Homebrew PCBs

Adam,

Bill's idea with the T shirt press is something to look into. 
Anything that can apply heat and moderate pressure can be used for 
dry film lamination.

I have applied the dry film by laying it on the clean copper surface 
and then putting it in a nylon "turkey bag". Seal the edges with 
masking tape and hook up a small diameter tube to a vacuum pump. The 
pump will evacuate the air and force the dry film tightly against the 
copper. Then you could just use a regular laundry iron to heat it 
and "iron" it on.  A small airbrush compressor hooked up backwards 
will make plenty of vacuum for doing this. Try this method for hobby 
boards because it really works good and isn't too hard to do.

I used a DuPont HRL-24 laminator in the past but as you mentioned, 
they are big and expensive to operate. I sold that beast and got a 
small table top laminator. The unit I use is made by the Steven 
Daniels Company. It accepts 3" core rolls and has adjustable tension 
and board thickness. The adjustable tension on the roll is what you 
need to get rid of the wrinkles.

I used three different photoplotters over the years. My first one was 
a Gerber Scientific 3244. This was a vector plotter with a mechanical 
wheel that held up to 34 apertures. These apertures are a small piece 
of negative film with the pad shape on it at 3:1 scale. The wheel 
rotates to the proper aperture number by software control and exposes 
the film via a lense and shutter. The table size was about 20" x 26". 
This plotter would directly read a DOS diskette and plot the job. If 
you only want to plot your own work then this plotter would be a good 
one to have since you could match your CAD apertures to the 
mechanical wheel and plot your films. This plotter will plot the 
typical small hobby board in two or three minutes. 

I sold this machine and stepped up to a Gerber Cresent raster laser 
plotter for the big stuff. This was also a good plotter but required 
green lights in the darkroom. This made it difficult because most of 
our film was processed under red light. We had to have two darkrooms 
which was a pain. 

The best plotter we ever used was made by Lavenir Technology. It was 
a model RPG-1622 and could process up to 16" x 22" films. The 
exposure head has 100 special LED's that increment in the Y axis and 
the whole exposure head travels back and forth in the X axis to 
complete the plot. The model I have can handle about 250 different 
aperture shapes and sizes. It is a desk top model. If you ever find 
one of these cheap don't pass it by. I bought mine in 1989 and still 
use it. They never break and are very accurate. You can plot positive 
or negative films with this unit. 

The film I use these days is Kodak AGX-7. This is a heavy .007" thick 
film that is made for photoplotters. The cost is about $3.50 per 16" 
x 20" sheet. Kodak also makes this in a .004" thickness which would 
be less costly but not as stable as the thick stuff. 

For the absolute finest detail you should use a vector plotter since 
it plots point to point and the lines have a very sharp edge. The 
raster plotters are more flexible to use but don't have the sharp 
edge like a vector unit. You will almost need a microscope to see the 
difference though and by the time the etching solution has done its 
job everything is smoothed out anyway.

Bottom line:  get a small table top laminator or turkey bag setup and 
if you can ever find a Lavenir plotter grab it. You won't be sorry. 
If it's working when you get it, chances are it will keep going for 
many years. 

Tom

--- In Homebrew_PCBs@yahoogroups.com, Bill Higdon <w.higdon@a...> 
wrote:
> How about using a "T" shirt press? you know the items used to apply 
> decorative heat transfers to t shirts.
> Bill Higdon
> Adam Seychell wrote:
> > Hi Tom
> > 
> > twb8899 wrote:
> > 
> >>Bob,
> >>
> >>Most of my boards are rather simple and single sided. I use dry 
film 
> >>photo resist on FR-4 (glass epoxy) and CEM-1 (paper base)
laminates. 
> > 
> > 
> > 
> > I am wondering how you apply the dry film. I have a lot (30 
meters x 16" roll) of dry film 
> > at home for making PCB's. Its excellent to use once it has been 
applied to the board. I 
> > made a rubber roller to apply the film on the board while cold. I 
then heat it in oven at 
> > 80°C for 10 minutes to get it sticking on really well. It's 
difficult to avoid wrinkles 
> > and air bubbles without a proper laminator. I find applying the 
film the most difficult.
> > 
> > I once had a chance to buy a proper dry film laminator for fairly 
cheap at an auction, but 
> > the machine stood 2 meters tall and weighed couple hundred 
kilograms. This machine is ok 
> > if your laminating hundreds of panels in a single day, but for 
the hobbyist with limited 
> > sotrage space and money there has to be a better way.
> > 
> > 
> > 
> >>I make my films using a machine called a photoplotter. This 
machine 
> >>takes the data from a CAD system and "draws" the image on 
> >>photographic film for a perfect image in a positive or negative 
> >>format. These films are known as a "phototool" in the industry. 
> > 
> > 
> > How does this photoplotter work ? I've heard that some use a red 
laser and scan across a 
> > rotating drum with the film wrapped around. I priced photoplotter 
film and its very 
> > expensive. I've remember you once mentioned that there is a lot 
of used PCB equipment on 
> > the market, are there any fairly cheap photoplotters around ? Are 
these machines too big 
> > for a home lab ?
> > 
> > 
> >>I have never used the laser or ink jet methods but know others 
that 
> >>have had excellent results with these methods. I believe they use 
> >>some type of translucent paper for printing which will allow UV 
light 
> >>to pass through. 
> > 
> > 
> > 
> >>I still have a process camera but prefer the photoplotter because 
the 
> >>film is always perfect. If you look at a photoplotted film with a 
> >>microscope you will notice that it has excellent film density. 
There 
> >>are no gray areas. The film density goes from opaque black to 
clear 
> >>and back to black. It's difficult to get even the best cameras to 
> >>make films like this. 
> > 
> > 
> > I've looked at inkjet printers transparencies under a microscope 
and the line edges are 
> > very jagged. This is individual ink droplets scattered around the 
edges. There are no gray 
> > areas however. After I expose and develop the dry film and then 
look under a microscope I 
> > can clearly see the jagged edges reproduced from the inkjet 
prints. The film density of 
> > black ink in inkjet printers is never any problem for UV 
exposure. The main thing to watch 
> > out for is pin holes, but that depends entirly on what 
transparency and inkjet ink your 
> > using. Epson brand stuff give the best prints I've seen.
> > 
> > Adam