Project Number: C96-21

Testing of Electronic Hardware for Elevated Temperature Use

Point of Contact: Dr. Patrick McCluskey email: mcclupa@calce.umd.edu Phone: (301) 405-5323 Fax: (301) 314-9269

Objective

Background

Approach

Work Accomplished

Objective

Evaluate the high temperature performance of selected prototype modules designed specifically for elevated temperature operation by using elevated temperature and temperature cycle testing.

Background

The development of electronics which can operate at highly elevated temperatures has been identified as a critical technology for the next century. Initiatives in this area are now being pursued by the Army, the Air Force, and many commercial avionics and automotive electronics companies and their suppliers. Limiting temperature to below 125° C has become a severe design constraint. It hinders the development of distributed control systems, smart sensors, and remote actuators, and it increases the cost of electronic systems used to monitor such environments as automotive underhood, anti-lock brakes, aircraft engine, aerospace propulsion, chemical process, and well logging. The costs are a result of the additional size, weight, expense and reliability risks related to remote placement or cooling of these electronic assemblies.

This past year, a report was generated describing generic materials-related limitations to the use of electronics at elevated temperatures up to 200° C, including relevant mechanical, electrical, and thermal properties of materials and their relationship to temperature for all levels and elements of packaging. This information was used to identify key technical challenges to the use of six modules at elevated temperatures and to suggest alternate materials and designs. This year's project will experimentally evaluate the modules for elevated temperature use.

Approach

Testing will consist of step stressing modules from 100^o C up to 200^oC in steps of 10^o C to determine the temperature at which they cease to function. Modules will then be subjected to 500 hours of aging at a temperature 10^o C below the temperature at which they ceased to function. At the end of the exposure, modules will be electrically tested for system performance and failure at the module manufacturer's facility. At each temperature, overstress and wearout failure sites and modes will be identified. Evaluation of the degradation of the assemblies will include but not be limited to a visual and optical microscopic examination for wire insulation failure, component overheating, board/substrate deformation, board/substrate delamination, and package through cracks. In addition, failed ICs will be examined by CSAM for delamination and cracking. They will also be examined by EDS for lead and connector corrosion. ICs will be cross-sectioned and examined with E- SEM for evidence of lead/solder and wire/wirebond intermetallic growth. Resistors will be examined for signs of melting or changes in resistivity. Capacitors will be examined for decreases in insulation resistance.

Work Accomplished

Two modules have been chosen for analysis. These modules have been carefully selected to contain many of the components and packaging elements which were identified as being potential high temperature limitations in the previous effort C95-18, The Use of Electronic Hardware at Elevated Temperatures. In addition, these modules represent both ceramic and organic technologies.
Design analyses have been performed which have shown that while both modules perform to temperatures well in excess of 125°C, they do have several elements which limit their use at 200°C. These are listed in "Summary of design analysis". An explanation of these limitations is provided in the report "Packaging Reliability for High Temperature Electronics: A Materials Focus".
Four units of each module have been step stressed at a series of ambient temperatures from 100°C to as high as 200°C, in 10°C intervals. Modules were held at each temperature level in the powered condition for at least 10 minutes to allow the module to stabilize at temperature. The modules were monitored for functionality at each temperature level and failure analysis was conducted to identify the failure modes and sites. The results of the step stressing closely agreed with the concerns identified through design analysis, as shown in "Summary of step stress testing."
Testing was performed to identify the effects of long term aging. For each module type, samples were held at 150°C for 500 hours in the powered state. The automotive voltage regulator was monitored electrically in-situ for failure while the ring laser gyro was returned to the manufacturer for testing after each 100 hours of exposure. Failure and degradation analysis is in progress.
A report on this effort containing the results of the testing is available to members as "Packaging of Electronics for High Temperature Environments"