A new analytical model that accounts for the shape of solder joints, with a special emphasis on the determination of the mechanical properties of PCBs.
Hooke Electronics in France has developed a new analytical model to evaluate the thermomechanical reliability of SAC305 lead-free solder joints. The approach is designed for electronics exposed to significant thermal cycling in sectors such as aerospace, defence, medical, and industrial applications.
It is intended to replace older simplified analytical models, which often lacked precision, while offering a faster and more accessible alternative to Finite Element Analysis (FEA).
The SAC305 alloy, made of 96.5% tin, 3% silver, and 0.5% copper, is the industry standard replacement for tin–lead solder after restrictions on lead use under RoHS and REACh regulations. Ensuring its reliability is critical, as thermal fatigue can lead to failures in printed circuit board (PCB) assemblies over time.
This new analytical model estimates solder joint life and calculates PCB thermal properties, such as density, conductivity, and specific heat, without the need for resource-intensive simulations.
It incorporates solder joint geometry and the mechanical characteristics of both the PCB and its components into a simplified elastic–plastic and viscoplastic framework to simulate deformation and creep under temperature cycling.
Development involved calibrating the model using 83 datasets from durability tests across different packages, PCB stack-ups, and thermal cycling conditions, followed by validation with 23 additional datasets. It has been tested on common surface-mount components, including ball grid arrays (BGAs), chip components, and Ceramic Leadless Chip Carriers (CLCCs).
