Home PCB etching - one for the hobby-ists

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echoes

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I'm resurrecting an old hobby and wonder if anybody of a similar persuasion has a reliable recipe for exposing and etching copper-clad board?

I'm not after perfection - smallest track / space is > 0.5 mm.

I'll be using:
- either aerosol photo-resist or photo-sensitive board (have both)
- Decent quality inkjet transparency (probably)
- NaOH developer
- FeCl3 etchant.

I'm after starting points for developer concentrations and exposure timings that work reasonably well. I'll do some tests as well, but it's been so long...
 
echoes said:
I'll be using:
- either aerosol photo-resist or photo-sensitive board (have both)
- Decent quality inkjet transparency (probably)
- NaOH developer
- FeCl3 etchant.
I'm after starting points for developer concentrations and exposure timings that work reasonably well. I'll do some tests as well, but it's been so long...
Click to expand...
Opinions will probably vary consdierably. What works for me...
NaOH - about "2 teaspoons per litre", pro rata
FeCl3 - about 200g/litre
sodium persuphate is much less messy than FeCl3 - about the same concentration
Exposure will obviously depend upon what you're exposing with. Using a standard small exposure box with 2 x 8W UV tubes, probably in the range 5-15 minutes (10 mins is a good start point).

Now let's see what others say!

Kind Regards, John
 
Thanks John.

Yes it's a small 2-tube exposure unit. Been googling around and finding exposure times from 1 min - 15 mins, but that rather depends on the photo-resist thickness, or board manufacturer.

I'll give your recipe a go and see what happens.

I have the Iron (III) Chloride in bulk, and I do remember some ruined T-shirts, but this stuff is already in liquid form.

All very different to the spun-on 1 micron resist and 20 seconds exposure with glass lithographic plates that I'm more recently familiar with from my device fabrication days.

I won't be getting yellow light bulbs. And red ones just attract the wrong sort.
 
echoes said:
Thanks John. Yes it's a small 2-tube exposure unit. Been googling around and finding exposure times from 1 min - 15 mins, but that rather depends on the photo-resist thickness, or board manufacturer.
Click to expand...
As you say, it varies a lot, depending on the resist. However, if (as you said), you're not dealing with very fine tracks/gaps, it's not all that critical (at a DIY level).
echoes said:
I'll give your recipe a go and see what happens. I have the Iron (III) Chloride in bulk, and I do remember some ruined T-shirts, but this stuff is already in liquid form.
Click to expand...
Fair enough - but it ruins everything in sight, not just T-shirts :-)

Let us know how you get on.

Kind Regards, John
 
You can get Fe3Cl stain remover which IIRC works quite well. I bought some from Rapid years ago.

Other than that I can't advise, having done all my hobbyist exposures using plate glass and a window ledge. Usually left for about 1/2 hour I think.
 
Do it in the shed, if you do not have one - get one.

Dont do it in the house or SWMBO will kill you when it spills :)
 
You will need good and consistant process control of concentration, temperature and timing if you are to be successful at 0.5 mm.

One the things that happens when the etching is too aggressive ( over temperature or too high concentrations ) or too long is the sides of the tracks are over etched so while the surface is 0.5 mm wide the area in contact with the board can be considerably less. In extreme cases the track remains conductive along its length but some areas of ot are detached from the board.

Finding a local PCB manufacturer who will etch your boards for you will avoid a lot of fault finding due to broken tracks.
 
Still I think 0.5mm (~20 mil for those of us who think about our PCB designs in imperial units) is well within reach of what a hobbyist can etch with reasonable reliability. Heck i've seen hobby etched boards with 0.5mm pitch SMT components on them which must have meant that the min track and gap was at most 0.25mm (~10 mil).
 
plugwash said:
Still I think 0.5mm (~20 mil for those of us who think about our PCB designs in imperial units) is well within reach of what a hobbyist can etch with reasonable reliability. Heck i've seen hobby etched boards with 0.5mm pitch SMT components on them which must have meant that the min track and gap was at most 0.25mm (~10 mil).
Click to expand...
I agree. Over the years, I've produced countless boards with tracks of 0.5mm or less, and have had very few problems (once initial experiments had been conducted). DIY methods would clearly not be satisfactory for 'production quality' (or for any 'critical' applications) but, with a little care, can be pretty reliable.

As I'm sure most people realise, particularly when one is dealing with fairly small tracks/gaps, it's usually preferable to print a 'reversed' (mirror image) layout onto the transparency, so that one then puts the ink side in contact with the copper. This eliminates having the thickness of the film between the image and the copper, thereby reducing the amount of light which 'gets around the sides' of the image (which can result in the 'undercutting' phenomenon which bernard has mentioned).

Kind Regards, John
 
Thanks for all the input & tips. I have produced DIY boards before, but that was over 20 years ago now (apart from a small stint when I was an electronics engineer producing prototypes).
Some things stick with you, but it's small but crucial details which get hazy.

I have read that tracing paper rather than transparent sheets for printing the pattern gives good results and resolution with inkjet, but never tried it.
 
JohnW2 said:
As I'm sure most people realise, particularly when one is dealing with fairly small tracks/gaps, it's usually preferable to print a 'reversed' (mirror image) layout onto the transparency, so that one then puts the ink side in contact with the copper. This eliminates having the thickness of the film between the image and the copper, thereby reducing the amount of light which 'gets around the sides' of the image (which can result in the 'undercutting' phenomenon which bernard has mentioned).
Click to expand...

Yes, I'll be printing such that the inked side is in contact with the board.

I remember having to go carefully when etching mesas in GaInP (I think) - that etch had a tendency to undercut sideways more quickly that it etched down, resulting in skewed mesas.
 

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