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Old 3rd Dec 2019, 1:47 pm   #11
David G4EBT
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Join Date: Feb 2003
Location: Cottingham, East Yorkshire, UK.
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Default Re: PCB Artwork transfer

Quote:
Originally Posted by Oldcodger View Post
Wendy- for more complex stuff, David G4EBT has provided more than a few solutions in his posts, using negative resist. I tnd to use various software to move my chosen PCB software to give me a negative image.
Firstly, the advantage of the beguiling technique which is the subject of this thread is that it removes the need for a UV exposure box, the need for an acetate mask, and for developer. In the video, I would have liked to have seen a close-up image of the tracks to see the quality of the finished product because I can't say that I was impressed with how he rubbed the image onto the laminate. If doing that only moved the artwork just a fraction of a mm it would be enough to create a junk PCB. With any technique, there are several variables which determine failure or success.

For some time now I've used the negative resist UV dry film technique and stick with it as I get consistently good results.

As with positive resist (such as pre-sensitised board or sprayed on positive UV lacquer), this method requires an acetate mask to be used in a UV light box but the mask must be a negative. With negative resist dry film, and clear areas one exposed and developed will remain as the etch resist and any black areas of the mask, which haven't be exposed to UV, will be washed away in the developer. (Soda ash).

At risk of taking this tread off topic, to answer 'Oldcodger's' query about image inversion to create a negative, it takes only a few moments using a program such as 'MS Paint' to invert a positive image. I've taken some screen shots of a solid state LED magic eye PCB project. The shots aren't very clear but the inversion steps are as follows:

1) Open the image in 'Paint'.

2) Click on 'Select' as shown in red square at top of picture, then using the mouse, encompass the image with your cursor by dragging the cursor around the image. (See the dotted line around the image).

3) With the cursor somewhere on the image, right click with the mouse and a drop down menu will open. At the bottom of the menu is an option 'invert colour'. Left click on that, and the image will change from positive to negative, reversing the colours.

Then save the image as 'PCB Negative Mask' or whatever so you keep the original positive image too.

I hope the pictures - poor as they are - show the three simple steps.

The invert facility is useful in many other ways - not just for PCB masks.

For example, I've mentioned elsewhere that it can be used to seemingly print white lettering on a coloured background by first creating the lettering in the desired colour of the background - black, blue, brown, whatever - then inverting the image. Fourth pic below - a Little Maestro back panel with white lettering on a brown background by inverting the image. (Text written in brown on a white background in the upper image, then the colours inverted in the lower one).

If there is to be any more discussion on this, I think it will have to be in another thread so that this 'cold toner transfer' thread can stay on topic.

It will be interesting to see what results are achieved.
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