Making your own single sided PCB using photoresist board

[Sangoma]

I would agree that transparency should be used at least until the process is working OK. The mottled effect seems to be common to a number of your photos, suggesting there may not be enough contrast (to UV) between the paper and print)

There should be no photoresist on the non track parts, otherwise you end up with areas no etching, then the tracks being etched when you extend the time to try and etch those stubborn parts.. I've never tried rubbing it lightly as someone suggested, but it may well help.

When you develop, can you see the photoresist floating away from the areas to be etched? On mine, I see the tracks appear, then the photoresist floating off, as two distinct stages.

20C isn't ideal, but it shouldn't cause the problem in the photo.

 

[jpanhalt]

Sorry about using a chemical term, precipitate. Think of it like mud settling from water, or like if you have a solution and let it evaporate. The residue is a precipitate. Areas in that first photo looked like maybe there was some residue, as if some salt solution had been allowed to evaporate. Incompletely etched copper can look the same. Based on your follow-up experiments, I think it is probably incompletely etched. Scraping with a fingernail or blade will show conclusively whether it is copper or residue. The residue will be removed, the copper will look metallic.

As for removing the resist, I agree that it must be removed completely from areas that need to be etched. Water will bead up on the resist, but not on the bare copper.

John

 

[Ja7me]

Hi Sangoma,

I only seem to notice one stage in the development process, the tracks become darker. I do not notice the photoresist coming away. But the liquid to tend to darken, which is probably the photoresist being dissolved away. What transparent film would you recommend i buy, can it be bought from major high street stores, or does it have to be ordered online.

Jay

 

[Ja7me]

Ok john, I will try scraping the surface of the board when i get home. Thanks for the tip about the beading up of water on resist. This sounds like a handy way of knowing if the development process has been done properly.

Jay

 

[bryan1]

I got a heap of UV resist pcb boards off fleabay for a cheaper price than normal pcb board and I found even using 2 transparencies over leaved to increase the darkness of the tracks still ended up with coasters rather than a usable pcb. So before I got my cnc going all i did was firstly scrub off the UV resist with a SS scrubber then ensure the copper is 110% clean and final clean with some rubbing alcohol. I print the pcb layout onto glossy paper then just iron it on then soak in warm water for 20 minutes so the glossy paper will rub off easier. Never had a failed board (apart from design stuffups) but now after I designed the circuit in Sprint Layout I just export the gerber and drill files and mill the boards on my cnc.

Regards Bryan

 

[Sangoma]

Hi Sangoma,

I only seem to notice one stage in the development process, the tracks become darker. I do not notice the photoresist coming away. But the liquid to tend to darken, which is probably the photoresist being dissolved away. What transparent film would you recommend i buy, can it be bought from major high street stores, or does it have to be ordered online.

Jay

Any one for your printer. Some lasers need a white strip on the leading edge, but that is rare now. You must use film designed for a laser printer if you use a laser printer, as ordinary OHP film will buckle and jam with the heat of the fuser.

 

[Ja7me]

Hi Bryan,

I have herd of the iron method before. And to be honest it sounds like much more work. What brand was the pcb's you purchased. Maybe it was them particular boards that were the problem, have you ever tried the photoresist method with a different (well known) brand?

Jay

 

[Ja7me]

Ok, this is really getting me down now. I have just had another failed board. These were the changes I made.

- I redesigned my circuit so that many areas were filled with copper pour, to minimise etching.

- To try and improve the exposure part of the process, I printed my circuit twice on 90gsm tracing paper, then stuck them together so tracks lined up perfectly. When holding it up the window it seemed very dark, was much better than how it was before. Before it seemed to let some light though when holding up to a window, however the toner is always uniform, with no patches. I would say doubling it up almost lets no light through, It seems totally black even when held against a bright window.

- I poured my ferric chloride into a bottle, I then added a little more ferric chloride to make it stronger, probably about 15 grams. I than gave the solution a good shake. I then poured this into a plastic tub slightly bigger than my pcb. This tub was then put into a large tray full of boiling water. This was to ensure that my etchant would stay hot. I also had the heater on, I work in a tiny out building which gets warm quick.



This was my procedure:


Exposure time:

5min warm up
4min exposure


Development:

Was in there probably for a total of 1min, maybe slightly less. I removed it when I the tracks were brown, and the rest looked salmon in colour. I did not see photoresist floating away like others say on this forum, but the solution does get slightly darker. I believe it must be working though, as the areas that were exposed to UV light became salmon in colour, while the tracks were brown in colour.


Etching:

I placed my board into my ferric chloride (which was being warmed up with the surrounding boiled water for about 5min). I then agitated the solution for about 10secs. 10minutes later I added more boiling water to the tray, to ensure my acid still kept warm.


Results:
There has been a slight improvement, there does not appear to be any precipitate issues, mentioned with my first boards. Plus pitting on the large strip of copper is minimal. However , all tracks appear to be attacked by the etchant, they look wavy like the tracks in the previous pictures I sent. The board is still in my acid. At this point I am started to think it is the acid, but at the same time I know it should actually work really well considering how fresh it is, and the added heat. So far its been in there about 2 hours, there is no green substrate showing, so no copper has yet been fully removed. Is the board still protected with photoresist?, is this why the acid has little effect?

What do you people think I should try next, what would you do in this situation? Comments will be very much appreciated.


Jay

 

[jpanhalt]

Without even seeing the board, I can say it is not the ferric chloride. You can used saturated ferric chloride, that is keeping adding crystals until no more dissolves all the way to a fairly dilute solution. The saturated will be viscous (thick) and probably work a little slower at low temperature, but it will work the same as more diluted solutions.

Get some clear transparency film for overheads and stop wasting money on trying to use tracing paper. You want reproducible results, and not have to go through this every time you try to make a board.

John

 

[bryan1]

Hi Jay,
The UV boards I got here are Kinsten Brand and the major problem I had was my laser printer wouldn't print dark enough even with 2 pcb images so I first tried that iron on method using glossy paper and it worked a treat. I just cut the glossy paper to the pcb size and use sticky tape hole hold it in place, then place the pcb on say a hard cover book with a tea towel over it. I iron until the tracks show thru the paper and as far as being more work it actually a pretty quick process.

* design the pcb art work----- hours,days whatever
* clean UV resist off board ----- 5 mins max to get it ready
* iron board ------- 3-5 mins depending on size
* getting paper off ------ upto 20 mins but I do other things instead of watching it release.
* the pain of manually drilling holes ----- see the above reason why I now do my boards on a homemade cnc.

Regards Bryan

 

[Ja7me]

On a home made cnc? That's like that would be expensive and complicated to make

 

[jpanhalt]

Home CNC is very popular. As much as I like the feel of machining chips, I am even converting my mill over to CNC. Here is a link to a very large site: https://www.cnczone.com/forums/forum.php You will find machines made from plywood using stepper motors harvested from old printers to much more sophisticated and expensive machines. Of course, the other toy I absolutely need is a 50W laser cutter.

Back on topic, I hope you will stick to the photo resist method. It works well, and I haven't had a spoiled board in over 10 years. When you find the variable that is messing your process up, the rest will be simple.

John

 

[Ja7me]

Hi everyone,


I have finally found where I was going wrong. My developer was way too weak. Once I made it stronger I then noticed my photoresist coming away almost instantaneously. It then took me around 20 minutes to etch.

Thanks for all your help guys.



Jay

 

[jpanhalt]

That is great news. Can you share a picture?

Just FYI, sodium silicate is also known as "waterglass." It is basically what you get by dissolving glass in strong alkali like sodium hydroxide. Wikipedia describes its properties (https://en.wikipedia.org/wiki/Sodium_metasilicate).

If you have continued problems with consistency of your developer and want to save a little cost, you might consider switching to a solution of sodium hydroxide (lye) in water. The molecular weight of NaOH is 40. I use 0.4 mol/L (i.e., 16 g/L) for my PCB's. You may want to try a concentration of about half that for yours. My brand of PCB will not develop completely with sodium silicate alone. Development with NaOH is quite rapid and shows a nice color change too. The unexposed areas are fairly resistant, and over development has not been a problem. NaOH is so cheap, I make it up fresh each day of use.

John

 

[3v0]

This should be moved to: Circuit Simulation & PCB Design

Hi everyone,


I have finally found where I was going wrong. My developer was way too weak. Once I made it stronger I then noticed my photoresist coming away almost instantaneously. It then took me around 20 minutes to etch.

Thanks for all your help guys.



Jay

This is one of the reasons I dislike photo resist. If is fine if you use it frequently but for 'now or then use' a process where you do not have to put up with aging chemicals and boards is easier to use. Given that you can have plated through boards made inexpensively it is hardly worth the effort to etch yourself.

 

[Sangoma]

This should be moved to: Circuit Simulation & PCB Design



This is one of the reasons I dislike photo resist. If is fine if you use it frequently but for 'now or then use' a process where you do not have to put up with aging chemicals and boards is easier to use. Given that you can have plated through boards made inexpensively it is hardly worth the effort to etch yourself.

I think it depends where you are, in SA it was cheap to have boards made. In the UK it seems the companies want a years income from one small board!

Aslo I often design a board during the week, then make the board and build at the weekend. There is a lot of other factors apart from cost.


Anyway, glad the problem is solved, out of interests did it appear as if the photo resist floated off the board? Would be nice to know if it looked the same as the spray on resist when developing.

 

[Ja7me]

Yes the photoresist appeared to float away from the board within seconds of it being in the developer.

 

[3v0]

I think it depends where you are, in SA it was cheap to have boards made. In the UK it seems the companies want a years income from one small board!

Have a look at OSHpark.com. They make 3 boards at $5 sq in. You get 3 4" PCBs for $20 No setup or shipping.