Positiv 20 - Printed Circuit Exposure Spray
O-naphtho-chinon-diazide and Novolack based liquid photo-positive resistor used in the production of printed circuit boards.
PROPERTIES
POSITIV 20 is a classic liquid photoresist that transfers patterns directly onto work materials for etching. The varnish resists strong acidic etching products, but can be easily removed by solvents (ester, ketone) or aqueous alkalines.
The varnish is most sensitive to light in the near ultraviolet range (UVA). Therefore the varnish should be applied in yellow light or dark daylight.
APPLICATIONS
The main application for POSITIV 20 is the production of printed circuit boards. The transparent positive pattern in the circuit diagram is conveyed accurately. Light-proof surfaces e.g. electrical circuits remain present after etching.
Other applications include photo-lithography on metal or glass.
INSTRUCTIONS
Instructions for manufacturing printed circuits:
Surface preparation
Surfaces are free of oil and oxide should be. Water-based cleaning process is available. Household scouring powders are ideal when preparing metal surfaces manually. Solvents are used only when dirty, oily stains need to be removed. The last step of the cleaning process should be rinsing with demineralized water.
At this stage, the cleaned surface should be completely wettable and therefore water-repellent areas should not be left. The cleaned board should be left to dry in a dust-free environment.
Coating
After the cleaning phase, the copper plate positioned horizontally is coated by spraying POSITIV 20 from a distance of 20 cm. The best results in achieving a uniform coating are achieved by spraying continuously in a zigzag pattern. A typical coating thickness is 6-8µm and has a bluish color. The aerosol can should not be held too tilted to overcome discontinuities when spraying.
Lacquer is sensitive to UV light and therefore exposure to direct sunlight or bright sunlight should be avoided. Coated materials can be stored in the dark at 25°C for up to 4 weeks.
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Drying After the film is applied, the sheets should be dried immediately in the dark. The drying temperature should be gradually increased to 70°C and kept at this temperature for approximately 15 minutes. Infrared or forced air drying is possible. When using air drying at ambient temperature (minimum 24 hours), the quality of the film will allow only very simple operation. Adhesion is poor and the risk of dust entrapment and pinholes is high.
Exposure
The transparent circuit diagram must be placed flat and without errors on the copper plate. Paper-based diagrams can be made transparent using Kontakt Chemie TRANSPARENT 21. Spectral sensitivity for photoresist POSITIV 20 lacquer is in the 340 to 420 nm wavelength range, so UV lamps can be used to expose the film/copper plate. At an exposure power of 100 mJ/cm², the exposure time will be approximately 10 seconds for a film thickness of 8 µm.
In practice, the lamps are illuminated from a distance of 25-30 cm. When used, exposure time is between 60 and 120 seconds. It is recommended to allow the lamps to warm up for approximately 3 minutes.
Development
The exposed plate is developed by immersing it in a sodium hydroxide bath (10 g/l sodium hydroxide in water) at ambient temperature for approximately 60 seconds. The exposed polish dissolves. The development process can be supported by small bath rinses. Once developed, the plates are rinsed thoroughly with water.
Etching
Etching of copper and brass plates is best done with an iron-3-chloride solution (400 g/l water). The required time is between 30 and 60 minutes. Heating the solution to 40°C plus small bath movements will aid cauterization. At the end of the etching process, the plates should be rinsed extensively under running water.
Removing remaining varnish
After etching, remaining varnish will be removed from the circuits. This is best done with acetone at ambient temperature.
We recommend applying a film of Flux SK10 to PCBs in case they are not processed immediately. Flux SK10 varnish protects circuits from oxidation and also acts as a highly effective flux during subsequent soldering.
Finished PCBs are coated with PLASTIK 70 or PLASTIK 70 to protect from environmental moisture. It can be coated with SUPER.
Possible deficiencies during application and their causes:
Bad adhesion, bubbles or spot formations
- Product shelf life (18 months) has expired, see date on aerosol can
- Presence of anti-cross-linking impurities: cleaning and rinsing with scouring powder.
- Summer heat during application: Reduces spray distance.
- Aerosol may be too cold, fresh from the refrigerator: leave at ambient temperature.
- Too high drying temperature: not exceeding 70°C.
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Pinhole formation
- Inadequate drying: dry at the recommended temperature of 70°C.
- Very fast drying: gradually increase over a period of 15 minutes. temperature up to 70°C.
- A very long development time: do not exceed 2 minutes
Other applications of POSITIV 20
- Glass etching: the lacquer is also resistant to 40% strong hydrofluoro acid and therefore makes it possible to etch glass. Adhesion can be improved by a temperature treatment at approximately 120°C.
- Production of durable lettering or graphics: Treatment of a temperature varnish at 190°C will result in durable lettering or graphics having a blackish brown color.
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Safety precautions:When working with the chemicals mentioned above, safety and usage instructions must be strictly followed. Skin and eye contact should be strictly avoided. We recommend the use of protective clothing, gloves and safety glasses. Use only in well-ventilated areas.
A safety data sheet (SDS) according to EU directive 91/155/EEC and amendments is available for all CRC products.
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