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Device Determining Temperature and Stress Profile of Solder Balls During Thermal Cycling

IP.com Disclosure Number: IPCOM000035120D
Original Publication Date: 1989-Jun-01
Included in the Prior Art Database: 2005-Jan-28
Document File: 3 page(s) / 37K

Publishing Venue

IBM

Related People

DiGiacomo, G: AUTHOR [+2]

Abstract

Solder ball (C-4) fatigue models require the knowledge of strain rate and stress as a function of time to reflect the effect of stress relaxation through a time limit beyond which the stress is no longer effective to produce fatigue damage. This article provides the means to achieve the proper model with a time limit parameter rather than involving strain rate and stress relaxation which are unresolvable.

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Device Determining Temperature and Stress Profile of Solder Balls During Thermal Cycling

Solder ball (C-4) fatigue models require the knowledge of strain rate and stress as a function of time to reflect the effect of stress relaxation through a time limit beyond which the stress is no longer effective to produce fatigue damage. This article provides the means to achieve the proper model with a time limit parameter rather than involving strain rate and stress relaxation which are unresolvable.

To interpret solder ball fatigue, one has to determine the effect of strain rate and stress relaxation simultaneously during thermal cycling, when shear strains are produced in the solder ball because of the thermal mismatch between the substrate and the chip. The strain increases as the solder ball distance from the neutral point increases. The solder ball fatigue damage is a function of the shear strain, maximum temperature of the cycle, frequency, dwell time at the maximum temperature, and strain rate. The latter two variables are not considered (or properly accounted for) in the model due to experimental difficulties in determining and separating the effects. In addition, there is a maximum dwell time (dwell limit) beyond which the stress is

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relaxed below a threshold producing no further fatigue damage. Such time varies with the strain rate and dwell within the time limit before the stress reaches the threshold and becomes ineffective. It is a key parameter which dictates the lowest significant cycling frequency used for field fail projections.

Figs. 1 and 2 show a test apparatus 10 including a pressure transducer 12 and temperature sensors (not shown) designed to obtain simultaneously the temperature and stress profiles of a sample 14 such that the strain rate and strain data are dynamically recorded as a functio...