PROJECT TITLE :

Height Measurement of Micro-Solder Balls on Metal Pad by White Light Projection

ABSTRACT:

Micro-solder balls are commonly used in wafer-level ball grid array (BGA) packages as an interconnection medium. To live the height of a micro-solder ball on a metal pad, we tend to propose a white light projection methodology to avoid interference from pads in the shadow of the ball. The optical projection of a solder ball underneath the illumination of a parallel white light-weight beam is studied, and therefore the relationships between the ball height, ball radius, and shadow length are deduced. An experimental platform with a straightforward optical system and white light emitting diodes lighting supply is constructed to get ball and shadow pictures, and a program developed to process these pictures and calculate the ball height. The heights of the balls on a BGA chip are measured using this new methodology, and the results verified employing a industrial optical profiler. This method isn't sensitive to the patterns on the substrate surface and has nice potential for future application.