Creep-Fatigue Life Evaluation for Sn-3.5Ag Solder

Abstract

This paper studies the creep-fatigue life evaluation of Sn-3.5Ag solder under push-pull loading using fast-fast, fast-slow, slow-fast, slow-slow, and strain-hold strain waves. Extensive creep-fatigue data were generated using these strain waves and the applicability of four conventional creep-fatigue damage rules, the linear damage rule, the frequency modified fatigue life, the ductility exhaustion model, and the strain range partitioning method, was examined. No conventional damage rules evaluated creep-fatigue lives accurately. Only the grain boundary sliding model, developed recently for solders, predicted creep-fatigue lives with a small scatter.

Uniaxial Ratchetting Behavior of Solder Alloys and Its Simulation by an Elasto-Plastic-Creep Constitutive Model

“…It is noteworthy that the difference in the uniaxial ratchetting strains at the 0.4%/s and 0.04%/s strain rates is smaller than the difference between 0.04%/s and 0.004%/s for both the Pb-free and Pb-containing solder alloys. This result shows that the strain rate effect on the strain hardening decreases with increasing strain rate, as studied by Nozaki et al 36 They showed that there is almost no strain rate effect on strain hardening over the 1%/s strain rate in the case of the solder alloys.…”

Creep-Fatigue Life Evaluation of Sn-3.5Ag-0.5Cu-Ni-Ge Solder at Low Temperatures

“…(1)～ (13) されている疲労試験や，静クリー プ試験，クリープ疲労試験のほとんどが 313K(40℃)程度と，室温度以上の実験結果に限られている．低温度で の疲労試験やクリープ疲労試験は，その技術的な困難さから知見が充分に得られているとは言い難い．著者は， これまでに 253K および 273K での低サイクル疲労試験 (14) を行い，Sn-37Pb では応力-ひずみ関係に及ぼす試験温 度の影響が著しいことや，Sn-3.5Ag の低温度での疲労寿命評価にはひずみエネルギーが有効であることなどを明 らかにするとともに，はんだの寿命評価法の信頼性向上のためには，低温度での実験力学的検証も重要であるこ とを述べてきた． 本研究では， Sn-3.5Ag 系に Ni， Ge を添加した Sn-3.5Ag-0.5Cu-Ni-Ge5 元はんだを対象として， 低温度での引張・ 圧縮疲労試験およびクリープ疲労試験を行いデータの蓄積を図るとともに，クリープ疲労寿命評価について検討 した．なお，Sn-3.5Ag-0.5Cu-Ni-Ge に関する実験データの数 (15) は乏しいので，まず，主要元素含有量が同程度で あり， かつ材料に関する実験的知見が豊富である Sn-3.5Ag の実験データを基にして代表的なクリープ疲労寿命評 価法の適用性を定性的に検討した．その後，本研究で得られた Sn-3.5Ag-0.5Cu-Ni-Ge の実験データを用いて，低 温度でのクリープ疲労寿命評価法の精度向上を試みた． …”

Creep-Fatigue Crack Growth in Sn-3.0Ag-0.5Cu Solder

“…The stress ranges decreased with the number of cycles which results from the cyclic softening (7) and crack growth. No mean stress exists in the pp and cc waveforms, but tensile and compressive mean stresses are found in the pc and cp waveforms, respectively.…”

“…8, following the strain partitioning method proposed by Manson (7) (31) . Table 3 summarizes the strain components partitioned at crack length of 2mm in all the waveforms.…”

“…In their work, the crack growth rates of several heat resistant steels were well correlated with either ∆J f or ∆J c , and no intermediate regime was found. Nozaki et al (7) and Mukai et al (42) reported that elastic-creep constitutive equations were sufficient to describe the inelastic deformation under creep-fatigue conditions for solders, which implies that creep deformation dominates inelastic deformation and time-independent plasticity is insignificant. …”