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Calibrating the developing solution
Before we start developing, we need to determine how quickly the developing solution removes unexposed photoresist.
Note on preparing test coupons: Regardless of whether you use immersion, bubble-assisted, or spray developing, always develop a test sample to see how long it takes to totally remove any unexposed photoresist (or soldermask). If possible, it is a good idea to image, a set of sensitized (laminated with photoresist) copperclad panels whose resist geometry is representative of the minimum sized feature in your circuit design. In most cases, mixed blocks (1 in. x 1 in.) of horizontal, vertical and crossed (cross-hatched) 0.010 in. (0.25mm) traces on 0.020 in. (0.51mm) centers act as very effective probes for measuring many facets of developer and etchant performance. This is referred as an "imaged test coupon", or simply a "test coupon". These coupons can also be used to calibrate your etcher if you are using electrochemical etching to define your circuit pattern.
If you do not have time to make test coupons, you can use a scrap of copperclad that has been covered with the photopolymer you will be developing. It will not yield any information on how well the bath will develop your circuit pattern, but it will give a good first estimate of how long the board needs to stay in the developing solution.
Read the chemical handling safety procedures until you understand them. FOLLOW THEM TO THE LETTER!
Proceed as follows: