed resist, you will see it dissolving and turning opaque or milky. Then wash the resist away under a running tap, you can assist this by gently brushing it off with an old paintbrush under the tap. Have a really good look to see if you got all the resist off look carefully as it can be difficult to see. If there is any left put it back in the solution for another minute and wash off again. Don’t leave it in for too long however as it may start to dissolve the exposed stuff too. Once your satisfied you have got it all off put it back under the UV to see if you missed anything, if you did, strip the brass with acetone (see stripping at the end) and start again. Pain in the neck I know, but you haven’t yet etched it so you can reuse the brass. Better to find out now rather than once you've etched it in my opinion.

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Etching

To etch we are going to use an acid to erode away the brass. Sodium persulphate is an etchant used in making PCBs, other etchants are available including ferric chloride, ammonium persulphate & potassium persulphate.

For sodium persuphate a 20% solution is needed so multiply your weight/volume of water require by 0.2, so for 50ml of etchant weigh out 10g of sodium persulphate. I haven’t tried other etchants yet, so other ones may need different concentrations. This is also highly corrosive and will cause chemical burns.

Find a suitable non metallic container and stirrer and dissolve the etchant in the appropriate amount of water in the same way as you made the developer, and warm it up for use, for me that’s put it back in the airing cupboard again. (It may take a few minutes of stirring to fully dissolve.)

Submerge the brass in the etchant, as the etchant tends to become more concentrated at the bottom give it a stir every 10 mins or so until fully etched. The pic shows pin holes starting to appear after 28mins and after 50mins it was fully etched. Keep an eye on it. I nearly over etched this one as I was writing this article at the time. Don’t forget the areas that are going to be etched from one side only will carry on being etched until it is washed off and also the etchant will start to undercut from the sides. So as soon as you are satisfied that it is fully done. Remove it from etchant and fully rinse it under a tap.

The etching time will increase as the etchant becomes exhausted the more times you use it, the same will happen with your developer.

9398436735_125c1a3158_h.jpg

Stripping

Soak the PE in acetone for a few minutes to remove the resist, it should start to peel of but might need a little help. The acetone will become purple in colour and becomes a fantastic dye so watch you don’t spill it, I have a bottle I keep the used acetone in just for cleaning PE. The photo actually shows it in water and is just for illustration!

If all is well you've just made your first PE, go have a beer or three to celebrate.

Things you need

Brass http://www.ebay.co.u...=item5d304537b0

Dry film http://www.ebay.co.uk/sch/i.html?_odkw=dry+film&_osacat=0&_trksid=p2045573.m570.l1313.TR0.TRC0.Xdry+film+photoresist&_nkw=dry+film+photoresist&_sacat=0&_from=R40

OHP film http://www.ebay.co.uk/sch/i.html?_sacat=0&_from=R40&_nkw=inkjet+ohp+film&_sop=15

UV Light http://www.ebay.co.uk/sch/i.html?_trksid=p2050601.m570.l1311.R1.TR10.TRC0.A0.Xuv+na&_nkw=uv+nail+lamp&_sacat=0&_from=R40

Sodium hydroxide, caustic soda cleaning product section of ASDA Tesco etc

Glass sheets - cheap photo frame

Spatula http://www.ebay.co.uk/sch/i.html?_sacat=0&_nkw=laboratory+spatula&_frs=1

Etchant

Different types are available - Sodium persulphate, ferric chloride, ammonium persulphate & potassium persulphate.

Couldnt find the Sodium persulphate I used doesnt seem to be listed,

http://www.ebay.co.uk/sch/i.html?_odkw=pcb+etchant&_osacat=0&_from=R40&_trksid=p2045573.m570.l1313.TR0.TRC0.Xetchant&_nkw=etchant&_sacat=0

Edit 28/8/13

Looks like the Sodium persulphate is listed on ebay again

http://www.ebay.co.uk/sch/i.html?_trksid=p2047675.m570.l1313.TR0.TRC0.Xsodium+persulphate&_nkw=sodium+persulphate&_sacat=0&_from=R40

Containers, I used lab beakers, do a search on Borosilicate beaker

Scales, search pocket scales or micro weighing scales

Stirrers grab a hand full at McDonald’s

Timings & quantity's

Exposure 45sec per side

1ml of water weighs 1gram

Developer 5% strength 2-3mins at 38°C

Etchant 20%strength 45min to 1:30 at 38°C (Sodium persulphate)

Single side etch

To make a single side etch, still apply resist to both sides of the brass and expose the rear completely. etching time will be double as the etchant can only eat through the brass from one side so has twice as much go through to meet the other side.

I'll make updates to this as I find new things but in the meantime good luck!

Mark

Edited by Cheshiretaurus

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http://www.micromark.com/micro-mark-pro-etch-photo-etch-system-export-version,8347.html

l know micro mark has a PE kit available but the chemicals are only for within the states but the rest of the kit is available in an export version. Been looking at it for a while but right not l do not have a suitable place to use it at the moment. Thanks for the post. I found it very informative

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I have made PCB's in the past so I have most of the kit required to do this. An excellent tutorial, thanks for taking the time to do it.

Oh and you don't realy need the UV light, strong sunlight works fine.

Edited by Nigel Heath

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Oh and you don't realy need the UV light, strong sunlight works fine.

Good point Nigel that would work, I've added that in, but it carries a bit of a chance of over exposing.

Added some more stuff in too and corrected some typos

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Brilliant. Thanks everso for putting this up. Even if I never get doing my own at least I know how its done now.

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Many thanks for posting very good how to do, like this sort of thing always interesting to learn.

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Coo, ruddy nora! That's really very clever, but I think Eduard are still going to be getting my business... I can just see my carpet after I've started playing with all that stuff...

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Nigel

Pressing CTRL+D together will save the current URL in your browsers bookmarks.

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Oh so its just adding to my favorites, I did know how to do that, I thought bookmarks were something different.

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Where do you put the waste material, after you have done the etching

I have some plastic bottles I store it in between uses until its strength is exhausted, For disposal the sodium hydroxide can be flushed down the sink as it is after all drain cleaner, for the etchant it can be disposed of at the waste chemical section of your local tip .

Edited by Cheshiretaurus

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Interesting stuff! I used to dabble with diy PCB etching back in the day. I didn't realise photo etched parts used similar techniques!

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Your excellent tutorial inspired me to have a go at photo etching and to join this forum. However, I hit a problem. After exposure in the fingernail thingy I tried to remove the protective layer from the top of the resist and found that the resist peeled off with it, both hardened and non hardened. What have I done wrong? A few possibilities come to mind.

 

1.  I didn't expose it for long enough

2. Trying to take the protective layer off too soon

3. Not managing to get all the air or water squeezed out

4. Not cooking it enough in the laminator

5. ???

 

I looked at a couple of photo etching tutorials on Youtube and noticed a couple of things they do differently. Firstly they don't use a blob of water but apply the film directly to the metal. Secondly they don't use a folded sheet of paper to protect the metal and/or the laminator and they run the metal and film through the laminator three or four times. So I tried their way. The first thing I found that it was much harder to apply the film to the metal without creasing it or getting it to stick to itself. Based on my experimental sample size of one I can't be sure whether this was just a coincidence. The second thing I found was that after four passes through the laminator it appeared that the heat had made the film bubble up in places. On the plus side I found that I could easily remove the protective film, even before exposing to UV, while leaving the photo resist in place undamaged on the metal (apart from the bubbling).

 

Any ideas how to get it right without too many experiments?

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Ooh, what a helpful thread. I've been looking for something like this as I have aspirations in this direction, but have only tried single sided etching with the laserjet printing/iron-on resists which I haven't found sharp enough for fine work and unreliable for large areas.

 

One thing I would add is that permanent markers can be used to touch up any small defects in you resist. These are some parts I made for a 1:8 Sopwith Camel model and the legend 'Test A' was written using a permanent marker. I'm using the Edinburgh etch system (Ferric Chloride with citric acid catalyst). For reference the grid behind the brass is 1cm squares.

 

p1050091.jpg

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oh god, another awesome thread....now i'll have to learn  drawing in software!

 

- what is the thinnest brass that can be etched?

 

i'm making some German tank washers in 0.1mm atm, could something so thin be etched?

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