The photolab workhorses: artwork protect films are becoming standard as fine lines become the norm.
Artwork protect film, or APF, is an overlaminating film based on typically thin, clear polyester films coated with a pressure-sensitive adhesive that is applied to artwork to improve its durability and life. Higher performing varieties of APF also include a chemically resistant slip coating that enhances its ability to protect the underlying artwork.
APFs have been available for more than a decade. Originally developed as 0.0005"-thick polyester film with an adhesive coating, protection films were used for direct lamination to the production phototool of choice (either diazo or silver-based). Their task was simple: to prevent potentially damaging scratches from occurring on phototools sent into production to expose the photoresist-coated PCB. A scratch-free phototool meant less time spent reworking both the phototool film and exposed and developed panel.
With the move to finer lines and spaces came enhanced APF films capable of finer line edge resolution. In addition to finer line edges, the new generation of APFs brought improved levels of scratch resistance and include a top coat on the APF material that makes the cleaning of LPI inks and resist chips much easier.
Today, the industry's gold standard is the 0.00025" (6 [micro]m) polyester film with a 2 [micro]m adhesive and a top coat to reduce scuffing and provide easier removal of resist and LPI inks. To incorporate even finer resolution properties, one manufacturer has introduced a 0.000125" (3.5 [micro]m)-thick APF for the ultimate in fine-fine reproduction.
In the past, many fabricators thought of using an APF only for long-run boards. But reducing scrap rates, rework time and costs, and improved cycle time on the production floor are more critical than ever. Companies are realizing the value of using protection films now that the cost of APF has dropped significantly at the end-user level.
Most APFs on the market today are produced with an "overcoat" on the topside. This overcoat is engineered to give users the best of both worlds: it combines a "hard coat" that effectively reduces scratches and scuffs and a "slip coat" with anti-stat for ease of cleaning and the removal of LPI inks and resist residue. This topside coating is formulated with a slight matte agent that improves alignment to the PCB panel. (Purists, take heart: APF is also available without a topcoat.)
Applying and working with APF is relatively uncomplicated. The first move is to settle on which style of laminator will best satisfy your needs. It should be noted that the lamination process is a cold lamination; no heat is required. Most APF manufacturers offer laminators in two configurations: a tabletop unit and a standalone floor unit. A tabletop laminator's compact design is geared to placement on a fable within the photolab cleanroom. Typically, this style will accommodate APF up to 24" wide by 500" long.
Floor-model laminators most often include a stand, a tacky adhesive roller setup to clean the phototool before lamination and a HEPA filtration system to maintain a clean lamination environment. Standalone versions have a larger footprint than tabletop units, and accept film widths of up to 30".
Next, decide which APF thickness--6 or 3.5 [micro]m--best fits your specific application. Of the shops I know, the overwhelming majority have opted for 6 [micro]m thickness. This provides the user with excellent image reproduction down to 0.003" lines and spaces. Note: if working below 0.003" lines/spaces, consider 3.5 [micro]m APF.
You'll also want to decide which companion roll material will function best for your operation. (The companion roll material serves as the carrier/backing material during the lamination process.) You have two basic choices: an anti-star polyester film--perfect for a cleanroom operation--or a paper roll. It's my experience that most shops using APF today prefer the paper companion roll. Photolab technicians tell me that the paper roll is simply easier to work with than polyester film material.
With your choice of laminator, film thickness and roll material completed, you're now ready to load and thread the artwork protection film into the laminator. This is quite easy if you follow the threading diagram and suggestions provided by the manufacturer. (I have 10 thumbs and even I can do this in no time!)
Once the laminator is threaded, run a few feet through the unit to verify correct tracking. Then perform a visual inspection; look for wrinkles at "nip rollers"--where the actual lamination takes place--and smooth any wrinkles. When you see a smooth, non-wrinkled attachment of the APF on to the paper or film companion roll, you're ready to laminate phototools. To remove any doubt, conduct a trial lamination using a piece of scrap film. Although APF products are engineered for ease of cleaning and to reduce attraction to dirt and debris, it's absolutely critical that the environment, including the artwork itself, be free of dirt and debris.
Next time we'll dig deeper into the application techniques for using APFs.
JEFF JARVIS is senior territory manager at InteliCoat Technologies (intelicoat.com). He can be reached at firstname.lastname@example.org.
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|Title Annotation:||Better Phototooling|
|Publication:||Printed Circuit Design & Manufacture|
|Date:||Jul 1, 2004|
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