pcb development

Hmm, looks like overexposed/overdeveloped.... Did You make a Exposure-Set? Eg. get a piece of Pcb-Board, a piece of cardboard and Your film with a Circuit. Put it on the UV-Lamp with all but a 10mm stripe covered by the cardboard, expose half=20 the usual time. move the cardboard to expose 10 more mm, expose one more tenth oft the usual time. Repeat until two times usual time are reached.

develop, etch...

Look!

write down the time of the best strip...

Hth, Michael Buchhholz.

It looks to me like the UV has blead round the edge of the artwork.

I would recommend drawing the artwork in reverse and putting the ink side directly against the photoresist.

I use a similar technique (but using a inkjet printer and plastic film) and have been able to produce some very clean results.

Steve

I did print it on an plastic sheet (acetate) on a laser. I mirrored it and then put the ink side down. And then a sheet of glass on top of it to keep it flat.

I haven't done a test strip yet but will maybe try that today.

Thanks,

Okay - I think I have some improvement here but this is still with very big tracks. Can I get some feedback on this:

Just as a side note - it was extreme underexposure - 20sec vs. 2 mins that I'm doing now - I'll maybe try more and see how it goes.

I started at 20secs though because I have 6 x 15W tubes.

Cheers!

In that case its getting the right amount of UV exposure and the right strength of developer and development time. Time to experiment.

I have used this technique for SMT 0.05" pitch (0.03" wide) tracks - I would easilly expect to be able to get down to 1mm pitch with a 600DPI printer.

Steve

Thanks - It was exposure time (I was doing 20sec instead of 2 mins because I have a big UV box and thought I could get away with it.

I thought most glass was U.V. opaque.

I thought glass wasn't naturally UV opaque unless it had additives like with plastic. Most glass (for pictures, internal windows, etc.) doesn't as far as I know.

I've always associated a 'green' tinge with additives and additivies to the posiblity of UV resistance and hopefully the lack of tint with no UV resistance - but I could be totally wrong ;)

Depends on wavelength, but usually it's not opaque to the longer uv wavelengths (nearest to blue) unless it's designed to be.

You can get a tan through ordinary window glass.

All glass is UV resisting, which is why most film lighting lights have glass in them while UV suntanning lights don't.

The exposure unit that we have at the old factory places the material directly in front of a big mercury tube, but rotates the material after you have loaded it so the rays don't escape.

I think you will find the Epron erasers use direct UV light as well, they use a draw or a switched cover for safety.

Peter

-- Peter & Rita Forbes Email Address: snipped-for-privacy@easynet.co.uk Web Pages for Engine Preservation:

EPROM erasers use UVC light (about 250nm).

PCB Protoresist is normally semsitive to wavelengths in region of 350 - 400nm (UVA)

Steve

Okay - I've started trying to make some d/s boards and have run into another funny. It seem that the image after developing is 'smudged' - its not actually smudged but it looks like that. It looks like the image is missing an area like it has been rubbed off or something.

This only happens on one side and irrespective of how carefull I am placing it in the developer/etc.

Any ideas?

This is as good as I've gotten it so far - as you can see there is still a problem with the second side, although the one side is perfect. Each step is done vertically so I'm really struggling to figure out whats going wrong.

"James Varga" schrieb:

Not long enough exposed or Lamp not centered. Maybe (if You use a 'face tanner') one of the Tubes emits fewer UV?

just my 2 cent.

Michael.

"James Varga" wrote

I take it the trace widths and pad sizes are the same on both sides? Traces and pads are thicker on side 2.

Side 2 looks like it was one (or more) of:

o under etched o under developed resist o bad artwork o under exposed resist

My guess: under etched.

You may want to lift the board and spin it 1/2 turn at the midpoint of the etching time: that way both sides should get etched the same amount (maybe). Increasing etching time for 2 may result in over etch on 1.

"Nicholas O. Lindan" schrieb:

Sorry to disagree: Underetched woud show blank copper where the Traces are too big, but as You can see there ist violet resist all over the traces. If the resist would change colour at the faulty Traces, i woud suggest underdevelopment, but i still think=20 there's something wrong with the exposing process..

Michael.

P.S.: If this resist don't change colour when being exposed, it can also be underdevelopment (Board not lifted while developing, so there was no NaOH at he bottom side?)

I don't agree either - but I don't know the cause.

Is this a positive or a negative resist (are the tracks on the artwork black or clear)?

Are you applying the resist yourself, or are you buying ready-covered board? Could the board be duff?

You might try PhotoEZ stencils ...

Shirley (circuit bridge)

Shirley .