Creep-caused fracture of PbSn solder joint

This paper analyzes two failure cases of creep-caused fracture of PbSn solder joint, including the joint between the wire and solder cup in the connector and the joint between the integrated circuit (IC) pins and the printed circuit board (PCB). The environment conditions, for the creep of PbSn solder joint is demonstrated, including the temperature and stress level. The stress origin and fracture morphology are summarized based on the failure analysis. Besides, the developing process of creep-caused fracture is explained. The paper comprehensively clarifies the creep mechanism of PbSn solder and consequently provides significant guidance for the reliable electronic assembly to avoid the creep-caused damage.

Pb-Free Solder: New Materials Considerations for Microelectronics Processing

A single printed circuit board includes thousands, sometimes even hundreds of thousands, of solder joints. The failure of even a single solder joint is usually enough to compromise the functionality of an electronic device or system. PbSn solder had been the standard ma te rial for these joints until various regulations around the world began to limit Pb use. SnAgCu and related alloys are quickly replacing PbSn, but much still needs to be understood and controlled. None of the paradigms for understanding the mechanical response of PbSn alloys is applicable to lead-free alloys. Much of the surprising behavior of SnAgCu solder arises from the complex and fascinating nature of its solidification behavior. In this ar ticle, the impact of solidification on the microstruc ture and therefore the mechanical properties of these solder joints will be addressed in the context of microelectronics proc essing. The need for better simulations of SnAgCu solder behavior will also be examined. Notably, modelers will have to account for a variety of new parameter dependencies not previously considered.

Microstructural Damage and Evolution of a PbSn Solder Alloy Under Isothermal Cyclic Loading

In our recent experiments, torsional specimens of PbSn Solder Alloy were cyclically loaded under different loading levels at both room temperature and high temperature (1008C). In these experiments, the Pb-rich phase size and micro-crack damage were also observed using scanning electron microscopy in-between loading cycles. At the moderate strain rate (10−4), the growth of Pb-rich phase does not differ much for both temperatures. At room temperature, the damage in the form of micro-cracks along the Pb- and Sn-rich phases are formed during early cycling, and the damage accumulates as the cycling proceeds. At high temperature, the damage does not accumulates as fast as for the similar strain level in room temperature, due to the lowering of stress level in high temperature and dynamic restructuring of Pb-rich phase.

Mechanical Behaviour of Two Sorts of MCM Structures

ABSTRACTWe analysed the mechanical response of samples, representing Flip-Chip bonded type structures. Two sort of distributions of the PbSn solder bumps, interconecting a chip to a substrate were investigated. The mechanical response was established from macroscopic shear and tensile tests. The microstructural evolution to complete mechanical failure, was observed during similar tests, but performed in a Scanning Electron Microscope. These in-situ tests revealed a preferential crack nucleation site in the samples, specific to one of the interfaces. A complementary numerical analysis was developed, for trying to explain the preferential crack opening site.

An Experimental and Finite Element Study of Thermal Fatigue Fracture of PbSn Solder Joints

A solder joint specimen has been designed to determine the stress/strain hysteresis response and fracture behavior of 90 percent wtPb/10 percent wtSn solder alloy. The specimen consists of an Al2O3 beam and an Al 2024-T4 beam bonded together at the ends with solder. The specimen is subjected to thermal cycling to failure between 40°C to 140°C with a 10°C/min ramp rate and 10-minute hold times. Stress/strain hysteresis loops were experimentally determined as a function of thermal cycles. A method based on the stress relaxation data at hold times has been developed to determine the steady state creep parameters of the solder. A constitutive equation for the solder alloy based on elastic and creep deformation has been formulated and implemented in a finite element code, ABAQUS. Good agreement was obtained between the finite element model and the experimental results. In the thermal fatigue test, crack length versus number of thermal cycles was measured for two different shear strain ranges, and the fracture surface was examined with SEM. The SEM results show a combined transgranular and intergranular fracture. In addition, a significant amount of secondary cracks and voids were generated during thermal fatigue which led to material weakening. A thermal fatigue model based on the C* integral, the measured stress history, and creep properties was employed to model the fracture behavior.