Dry-film Photoresist Specifications and Processing

Process	Parameter	Detail / Notes	Range	Optimum
Pre-lamination	drying time	oven @ 110°C±5°C	15 - 20 min.	15 min.
Lamination	temperature	Think & Tinker Dry-film Laminator	115°C±5°C	110°C
Lamination	speed	Think & Tinker Dry-film Laminator	3 - 6 ft./min	4 ft./min. ⁽¹⁾
Exposure	Stouffer Step	21 step, variable neutral density wedge	7 - 9	8
	energy	energy density in miliJoules per square centimeter (350 - 420 nm)	25 - 60 mJ/cm²	-
	time	Tinker & Tinker UV Source Kit	calibrate each roll	calibrate each roll
	color	initial - glossy light blue after exposure - glossy blue
Post-exposure hold time	time	the total hold time between lamination and development should not exceed 8 hours	0.25 - 8 hours	15 min.⁽²⁾
Development	breakpoint	the image should appear to be 100% developed to the naked eye.	50 - 65% of total dev. time	60% of total dev. time ⁽³⁾
	temperature	bubble assisted developers	29°C±6°C	29°C
	temperature	spray developers	31°C±6°C	31°C
	chemistry	anhydrous sodium carbonate (soda ash, weight%) ⁽⁴⁾ sodium carbonate monohydrate (weight %)	0.80 - 0.90% 0.95 - 1.05%	0.85% 1.0%
Pre-etch drying	time	100°C±5°C	-	5 min.
Stripping	chemistry	NaOH (sodium hydroxide) @ room temp.	1.5% - 3%	1.5%

Notes
1.	With a Think & Tinker Dry Film Laminator, the midrange position of the speed control knob (at 12:00) corresponds to a web speed of approximately 4 feet per minute.
2.	Strictly speaking, 4615 can be developed immediately after exposure. We have found, however, that for fine line circuit patterns, letting the panel sit for 15 minutes after exposure enhances the adhesion of the thin traces to the underlying copper.
3.	The recommended breakpoint for 4615 is 50% of the way though the developing time. The image has reached "breakpoint" when,to the naked eye, the pattern looks to be fully developed. Visual breakpoints can be very misleading. A more accurate evaluation can be made by carefully running your ungloved fingers over the surface of the panel. If you can feel a distinctly slimy or slippery coating in areas that appear to be free of photopolymer, the image needs more time in the developer.
4.	Two forms of sodium carbonate are commercially available. Both can be used to prepare DF 4615 developing solution: Soda ash (anhydrous sodium carbonate); Na₂CO₃ Sodium carbonate monohydrate: Na₂CO₃H₂O* The monohydrate form contains 17% water and is the more chemically stable form of sodium carbonate.
5.	If properly imaged, the dry-film should be tough enough after developing to scrub with a kitchen sponge to remove any residual traces of adhesive or photopolymer from the exposed copper areas. This may be necessary if tray or bubble assisted developing is used. Boards developed with high pressure spraying equipment do not generally need this extra attention.