|−|Exposure times for the PCB vary depending on the exposure method. For instance, if you're working with a single sided board and plan to develop using the overhead florescent lights I recommend about 15 minutes of exposure. Before peeling off the tape and exposing the PCB, make sure to have a flat plate of glass such that you can lay the transparency over the peeled board and then lay the glass over the transparency so that it is flat against the PCB. It is helpful to dim the lights during this step to minimize exposure until ready. Once exposure begins do not move the board. |+|
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|−|If you are building a double sided board, it will be a good idea to use a uva light chamber so that you can expose evenly on both sides. If you do not have one here is a link to construct one using leds. [http:// www.instructables.com/id/UV-LED-Exposure-Box/] |+|
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|−|Another method to expose a double sided board without a light chamber is to secure the transparency on both sides of the board and then expose each side individually for the same amount of time. | |
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|−|Expose long enough such that all of the uncovered copper goes away but not so much such that the protected copper goes away. |+|
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|−|Note exposure times in a UVA chamber will be much less than 15 mins. | |
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the board is necessarily exposed, develop the board by swishing the board around in a solution of NaOH. This should be done until the exposed portions (where light was able to hit the board) are clean copper. There should still be traces where the copper will be on the final product. |+|
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Revision as of 13:35, 6 February 2019
Prepare the board resist developer solution using 10g of pure NaOH granules (meter using analytic balance) per liter of water (about 250ml in the small tray more than suffices). Room-ish temperature is sufficient, hot is bad (accelerates development and punchthrough, potentially just stripping all resist from the board).
Holding the board in a gloved hand, immerse and gently swish/agitate it. You should promptly see green streaming/boiling/clouding off the board and the emergence of the artwork pattern. Inspect closely every 30 seconds or so - the exposed copper to be etched should be bright and shiny. Any hint of gumminess means that there is a thin film of resist still clinging to it.
If the developer is fresh, this gumminess means that the board was underexposed. There's nothing to lose at this point by keeping going in development to see if it will clear. It will not be too very long before the caustic will begin to strip the unexposed resist as well, however.
Once done, rinse both sides under fast running cold water to get the caustic off. Gently DAB dry using a paper towl. DO NOT rub: The resist isn't a delicate flower but it's not that tough either.