Photo Resist Problem

[jsurg]

HI to All

I am a knife maker in South Africa and have been unable to find a local supply of the stencil material you use in USA so have been using Positive20 which is the spray type photo resist used for making PCB's and used here by many makers.

This works fairly well with reasonable results with artwork printed off onto transparency and exposed under UV and etched in Ferric Chloride.

However I want to use a PSU with felt tip and salt water etc as disscused on many posts and Bob Warners site.

My problem is that the photo resist is eaten away after a few dabs of the positive lead, so it is destroyed before any etching takes place.

I am assuming that it is the photo resist that is not suitable for this process, however I have read many posts of people who seem to be using it.

I have the choice of voltage current options all do the same:
12vdc @ 10amps
12vdc @ 1amps
5vdc @25amps
5vdc @ 0.5amps
3.3vdc @ 14amps.

I have a feeling that I am using a incorrect combination of vdc and current limit for use with photo resist.

As great a design is of the Electro-Etch unit is it gives no indication of the current limitations of the transformer other than to say it is a 25vac, but it could 1amp or a 5amp rating. The bridge rectifiers it rated at 6amps but the amount of available current is determined by the transformer current limitations to start with.

So can anyone throw any light on why the photo resist does not withstand the etching process?

And what the correct voltage/current limitations should be when working with spray on photo resist?

Is there something else that needs to be done to harden (other than normal heat drying) the photo resist to withstand this process?

 

[Reg ELLERY]

May be not the answer your looking for but may be of some help.
If you reverse the polarity it has a different effect on the metal.

I use stensils cut from adhesive plastic tape for my logo. On way it leaves a black mark the other way it leaves a grey mark the diference is quite a lot. However I use a carbon block as an electrode not felt.

I am not sure how fine your etch design is but I went to the local sign writer working on a machine in his back room. Does not have to be a large company.

good luck hope I did not waste your time. Ps I use a 12v battery charger for a few seconds. Lower voltage and low amps also works.

 

[jsurg]

Hi Reg

Thanks for the info, it has given me a few idea's

 

[rashid11]

you can also order a few blank stencil sheets and some developer
from US. It will last quite a while and take all the guessing out.

It is also very inexpensive.

I'd hate to ruin a knife with botched marking

 

[jsurg]

thanks rashid11, have thought about that but I think the delivery cost from US to SA on small amount would probably be prohibitive. There is a local knife material supplier (one of only about 3 in SA) that is looking at importing it but as yet to do so. Also it is nice to have a local supply of material as there is nothing worse than needing something urgently and not being able to get it quickly due to long delivery time.

The main thing is that the process "should" work with spray resist!