Three-dimensional x-ray laminography as a tool for detection and characterization of BGA package defects

Abstract

Non-destructive examination of the layers of a built-up substrate was achieved using three-dimensional (3-D) x-ray microlaminography, with successful separation of layers as thin as 8 /spl mu/m. The same technology was used to create reconstructed images of both surface and internal details of inner solder balls in a ball grid array package soldered to a printed circuit board. Microlaminography was also used to identify bond-wire shorts in the plane of the solder resist of a ball grid array assembly, and these were subsequently verified by destructive physical analysis. This plane is 20 /spl mu/m thick and immediately adjoining a plane of copper traces; the success demonstrates the capability of microlaminography to resolve and separate very fine detail internally within IC structures. The limits of capability of this machine were also determined; it was found that a crack of approximately 5 /spl mu/m wide in a copper trace of a BGA was not detected by the machine. As an introduction, the technology and methodology of 3-D x-ray microlaminography are explained. The results from a microlaminography system adapted for failure analysis in integrated circuit packaging are presented. It is shown that such results could not be extracted by two-dimensional (2-D) x-ray or other nondestructive methods.