Investigator: Ewa Drescher-Krasicka

Technical Description:

The accumulation of stress in electronic chips can be caused by condensation of moisture in plastics and thermal fatigue during usage or by unavoidable mismatch of the coefficients of thermal expansion between silicon (die) metals (wires) and polymer filler. The growing and accumulating stress creates cracks and delaminations in electronic packages. Failure of one chip in an electronic device frequently causes failure of the device. While modern technology has many techniques for detecting mechanical defects in electronic components, the present urgent requirement of the electronic industry is to detect the area of material which can fail due to concentration of residual stresses. The scanning acoustic microscopy was successfully implemented for detection of popcorn cracks, and delamination in electronic chips. Routine tests are available for control on line for hidden mechanical defects. There is a need for a fast and reliable technique for detecting undesirable accumulations of residual stresses in electronic and microelectronic components.

Technical Objectives:

• Develop test methods needed to detect residual stresses in electronic components.

• Develop test methodology to achieve a known state and level of residual stresses in multilayered chips.

• Apply Scanning Acoustic Imaging of Stress (SAIS) for stress detection in electronic chips without mechanical defects.

• Apply SAIS for detection of residual stresses in electronic components containing cracks.

Anticipated Outcome:

• Detection of the areas containing high residual stresses in electronic chips.

• Recommendation guidelines for the software change in the "Sonix" scanning acoustic microscope in order to separate the two different acoustic modes, shear and longitudinal. The acoustic images obtained by use of a single mode for scanning can be compared with the existing theoretical calculation of the distribution of stress.

• Recommendation guidelines for calibration of the stress value obtained from acoustic images with the residual stress calculations by finite elements modeling (FEM) analysis and analytical solutions.

Accomplishments for FY 1995:

• SAIS technique was successfully applied for detection of residual stresses in electronic components containing "popcorn" and under surface cracks. Surface acoustic waves of high frequency create the acoustic microscope images of the distribution of residual stresses beneath the surface.

• Longitudinal and shear waves were used to detect the cracked areas and the stressed area around the die.

• Semiconductor devices (power switches), subjected to different numbers of fatigue cycles, were prepared for imaging of the increasing residual stresses up to mechanical failure.

Impacts and Technical Highlights:

• NIST prepares in cooperation with Sonix Inc. software and procedure guidelines for routine control of residual stress in electronic components. (CRADA).

• U. S. Patent 5406849 issued 04/18/95. Ewa Drescher-Krasicka and John A. Simmons Method and Apparatus for Detecting Guided Leaky Waves in Acoustic Microscopy.

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Last modified: Mon Jan 06 09:46:15 1997 Metallurgy Webmeister