Electronic Medical Device Reliability

Objective

The growing sophistication of electronic medical devices results in 

two broad benefits for both individuals and society: improved survivability in the face of disease or injury and greatly enhanced quality of 

life. However, for both economic and public acceptance reasons, these 

benefits require that the medical devices maintain high reliability over 

well-defined lifetimes. To assist the medical electronics industry in 

achieving the needed reliability, this project is intended to provide critical test data, standard test structures and standard test procedures 

to provide understanding of failure processes, thereby improving reliability of the devices.

Impact and Customers

This project will reduce the need for surgeries to replace failed implants, thereby improving safety and quality of life for implant 

recipients and reducing medical expense to society. It will provide assessment tools for the external electronic devices that support the implants, 

thereby decreasing time to market and regulatory barriers.

Capacitor and board fabrication companies have indicated that they would 

use nondestructive evaluation inspection tools, if available.

Knowledge of failure processes and development of reliability protocols 

for parylene C will provide companies and the Food and Drug Administration (FDA) with tools for assessing proposed coated implanted electronic 

devices.

Three industry-driven projects—medical electronic components, implanted electronic leads, and portable electronic medical devices—will result in 

industry-accepted reliability criteria.

Approach

Capacitor nondestructive evaluation and parylene C activities involve distinct approaches, although certain tools are common to both: optical and 

electron microscopies, furnace thermal treatments, post-measurement 

sectioning and failure analysis.

Capacitor nondestructive evaluation work focuses on ultrasonic resonance 

measurements because structural damage changes the resonance spectra 

of the capacitors. Isolated capacitors are measured in a two-point, continuous wave, ultrasonic transducer-driven instrument from 1 MHz – 3.5 MHz. 

Mounted capacitors are tested over the same frequency range but are 

driven by the ferroelectric properties of the capacitors themselves; i.e., a 

DC voltage is applied to the capacitors to align domains and an AC voltage 

is simultaneously applied to activate the resonance vibrations. Nonlinear 

properties are investigated by applying pulsed voltages to the capacitors 

and monitoring the resultant signal decay and Fourier transform.

Parylene properties are measured by a frost-point water permeation 

system, a nanoindentor for measuring elastic, viscoelastic, and hardness 

properties, and a profilometer to measure substrate and coating surface 

geometries. Colleagues at the FDA are providing X-ray spectroscopy measurements.

International 

Electronics 

Manufacturing 

Initiative

•

Food and Drug 

Adminisration

•

Industry partners

BIOMEDICAL AND HEALTH
BIOMEDICAL AND HEALTH

We have shown that, while large-scale accelerated testing will detect defective batches 

of capacitors, e.g., caused by contaminated 

dielectric, it will not eliminate the short 

lifetime capacitors that result in premature 

failure and necessitate early, expensive and 

potentially life-threatening surgery. Those 

capacitors that result in early device failure 

were found to be independent of all accelerated failure test parameters and of manufacturer. It was concluded that early device 

failure was caused by isolated capacitors 

damaged either during fabrication or during mounting. Nondestructive evaluation 

protocols that can provide 100% inspection for both free-standing and mounted 

capacitors are required to eliminate these 

components. Such nondestructive evaluation tools are being developed for both isolated and mounted capacitors, based upon 

changes in ultrasonic resonance spectra. 

We have demonstrated that as-received 

free-standing and mounted capacitors exhibit the same resonance frequencies (±25 

KHz), but capacitors that show unusual 

leakage current behavior after accelerated testing have quite different resonance 

spectra. This suggests that ultrasonic resonance spectra may provide a viable tool for 

detecting damage in capacitors at levels 

well below those required to modify actual 

capacitance values. 

Mechanical properties of parylene C, currently used to coat implants such as stents 

and proposed for coating implantable electronic devices, have been shown to depend 

upon the chemistry of substrates even for 

thick (e.g., 16 μm) coatings. Parylene coatings laid down upon Al, Cu, and stainless 

steel substrates had 10% variation in indentation elastic constant and hardness 

values, although both elastic constant and 

hardness were highly reproducible for a 

given substrate. The error bars in Figure 3 

represent the 95% confidence range. This 

variation does not correlate with the elastic 

properties of the substrates, indicating that 

there is a chemical effect of the substrates 

on the mechanical properties of the coatings even for 16 μm thicknesses.

Steady state water permeating through 

multiple 16 μm thick free-standing parylene 

coatings has been measured to be 3 ppm 

to 5 ppm at our measurement gas flow rate. 

Heating one of the coatings to 120 oC increased the steady state water concentration to 25 ppm, suggesting that permeation is strongly influenced by the crystal to 

amorphous ratio in the coatings.

An industry-driven consortia addressing 

the high failure rates of implanted electric 

leads has just requested that NIST assess 

the individual companies’ proprietary lead 

testing procedures and develop a “best 

practice” test procedure for the industry.

Two activities from the International Electronics Manufacturing Initiative in which 

project members participate, Component Specifications for Medical Products 

and Qualifications for Portable Medical 

Products, have just been converted to official projects by the initiative. The goal of 

the projects is development of industryadopted reliability acceptance criteria for 

medical-grade electronic components and 

portable devices.

Learn More

Nikki Goldstein, Ward Johnson, 

Sudook Kim, Chris Poling, Grady White

Grady White

Physical Scientist

303-497-4638

grady.white@nist.gov

http://www.nist.gov/mml/acmd/biological_environments/medical-devicereliability2.cfm

Publications

A Verwolf, GS White, CM Poling, Effects of substrate composition and roughness on nanomechanical 

properties and conformality of parylene C coatings, Submitted to J. Applied Polymer Science (2011).

A Verwolf, Transient liquid water transport through low-permeability polymer coatings, Submitted to 

J. Membrane Science (2011).

SA Kim, WL Johnson, GS White, and R Roberts, Ultrasonic detection of defects in multilayered ceramic capacitors for active implantable medical devices, Medical Device Materials: Proceedings of 

the Materials and Processes for Medical Devices Conference (2011). 

A Verwolf, Design and optimization of a permeation testing system for polymer films, Medical Device 

Materials: Proceedings of the Materials and Processes for Medical Devices Conference (2011).

Figure 1. Leakage current (VR/106 A) showing capacitor 

failure about 650 h into test.

Figure 2. Resonant ultrasound spectra of 4 as-received 

(bottom) and damaged (top) showing shifts in spectra 

resulting from accelerated testing.

Figure 3. Elastic constant (reduced modulus) at surface 

of 16 μm thick parylene C coating for three substrates, 

Al, Cu and stainless steel, based upon 300 measurements for each substrate.

4d_bio-11/12

Accomplishments