Photo+ pcb board etching problem

Sangoma said:

I use 60 UV LEDs, no box, just hold them about 30cm above the board and move them around a bit to get even exposure. It works fine for boards up to 10X16 cm, I plane to make another set if I want to do larger boards.

You need to check the specs of the LEDs and make sure the wavelength matches the resist. Got them on fleabay, quite cheap.

Click to expand...

It could be a simple and good option because I can also use positiv20, unless the UV leds were expensive here
https://www.conrad.de/ce/de/product...lett-Min-407Max-412-nm-Ausfuehrung-Wasserklar

My fluorescent bulb is a bar type. I will post a picture of a typical board later. Stick with the photo resist. IMHO, it gives the best PCB's.

John

When I do boards using the photo process, I use a pair of tubes, F15T8/BL, at 4 inches from the contact frame. I expose the boards for 90 seconds if I use film positive artwork, or 150 seconds if I print my artwork on a drafting paper called "Clearprint". It usually only takes 30 seconds or so to develop them properly using the diluted NaOH developer. I heat my etching solution to about 120F and it only takes 6-7 minutes to etch fully, if the etchant is relatively new. I'm usually very pleased with the results.

The PCB stock I use is purchased from Circuit Specialists <LINK> and the developer is GC Electronics #22-226, diluted 9 parts water to 1 part developer. Standard ferric chloride is my preferred etchant (since I bought a gallon of it some years ago and have yet to use it all up).

For some time now, however, I've been using a direct-plot method for prototyping. I use my trusty Hewlett-Packard 7221T flatbed plotter to plot the artwork directly on the bare copper laminate with an etch-resistant pen and etch it immediately afterwards. Great results there, too.

Here's an example of a board I did a few years ago with photo resist. Note the absence of small holes in the large copper pour areas. The smallest trace I usually use is 24 mill, unless there is a need to go smaller. Obviously, I could have gone considerably smaller here, but there was no need to do that.

John

jpanhalt said:

Here's an example of a board I did a few years ago with photo resist. Note the absence of small holes in the large copper pour areas. The smallest trace I usually use is 24 mill, unless there is a need to go smaller. Obviously, I could have gone considerably smaller here, but there was no need to do that.

John

View attachment 71091

Click to expand...

It was beautifully exposed and etched. I hope I will have some results like this example soon. I am thinking about working on the exposure setup depends on the ideas you shared.

Today, I realized something about the board which I shared before at post #14. I had left the board somewhere on the shelf after I got some useful result at post #15 with contact printing and I started building the circuit. The one in post #14 which I tried with photo-exposure was laying among the scrap boards more than a week and I think It was partly covered among them. Today I realized that the uncovered regions are changed their yellow colour to the normal copper colour. Here is the picture


Now, I dropped some Fe3Cl to the both yellow and copper-coloured regions and waiting for the result. I have just wanted to share this to complete the story. If something happens, I will share another picture and I might even try to etch it with Fe3Cl or sodium persulfate...

Looking at your picture, there is still photoresist on the entire board. You either haven't exposed it enough or haven't left it in the developer for long enough.

picbits said:

Looking at your picture, there is still photoresist on the entire board. You either haven't exposed it enough or haven't left it in the developer for long enough.

Click to expand...

Yo can read the exposure and development times for this board in previous posts. But you are right about the presence of photoresist on the board. Even though I dropped Fe3Cl on the board and kept it for more than an hour, there is no signs of etching...

I've made hundreds of homemade photopcbs - probably around 200 in the past year (I landed a contract to do a load of demo boards in a hurry). Unless your board is 100% clean of photoresist (in the right areas) you'll have issues with the etching.

Even fingerprints on the bare copper slows the etching down significantly - it's quite surprising the difference a few seconds extra in the developer makes.

I find that when my developer gets a bit tired after a few boards, gently wiping the surface of the board while it's developing with some disposable paper towel and agitating the board helps. Don't be afraid to take it out, give it a rinse and inspect it to make sure you are down to bare copper.

My boards etch at 8-10 minutes with a FeCl temperature of 38 degrees and a little agitation (my tanks don't have bubble bars). A fresh batch of developer (500ml) will develop the first board in around a 45 seconds to 1 minute while futher boards take a bit longer - I normally change the developer when it takes more than a couple of minutes to develop a board.

As you stated before, your developer is 10g of NaOH per liter or about 0.25 molar. The developer I use is 0.4 molar, which would be 16 g/L. I assumed your formula came from the manufacturer or from someone who had also used the same boards. I

At this point, trying a stronger developer may be worth the effort. Start with 0.4 molar. If that doesn't work, then make 1 molar (20g/500 mL). If that much NaOH doesn't dissolve readily, let us know immediately.

Also, please confirm that the board you show in post#25 was treated with developer before you added FeCL3 to it.

John