Control of Low Temperature Co-fired Ceramic Shrinkage for Unconstrained Sintering

The shrinkage of Low Temperature Co-fired Ceramics (LTCC) during firing is one of the most difficult features to control in LTCC fabrication, as many factors may impact on the result. The shrinkage given by the tape manufacturer is not perfectly transposable to a production environment where preparation, use and equipment is not in exact accordance. Thus, predictable shrinkage models are of main importance in order to fabricate LTCC devices according to specifications. The objective of this work is to develop such models for the Ferro L8 tape using the powerful Design of Experiments (DOE) technique. Four factors are varied; the stack thickness, the device surface, the applied pressure and the temperature during lamination. Other factors such as operator, lamination time or firing profile are kept to a fixed value during these experiments. The result variables are lamination quality and x, y and z-direction shrinkage. Lamination quality is found to be mainly impacted by the interaction between the stack thickness and the surface area of the stack, while for the z-direction shrinkage this interaction together with lamination temperature are significant factors and finally for the lateral shrinkage the main effects stack thickness, surface area and temperature are significant. Numerical models for shrinkage in z- and lateral directions are established. This work enforces the understanding of the shrinkage of LTCC and permits for the Ferro L8 users correctly compensate the layout for shrinkage.