etching my first pcb's

[foTONICS]

Hey all,

I've always wanted to give etching a shot and recently I've started acquiring all the necessary stuff to do so. It's a little hard being that I don't have a lot of room in my apartment and I doubt the wife wants containers full of ferric chloride on the kitchen table but there's always the balcony!

So here is a shot of the circuit I'm attempting to etch, this is it's current state using protoboard. The circuit is just a microcontroller with a regulator, crystal, and some DE9/BNC connectors that are out of frame. This circuit makes a good candidate as it's simple, already works, and has TONS of wires connecting all the I/O on the underside of this board.

I'm using single sided positive pre-sensitized copper clad boards. I read about all different kinds of light sources and exposure times so it's going to be a lot of trail and error I feel. I'm going to start off with using a 75w incandescent bulb 6 inches above the board with a 10 minute exposure time. here is the circuit I'm going to etch:



I have a couple mason jars that I'm going to use as containers to slosh the board around in. This is as far as I have gotten so far but I will post more once I experiment with a couple boards, hopefully tonight but dependant on time.

 

[Supercap2F]

Quite a coincidence that you would mention this - I just bought a bunch of supplies for etching PCBs for the first time too yesterday! I wanted to try out both methods (toner transfer and photoresist), but got kind of low on cash after buying the supplies for the toner transfer method.

Where did you get the clear transparencies for the photoresist method from? I looked around for them but couldn't find anything that would work.
Dan

 

[foTONICS]

I got the transparencies from staples, they only had one pack in the entire store so it may not be something that a lot of people carry, just make sure you get the ones that are specially made for whatever printer you're using. These ones have a rough side and a shiny side

I bought these since I have an inkjet printer:

 

[Supercap2F]

Wow, that's kinda on the expensive side for me! It does appear that the version for laser printers is a little cheaper though.

I have heard that tracing paper works okay, but since it's so opaque I would assume that it would take quite a bit longer to expose.
Thanks
Dan

 

[foTONICS]

I got them for $57 canadian here, wonder why it's pricier in the states. I warranted the extra cost because I don't do that many PCB's so these transparencies will last me a long time (especially if you print multiple circuits on each page)

 

[BobK]

I think you will find a very long exposure time with an incandescent bulb. They do not produce much UV. A fluorescent bulb is much better. I use a 12 inch fluorescent about 8 inches from the board and have an exposure times of 12 minutes.

Bob

 

[davenn]

I think you will find a very long exposure time with an incandescent bulb. They do not produce much UV. A fluorescent bulb is much better. I use a 12 inch fluorescent about 8 inches from the board and have an exposure times of 12 minutes.

Bob

@foTONICS Take heed of what Bob has said a fluorescent is better ... but will still take some time to expose correctly
BUT you really should be using a proper UV tube mounted in a suitable eye shielding box


Dave

 

[BobK]

I will suffer 12 min exposures to avoid UV exposure problems.

Bob

 

[Old Steve]

Incandescent lamps probably won't work.
It's well worth buying a fluorescent UV tube. Two is even better for an even exposure. Mine are a pair of 18" tubes:-



On a pre-sensitised PCB blank, exposure time is 90 seconds at about 3" distance.

I found a cheap picture frame at the hardware to hold the blank and the transparency in place. The back can be easily reoved, (has swinging catches), and I tape the transparency to the inside of the glass, then tape the PCB blank on top, add a couple of sheets of printer paper to keep things clean, then put the backing back on the frame:-



The film I use is GCC Laser Film (Red Label) in a box of 100, available here:-
http://www.power-tech.com.au/products/index.php?dispatch=product_features.view&variant_id=2
This film has a matt finish, and works slightly better than the gloss types.

My positive-acting pre-sensitised "Kinsten" PCB blanks come from here:-
http://www.kalexelectronics.com.au/

I hope this is useful to someone.

To avoid UV exposure to my eyes....................................................I close them.
(The picture frame blocks most of the UV, and I could mask off the remaining exposed part of the light, but have never got around to it.)

Edit: And I forgot to mention - I've found that 10g of caustic soda crystals per 1 litre of water works every bit as well as buying commercial developer. Costs virtually nothing, and develops the exposed board in about 30 seconds.

 

[Supercap2F]

Edit: And I forgot to mention - I've found that 10g of caustic soda crystals per 1 litre of water works every bit as well as buying commercial developer. Costs virtually nothing, and develops the exposed board in about 30 seconds.

Are you referring to Sodium Carbonate (aka Soda ash, aka soda crystals, aka washing soda), or Sodium Hydroxide (aka caustic soda, aka lye)?
Dan

 

[Old Steve]

Are you referring to Sodium Carbonate (aka Soda ash, aka soda crystals, aka washing soda), or Sodium Hydroxide (aka caustic soda, aka lye)?
Dan

Sodium Hydroxide. (Yep, the hot stuff, but not at all hot at 10g per litre.)



I guess gloves are recommended, but I've never found them necessary. Never had any burning or itching sensations. It's too dilute at that rate.
I'm very careful when initially mixing a batch, then once the pure stuff is safely stored away, it's not a worry.
After mixing, I store it in a plastic, screw-top bottle. (Never in a metal container.)
Always add the caustic soda carefully to the surface of the water. NEVER pour the water onto the caustic soda, and only use cold water, not warm or hot. (These directions are on the label.)

Edit: If you buy commercial developer, you'll be getting exactly the same thing, but paying through the nose for it.

 

[foTONICS]

If you buy commercial developer, you'll be getting exactly the same thing, but paying through the nose for it.

Too bad I didn't find out about caustic soda before hand...

Anyways, I finished working on the board tonight and I'll have to say I'm rather impressed that I didn't manage to muck it up on my first try, here she is:


so I changed a few things from what I said earlier. I switched to a 100w CFL that gives out about 1600 lumens and I sat it 10 inches above my board for 10 minutes. I put it through the developer for only about 30 seconds to 1 minute and used a q-tip to aid in removing the resist. After the cold water dunk I dropped it in the ferric chloride and let it sit, checking everything 5 minutes to agitate it. After about 20 minutes I noticed that that board was barely being etched and started to worry that I didn't develop long enough and a thin layer of resist was still present on the board. After the 20 minute mark I started to rub with my fingers (gloved) a little more generously than felt comfortable doing and noticed the copper starting to come off very fast.

The only bad thing about this board would be the amount of time it spent in the ferric chloride. The smaller traces have a sort of pitting on them and one of the copper labels named 'R2' was either etched away from the duration or from my fingers. In the future I will develop for a little longer, be a little more vigorous with the etching, and make my traces wider.

Any other suggestions?

 

[foTONICS]

Here's my nifty darkroom light I whipped up in about 15 minutes.

 

[Old Steve]

Too bad I didn't find out about caustic soda before hand...

Anyways, I finished working on the board tonight and I'll have to say I'm rather impressed that I didn't manage to muck it up on my first try, here she is:
View attachment 21912

so I changed a few things from what I said earlier. I switched to a 100w CFL that gives out about 1600 lumens and I sat it 10 inches above my board for 10 minutes. I put it through the developer for only about 30 seconds to 1 minute and used a q-tip to aid in removing the resist. After the cold water dunk I dropped it in the ferric chloride and let it sit, checking everything 5 minutes to agitate it. After about 20 minutes I noticed that that board was barely being etched and started to worry that I didn't develop long enough and a thin layer of resist was still present on the board. After the 20 minute mark I started to rub with my fingers (gloved) a little more generously than felt comfortable doing and noticed the copper starting to come off very fast.

The only bad thing about this board would be the amount of time it spent in the ferric chloride. The smaller traces have a sort of pitting on them and one of the copper labels named 'R2' was either etched away from the duration or from my fingers. In the future I will develop for a little longer, be a little more vigorous with the etching, and make my traces wider.

Any other suggestions?

Pre-heat the ferric chloride solution. That will speed the etching process.
I keep my etchant in a plastic jug, and put it in a bucket, then fill it as far as possible, (without making the jug float), with boiling water from the electric jug, about 10 minutes before I need it.
The more agitation the better, too. I use a small PCB etching tank, with a fish-tank air-pump attached. It has an internal channel leading from the hose that goes down, then across the bottom, with a row of fine holes along it at the bottom, to provide heaps of bubbles rising past the board. It etches a board in a couple of minutes. You can see one of the clips that I use to hold the PCB, hanging on the outside, too:-

 

[Old Steve]

And you don't need a darkroom light at all, just make sure the blinds are closed and you don't have a CFL or fluorescent light too close. No need for dark like traditional photography. The photo-sensitive coating is very forgiving in that regard.

Nice job, by the way. Good to hear you swapped to a CFL. An incandescent produces no UV.

Edit: As you say, thicker traces whenever you can, too. When I have plenty of room to spare, I make my tracks 0.024" wide, with 0.015" or 0.012" when I need to squeeze between pads on an IC. (Through-hole, I don't play with SMD.)

 

[foTONICS]

with a tank that big how many times can you use the same etchant? do you need to replace everything in the jug each time?

 

[Old Steve]

with a tank that big how many times can you use the same etchant? do you need to replace everything in the jug each time?

I only fill it to the horizontal line nearest to the top. That takes 1 litre. And I mix a new batch of etchant every few years. I've never kept track of exactly how many times I re-use it, but it's a lot. When I pour it into the etching tank each time, I leave the sediment in the bottom of the jug.
Some evaporates each time I use it, so I just regularly top it back up with some hot water just before using it.
The developer, on the other hand, can only be used a few times before it starts to slow down.

 

[Supercap2F]

@Old Steve Do you use strait ferric chloride to etch your PCBs, or do you dilute it with water?

Sorry bout the partial thread hijack foTONICS, I think I will have to start another thread documenting my progress.
Dan

 

[Old Steve]

@Old Steve Do you use strait ferric chloride to etch your PCBs, or do you dilute it with water?

Sorry bout the partial thread hijack foTONICS, I think I will have to start another thread documenting my progress.
Dan

I use Ferric Chloride, but I don't buy it in solution. I buy it in solid blocks, which I then mix into water.
It's pure, anhydrous ferric chloride from "Ultrakeet"
(I mix 500g FeCl with 2 litres of water. There's an exo-thermic reaction when I mix it - it gets quite warm, verging on hot.)
I've never used the pre-mixed stuff, so can't help, I'm sorry.

 

[foTONICS]

here it is with components: