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As my electronic circuits grow more complex, i've been looking for a way to produce professional quality PCB's on the cheap. I've tried all of the hacks and was not satisfied with any. I recently came across an idea for an exposure unit based on UV leds. I was unaware UV leds existed until now. By using these I've managed to build myself an effective UV exposure unit for producing high quality PCBs at a fraction of the cost of commercial tube based units. Here's how I built it;
UV LIGHT CAN CAUSE PERMANENT EYE DAMAGE DO NOT LOOK AT UV LIGHT DIRECTLY EVEN FOR A SHORT TIME.YOU HAVE BEEN WARNEDAbove is my finished unit. At the heart of the unit is 24 UV Leds. Using a simple circuit the array can be powered from 12V and produces enough UV light to properly expose a PCB in around 5 minutes. (Click on the image above for a the full sized image). The circuit could not be simpler. Each pair of UV leds is connected in series with a 120 Ohm (120R) resistor. This produces the desired 3.3v across each LED and the current draw of the whole unit is around 300mA. I've included a switch to save the power connector from constantly connecting and disconnecting. The circuit board is painted silver on the up facing side to maximise upward reflectivity of the UV light. The box is an old wine case which originally contained three bottles of fine wine. I had to drink them (hic!). I needed the box!! The box is covered with a piece of plain window glass. I use a tightly fitting piece of foamcore board to cover the unit when in use. Here's the circuit diagram. The LEDs were purchased from Ultra LED in the UK. They cost 39p STG each. |
