Medical Electronics Symposium Conference Proceedings


Authors: Robert Allen, Benjamin Schnitz, Jeffrey Stewart
Company: MicroNova Technology, Inc.
Date Published: 5/19/2004   Conference: Medical Electronics Symposium

Abstract: The authors have developed a unique micro-sized, surface mount load cell (containing an embedded semiconductor micro-strain gage and three low-profile resistors in a Wheatstone bridge configuration) utilizing ceramic, leadless inverted device technology. The load cell, which is only .160" long x .095" wide x .055" high (4.1 mm x 2.4 mm x 1.4 mm), is ideal for implantable orthopedic and smart prosthesis applications to monitor bone fusion after surgeries, track wear and subsidence of joint replacements, facilitate design of prosthetic devices, and measure other forces exerted on or by the human body.

The unique assembly incorporates an 8-post leadless inverted device fabricated via dry-pressed ceramic and micro-machining processes. The resulting alumina (~96%) configuration is patterned via a sputtered nickel-gold metallization over a sintered moly-manganese or tungsten base metal for the interconnection posts (external solder pads) and internal component attachment of the semiconductor micro-strain gage and low profile resistors. Custom patterns and internal component isolation are accomplished via laser scribing. The dry-pressed ceramic provides a bio-compatible and very smooth rigid body that allows forces to be applied to the backside (top after mounting) of the load cell. Resulting strains and forces are transduced using an internal Wheatstone bridge configuration with surface mount 0201 resistors.

This paper discusses the materials science and finite element analysis that contribute to the design feasibility of a micro-sized, ceramic, surface mount load cell. Various medical applications are briefly discussed.

Key words: dry-pressed ceramic, 96% alumina, Micro-LIDs(TM), leadless inverted devices, load cell, semiconductor micro-strain gage, finite element analysis; Wheatstone Bridge.

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