Effects of solder balls and arrays on the failure behavior in Package-on-Package structure

•Effect of solder balls and arrays on failure behavior of PoP structure is obvious.•The failure process under tensile loading is the deformation-cracking-unsticking.•The failure process under bending loading is deformation-unstability.•The relation of stiffness and ball number is nonlinear. Its extreme value is 2 × 9.•The critical deformation of tensile type is ten times than that of bending type.

In this article, the failure behaviors of different solder balls and arrays used in a commercial produce were investigated experimentally and computationally. The results indicated that the effect of different solder balls and arrays on the failure behavior of Package-on-Package (PoP) structure cannot be ignored. For example, the failure mechanism of a structure with 2 × 15 solder balls could be characterized as a deformation-cracking-delamination model under axially tensile loading, while as a deformation-instability model under three-point bending loading. The allowable deformation of the former is ten times larger than that of the latter. In addition, the failure behavior for a structure with different solder balls and arrays varies. It is strongly dependent on the stiffness of PoP structure, which is dominated by the number and array of the solder balls. The relationship between the stiffness and the number appears nonlinear. More specifically, there is the maximum value for a structure.