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Dry Film Lamination

Written by Chuck. Posted in Preparation

 
This process used to laminate film to the PCB board is the same for both photo resist and solder mask.  This process is referred to as dry film lamination.
The key result of this process is to apply whichever laminate you're using, to the PC Board, without wrinkles or other defects.  It can be accomplished easily with just a little practice.
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For both dry-film photoresist and soldermask -- the product is supplied as a laminate consisting of three layers.  A peel sheet (or release-liner, the film and an ultraviolet (UV) transparent cover sheet.

  • Peel sheet: A polyolefin release liner that covers the thermally active adhesive on the bottom of the photopolymer.
  • Film layer: A UV curable, aqueous-developable, super-viscous-liquid film. This is what you want laminated, exposed and developed.
  • Cover sheet: The outer covering of the multi-layered film is usually made of heat resistant polyester (PET, a.k.a. Mylar). Since it functions as an oxygen block (see below) as well as a protective layer, it should remain in place on the outer layer of the resist until the board is ready to be developed. The cover sheet should be left in place at least 15 minutes after exposure and should only be removed immediately prior to developing.

Introduction

I purchased a used Akiles 12.5" Smart-Lam laminator on EBay for $228.49.  It came with a ton of laminating pouches.  Everything from 11x7 to 2x3.  Although these pouches are not required for this processes, they do come in handy for other projects.  It has a little quirk noise at times, but does the job magnificently.
SmartLam
Akiles SmartLam
According to Think and Tinker, many of the low cost "pouch" or "pocket" laminators currently on the market make adequate dry-film laminators. If the laminator is able to feed a standard piece of 0.062" FR-4, two layers of laminate, attached to a paper carrier without stalling, it will probably photosensitize your boards just fine. A safe way to test the capability of your laminator is to gradually increase the thickness of a stack of paper inside the carrier that you feed through the unit until you can hear the clutch start to slip (usually a loud clicking sound), or the drive motor groans from excessive labor. If it easily passes a stack of paper that is as thick as the PCB you intend to fabricate, plus both layers of dry-film, you're in business.
For small infrequent jobs this type of pouch laminator is the best way to go.  You can use a full blown hot-roll machine but remember the roll of film has a shelf life so unless you're using whole rolls in just a few months you'll find this impractical.
You could also purchase pre-laminated photo-resist PC boards -- but they won't work with the copper plating mask method I use, and you'll still need to laminate the soldermask.
Laminating-dry-film-thumbnail
Laminating dry-film tutorial video

Applying dry-films

  1. Setup your area with the equipment and materials you need.
  2. Set up your laminator and warm it up for about 5 minutes.  I use a medium temperature and medium motor speed on my laminator.  See the specification sheets of your material for the proper temperature of the dry-film that you're using.  Make sure the rollers are clean.  If not, then clean them according to the cleaning procedure below.
  3. In the preceding step we thoroughly cleaned and dried the PC Board.  Take a moment now to make sure it is completely dry.
  4. Using two pieces of tape, remove the dull peel sheet from the laminate, then place this side down on the copy paper.
  5. Tape the edge, which will go into the laminator first, to the sheet of copy paper.  Life the other side of the laminate with the razor knife and slide the PC board underneath it.
  6. Feed the sheet of copy paper, with the taped edge first, into the laminator.  Hold the free edge of the laminate up against the first roller while the PC Board feeds into the machine.  Perform this step carefully to avoid wrinkles.
  7. Once the copy paper/PC Board comes out the other side, feed it through a second time for a final lamination.
  8. Place the copy paper/PC Board on the cutting board and carefully trim the edge of the PC Board to free it from the carrier.
  9. Perform this process again on the other side, if using a double sided board.
  10. Carefully inspect the final product for defects.  If you mess up you can peel the cover sheets and strip the laminate from the PC Board using the appropriate stripper.  (Note: You probably won't be able to strip the soldermask, so don't mess up with that laminate.)
  11. The board is now ready for imaging and developing.

Materials

  • Pouch type laminator
  • Two sheets of copy paper
  • Scotch Tape
  • Razor knife
  • Cutting board

Tips

  • Be wary of grit and dirt.  You do not want and dust, grit or other material sticking to the rollers of the laminator.
  • Removing the peel layer is best done with two pieces of scotch tape as shown in the video.
  • Watch for wrinkles.  Wrinkles will ruin the result of this process.  With a little practice you can achieve wrinkle free results.
  • Depending on your laminator, you may be limited to certain thicknesses of PC Board.
If you do not have a laminator, you may try this other process.  I have not tried laminating a PC Board, but I am including as an alternative.
 

References