Work out solder joint fatigue instantly with clear inputs, formula shown and shareable results.
Shear strain in a solder joint is CTE mismatch times temperature swing times distance from the package centre, divided by joint height. Corner joints on a large package therefore fail first, and the Engelmaier relation converts that strain into a cycle count.
Solder fatigue
shear strain = dCTE x dT x DNP / joint height; Nf from the Coffin-Manson/Engelmaier relation
Distance to the neutral point is largest there, so displacement — and therefore strain — is greatest. Corner glue or underfill directly targets this.
Strain is displacement divided by height, so a taller joint spreads the same displacement over more material. This is why column-grid arrays outlast ball arrays.