Method and system for determining lead coplanarity

Abstract

The coplanarity of leads (,) of an integrated circuit (IC) in a surface-mount technology package (SMT) (,) can be determined by means of a plurality of views without the use of a conventional pedestal (,), without the use of an associated Z-axis actuator, and without the associated delays required to deploy such a Z-axis actuator. In the invention, three leads (,) of SMT package (,) are arbitrarily selected to define a virtual reference plane (,) in a first or virtual coordinate system, and the positions of the unselected leads are measured with reference to the virtual reference plane (,). For convenience, the virtual reference plane (,) can be defined as Z=0 and may have height coordinates in Z that are negative or positive with respect to the virtual reference plane (,). The virtual coordinates are analyzed, and three leads (,) having the lowest Z coordinates are determined to define a virtual sitting plane (,). For convenience, the virtual sitting plane (,) can be defined as Z=0 in a second or real coordinate system. A mathematical transformation that relates the first coordinate system to the second coordinate system is determined, and the coordinates for each lead (,) of SMT package (,) are subsequently transformed from the first coordinate system to the second coordinate system. In the second coordinate system, each Z coordinate directly corresponds to the lead standoff value (,) that largely determines the acceptability of the inspected SMT package (,). A variety of techniques are optionally employed to determine whether SMT package (,) is bi-stable.