Inspection of micro-solderballs on a semiconductor bumped wafer using optical shadowgraph

Abstract

We describe a simple way to effectively measure the height of a micro-solderball of a micro-ball grid array (micro-BGA) on a bumped wafer. The proposed method derived using a white-light illumination source can perform a speedy whole field inspection of the microsolderballs. The optical system consists of a white-light telecentric configuration and a long-working-distance microscope with a telecentric objective. The optical axes of the illuminating light and microscope are symmetrically arranged with respect to the normal of the test surface and hence the technique is applicable to optical measurement on a mirrorlike test surface, such as a silicon wafer. The height of a solderball is computed from a simple formula based on the geometry of the specimen and the system configuration. Experimental results demonstrate that the height of a micro-solderball can be readily measured with accuracy in the order of micrometers.

Projection optics design for tilted projection of fringe patterns

“…There have been a few noncontact optical shape measurement methods proposed in the literature: laser triangulation, [1][2][3] confocal microscopy, 4,5 sinusoidal pattern projection, 6 and moiré interferometry. 7,8 However, these methods suffer from either low speed or high sensitivity to noise. In an earlier work we proposed a new mechanism for reconstructing wa-fer bump surfaces in 3-D. 9,10 As shown in Fig.…”