High density MCM-C utilizing tape dielectric and photopatterning processes

Two significant extensions of ceramic thick film substrate technology have gained increasing acceptance as a means to produce MCMs. The first is low temperature cofired ceramic packaging, which exploits the thickness control of a pre-cast insulating tape dielectric combined with the ability to combine several sintering steps into a single firing. The result is a high density, cost-effective substrate/package. The second extension is subtractive conductor and via geometry formation using photoprocessing and wet chemistry. Well defined 12 μm conductor tracks and fine 50 μm interconnecting vias allow for precise circuit geometries. In combination with high conductivity tracks and low loss/low dielectric constant materials, microwave components may be produced cost effectively. In theory, the marriage of these two technologies would have even greater technical benefit in balancing performance with cost per circuit. In practice, this combination has not been practical due to the inability to pattern conductors and vias in high volume production with yet-to-be-cofired tape. An alternative approach is described using the strong points of both dielectric tape and subtractive processing technologies. Simulated MCM-C multilayer substrates using an alumina base substrate and incorporating tape dielectric layers and photopatterning techniques to produce conductor tracks and components are presented. Also, LTCC modules post-processed with subtractively processed thick film are also discussed. Data is shown outlining the density capabilities of multilayer substrates which enable complex MCM designs to be produced cost effectively