Artwork protection films for phototools: APFs and attention to detail can improve the PCB imaging process.

MY JULY COLUMN focused on artwork protection films. These polyester protection films--in .00023" and .00013" (6 and 3.5 [micro]m)--are laminated to the working phototool. An increasing number of PCB manufacturers are discovering that APF is an effective and cost-efficient way to protect the phototool films. The benefits most often cited by PCB producers include significant reductions in scratches and scuffs on the working phototool and easier removal of LPI residue and resist chips. This can mean up to six times greater life expectancy for the phototool artwork.

APF offers a number of important production advantages. The protective film applies easily to the phototool using a simple cold lamination process for either diazo or silver film phototools. APF also offers exceptional resolution properties (down to 0.002" line and space), virtually eliminates scratches and makes cleaning the phototool with film cleansing solutions from alcohol to MEK fast and easy. Another advantage: significant savings in production costs.

In typical applications, PCB manufacturers are faced with replacing their unprotected phototools after about 250 exposures because of scratches caused by frequent handling or the buildup of LPI residue. By eliminating scratch and ink buildup problems, manufacturers can achieve 1,250 or more exposures with one piece of film. Think of the cost savings with six times the yield: dramatically less film, less processing chemistry, less touch-up time and improved cycle time on the production floor.

The lamination process for APF is fairly straightforward. It's as simple as feeding your phototool through the laminator. Here are the before and after steps of the process.

Before you begin laminating, be sure your phototool is ready for the production floor. After your film plot or duplication, verify that your film lays flat and check the film's D-min and D-max. Remember, if you're using a diazo photon tool, you'll want to perform a "burn hack" (sometimes referred to as "out-gassing") before taking your densitometer reading. This is a critical step when using diazo films and APE The burn back helps ensure a stable D-max reading and will burn away any undeveloped diazo molecules and color couplers. These molecules and color couplers, during production floor exposures, get released from the phototool in the form of a gas, and then show up as trapped air pockets between the phototool and the APF.

Next, thoroughly inspect your phototool for pin holes, imaged-on defects that need removal and sharp line edges. Remember to avoid applying your touch up inks too thick; you don't want a glob of ink that could affect image resolution in the area you just touched up. Now comes the critical step of cleaning your film with an appropriate cleaner. Be sure you have removed any touch-up scraping, dust and other debris and fingerprints. Fingerprints pose a special problem because if they are not completely removed, they will show up as tiny bubbles, formed from the oil on hands and fingers.

Now we're ready to check the laminator. Visually inspect and wipe or vacuum away any dust, ink and debris within the laminator housing. Cleanliness in and around the laminator is essential. If you end up laminating dirt between the phototool and the APF, you could cause a defect on the imaged PCB panel. Remember to have plenty of APF on the roll. (You don't want to run out.) Check the cleaning nip roller and wipe it off with alcohol and a cloth if it's dirty. Do the same thing for the lamination nip rollers.

If you have not processed a lamination recently, run a few inches of APF and verify there are no wrinkles occurring at the nip rollers and inspect the now laminated companion roll material to assure a smooth, wrinkle-free appearance. If this is your first lamination of the day, I suggest you run a piece of scrap film to make sure all is well; this also provides the opportunity to verify the flatness of the phototool, i.e., no curl. If curl is apparent, try making a slight adjustment to the mandrels--no more than one quarter of a turn--to both the APF mandrel and the take up roll mandrel at one time. Then run another piece of scrap film and re-check for flatness.

Now you are ready to laminate your phototool. Many laminators have a guide at the front of the machine that helps position the phototool to the APE Lay the phototool on the feed tray next to the guide and bring it evenly up to the nip roller or cleaning roller, which will grab the film and start the lamination process. As a side note, some shops will coat the entire piece of film while other shops will leave a small space on the left and right sides of the film to speed up cutting the film off the companion roll paper or film. Either technique works well provided you remember that if you are not laminating the entire piece of film, you must have at least one inch greater APF coverage than your imaging area on the PCB.

Once the lamination is completed, remove the phototool from the companion roll paper or film. Place the laminated film on a flat surface or light table. Re-inspect the film checking for a smooth lamination free of wrinkles; make sure no foreign material gets sandwiched between the phototool and APE Check for flatness of the phototool. Congratulations! You are now ready to send an expertly laminated phototool to the production floor.

JEFF JARVIS is senior territory manager at InteliCoat Technologies (www.intelicoat.com). He can be reached at [e-mail]