I should add some explanation to the photos I took earlier
and uploaded to the following location;
http://members.optusnet.com.au/~eseychell/picturesThe dry film I'm using is a product from MacDermid part
number AquaMer MP215. Its dated 1998, but still seems to
work perfectly fine for me. I bought it about 2 years ago
from a guy who owns a small PCB fab shop and he sold be
about 20~30 meter roll for AU$20. I store it in the fridge
just to be safe. Its appears to be a high sensitivity type
of resist, since exposure takes less than 10 seconds in
direct sunlight on a summer day.
I had built a hand roller to apply the film. The design of
the roller is based on many hours of experimenting with dry
film, and learning how to get the stuff on without wrinkles,
or trapped air bubbles and relatively free of contaminants.
The technique uses a film of hot water on the surface of the
copper while the the resist is being applied by a roller
with an even pressure. The idea of using water came to me
after reading articles about "wet lamination" published on
PCB industrial web sites. I have found the water has three
major advantages over dry hot rolling.
1) It virtually eliminates the wrinkling problem because the
film does not instantaneously bond to the copper, allowing
some movement as the film contacts the copper.
2) Trapped air bubbles are reduced because the water
displaces air.
3) Dust and surface contaminates are dramatically reduced
since the water washes the surface clean. This is probably
the most biggest benefit.
http://members.optusnet.com.au/~eseychell/pictures/roller_bottom_view.JPGA bottom view of the hand roller is shown in this photo;
The red board screwed to steel right angle is a support for
the resist while rolling on the film (see later photos).
http://members.optusnet.com.au/~eseychell/pictures/micro_etch.JPGAfter scrubbing the PCB clean with caustic engine degreaser
I dip in room temp ammonium persulfate for 20 seconds to
further clean the copper and roughen its surface. This step
increases photoresist bonding.
http://members.optusnet.com.au/~eseychell/pictures/cut_to_size.JPGThe film is cut to a size just a bit smaller than the PCB so
it will leave one edge uncovered a few millimeters.
http://members.optusnet.com.au/~eseychell/pictures/remove_protective_film.JPGThe resist is laid on the board and the polyethylene
protective film is removed. The film is then pulled over the
roller so it wraps around about halfway. Its important to
keep the film square with the roller so it doesn't move off
to one side when rolling on the PCB. I draw a series of
lines on the red board to help square up the film.
http://members.optusnet.com.au/~eseychell/pictures/boiling_water.JPGBoiling water is pored over the PCB to both heat and wet it.
The heat makes the film soft and bonds strongly to the
copper surface. The PCB is laying on a large block of
polystyrene foam.
http://members.optusnet.com.au/~eseychell/pictures/roll_application.JPGThis is the actual rolling on of the film. I apply pressure
(sorry no numbers) and slowly move forward.
http://members.optusnet.com.au/~eseychell/pictures/resist_applied.JPGThis photo is of the PCB after the resist is applied.
http://members.optusnet.com.au/~eseychell/pictures/after_exposure.JPGAfter exposure you can see the faint image of the masked
pattern in the resists. The resist becomes pinker after
exposure. In this photo I'm pealing away the protective
Mylar film from the resist. The main purpose of the Mylar
film is to act as an oxygen barrier during exposure.
http://members.optusnet.com.au/~eseychell/pictures/developing.JPGThe typical developing method shown here. A solution of
10g/L sodium carbonate heated 30°C to 40°C.
http://members.optusnet.com.au/~eseychell/pictures/resist_processing_finished.JPGThe board after developing is rinsed and microetched once
again to remove any traces of resist. Placing the PCB in an
acidic solution also stops continuing developing of the
resist, which can otherwise lead to "furry edges" if left
too long (1+ minutes). The next step will the remainder of
the pattern plating process, i.e. tin plating followed by
photoresist strip and alkaline copper etch. This method is
not the normal hobbyist way, so typically a negative
photomask will be used with a negative acting dry film
photoresist followed by copper etching in FeCl3, ect.
http://members.optusnet.com.au/~eseychell/pictures/Epson_inkjet_film.jpghttp://members.optusnet.com.au/~eseychell/pictures/resist_image_on_copper.jpgOut of curiosity I took some microscope shots of the
photomask pattern and the same pattern in the developed
photoresist (after "microetched"). This is good indication
the processes went ok, at least in this part of the artwork :).
regards,
Adam