The pressure to reduce costs has many designers rethinking their material selections. Precision-flow devices, for instance, traditionally were constructed of thin stainless steel, prototyped using electrical-discharge machining (EDM), and then mass-produced by electroforming. But a spec change to plastics has many manufacturing engineers scrambling for new ways to fabricate medical devices that have flow requirements. Laser micromachining, they find, has both the quick-turn prototyping capability of EDM along with the mass-production capability of electroforming.

Other high-volume manufacturing processes for precision plastic flow devices such as injection molding, plasma process, and traditional milling, are now exposing their shortcomings as devices are designed smaller. Laser micromachining can make up for them.

Injection molding, for example, spearheaded mass production of plastic devices. But smaller designs now call for micro-plastic injection technology and hot embossing techniques, such as LIGA from Germany and MEMS. Although plastic-injection molding is cost effective, complex and tiny 3D parts often break. This has prompted designing more-durable 2D plastic alternatives. These make laser micromachining ideal for prototyping and mass production. Still, mold making and laser technology can coexist where excimer lasers use lithography techniques on PMMA (polymethyl methacrylate or Acrylic) as a master mold for subsequent electroforming and plastic-injection molding.

And plasma, usually a surface treatment and batch process, suffers from nonuniform gas flow in the chamber and under-etching problems caused by its non-isotropic material behavior. Still, plasma and laser technology can coexist. For example, flexible circuits with small laser-milled vias are plasma cleaned for plating or bonding consistency.

One particular area of close synergy between laser micromachining and plastics lies in the manufacturing of minimally invasive medical devices. For biocompatibility and other reasons, plastics tend to be polyurethane, polyimide, nylon, pebax, polyethylene, or bioabsorbable materials such as PLLA. However, laser technology is suited for almost all types of plastics. A few medical examples of excimer-laser capabilities include:

Precision liquid regulators. Ink-jet-nozzle technology has fostered the acceptance of plastic orifices to tightly regulate ink flows. A trend in the printer market from nano to pico-liter control of ink flow has produced manufacturing techniques which transfer well to other markets, such as medical devices.

Embolic protection devices are increasingly important in percutaneous vascular interventions to alleviate vessel blockage. Working with drug-eluting stents for the saphenous vein graft and carotid arteries, embolic-protection devices capture emboli or plaque before it travels downstream to the brain, thereby preventing a stroke. In cases of a chronic total occlusion, laser-drilled embolic filters or balloon aspiration devices are becoming more critical for patient safety.

Bioabsorbable stents may be the next generation. Current designs are a polymer-coated metal stent. Unlike stainless steel or Nitinol designs, bioabsorbable stents are fabricated from a plastic material that dissolves into the bloodstream over time. Today's drug eluting stents remain in the artery. Bioabsorbable stents will begin emerging from clinical trials by about 2009. The plastics in such stents will be shaped by excimer lasers.

Catheter-based thrombectomy devices offer an alternative to traditional drug therapy or surgical techniques to dissolve thrombus or blood clots in the coronary artery as well as the peripheral arteries and veins. Laser micromachining can prototype, develop, and manufacture skived slots and holes of percutaneous transluminal coronary angioplasty balloon catheters, fixed and over-the-wire balloon catheters, perfusion balloon catheters, and laser-angioplasty catheters.

Electrophysiology devices such as ablation and mapping catheters are used to treat cardiac arrhythmia, an abnormal beating of the heart. Excimer lasers are ideal for selectively stripping polymers from metal-mesh braids because depth can be precisely controlled. The ablation threshold to etch plastics is an order of magnitude lower than the threshold of metals, letting the laser machine plastics without damaging underlying metal.

A bifurcation lesion is a difficult intervention for cardiologists because the main and side-branch arteries have different diameters. Excimer lasers can be used in a “Laser Lathe” configuration to perform 3D machining by reshaping the OD of tubes or balloons. For complex devices, excimer lasers are used with nine-axis machining workstations with auto focus to create non-planar geometries.

Although laser micromachining is a natural fit for micro holes (•0.006-in. diameter) where traditional mechanical drilling cannot compete, it's also useful drilling or skiving larger holes and slots (0.040 to 0.100 in.). In these cases, lasers offer tighter dimensional control (as small as 0.0002 in.) and equally important, a more consistent and reproducible product where manufacturing techniques such as Statistical Process Control play decision-making roles for manufacturing and quality-control engineers.

Drug delivery infusion products are a natural beneficiary of such direct, single-step technology that drills holes with diameter tolerances of 0.0001 in. Applications include handheld nebulizers, variable-release medications, pain management, and intravenous regulators. Excimer laser beams can be split into several beamlets using holographic or other beam-splitting techniques.

Respiratory equipment benefits from laser micromachining, which makes a final exit hole or slot with higher precision and tolerances than possible with traditional drilling. Respiratory applications can use laser micromachining on plastics, ceramics, and ultra-thin metal foils. Examples include flow meters and gas regulators, aerosol and oxygen face masks, and disposable emergency oxygen resuscitators.

Excimer lasers in a nutshell

Excimer lasers are gas-powered designs, producing high average power in the ultra-violet spectrum of 193nm, 248nm, or 308 nm, as opposed to longer wavelengths that come from CO2 or Nd:YAG lasers. The short wavelengths allows the shaping of plastics and ceramics by photochemical ablation, a process that breaks molecular bonds and vaporizes material, thereby producing less debris and better edge quality than longer wavelength lasers. These UV lasers are best for micromachining plastics but also work well on ceramic, metal, and glass.

The laser is also useful for area processing. In a technique similar to that used to make microprocessors, a mask shields an area to remain uncut while the excimer laser etches the unmasked area, which can be up to 50 mm².