Project Number: C97-01

Accelerated Testing of PEMs for Long Term Storage Applications

Point of Contact: Dr. Pat McCluskey email: mcclupa@calce.umd.edu Phone: (301) 405-0047 Fax: (301) 314-9269

Objectives

Background

Approach

Work Accomplished

Objectives

To assess the potential for failure of PEMs subjected to temperature cycling and unbiased highly accelerated temperature-humidity testing.
To relate the observed failures to degradation observed in parts subjected to actual long term storage.
To validate physics-of-failure based acceleration transforms for the dominant failure mechanism

Background

The recent decision to consider PEMs for use in strategic applications, particularly wooden rounds, has generated interest in the effect of extended periods of dormancy on the reliability of PEMs. In particular, there is concern that exposure to elevated temperature/humidity will produce more corrosion in stored devices than in operating devices, because stored devices lack the power dissipation which helps keep condensed moisture off the surface of the die.

There is, therefore, a need for characterizing bond pad metallization corrosion during long term dormant storage. Such an analysis would reduce the time needed to gather data for risk assessment on the use of PEMs in weapon systems. This timely assessment of the reliability risks in a weapons system containing PEMs would provide operating and support cost reductions over the life cycle of the system.

This project is a continuation of project C96-24 in which the design of experiments was developed, the parts were selected and obtained, the test procedures developed and related studies on commercial insertion completed, including:

Susceptibility of plastic packaged discrete transistors to temperature cycling and temperature-humidity induced failures.
Analysis of PEMs for use in the F-22.
C96-31: Experimental degradation analysis of stored PEMs and assemblies

Approach

A number of devices of 4 different part types, including PLCC, PQFP, and SOIC, from various manufacturers will undergo temperature cycling and unbiased HAST testing, according to a modified DoE plan based on the one developed in C96-24. Devices will be representative of state-of-the-art silicon processing technology and the full range of functionalities. The test sequence will include:

Devices will be preconditioned prior to accelerated testing as per JEDEC A113.

Devices will then be subjected to 150 temperature cycles at temperature extremes which permit freeze-thaw cycling. The extent of delamination and cracking induced by cycling will be monitored using C-SAM.

Devices will then be subjected to unbiased HAST testing with devices being tested at the following condition:

140^oC, 85% RH

Parts will be removed from the chamber and given full functional testing at three temperatures to monitor for failure, every 200 hours. The tests will be conducted to t50 or a maximum of 1600 hours. The time to failure by HAST will be used to calibrate and validate both empirical and physics-of-failure expressions for bond pad metallization corrosion.

Work Accomplished

Collected and characterized the parts for testing

Developed fixtures for preconditioning and environmental exposure

Identified and summarized existing models for moisture ingress in "Moisture Diffusion in Epoxy Encapsulated Packages"

Preconditioning of the components