Photographic PCB Manufacturing
Home production of precise printed circuit boards
Introduction
I began making printed circuit boards at home because drawing tracks manually with a permanent marker and ruler was slow, inaccurate and unsuitable for more complex layouts. Hand-drawn boards were often asymmetric, slightly crooked and vulnerable to under-etching when the marker layer was not perfect.
The older manual method used a copper-clad fibreglass board with a typical copper thickness of about 35 µm. A 1:1 component layout was printed on paper, hole positions were transferred to the board and the copper tracks were drawn by hand with an etch-resistant marker. The unwanted copper was then removed in ferric-chloride solution, usually in approximately 20–30 minutes.
Photographic PCB Process
The photographic method is much more precise and can be used successfully in a home workshop. It produces straight tracks that accurately match the artwork, supports fine conductors and makes it possible to manufacture relatively complex boards. The process requires a photosensitive PCB or positive photoresist, a suitable developer and a UV exposure unit.
- Prepare the board. Use a board supplied with positive photoresist or apply POSITIV 20 to a cleaned conventional copper-clad board.
- Prepare the artwork. Print the PCB pattern at 1:1 scale on laser-printer transparency film. Dense black areas are essential; two identical transparencies may be aligned together if necessary.
- Align and expose. Place the artwork directly against the photosensitive layer with the correct orientation and press it down with clean glass. Expose it with a suitable UV source, preferably in the approximate 350–450 nm range.
- Develop. Immerse the exposed board in the recommended developer until the unprotected pattern becomes clearly visible. Avoid excessive development time.
- Etch. Remove the exposed copper in ferric chloride or another suitable etchant. Agitation and moderate heating improve uniformity and speed.
- Finish the board. Wash the board, remove the remaining resist, drill the component holes and inspect all tracks for shorts or interruptions.
Exposure Unit and Practical Notes
A mercury lamp from street lighting can be used as a strong UV source, but it requires the correct ballast, enclosure and electrical safety precautions. UV LEDs are a safer and more compact alternative when distributed uniformly over the exposure area. Exposure time depends on the source, distance, resist and transparency density, so it should be established experimentally using a test strip.
The artwork must remain in close contact with the board. Thin picture-frame glass worked well for my small boards. Correct artwork orientation is essential, especially for bottom copper layers and mirrored layouts.
Project Images
