Patterning of flex circuits

Santa Clara and Corona, CA-Tamarack Scientific, a systems integrator and laser job shop, is using high-power excimer lasers for laser direct patterning of high-density flex circuits.

Santa Clara and Corona, CA-Tamarack Scientific, a systems integrator and laser job shop, is using high-power excimer lasers for laser direct patterning of high-density flex circuits. This dry, one-step process has been configured for both reel-to-reel and roll-to-roll production. Manufacturers are already using the system to fabricate RFIDs, disposable medical sensors, and component circuitry for ultra-compact phones and PDAs.

The Tamarack workstation uses the high pulse energy of the Coherent Lambda SX 315C, which delivers 1050 mJ at 308 Hz. This laser enables the metal pattern for an entire circuit to be formed with a single pulse. In this mask projection process, the laser beam interacts with the metal-plastic interface and lifts a thin, uniform layer of vapor-deposited metal from the substrate. The metal layer thickness must be less than 400 angstroms, which ensures a complete lift with clean edges and no breaks-even on lines as narrow as 10 microns. The optimum thickness is around 200 angstroms, which is more than sufficient for most flex circuit applications, which typically don’t carry high current. At this thickness, a circuit with area up to 400 mm2 can be processed with each pulse. And at 300 pulses per second, this laser process can generate 18,000 circuits per minute.

Tamarack has successfully demonstrated this process with several different flexible plastic substrates (PET, polyimide, PEN, and PMMA) and a range of conductors, including copper, gold, silver, platinum, and titanium. Matt Souter of Tamarack notes that end users cite several advantages of the laser-based method, the most important being process simplicity. “The traditional wet photochemistry method uses about seven separate steps, if you include all the individual exposure, etching, and cleaning processes. You also have to purchase and dispose of the chemical reagents. Our technique is a single step, and is competitive in terms of results. In laser processing, the metal debris is removed as it is formed by a vacuum system that traps the precious metal, allowing recycling of this valuable material.”

Single-pulse processing capability brings another set of advantages in terms of speed and ease of integration. Specifically, the 30ns pulse duration of the excimer means that this reel-to-reel process can be performed with continuous motion-the motion appears frozen at the 60-meter-per-minute web speed. Alternatively, for production lines set up to handle wider rolls rather than single-width reels, Tamarack uses a stepped motion of the roll with flying optics taking the beam across the web direction.

Contact Ludolf Herbst, Coherent Inc, www.coherent.com, or Matt Souter, Tamarack Scientific, msouter@tamsci.com, www.tamsci.com.

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