How to make a PCB with 15 years old Positiv 20

[popilin]

If your photoresist is over don´t worry, here is a solution
Low Tech Method

1)Surface Preparation
The copper must be free of grease and oxide
a)Clean first with steel wool or a Scotch Brite
b)Rinse with water
c)Clean with a piece of cotton and soft abrasive powder (Thoose for cleaning the bathroom) wett with water
d)Rinse with water
e)Immerse the plate 10 minutes in a solution of 20g sodium hidroxide in 1litre of water
f)Rinse with water, much water (Don´t touch the copper with your fingers)
g)Dry with tissue paper and a hair dryer
h)With a soft paintbrush remove the dust just before coating

2)Coating
The room must be poor illuminated (40W Common Filament Lamp NOT low consumtion)
a)The plate and the photoresist must be at ambient temperature (Ideally 20º Celsius)
b)A clean room is made sprying water into the room so the dust particles slow down
c)Dry the floor and close the door
d)With the plate horizontally spray from a distance of 20cm by continuosly spraying in a zigzag pattern
e)Cover the plate with something like a Tupperware to avoid the dust
f)Switch off the light, now is a dark room (Work at night)
g)1 hour later, switch the light on, and dry the photoresist with a hair dryer. IMPORTANT:No more than 30º Celsius for 1 minute, again with fresh air, and again at 30º for 1m until the photoresist is dry by touch
h)Place the plate in a dark place 24 hours to completely dry

3)Exposure
With almost six 20W common daylight tubes at 10cm of the plate, exposure time is about 10minutes

4)Developing
With a 15 years old photoresist forget the classical developer (7g of sodium hidroxide in 1litre of water) Don´t work
We need something better, like Seno 4007 (Sodium Metasilicate) 25g in 1litre water
Time to develop: aprox 2minutes
Rinse with water

5)To obtain best resistence to etching heat at 70ºC for about 10m

Luck!