Making your own single sided PCB using photoresist board

[Ja7me]

Hello everyone,

I have been making some single sided PCB's over the last few months. However, I am experiences some difficulties. Sometimes the process seems to work fine, but sometimes the etching process eats away at my copper tracks, which makes the board unusable.

This is my set up:
- UV light box (megauk)
- Developer (Sodium hydroxide free) I use a concentration of 15g developer, to 800mL of water.
- Ferric Chloride etching crystals, I use a concentration of 250g, to 600mL of water.
- PCB photosensitive copper board
- Temperature. I do this process in my shed as electronics is just a hobby, temperature is usually between 10 and 20 degrees Celsius.

This is the process I use:

Create image:
Printed on heavy tracing paper using a laser printer, I print at least 600dpi. I try to configure the setting on the printer to print as black as possible, in the highest resolution.

Expose photosensitive PCB to UV light:
First of all I warm up the light box for 5min. I then place my PCB photosensitive side down on the image (so it is touching the toner side of the image). I then expose to UV light about 6min.

Develop image:
I place the PCB into a tray which contains the developer. It stays in there until I clearly see the image, the image usually changes from faint yellow to a brown colour. This usually takes about 10 seconds. I do not bother agitating the solution, as it seems to work fast anyway. I then rinse with water.


Etching:
I then place my PCB into a tray containing my etchant. Usually it can take hours for all unwanted copper to be removed. Once removed I then rinse with water.



Now here is the confusing part.

Last month I done this process with fresh etchant and developer, at first I did not get good results, my copper tracks seemed to etch too. Then after many, many tries, it started to work, and work for quite a few boards. When it works I acheieve good results, all tracks are perfect, even tiny ones.

This month I renewed the developer and etchant. I start to get my copper tracks etched again.

I have a feeling it could be the timing on my developing, but not sure. What do you think?, I would appreciate any help on this. It is driving me mad, is this process supposed to be simple?
What happens if a PCB is underdeveloped or overdeveloped?



Kind regards,

Jay

 

[misterT]

Last month I done this process with fresh etchant and developer, at first I did not get good results, my copper tracks seemed to etch too. Then after many, many tries, it started to work, and work for quite a few boards. When it works I acheieve good results, all tracks are perfect, even tiny ones.

This month I renewed the developer and etchant. I start to get my copper tracks etched again.

Fresh new etchant is stronger and works faster than used one. You should monitor the etching process closely.. at least every five minutes depending on how strong the etchant is.

You should design your PCBs so that only small amount of copper needs to be etched away. You can do this by using copper pour. If you do not use copper pour, the etchant becomes "used" very quickly. Also use wide tracks whenever possible.

Could you post an image of a good PCB and a bad PCB? We might be able to give you good advice based on photos.

 

[Ja7me]

Hi misterT (good name by the way)

This is a very good point about the copper pour, it is the first time I have heard of that. Currently large areas of my pcb that are not used are solid copper. But the copper pour will be useful for the smaller parts of my PCB. I did not think of doing these area's in a hatch fill style.

My etchant appears to be rather weak, it literally takes me about 5 hours to etch a pcb. With no agitation. I do check the process and notice that when 50% (aprox) of the pcb is etched, tracks become attacked too. Becuase of this, I do not believe I am over etching.

Regards,

Jay

 

[misterT]

My etchant appears to be rather weak, it literally takes me about 5 hours to etch a pcb. With no agitation.

Your etchant is too weak. And because you leave the board etching for a long time without agitation, it etches unevenly. Etching should take less than an hour.. Maybe even less than 15 minutes (with heated etchant and agitation). And you should agitate (rock the tray gently from side-to-side). Faster etching produces better edge quality.

If you send a photo of a bad PCB, we can probably tell if the problem is in the development or the etching.

 

[Ja7me]

Ok I will make sure I take a photo today. I appreciate your help on this.

Jay

 

[Sangoma]

It is simple, simple to get wrong as well as right.

I don't think your shed is warm enough. I etch at around 25C. I stand the etching container in a larger container of hot water.

There are other threads that discuss the concentration of developer, and of lights. It sounds like your light is a commercial unit, so that should have accurate guidelines for exposure.

Developing will depend on the photoresist, temperature, developer mix and time. Usually there is quite a bit of lattitude, I take the time it looks done, ie clearly defined tracks and photoresist washed off by the developer, then add half that time. This makes sure that all the resist is removed but still stays well within the max time.

I started making boards again a few months ago after a long break, and it took me quite a few boards until I got the feel of it again, now my exposure and developing are both around 50 seconds, and my etch time around 25-30 minutes, and the results are consistent.

 

[jpanhalt]

Hi Jay,

The pictures requested by Mister T will be the greatest help. In the meantime, here are some comments or questions about your method.

- Developer (Sodium hydroxide free) I use a concentration of 15g developer, to 800mL of water.

Is the developer a liquid or solid? If solid, it may be sodium carbonate. If you add a drop of developer to vinegar, does it fizzle with release of gas?

- Ferric Chloride etching crystals, I use a concentration of 250g, to 600mL of water.

Is the ferric chloride you use greenish yellow or dark brown?

- Temperature. I do this process in my shed as electronics is just a hobby, temperature is usually between 10 and 20 degrees Celsius.

That temperature is on the low end of what most people use. I personally heat to about 60°C and suggest that you try to get at least 35° to 45°C. Putting your etching vessel in a large bowl of hot water will help. As several factors affect etch rate, and temperature is one of them, be sure to monitor the etching process visually and don't just rely on time.

Finally, what brand of photosensitized boards do you use? If no brand, where do you buy them?

John

 

[Ja7me]

Hi John,

- My photoresist board is from a company called megauk (part number 03-5108-1), I believe this to be a good quality brand.

- My developer is Sodium Metasilicate from RS (part number 690-849), it is a white power that I mixed according to the instructions.

- My ferric chloride is from farnell (part number 130539), it come in separate solid chunks, and had a dark brown appearance. I mixed it with water according to the instructions. Once mixed it seems to have a slight green tint, but I cannot remember if it had this green tint before or after I started etching boards in it.

- The temperature thing is a good point, I know I should really invest in a heating unit. But I did have this process working fine once, without the need to heat it. There seems to be so many different factors that effect this process. I am currently working, but will upload a photo of my etch attempt when I get home.


Jay

 

[Ja7me]

Hi Sangoma,

Your exposure time is much less than mine, megauk the company who I purchase my photosensitive pcb's from recommend around 3min exposure time. The first time I started etching boards I experimented, and found that 6min worked better for me, I was getting good results so I stuck with it. This is what I find difficult about this process, it is not clear where I am going wrong. It is hard to say if I am going wrong on exposure, development or etching. If I don’t know what part of the process I am going wrong it is hard for me to do it scientifically, such as adjusting times etc. What actually makes my tracks etch too, would it mean my photoresist is coming off?


Jay

 

[geko]

If you over expose the board in the UV light that will cause the photoresist to lift even on the unexposed parts since the toner on the artwork isn't 100% UV blocking.

Also, if the developer solution is on the strong side it will very quickly start to weaken the unexposed areas of the artwork. I find that mixing up the developer on the weak side and also gently rubbing the surface of the board while in the solution allows for a more controlled developing.

For what it's worth I wrote up a page on how I make my PCBs here:

https://picprojects.org/projects/makepcb/index.htm

 

[Sangoma]

Hi Sangoma,

Your exposure time is much less than mine, megauk the company who I purchase my photosensitive pcb's from recommend around 3min exposure time. The first time I started etching boards I experimented, and found that 6min worked better for me, I was getting good results so I stuck with it. This is what I find difficult about this process, it is not clear where I am going wrong. It is hard to say if I am going wrong on exposure, development or etching. If I don’t know what part of the process I am going wrong it is hard for me to do it scientifically, such as adjusting times etc. What actually makes my tracks etch too, would it mean my photoresist is coming off?


Jay

OK, now we know you are using a developer that is supplied as developer, what do they suggest as a development time?

If they say for example 60 seconds to 120 seconds, try around 90 as a start.

I found several things caused tracks to be etched away. Over exposure, over development, to weak/exhausted/to cold etchant causing long etching times and undercutting, board not cleaned properly meaning long etching times as you try to etch the dirty parts, under development and the same long time trying to get the board to etch where the photoresist has not been completely removed.

This is not a very precise way of doing it, but I expose for the minimum time that results in seeing the track patterns clear and dark within a short time of being in the developer, and then add 50%. Use a strip of board and cover it, uncovering it in steps (10 secs, 30 secs or whatever suits your lamp) then develop. and etch, the shortest quickly etched piece can be your starting time.

I do the same with the developing, within a few seconds I see the tracks, then it looks as if the photoresist is floating of the board, then it look like it is finished, and I add 50% on to that.

Once I had done this, I found any small changes were taken care of and I didn't need to alter anything. At first I wondered if it was really possible to make a decent board every time, after a few practice runs, it is now like making a cup of tea, so don't despair

 

[Ja7me]

Thanks geko, what you said does make sense, I will give it a go tonight with less exposure time. I will also make my developer weaker and make my etchant slightly stronger (as recommended by others)

Jay

 

[Ja7me]

Sangoma

It does not seem to suggest a development time on the instructions. From what people say on this forum it seems like I am doing quite a few things wrong.

This is what I will try tonight:

Exposure time: decrease from 6min to 2min.
Development: Make slightly weaker, develop until a sharp image appears, then develop for 50% longer.
Etching: Make stronger, frequently agitate, keep an eye on it.
Temperature: Try and make the surrounding environment warmer, this will be hard as it is super freezing outside, but will try my best.


I really hope it will be like making a cup of tea

Jay

 

[Sangoma]

Sangoma

It does not seem to suggest a development time on the instructions. From what people say on this forum it seems like I am doing quite a few things wrong.

This is what I will try tonight:

Exposure time: decrease from 6min to 2min.
Development: Make slightly weaker, develop until a sharp image appears, then develop for 50% longer.
Etching: Make stronger, frequently agitate, keep an eye on it.
Temperature: Try and make the surrounding environment warmer, this will be hard as it is super freezing outside, but will try my best.


I really hope it will be like making a cup of tea

Jay

I don't think to say that you are doing things wrong is really the right way to put it, there are so many variables as you say, there is no right or wrong in many cases, it's just getting the right combination of rights.

Put your etching bath in a bowl of hot water, then go and boil the kettle, when you can put your fingers into the bowl (best not to try the etching solution) replace half the water in the bowl with fresh hot water from the kettle, and get the kettle ready for the next refresh


Or convince the management that it is better for your health to work in the kitchen I do mine early in the morning, mainly to keep the nice coloured solutions out of the way of my 2 year old.

I can't comment on your exposure time, but I think you are heading in the right direction if you had tracks etch away. You can usually see in the developer if the exposure time is too short, as the pattern won't appear sharp within a few seconds.

Watch for the resist floating away, looks more like ink streaks in the developer.

 

[Ja7me]

2 X Failed PCB

Hello everyone,

Attached are images of two PCB's I attempted to etch a few days ago. I will look forward to your feedback .

See my first post for timings and conditions of the process.


Regards,

Jay

 

[jpanhalt]

The most striking features I see in the first and last images are: 1) pitting of the large unexposed area; 2) something that looks like a precipitate in the first image; and 3) an area (last image, right half, top) that looks severely under-etched. Somewhat in contrast, in the center three images, there is still pitting but there appears to be severe undercutting of the traces.

The precipitate is hard to explain, unless it is just a variation in appearance of under-etched areas. Assuming it is a precipitate, what could cause it? Under acidic conditions, ferric chloride will not precipitate. The products from oxidation of the copper (i.e., etching results from oxidation of the copper) might precipitate, and you can get sludge after etching several boards in the same solution. I have never seen that sludge adhere to a board. Furthermore, your experience that old etchant worked better is inconsistent with that mechanism. Under alkaline conditions, ferric hydroxide will precipitate and may be hard to remove. Residual sodium metasilicate on your board from the developer could cause the iron hydroxide precipitate and/or cause a precipitate itself when exposed to the acidity of the ferric chloride solution.

Suggestion #1: Be sure the developer is thoroughly rinsed from the board. Rubbing with soft tissue or a sponge under running water may help.

If it is not a precipitate, but rather is just under etched copper, then that would point to under exposure and/or under development. I use dilute (0.4 mole/L) sodium or potassium hydroxide as a developer. My resist is quite different from yours and requires the stronger alkali for removal. That said, after developing and rinsing, I will either dip the board in etchant quickly and rinse or put a few drops of etchant on the board and see how they behave. With either test, the copper to be etched will turn a dull, salmon color and the etchant will wet only the areas to be etched. If the etchant beads up on those areas, then I know that board needs to be developed more, as there is remaining resist. With experience, one learns quickly what bare copper looks like, so it is very rare I need more development time.

Suggestion #2: Test your board after development for removal of the resist in the areas to be etched.

The pitting you see is possibly due to light leaks through your paper. I use a clear transparency, as used for overhead projectors. I also treat with dry-erase marker as described in my blog on ETO. Even without that treatment, one will get very good exposures. The dry-erase marker will only stop the small pin-holes. I have never seen large areas of pitting with a simple laser-printed transparency. Here is a direct link to the blog: https://www.electro-tech-online.com/blogs/jpanhalt/213-improved-laserjet-transparencies-pcb.html

Suggestion #3: Try an overhead transparency as your mask.

Undercutting and incomplete etching on the same board seem like contradictory results. One explanation might be that the etchant is too viscous. Heating it reduces its viscosity. It can also be diluted by adding 100 mL to 150 mL of water to 300 mL of etchant. I think you still need to get out of the basement with temperature, but dilution might help by itself. Also, agitation or stirring of the solution during etching might help.

Suggestion #4: Address possible viscosity effects by diluting, stirring, and /or agitation during etching. Warm to at least 30°C.

Finally, I do not see any signs of over-exposure that cannot be explained by other mechanisms. Nevertheless, it cannot be ruled out. If you make thin strips of black vinyl electrical tape, you can apply them to a small test area. They will be quite effective at blocking light. If you get undercutting with your normal mask, but none with the electrical tape, then you might have over exposure.

Suggestion #5: Consider a small test area with electrical tape as a mask and resist. No need to remove the tape after development.

Good luck and be sure to report back. Those are the worse looking boards I have ever seen made using the photoresist method, and I mean that in the nicest way. You should be complimented for your persistence.

If I had to pick only a few of the suggestions, I think if you switch your mask, get your etch temp to >30°C (even without dilution), and thoroughly rinse after development, you will have much better results. Whatever mask you use, be sure it is held closely to the board surface, but you already indicated you were aware of the need.

Regards, John

 

[alec_t]

Or convince the management that it is better for your health to work in the kitchen

Just don't get etchant on stainless steel surfaces, or you will etch those and incur the wrath of the management

 

[Ja7me]

PCB attempt last night

Hi Everyone,

Attached is my failed attempt last night. Even though I had my PCB in the etchant for about 4 hours, hardly nothing seems to have happened.

This is my procedure I used:

Exposure:
I decreased exposure from 6min to 2.5min.

Development:
I made this weaker. When a sharp image appeared, i then added 50% to the time. After i then rinsed.

Etching:
I made this slightly stronger, and agitated now and again.

Temperature:
I had the heater on, must have been at least 20 degrees C in there this time.

 

[jpanhalt]

That result is typical of underexposure and under-development.

Remember, the "precipitate" I described earlier may be a result of the same thing, if it is not a precipitate. You can use your fingernail to tell whether those areas to which I referred were precipitates or under-etched.

I think you need to use a clear mask until you get the other problems solved. I know it is reported that tracing paper works fine, but you have no way to inspect how it appears to UV except by looking at the results you are getting. A transparency will remove that variable until you get your exposure and development times fixed.

I would also recommended doing a stepped exposure. That is, put opaque cardboard or something over all but 20% of the board, expose 2 minutes, move it over another 20% and expose 2 minutes more, etc. You will then have 10, 8, 6, 4, and 2 minute exposures. Frankly, I have found under exposure to be a far greater problem than over exposure. The result from a little over exposure is a loss of sharp definition, but the broad is usable. Under-exposure will give you a non-usable board.

John

 

[Ja7me]

John,

Thanks for taking the time to look at my images and giving me a thorough explanation. I understand all your points except precipitate, I am unaware of what this means. I am guessing it is some kind of chemical reaction occurring in the etchant which creates a residue?

I must admit, after getting more pitting again last night, it come to my mind that my tracing paper is not good enough. However this has confused me as I have acheived perfect boards doing this same procedure, well I assume it to be the same.

Say If the mask made it impossible for the UV light to get through, would that mean it would be impossible to get pitting, or dodgy looking tracks? I will definitely try your idea with the mask, seems like I need the proper stuff rather than tracing paper. Plus I can try your pen idea. It will be an excellent way to determine if it is the exposure process.

Once the developing stage has been done, I usually ensure I rinse it for a good 10seconds under a tap.

Maybe I could try taking a picture after the development stage next time. Would you then be able to judge whether or not I am developing correctly?

After development, my tracks usually look sharp and brown. The surrounding area looks salmon colour. Are you saying that if I put a drop of etchant on the salmon part, it should not bead up, and if it does I need to develop more?

In order for the etching process to work correctly, should there be absolutely no photoresist on the non-track parts? if my mask could prevent UV light more on the track parts, would this mean I could expose for much longer, which will ensure the non-exposed resist should come away easier during development, which will mean easier etching?


Kind regards,

Jay