Homebrew PCBs

I should add some explanation to the photos I took earlier 
and uploaded to the following location;
http://members.optusnet.com.au/~eseychell/pictures

The 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.JPG
A 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.JPG
After 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.JPG
The 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.JPG
The 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.JPG
Boiling 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.JPG
This 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.JPG
This photo is of the PCB after the resist is applied.

http://members.optusnet.com.au/~eseychell/pictures/after_exposure.JPG
After 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.JPG
The typical developing method shown here. A solution of 
10g/L sodium carbonate heated 30\ufffdC to 40\ufffdC.

http://members.optusnet.com.au/~eseychell/pictures/resist_processing_finished.JPG
The 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.jpg
http://members.optusnet.com.au/~eseychell/pictures/resist_image_on_copper.jpg
Out 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