Thermocompression bonding of external package leads on integrated circuit substrates

A new technique for attaching external package leads to metallized substrates is presented. Gold-plated copper lead frames and gold-plated headed leads of various compositions are thermocompression bonded to metallized alumina substrates. The generated patterns on the substrates consist of an evaporated layer of gold over an evaporated layer of titanium. The leads are bonded simultaneously to form gold diffusion bonds between the leads and the metallized substrate. The lead frames are stamped from 0.005 inch and 0.010 inch thick copper. The headed leads range in size from 0.017 inch in diameter to 0.025 inch square. The various problems encountered in the development of this technique and their related solutions will be discussed. The bonding tool consists of a base for positioning the substrate and a bonding tip which applies the necessary pressure and temperature to produce a bond. The base and bonding tip for lead frames can compensate for camber and nonuniform thickness in the ceramic while the base and bonding tip for headed leads are noncompensating. The various parameters of bonding time, bonding temperature, bonding force, and bond strengths will be presented. In addition, hermetic seal evaluations will be discussed. A comparative cost analysis will be made between attaching leads individually by welding versus attaching all package leads simultaneously by the thermocompression bonding technique. This investigation has opened additional avenues toward determining the full scope and capability of thermocompression bonding in an area previously dominated by brazing and the sealing of metal to glass and/or ceramics.