In Situ Resistance Monitoring and Fatigue Life Prediction for Flip-Chip Solder Interconnects Using RAPID Mechanical Cycling Method

Abstract

A mechanical loading technique for reliability assessment of flip-chip BGA interconnects was developed as a rapid alternative to traditional temperature cycling methods. Sinusoidal shear loading was used to accelerate fatigue cracking within the solder interconnects of a chip-scale test while shear force and circuit resistance were monitored in situ with resistance increases of 30% considered the point of failure in tested devices. Test parameters were selected and optimized by leveraging finite element analysis (FEA) simulations of mechanical cycling and temperature cycling to select shear force, frequency, and test duration such that the inelastic strain energy density (plastic work density per cycle) achieved in the mechanical cycling test agreed closely with that predicted by FEA for more traditional temperature cycling tests. These FEA simulations were conducted using Anand's constitutive material model to make accurate predictions of the inelastic strain energy density, accumulation per cycle, and therefore fatigue lifetimes of chip-scale devices containing Sn63/Pb37 solder interconnects using energy based fatigue models. With optimized test parameters, this mechanical loading method was able to induce the same inelastic strain energy density into the flip-chip interconnects as traditional temperature cycling (as predicted by FEA simulations). By monitoring resistance in situ, determinations were made as to the affects this amount of damage had on the performance and reliability of the studied device. Failure localization and crack visualization was achieved using MicroCT imaging to study interconnect cross-sections. Thus, the total amount of damage predicted for a thermal cycling test by FEA simulation can be generated in flip-chip interconnects at a much higher rate by utilizing the mechanical loading technique, reducing overall test time duration and associated testing costs. Assessments can then be made as to the impact the fatigue damage has had on the electrical performance of the device. Additionally, inexpensive mechanically analogous Si test vehicles were used to make predictions about the reliability of more expensive SiC devices using this mechanical cycling technique.