Medical Device Link.

Originally Published EMDM March/April 2002

PRODUCT UPDATE

LCP-based flexible circuits prevent cross-contamination, while an electronic switch construction combines several types of switches and controls on a ready-to-mount panel.

Norbert Sparrow

Flexible circuits made from liquid-crystal polymer film exhibit lower moisture-absorption and gas-transmission rates than the more common polyimide-based components. Electronic devices that undergo frequent fluid- or gas-based sterilization are a key application.

The electronics sector continues to introduce technological innovations at a relentless pace. In this feature article, we focus on two products that may contribute to the design and manufacture of safer, more efficient, and, in some cases, more cost-effective medical equipment. Several other leading electronics suppliers to the device industry and their recent product introductions are profiled in the accompanying descriptions.

Process Overcomes Traditional LCP Production Hurdles

Flexible circuits based on liquid-crystal polymer (LCP) dielectric film feature properties superior to more commonly used polyimide-based components, but they have had limited acceptance. LCP is difficult to process, which has precluded its use as an alternative material in many cases. Now, 3M Microinter-connect Systems Div. (Austin, TX, USA) has developed a fabrication process that will make LCP-based flexible circuits desirable in a number of applications, according to the firm.

"The primary benefit of LCP is its low moisture-absorption and gas-transmission rates," says marketing manager Bill Balliette. LCP has a water absorption rate of 0.1%, whereas polyimide has a 1–3% rate. Consequently, LCP flexible circuits are suited for applications in which device electronics are in close proximity to a fluid or gas, which may raise cross-contamination issues. "Bioanalytical equipment as well as electronic devices that undergo frequent sterilization with some kind of fluid or gas" are among key applications, says Balliette.

LCP offers dimensional stability with respect to changes in humidity and temperature, a property that benefits circuits to which numerous small elements are bonded. "As more and more elements are added to electronic components and they are made smaller and smaller, you end up with a potential manufacturing problem," says Balliette, who cites the example of multielement transducers used in ultrasound equipment. "When you're ready to bond that sensor element, the leads may not line up properly. The more dimensional stability you have in the circuit material, the greater your ability to make that sensor array larger to cover more ground and capture more data."

3M processes its LCP flexible circuits in a manner similar to its polyimide-based components. "We build up the metal in a vacuumization process," says Balliette. This presents a number of advantages compared with laminating a copper foil over a substrate, which is how competing products are often fabricated. "When you etch away the laminated copper foil from the surface, it leaves the surface a lot rougher and you can't really get down to a fine pitch: the copper has a tendency to peel off," he explains. "Vacuum metallization, on the other hand, lets you get to a very fine pitch and the copper traces still adhere to the substrate." The chemical etching process, which is unique to 3M, and an absence of adhesives add value to the product.

LCP flexible circuits are designed to meet the needs of sophisticated electronic assemblies used in digital hearing aids, ultrasound transponders, and similar devices.

Switch Construction Simplifies Panel Design, Assembly

An electronic switch construction introduced by Duraswitch Industries Inc.(Mesa, AZ, USA) is another example of a company applying existing in-house technology to develop a product that offers an innovative solution to design engineers. Island technology, which enables the placement of various user interfaces onto low-cost flexible circuits, has its origins in the creation of fabricated freestanding switch component subassemblies such as the PushGate push-button, thiNcoder RT rotary encoder, and MagnaMouse cursor control. Prior to the introduction of switches such as these, designers of medical device user interfaces essentially had two options, according to Tim Kuhn, vice president of business development. If the engineers were integrating low-cost flexible circuits, they were limited to the use of push-button switches, resulting in multiple switches and complex and complicated panels. Or they could opt for soldered components and printed circuit boards, a much more costly alternative.

The introduction of Island technology considerably expands the options available to design engineers, according to the company. This construction can combine push-button switches, encoder rotary switches, and cursor controls in a complete keypad that is less than 3 mm thick. All of the switch components are individually sealed in a thin adhesive-foam matrix and are fully integrated within the assembly. "The ability to incorporate multiple types of switches on flex from Duraswitch's portfolio of customizable, durable, and reliable components allows manufacturers greater flexibility and improved options for simplifying their designs," notes Kuhn.

More Products:
Duraswitch Industries Inc.
Ault Inc.
Ultralife Batteries (UK) Ltd.
Keramos Advanced Ceramics
Elan Digital Systems Ltd.
Laird Technologies Bavaria GmbH
3M Microinterconnect Systems Div.
Tastitalis S.p.A.
EDS Ireland Ltd.
Etalon
Nordic VLSI

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