A few pointers...
To start out with I am using the presensitized boards from MG chemicals. Since this is my first try I am trying a simple design that I found on the internet. I am using a nice EPROM eraser that I found at my local surplus to do the exposing.
The UV wavelength of EEPROM erasers is a bit short (~250nm) for most presensitised boards e.g. the MG Chemicals unit uses 375nm, and many people use UV LEDs or bugzapper / nail polish curing lamps which are typically ~390nm.
I was not sure how long to expose the the board so I did 10 minutes. Overkill I know, but I did want to take a chance. While I was exposing I mixed up the developer. 1 part developer to 10 parts water. When the timer went off I developed the board, but in my excitement that the process was working I over developed it. On my second try I exposed for 15 minute, again overkill, but this time around I did not over develop it. I only left it in the solution for about 30 seconds. Hurray!
In my experience, the MG Chemicals boards are remarkably difficult to overexpose, but fairly easy to overdevelop if you
do expose them for a longer-than-optimum time. I suspect you'll find it easier to get better results by using a more appropriate light source and exposure times.
Trial and error is the only way to get a good ballpark for exposure in a particular setup. Grab one of the available PCB "test patterns" (or make your own), and try various exposure times. I usually cut a 2cm by 10cm strip off the end of the first board of any new type, and test exposure times up to 10 minutes (by covering it with cardboard and slowly revealing sections of the board & pattern) in 1 minute steps - there's no need for 30 second steps, unless the exposure time for that board type is known to be really short (e.g. Kinsten, which can overexpose in < 90 seconds).
(I know MG Chemicals suggest 10 minutes for their exposure kit; that uses normal daylight fluorescent tubes @ ~5" distance. My own experimental results range from ~7min with a cheap "black light blue" (~365nm) UV CFL @ ~2" distance, to 90secs~2mins with a ~385nm UV tube @ ~3")
I am using transparencies for the artwork mask that are for copy machines. I notice they distorted when run through the laser printer but since I was only using the the edge for a very small board I feel it was not significant enough that it did not matter.
Try using decent tracing paper - draftsman or good office-quality stuff, not the cheap school stuff. It may be a little harder to find than printer transparency sheets, but is usually cheaper (especially if you buy it in A3 & cut it down to A5 for use) and distorts a lot less.
Now it was time to etch so I mixed up the solution of 100 ml of vinegar and 100 ml of peroxide because this was based on what I had read was the mixture. In goes the board. The reaction is slow. I feel that it not working as well as I had read. During my research I read that adding salt helped. So after about 30 minutes I added some In hopes of speeding up the etch. I kept waiting and adding a little salt every now and then and after waiting over 2 hours I ended up overetching the board.ur results? I welcome any tips or feedback that are offered.
The only time I've ever been happy with that method is when I used >99.5% lab-grade acetic acid
. Otherwise, it's just too slow - you get bored waiting for it, and you end up overetching.
I use 30% HCl + 6% H
2O
2 (it's a little hard to get stronger than that here in Aus) in a 50-50 mix. As mentioned, work in a well-ventilated area and wear eye protection (safety goggles
at least), resistant gloves, and suitable (e.g. old
) clothing. I usually chuck the board in, agitate it gently by rocking the bath backwards and forwards, and wait for the copper to go beyond salmon pink - it's a bit hard to describe, but you'll see it go rough/dirty as the etchant really starts to 'bite'. At that point I lift the board out of the etchant, grab a bit of small foam sponge, and gently wipe the etchant up from the bath and across the board, turning occasionally. Small 3x3cm board usually take me just over 2 mins to etch, while larger boards can take ~5-7min.
As for the "environmentally friendly" aspect ... well, whichever way you look at it and regardless of the etchant used, you're making copper salts - which are mostly fairly nasty things from an environmental PoV.
- Ferric chloride + copper = CuCl(II) (i.e. copper chloride) + FeCl(II) (i.e. a different ferric chloride)
- Ammonium persulphate + copper = copper sulphate + SO4-2 (i.e. sulphuric acid, as soon as it finds any water)
- HCl + H2O2 + copper = one or more of the copper chlorides + chlorine gas + water
- Vinegar (acetic acid) + H2O2 + copper = copper acetate + water + (probably CO or CO2 or carbonic acid); as soon as you add salt (NaCl) to speed it up you're probably back to making copper chlorides (and something with sodium - sodium carbonate? - as well?)
So regardless of the etchant used, you really need to dispose of it properly (or at least neutralise & stabilise it) rather than just flushing it down the drain...
(BTW, don't trust my chemistry there - it's probably roughly right, but I'm an ecologist / environmental scientist, not a chemist - but they all end up with environmentally unpleasant compounds...)