Effects of plasticity on reliability in multilayered electronic packages

The effect of the constitutive response of the solder material on the reliability of large area solder joints within multilayered electronic packages is investigated subject to repeated thermal cycling. Solders that exhibit elastic and time-dependent plastic flow (viscoplasticity) were investigated. In accordance with traditional low-cycle fatigue models, the solder that exhibited extensive viscoplasticity exhibited fatigue cracking that can be modelled following a Coffin-Manson approach for crack initiation. Subsequent crack growth was pronounced. In contrast, the solder that exhibited an elastic response exhibited a substantially lower fatigue crack nucleation and growth rate. These results are then related to the overall design philosophy of the package.