Process issues and characterization of LTCC substrates

The interconnection for high density multilayer LTCC assembly requires via formation with precise via fill printing. Via formation down to 4 mil was accomplished by mechanical punching followed by via filling using high accuracy stencil printing. The print quality was studied by various manufacturing parameters for screen printing and important material characteristics, to achieve 4 mil line width. The collating process is critical to ensure the alignment of via holes. This can be accomplished by a simple fixture with alignment pins technique. Stacking holes on LTCC tape punched prior to the printing operation was compared with post punching after printing and drying operation. Upon successful stacking, good vacuum sealing was achieved. The sealing process was optimised to enable good lamination. Then firing profiles were investigated using two type of furnaces. A two stage process for debinding and sintering profiles combined with proper setter configuration resulted in defect free final product using a belt-type furnace. Similar results were achieved by using a single debinding profile in a box furnace followed by sintering profile in a belt-type furnace. The importance of using proper setters and setter arrangements is emphasized for the debinding and sintering process.