AFFECTS OF CYCLIC MECHANICAL LOADING ON

THERMAL FATIGUE OF SOLDER

January 2004

COLLEGE OF ENGINEERING
AEROSPACE AND MECHANICAL ENGINEERING, UNIVERSITY OF NOTRE DAME

AUTHORSKEVIN B. PETERS AND BENITO TORRES-MONTOYA
PRINCIPAL INVESTIGATOR
DR. JAMES J. MASON
RESEARCH ASSISTANTS
BENITO TORRES-MONTOYA AND DARRELL DUFFEK

INTRODUCTION

Automotive manufactures are increasingly using electronic controls in the production of today's vehicles. Many of these control modules are safely and efficiently replacing entire mechanical and hydraulic systems that once used mechanical controls while providing better reliability and performance. Hybrid Microcircuits (HMC's) are modules that use high-density surface mounted electronics on a multi-layer circuit board. HMC's are being developed for engine management systems, navigation, airbag deployment, automatic transmissions and electronically controlled steering and electric brakes systems and typically have a 3 - 5 year design cycle including prototyping and testing. Many of these hybrid microcircuits are exposed to harsh environmental conditions such as temperature and vibration causing premature failure.

OBJECTIVE

 Finite element analysis and simulation is rapidly becoming the tool of choice for reducing design costs, however, in order to have a strong degree of confidence in an FEA simulation, it must closely match reality or actual test data. The purpose of this research is to validate FEA models that predict solder fatigue experimentally through cyclic mechanical and thermal tests on HMC's.

APPROACH

 A combined test approach was implemented; the UUT (Unit Under Test) placed within an environment testing chamber where thermal cycling between -50 and 150 degrees C for 1 hour periods with 15 minute dwells at the extreme temperatures. The UUT is also subjected to 4 point bending where induced strain is varied between + 750u strain and -750u strain. Measurement and control algorithms were implemented using LabVIEW software.

RESULTS

 Solder joint analysis performed using simple linear elastic FEA for finding stress-strain distribution agree well with the observed failure modes.
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