The manufacture of ceramic microelectronic packages by the co-firing process involves deposition of trace refractory metalization on the unfired, or "green" tape cast of the ceramic IC carrier. The trace metal represents the package bond pads which the IC die leads attach to. The firing of the green tape shrinks the ceramic to a final, post-fired size. The shrinkage is predictable (on the order of 18%) to within a +/- "acceptable variation" tolerance. The standard variation tolerance is +/-1.0% of the nominal post-fired ceramic body dimension.
The trace metal being in the ceramic also shrinks predictably when the ceramic is fired, with the same +/-1.0% variation tolerance on size and geometrical spacing. If a first array of trace line metal is deposited on the green tape ceramic and is intended for post-fired registration with a second array of trace metal having a nominal dimension of 1.0 inches, then the final dimension of the first array may be 1.000+/- 0.010 inches.
Prior art methods of mounting the IC dies to the ceramic package bond pads include both manual and automated bonding processes. In the manual processes the electrical interconnection of the IC to the package require operator alignment of the IC interconnect wires (or ribbon) to the bond pads. After alignment a bonder machine secures the device leads to the bond pads by welding or soldering. Automated processes, such as tape automated bonding (TAB), require accurate positioning of the package bond pads so as to automatically receive the IC TAB leads in register. The +/-1.0% shrinkage tolerance creates problems with the TAB leads to bond pad registration.
While the bond pads may be made large enough to accommodate all manufacturing tolerances, including the shrinkage tolerance, this prevents increasing package density. The IC industry drive towards miniaturization requires high density packaging which prohibits this brute force method of lead registration.