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Positiv 20 vs Cramolin Positiv

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Azaruk

New Member
I have long been a happy user of Positiv 20, consistently getting superb results.

My stockist is now carrying the Cramolin product which appears to have very different properties.

I have very small areas on the developed board where the resist doesn't seem to have been exposed at all, leaving little copper dots all over the place which is extremely ugly and has the potential of causing electrical problems.

Does anyone have experience with Cramolin?

My setup is the same as the Positiv 20 technique:-

350nM UV tubes about 150mm away from the board. Two tubes are used, with the pcb artwork held down onto the panel with a piece of glass. I know glass absorbs a fair amount of the UV, so my exposure with Positiv 20 was around 10 minutes.

I have exposed for up to 15 minutes using Cromalin, but am stillgetting the same poor result.

I have been in the habit of drying my Positiv 20 boards in a warming drawer. Could the temperature have anything to do with it?

I am very frustrated over all this, especially over the number of bad boards when the chemicals cost so much in this country!
 

HarveyH42

Banned
I never got into photo-etch, because of the chemicals. I have some photography experience, and know the limited shelf life. I'm aware the process is a little different. I'd suspect the pre-sensitized boards. If you have a date code or lot number, might check the source or manufacturer, perhaps others have had the same problem, and you might get some replacements.

Can you post some pictures of the spots? There are a few people here that photo-etch.
 

j.p.bill

New Member
You might need to find out some information from the Cramolin people. I use pre-sensitized boards from Ever-Muse (positive resist). With a Kepro exposure frame, I get good results with a 1.5 minute exposure. The frame is glass over the UV tubes, so I doubt that your glass (unless you're using lead crystal) is soaking up the wavelength.
 

jbeng

Member
I've also been using the Ever-Muse boards and have gotten excellent results. My setup is F15tBL tubes (2) at 4 inches (~75mm) from common 1/4" plate glass (contact frame) with a 90 second exposure time. Haven't heard anything about the Cramolin stuff though...
Jeff
 

Azaruk

New Member
Thanks guys = to answer some of the points raised .....

The expiry date is 12/2010. Should be OK unless the distributor stored the stock at elevated temps.

The spots look like tiny dust particles, although the area is dust free, as is the glass and the positive transparency. Belive me - I have checked everything!

It seems the Cramolin doesn't have the same characteristics as Positiv 20 in that Positiv 20 is "self levelling' and gives a superb, even coating.

An associate in the printing industry suggested warming the can slightly before spraying, and spraying in a cool area to try and maintain the liqidity of the spray. It appears it's drying too fast on the board and doesn't have time to form an even coating.

As I said before, the results from Positiv 20 have been superb and I am mighty p***ed off that I have had to change to another chemical.

Checking the data sheets of both products shows many differences, but the basic procedure and technique remains the same.

Talk about FRUSTRATION!!!!
 

Azaruk

New Member
Cramolin success ......

Board preparation - as per any manufacturing method - VERY clean, grease-free and wettable. (I have a working techniques for this - so nothing changed)

Using the advice from my mate in the printing industry, I warmed the aerosol can in a jug of water from the hot tap in the sink, so have no idea of actual temperature.

Board was laid flat, in a cool area and the board sprayed from about 200mm away. I used a side to side motion and went over the board area twice.

This gave consistently coloured (good coverage) coating. I dried the board in a fan oven set at barely warm.

Exposure was 12 minutes using the dual tube UV source through 3mm glass.

Developer was 7 grammes of sodium hydroxide (caustic soda) per litre of water at room temperature.

Development time was around 40 seconds, leavinga very well defined track layout.

All of a sudden I feel a great deal happier!!!!!
 

Hero999

Banned
Azaruk said:
I know glass absorbs a fair amount of the UV, so my exposure with Positiv 20 was around 10 minutes.
Glass is fairly transparent at UVA wavelengths so it's generally not a problem here. To minimise UV absorbtion I normally clean both sites with alcohol.

It also helps if you choose your film carefully, I normally use tracing paper because it doesn't absorb UV like some over head projector transparencies do.
 
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