Use of Solid-State Diffusion in Hermetic Tin/Lead Sealing
Original Publication Date: 1985-Sep-01
Included in the Prior Art Database: 2005-Feb-19
This invention teaches the use of a modified heat treatment cycle during the initial sealing or seal reworking of multilayer ceramic modules used in integrated circuit chip packaging. This approach results in an improved and more reliable hermetic seal. Prior to the development of the invention, the module was simply subjected to a linearly increasing temperature up to a peak temperature (230ŒC) much above the Pb-Sn (lead-tin) liquidus temperature (190ŒC). This was to enable the Au (gold) coating on the module seal band to disperse in the Pb-Sn solder used for sealing and thereby form a hermetic seal. This method permitted an uneven distribution of gold in the solder joint. The localized embrittlement which resulted caused an unacceptably high failure rate of the seal.