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Photopolymer Dry-film Developing Module

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:
  1. Heat the bath to 115°F (46°C)
  2. Mount a test coupon in the board clamp. Obviously, you do not need to use a full sheet of copperclad. All you need is a panel 2 in. x 2 in. (or an imaged test coupon).
  3. Immerse the coupon into the bath and develop for 1 minute. Lift the coupon out of the bath and examine for signs of resist removal. If resist remains, return the sample to the developer.
  4. Lift the test sample out and examine the degree of developing every 30 seconds.
  5. When all of the resist has been removed, or when the test patterns in an imaged coupon are totally developed, thoroughly rinse and dry the sample and set it aside.
  6. Record the total amount of time the coupon was in the developing solution. Denote this time as "T" and record it in your bath maintenance log. Later, as you gain experience, you will use test coupons to determine when you need to dispose of your developing solution and start with a fresh bath.
  7. If you used an imaged coupon to test the bath, examine the test patterns under a microscope if available. If the resist elements do not appear to be totally developed, return the sample to the developer for 30 seconds. Remove, rinse, dry and inspect. If the image quality meets with your approval (no shorts, near vertical side walls, glossy land areas), record the total developing time as "T" in you maintenance log. If more developing is needed, continue as above until you are satisfied with the end results.

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