The correlation between stress relaxation and steady-state creep of eutectic Sn-Pb

Abstract

This paper surveys and compares creep and stress relaxation data on finegrained eutectic Sn-Pb. It examines the consistency of the available data on this extensively studied solder material and studies whether stress relaxation offers a reasonable alternative to the more laborious conventional creep tests. The data survey reveals systematic differences between the creep behavior of material that is grain-refined by cold work and recrystallization ("recrystallized") and that refined by rapid solidification ("quenched"). The recrystallized material has the conventional three regimes of creep behavior: a high-stress region with a stress exponent, n ϳ 4-7 and an activation energy Q ϳ 80 kJ/ mole (a bit below that for self-diffusion of Pb and Sn), an intermediate region with n ϳ 2 and Q ϳ 45 kJ/mole (near that for grain boundary diffusion), and a low-stress region with n ϳ 3 and Q ϳ 80 (suggesting a reversion to a bulk mechanism). The quenched material shows only two regions: a high-stress creep with a stress exponent, n ϳ 3-7, and a low-stress region with n ϳ 3. The mechanisms in both regimes have activation energies intermediate between bulk and interface values (50-70 kJ/mole). With minor exceptions, the stress relaxation data and the creep data are in reasonable agreement. Most of the exceptions seem to be related to the difficulty of capturing the full details of grain boundary creep in stress relaxation tests.

Effect of Sb Content on the Microstructure and Mechanical Properties of Eutectic SnPb Solder

“…For eutectic SnPb solder, n < 3 is often a sign of superplasticity, observed at high temperatures and under lowstress conditions. Conversely, n > 3 suggests a dislocation creep mechanism, typical of higher-stress conditions [30][31][32]. During creep, the processes of work hardening and recovery occur simultan When these rates reach a balance, a steady-state creep stage is established [23].…”

“…For eutectic SnPb solde is often a sign of superplasticity, observed at high temperatures and under low-stre ditions. Conversely, n > 3 suggests a dislocation creep mechanism, typical of higher conditions [30][31][32].…”

Fracture Mechanics of Solder Bumps During Ball Shear Testing: Effect of Bump Size

“…Our calculation also includes plasticity of eutectic Sn-Pb having a yield strength of $35 MPa with an assumption of negligible work hardening during the shear test. [16][17][18][19][20] Figure 2 presents the shear force as a function of displacement measured during ball shear tests of bumps of three different diameters. The results show that the shear force-displacement relationship is not identical, but rather differs significantly with bump size.…”

“…This assumption does not create significant error in our analysis because most solder alloys have a very low workhardening rate in the range of strain rates relevant to bump shear testing. [16][17][18][19][20] The contact area, A(U), can be estimated by extending the result from the Abbott-Firestone contact curve model. [24][25][26] Fig.…”

Stress relaxation behavior of lead-free solder joint

“…Similarly, Kanda [12] further considered the time-hardening relationship and Norton's law to describe the primary and second stress relaxation segment. These models were usually used to determine the parameter in creep equation, for the stress relaxation test save more time than creep test [13]. Moreover, there are some empirical formulas.…”