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