PCB 2012

A few years back, I decided to revamp my engineering school's student PCB fabrication facilities.

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A few years back when I was in engineering school, I was shown how to make PCBs using the photo-resist + etch method. As all electronics engineers should know, it's simple enough to do, provided you have the right equipment. The student-accessible gear was fine, until my projects started needing double sided boards with the kind of fine pitch SMD and tiny vias our antique (and single sided) light box couldn't resolve without pesky fringing and alignment issues.

As part of my final year project, I opted to make a new exposure box to eliminate the risky PCB-and-transparency-sandwich-flip and achieve a sharp enough image for 0.15mm features, and to be educational environment proof.

The basic rundown: a glass cartridge suspended between two 10W ultraviolet point sources (LEDs), an ATX power supply (recycling!), custom built constant current driver, and a home-brew PLC/HMI to handle the programmable exposure cycle, safety mechanisms, and communication to future PCB making devices.
  • 2 × 10W UV LED w. Lens, Holder & Heatsink Found them on Ebay out of China.
  • 1 × Recycled ATX Power Supply
  • 1 × Sheet of 16mm MDF And some wood glue, screws/brads/staples.
  • 1 × Litre of exterior house paint (white, semi-gloss). Exterior paint = more resistant to UV exposure.
  • 1 × Dual Channel Constant Current Driver or 2 * single channel. See schematics for my design.

View all 11 components

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zpyerhnp wrote 07/04/2018 at 03:43 point

Cool project, however, wouldn't it be better to do it the Stones way and paint it black? The inside of the box that is, to minimize non-aligned UV light bouncing off the walls and get cleaner lines?

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Eric Evenchick wrote 03/31/2014 at 17:39 point
Having worked with student design groups, I think that "educational environment proof" is the most impressive feature. With the glass cartridge approach, how well do dual sided boards turn out? Any issues with alignment?

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The Reverend wrote 04/01/2014 at 05:10 point
Having used Williams "PCB 2012" project to expose the artwork for my own final year design project PCB's I can attest to how well it works. I had no issue with alinement on double sided boards with tolerances and features of less than 6mil.

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Eric Evenchick wrote 04/01/2014 at 16:19 point
Impressive! Any details on how you built the glass cartridge and aligned the negatives would be great.

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William Pauli-McCahon wrote 04/02/2014 at 02:51 point
Thanks! I'll upload the design files for the cartridge sometime this week, as soon as I get a bit of time to go back and find them.

As for aligning the negatives, we typically cut one of the negatives down to have a smaller frame than the other, used a light box/tracing table to line up the two negatives (smaller one on top), then taped down one side to join them and keep them aligned, and stuck the PCB between the two sheets.

Not a hugely high-tech method, but it worked well. If you needed to do a production run, you'd just print several sets of negatives so you could load the next cartridge and unload the previous while the current board was exposing.

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