Methods for measuring plating thicknesses on TAB lead frames

Abstract

Plating three layer tape lead frames, used for tape automated bonding, offers a challenge to the electroplater because of nonuniform topography. Each lead frame contains large (typically .05 x. .05 inch) flat test pads located around the perimeter of the frame. These test pads are electrically connected to the bondable lead frame fingers which extend into an area in the center of the frame called the feature hole. The feature hole exposes these fingers to plating on all sides, while the test pads are exposed on only one side. In addition, the fingers are small in cross section (typically .003 x .0015 inches). Recent thickness measurements indicate that plating around the lead frame fingers is nearly twice as thick as that on test pad areas. Procedures and equipment were developed for measuring the thickness of the deposited material. Discussion was centered on the data obtained using the various measurement techniques and equipment.