Abstract
Precision flow devices are based upon volumetric control of a liquid, gas or solid. As the market demands of medical device products, instrumentation, test or consumer products become more stringent, the necessity for tighter and substantially smaller volumetric control has led to the emergence of new devices to regulate flow. Laser Micromachining Technology is a method to manufacture these devices.
Introduction
Cost reduction has caused OEM manufacturers to rethink their material selection. Traditionally many precision flow devices were constructed out of thin stainless steel or nickel/gold plating, initially prototyped using electro-discharged machining (known as EDM) and then mass-produced using electroforming techniques. However design engineers are looking to change to plastics and as a result, manufacturing engineers search for new manufacturing technologies to fabricate these plastic flow devices. Laser micromachining is regarded as a unique technology which has both the quick turn prototyping capability of EDM but the mass-production capability of electroforming.
To present a balanced view, there are proven high volume manufacturing processes for precision plastic flow devices. For example, plasma has the advantage of being a batch process but suffers the problems of gas flow uniformity in the chamber, masking and under-etching problems caused by its non-isotropic behavior. Still, plasma and laser technology can co-exist, as exemplified by the microvia printed circuit board revolution involving laser-drilled vias and post plasma cleaning for plating consistency.
Alternatively, plastic injection molding has been the flag bearer of mass production of plastic devices. However, as these device become smaller, micro plastic injection technology and hot embossing techniques, pioneered in Germany by the MEMS and LIGA revolution, have been introduced. However, although plastic injection molding represents the most cost-effective mass volume replication of plastic material, complex tiny 3-D parts often suffer from breakage. Therefore product designers continue to look for 2-D plastic device solutions which make laser micromachining an ideal choice for prototyping and mass production. Still, mold making and laser technology can co-exist, as exemplified by Laser LIGA, where excimer lasers, such as the Maestro 1000 Series, can use lithography techniques on PMMA as a master mold for subsequent electroforming and plastic injection molding.
However , like all technologies, traditional laser micromachining has inherent boundary conditions. It is normally used for fabricating planar components and not complex three-dimensional devices unless mold-making techniques involving stereo-lithography are implemented.
And lastly, although laser micromachining technology is been used to replace traditional metal machining as a cost reduction measure, there is still a synergy between laser technology and metals. There are two areas of interest. Firstly laser micromachining of thin metals are used for x-ray apertures and pinholes. Lasers have the unique property of being able to micro drill 5micron holes with +/-1micron tolerances. Secondly lasers have the potential to micro drill very high aspect ratios (material thickness more than 100x the exit hole diameter). Currently Resonetics (Nashua NH) has embarked on a two (2) year study to determine a practical method for high aspect laser drilling of metals. These studies have also sparked the considerable interest of the automobile industry.
Ink Jet Nozzle Plates
Resonetics (Nashua, NH) has the largest concentration of excimer laser micromachining systems (25 systems) in the US, with the possible exception of vertically integrated ceramic capacitor manufacturers. It is widely known that the majority of the world's plastic ink jet nozzles for ink jet printers are manufactured using excimer laser technology.
Traditionally, ink jet nozzles must be manufactured with nozzle holes approaching 15microns in exit diameter with diameter tolerances approaching 0.5 microns. In order to fabricate these polyimide or Upilex-based nozzles, long-line, narrow homogenizer optics,(from 14mm2 to 50mm2 areas) such as incorporated in the Maestro Series 2000, are used. Conversely, much more forgiving dimensional and positioning tolerances are possible if the plastic nozzle plates are used as gaskets or filters for the ink reservoir, rather than the final orifice plate.
Interestingly enough, the severe pressures of cost-reducing metal nozzles has resulted in the industrial ink jet printer manufacturers to borrow the laser micromachining technology. Resonetics has developed proprietary, "Variable Taper Angle" technology, known as "Pyramid" to produce plastic nozzle plates with the wide angle taper angle of electroformed metal nozzles. This type of proprietary variable taper angle technology has opened the door to the introduction of the Maestro Series 2500.
Medical Devices: Precision Flow
Precision Liquid Regulators
The commercial surge of ink jet nozzle technology has resulted in the common acceptance of plastic orifices as the device to tightly regulate the flow of liquid. The market trend from nano to pico liter flow and regulation of ink has fostered manufacturing technology which can be transferred to other markets such as Medical Devices.
Intervention Devices
The search for an alternative to CABG (coronary artery bypass graft) has led to a proliferation of minimal invasive techniques to remove plaque build-up in arteries and keep them clear from complications arising from restenosis and other issues.
Laser micromachining technology is sued in the prototyping, development and manufacturing of skived slots and holes of percutaneous transluminal coronary angioplasty balloon catheters, fixed and over-the-wire balloon catheters, perfusion balloon catheters, coronary stents and laser angioplasty catheter.
Although laser micromachining is a natural fit for micro holes (0.006" dia or smaller) (where traditional mechanical drilling cannot compete), a much wider accepted market is the drilling or skiving of larger holes and slots (0.040" to 0.100"). In these cases, lasers offer much tighter dimensional control (as small as +/- 0.0002") and equally important, offers a more consistent, reproducible product where manufacturing techniques such as Statistical Process Control play critical decision-making roles for the manufacturing and quality control engineers.
Drug-Delivery and Infusion Products
Since laser micromachining can drill holes with diameter tolerances of +/-0.0001", the fluid and drug-delivery market is a natural beneficiary of such direct, single- step technology. Handheld nebulizers, variable-release medications and intravenous (I.V) regulators are examples of where this technology can be used
In-Vitro Diagnostic Products
This market focuses on systems which allows sample testing of patient's blood and other body fluids. For example, laser can be used to etch glass to provide a grid pattern for cell counting. In this case, each etched line is only 0.0002" wide with 0.004" pitch between grids.
Respiratory Equipment
In the Hospital Respiratory Therapy market, laser micromachining technology is often used as a subset for the more traditional mechanical drilling and milling techniques.
It is quite common for a plastic injection molded device is pre-formed and laser micromachining enters later in the manufacturing process as a secondary drill process to make the final exit hole or slot with higher precision and tolerances.
There is a wide plenary range of respiratory applications, which can utilize laser micromachining technology for plastics, ceramics and ultra-thin metal foils. Some examples include flow meters and gas regulators, aerosol and oxygen face masks, disposable emergency oxygen resuscitators, disposable nebulizer products, apnea monitors and spirometer products.
For such cost-conscious products, laser micromachining systems can borrow from the mechanical drilling and routing machines and "gang" multiple laser beamlets together to allow parallel micromachining. In addition, part handlers such as conveyor belts, tumblers and pick and place machines can be implemented to minimize labor intervention
Urology
In the Urology field, urethal and Foley catheters are used as drainage devices for the bladder. Although these skived plastic tubes can be quite large in size (greater than 1mm), laser micromachining can offer more precise dimensional control as well as offer higher manufacturing consistency.
