Measurement of Mechanical Behavior of High Lead Lead-Tin Solder Joints Subjected to Thermal Cycling

Abstract

Failures in electronic packages under thermal fatigue usually result from cracking in solder joints due to creep/fatigue crack growth. Understanding the stress/strain behavior of such solder joints is the first step in characterizing their fracture behavior. A specimen has been developed to determine the stress/strain hysteresis response of 90Pb/10Sn solder joints under cyclic thermal loadings. Simple and special techniques have been developed to fabricate solder joints with relatively high melting points, such as 90Pb/10Sn. Four high-temperature strain gages are mounted on the specimen to measure mechanical strains which provide the basis for determining the shear stress and strain in the solder. A special Wheatstone bridge has been designed to improve the specimen sensitivity, e.g., 20 με/MPa in the test. Shear stresses in the solder as low as 0.5 MPa can be resolved accurately. The specimen was subjected to thermal cycling between 40°C to 140°C, with 10°C/min ramp rate and 10 minute hold times, in a thermal chamber developed in-house. Excellent experimental results have been obtained for 90Pb/10Sn solder joints in that detailed characteristics of stress relaxation and strain creep as a function of temperature were captured. The specimen developed is not only suitable for use in studying the constitutive response of soft solder alloys and other joining materials, such as adhesives, but can serve as a thermal fatigue specimen to study the fracture behavior.

Impact of the number of chips on the reliability of the solder balls for wire-bonded stacked-chip ball grid array packages

“…The von Mises yield criterion and kinematic hardening rule were applied in the analysis. The steady creep behavior of the eutectic solder in the simulation was governed by NortonÕs equation [32,33]:…”

Parametric reliability analysis of no-underfill flip chip package

“…The fatigue life of a eutectic solder joint can be predicted using an empirical Coffin-Manson relationship [7], [8], [12]- [14] (1)…”

Converting to lead-free solders: An automotive industry perspective

“…In this approach, not only the global mismatch loads but the local mismatch between the solder itself and the solder pads, together with any associated bending in the layers, are taken into account in simulating the deformation occurring within the solder joints during a thermal cycle. Using a constitutive equation of the form suggested by Equation 1, E tot = Ee + Ep + Ee (4) where the terms represent deformation rates corresponding to the terms defined in Equation 1. The creep rate is defined by Ec = A (sinhBcr)n exp(-Q/RT) (5) where A, B, and n are material constants;…”

“…An illustration of the complexities confronting a fracture mechanics analysis is highlighted by the results of Pao et aI., who have compared the fatigue behavior of eutectic and high-lead solder joints. 4 Examples of the stress/ strain hysteresis behavior of joints of both solders under the same thermal cycle conditions (Figure 9) illustrate the marked differences in behavior. Pao et a1.…”