Photoresist
Hi All,
I've made PCBs using photoresist material since I don't know when. (started out with asphalt laquer
) Using transparencies of the thinnest possible thickness and as clear as a mountain creek is best.
If the 'film' is not all the way black where it should be there is the possibility to make a contact copy using photofilm (offered in many electronics shops) or touch up using an EDDING400 for thick traces and an EDDING800 for fine traces. That kind of film has a different pixel solution which covers most of the pinhead sized blind spots without influence on the edges of traces and pads.
Photoresist may be very much different using different brands. The best I know of is BUNGARD (
https://www.bungard.de) which always has the same and EQUAL consistence of the photo layer. Exposure times will always be the same.
Using laser printers you might run into a problem just because of the kind of engineering. Many of those printers have a toner saving circuit which cuts back the toner if the software encounters large black areas. This results in pinholes within the copper area or even areas which might get overexposed since they are transparent.
Until now I used two different laser printers with best results even for double sided PCBs. (Scratching or cutting with a scalpel after development might damage the photoresist, resulting in a junk PCB)
The Epson EPL5700 had the toner saving option. It must be disabled printing PCB layouts using the highest possible resolution of 1,600X1,600 pixels.
Now using a FujiXerox DocuPrint203A it doesn't have that fancy option and prints clear deep black sheets of DINA4 format. (Its resolution is 1,200X1,200 pixels)
For a test make a small board sized 2X2 inches all filled with copper. The printed "layout" should be a solid black area. If there are still "clouds" visible try to reconfigure the printer setup or refer to the printer customer service for advise.
An excellent print is as black as an a..h... in a dark tunnel. (Fill the blanks
)
Regards
Hans