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--- pcbetching [2022-01-18 21:04] – [Cutting] jtdburton
+++ pcbetching [2022-01-19 20:58] – [Developing] jtdburton
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-===== Exposure ====
+===== Exposure =====
-Grab the laminator, some sellotape, and a pair of scissors from G1 before you start with this section.
 Currently (as of January 2022) the lab has NEGATIVE photoresist, which means the copper will be removed from the areas of your board NOT exposed to UV light.
-In the past the recommendation has been to use transparencies run off the laser printer for UV masking. This does not actually work very well because the "black" areas do not come out fully opaque. Tracing paper may work - as of this writing we don't have any. One good way to produce a UV mask in the absence of proper printables is to laser-cut your trace pattern into a scrap bit of very thin plywood or black acrylic.
+The best option for creating your UV mask is to print it onto some heavy tracing paper on the laser printer in G1. You may need to print and overlay two copies.
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+You can also cut your trace pattern into a scrap bit of very thin plywood or black acrylic.
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+Either way, once you have your mask ready, grab the laminator, some sellotape, and a pair of scissors from G1.
 Cut a piece slightly larger than your board from the roll of photoresist film kept wrapped in a black bag in the cabinet in G14. PUT THE ROLL BACK IN THE BAG - it's UV sensitive.
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 Make a solution of about 500ml water and 20g washing soda crystals (sodium carbonate decahydrate). There is a handy 3D-printed scoop to help you get the right amount of washing soda.
-Immerse the PCB in the solution for a few seconds, then remove it. You should now be able to easily peel off the transparent film on the front. Return the board to the solution and start gently brushing it with the paintbrush. You should notice bits of the blue mask coming off. Once all the copper you want to remove is exposed (this should take about 30-60 seconds), remove from the solution and rinse with plenty of water.
+Immerse the PCB in the solution for a few seconds, then remove it. You should now be able to easily peel off the transparent film on the front. Return the board to the solution and start gently brushing it with the paintbrush. You should notice bits of the blue mask coming off. Although it might look like all the unwanted copper is exposed after a minute or so, it actually takes about three minutes for the film to fully develop. After that time has passed, remove from the solution and rinse with plenty of water.
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