Josh,
Water makes the resist adhere quite well w/o bubbles, but it causes
two problems for me; ther first is the one you described, and the
second is the tendency for the resist to 'lump' instead of melt when
developed, leaving ragged edges.
I have a laminator, and it works well for the thinner board material,
but you do have to place the board into a carrier for this to work
properly.
On thicker board material, where I cannot use a laminator, this is my
method for applying it sucessfully:
This product is a 3-layer laminate, consisting of a photo-sensitive
polymer layer between two protective layers of clear plastic film.
It can be used without process equipment or exotic chemicals, and
develops easily in a slightly caustic soda solution.
Here is my own procedure for applying this resist:
I. Cut your board to size, clean and dry the copper
surface
· Whatever your finished board size will be, make it about
1/4" larger all the way around. This will allow you to do a final
trim later to remove any ragged edges or other defects after etching.
These defects tend to appear right at the edges of the board.
· Wearing latex gloves is helpful; you must clean any oils,
corrosion or other defect from the copper. One way to do this is to
use a scouring powder (like Kleen-King) and water. Very fine steel
wool is also OK. If the copper surface is already in good shape,
clean with soap and water only and dry.
II. Prepare the laminate and apply it to the the board
· Cut a piece of the laminate stock into a sheet about 1/2
inch larger than your board all the way around.
· Lay the laminate flat on a cool surface, and with the point
of a needle or Xacto knife, pick away at a corner until the
protective layer begins to separate.
Note: You will be able to separate the first protective layer only on
one side of the laminate, the other will not peel away until the
laminate is heated and cooled later on in the process.
. Heat a 3/8" thick aluminum plate to 125f. Lay the board on
it, and when it comes to temp, apply the resist 1/4" at a time,
moving your finger side-to-side to apply it evenly, while continuing
to peel back the protective layer as you go. Trim off the excess
material.
· Warm the board slowly using a hot plate and that piece of
3/8" aluminum plate. Move the temp up from room temp to 150f (max)
over 15 minutes, allowing the resist to cure to the board; Allow to
cool gradually. Test for proper curing by peeling back the outer
protective layer at the edges; if it comes away clean, it's OK; if
the resist comes with it, it's not cured yet. Do not remove the outer
layer entirely, just test the edges.
.I find that one layer of this material is not enough
protection (I got a lot of pin-hole penetration through the resist),
so I always add a second layer of resist, this time at room
temperature. Peel away the protective layer over the first layer a
bit at a time, and apply the second layer a bit at a time, peeling
it's first layer as you go. Cure the board again as in the previous
step.
III. Expose
· Using a negative image of your artwork, expose the board
with the proper light. I use a glass picture frame to hold the
artwork and board together, and expose it in direct sunlight for
about 15 seconds. Store in a cool, dark place for 15 minutes to allow
the polymers to set.
IV. Develop and etch your board
· I use Arm & Hammer washing soda (not baking soda), 1/2
TEAspoon (TSP) per 8 oz of water.
· Peel away the other protective layer remaining over the
photo resist, and pour developer over the board until the done, then
rinse immediately. The resist should slowly melt away. If it comes
off in clumps, strands or gobs, the resist did not cure properly.
· Now you can etch your PC board
· Resist can be stripped with Acetone, or if you don't like
Acetone, you can use a more concentrated developer solution (2
Tablespoons per 6 oz of water). Allowing either to sit on the resist
for a few minutes will cause the resist to bubble up and lift away
from the copper.
· Don't forget the final water rinse.
· Trim the board to size (this is where the ragged edges
disappear).
Hope this helps.../ Jim
--- In
Homebrew_PCBs@yahoogroups.com, "joshdewinter"
<joshdewinter@...> wrote:
>
> Hi
>
> MG Chemicals now sells a "Negative Photoresist Film" (product
#416-
> DFR5) that I believe may be Riston.
>
> I have tried it several times now with mediocre results. The
> traces turn out good when they turn out. The problem I'm getting
is
> actually getting the film to stick to the board uniformly before
> exposure.
>
> Someone suggested using water between the board and the film to
> allow rolling of any bubbles out from underneath with your thumb
> after positioning, then drying it in an oven at about 200 degrees
for
> 10 min to get it to stick.
>
> They were right, it worked great...until I tried to dry it.
Small
> mutations formed, sometimes in the form of lines, sometimes what
look
> like small blobs. They aren't bubbles per se, but somehow there
are
> areas of the film that appear to stick to the board at a deeper
level
> than the surrounding film, or maybe they are melting and deforming.
>
> The manufacturer recommends using a laminator to apply the film,
> which I tried initially, but it appears to have the same problem.
My
> laminator is adjustable heat, and I've tried from hi to low with
> similar results. I haven't as yet put the board between any
> protective sheets when laminating like you might to laminate paper
> items...I'm going to try that next (the manufacturer never
> specifically said to do it).
>
> Here are their instructions:
>
> http://www.mgchemicals.com/techsupport/416dfr_inst.html
>
> I clean the board ahead of time with steel wool, alcohol and
> acetone. I am using clean gloves throughout.
>
> Can anyone help me with any tricks to get this stuff to adhere
> uniformly?
>
> Thank you so much in advance!
>
>
> -Josh
>