Homebrew PCBs

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
>