Zero Shrinkage of LTCC by Self‐Constrained Sintering

Low shrinkage in x and y direction and low tolerances of shrinkage are an indispensable precondition for high‐density component configuration. Therefore, zero shrinkage sintering technologies as pressure‐assisted sintering and sacrificial tapes have been introduced in the low‐temperature co‐fired ceramics (LTCC) production by different manufacturers. Disadvantages of these methods are high costs of sintering equipment and an additional process step to remove the sacrificial tapes. In this article, newly developed self‐constrained sintering methods are presented. The new technology, HeraLock ^® , delivers LTCC modules with a sintering shrinkage in x and y direction of less than 0.2% and with a shrinkage tolerance of ±0.02% without sacrificial layers and external pressure. Each tape is self‐constrained by integration of a layer showing no shrinkage in the sintering temperature range of the LTCC. Large area metallization, integration of channels, cavities and passive electronic components are possible without waviness and camber. Self‐constrained laminates are an alternative way to produce zero shrinkage LTCC. They consist of tapes sintering at different temperature intervals. Precondition for a successful production of a self‐constrained LTCC laminate is the development of well‐adapted material and tapes, respectively. This task is very challenging, because sintering range, high‐temperature reactivity and thermal expansion coefficient have to be matched and each tape has to fulfill specific functions in the final component, which requires the tailoring of many properties as permittivity, dielectric loss, mechanical strength, and roughness. A self‐constrained laminate is introduced in this article. It consists of inner tapes sintering at especially low‐temperature range between 650°C and 720°C and outer tapes with an as‐fired surface suitable for thin‐film processes.