ABSTRACT
First-level packaging is designed to interconnect the device to the board while providing protection for the device against mechanical stress and chemical attack. In addition, in advanced packaging structures, first-level packaging can perform some of the signal processing and distribution functions as well. Wirebonding is the most common technique for interconnecting a silicon chip to a chip carrier or to the leadframe in a single-chip package. Gold and aluminum are the usual wire materials, although copper and silver have also been used. Package cases should be made of materials that protect the die circuitry and the interconnections to the leads from mechanical stresses and chemical attack. Lid seal materials are required to seal the lids of hermetic packages. Seal materials should have low permeability to moisture, high shear strength, favorable fatigue properties, low sealing temperature, good wetting properties with respect to the case and lid surfaces, and a coefficient of thermal expansion that matches the lid and case materials.
