HeraLock~(TM) 2000 Self-constrained LTCC Tape

摘要

A limitation of low-temperature co-fired ceramic (LTCC) technology involves the x - y shrinkage of LTCC structures upon firing and the control or tolerance of that shrinkage. This problem affects component design, materials utilization, lot-to-lot tolerance of fired components and surface circuit feature location. This paper discusses a novel method to prevent the x - y shrinkage of LTCC structures with the implementation of a new LTCC tape formulation. The HeraLock~(TM) 2000 tape is in most ways indistinguishable from a standard LTCC tape formulation. A modified form of CT2000 tape, HeraLock~(TM) 2000 is a lead-free and cadmium-free formulation with properties appropriate for general-purpose packaging, automotive modules and RF applications requiring low-loss at frequencies up to at least 6 GHz. The main advantage of HeraLock~(TM) 2000 tape is its unique shrinkage properties during firing. Most free-sintered tapes have shrinkage in the x and y directions similar to the shrinkage in the z-axis. In contrast, free-sintered HeraLock~(TM) 2000 densifies by shrinking primarily in the z-axis, leaving near-zero shrinkage in the x and y directions. In an example significant for large-format manufacturing, the x - y shrinkage on six-inch square parts (152 mm x 152 mm) fired with the standard profile was 0.114%+/-0.014%. In its green state, HeraLock~(TM) 2000 is handled similarly to conventional tapes. The only change in processing relative to CT2000 is a somewhat longer firing profile. The HeraLock~(TM) tape is compatible with standard design guidelines with respect to conductors or via holes. The HeraLock~(TM) formulation resists camber or show-through from co-fired conductors and is compatible with 100% coverage ground-planes on surface or buried metal layers. The paper concludes by discussing the advantages of HeraLock~(TM) HL2000 for the manufacturing LTCC modules. For example, cavity structures cut into the green HeraLock~(TM) tape show no x - y shrinkage or distortion after firing. Large area boards can be fabricated with minimal solder pad alignment problems - a common disadvantage of LTCC. these large area boards permit the fabrication of circuits in high volume at low cost. A further benefit compared to sacrificial layer constrained sintered processes is the ability to use co-fired solderable top conductors.