Section: Design/Components

Vendors address prototyping, production

Terry Costlow

San Diego - The market for flexible circuit boards is growing quickly, industry members who met here earlier this month agreed, but the infrastructure is still just starting to fall into place.

One thing that's necessary to move flexible boards into the mainstream is an affordable, quick-prototyping technique, according to Direct Imaging Inc. (West Lebanon, N.H.). Flex boards are tougher to make than rigid boards, so the "rough-and-ready" techniques used to prototype rigid boards can't be used for flex circuits. Given that premise, it's not surprising to learn that Direct Imaging's presentation at the IPC Printed Circuits Expo here detailed a prototyping offering that it calls System Two.

System Two lets engineers start populating a single- or double-sided prototype board about an hour after they complete their draft design. The system costs from $30,000 to $50,000, which can be amortized to just $2,400 per run if 60 designs are run over the course of a year. System Two is based on a direct-etch resist and a six-step process. Those steps go from CAD translation and resist application through drilling. Intermediate steps include etching, resist removal, solder masking and alignment/lamination.

Double-sided boards

Automated Systems Inc. (Brookfield, Wis.) also looked at single- and double-sided boards, but examined full production. There are different ways to create double-sided boards, and not all techniques are the same. System designers who simply ask for double-sided boards may have problems, since simple production techniques may not meet their requirements. Conversely, a fabricator who uses a more-complex option may create unnecessary expense. Designers should be aware of the differences when they pick the alternative that will be used in their product, according to Automated Systems.

Taking things to the next level, Parlex Corp.'s Flexible Circuit Products Division (Meth-uen, Mass.) has developed a technique for mass-producing multilayer boards. Multilayer boards have been far less popular than single- and double-sided boards, which have been comparatively inexpensive to manufacture. A technology dubbed PALcore uses epoxy-coated foil to create multilayer boards that are thin yet inexpensive.

Though flex circuits can live up to their name, a common rule is that once most flexible boards are installed, they can't be flexed, according to Acheson Colloids Co. (Skokie, Ill.). While acknowledging that flex circuits are becoming more flexible as the technology evolves, Acheson feels that polymer thick films provide an excellent alternative to flex circuits.

Engineers at Tessera Inc. (San Jose, Calif.) have used thin laminates to create either multichip modules or a version of what the industry calls a chip-scale package, a small array package that is only slightly larger than the chip itself. Tessera uses flex circuits to provide "a sea of vias" N&SQOT; in a multilayer board that also has very fine lines. The technique roughly matches the density and performance of thin-film substrates but provides better yields, according to Tessera.