On the porosification of LTCC substrates with sodium hydroxide
On the porosification of LTCC substrates with sodium hydroxide
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DOI：
10.1016/j.compositesb.2018.08.071
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发表时间：
2019-01
期刊：
影响因子：
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通讯作者：
A. Hajian;Doruk Müftüoglu;T. Konegger;M. Schneider;U. Schmid
中科院分区：
文献类型：
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作者：
A. Hajian;Doruk Müftüoglu;T. Konegger;M. Schneider;U. Schmid
低温共烧陶瓷（LTCC）出色的材料特性使其成为实现坚固、高度集成的基板或微机械器件封装解决方案的首选技术。然而，相对高的介电常数限制了它们在高频应用中的利用，因为另外在一个单个LTCC层中具有降低的介电常数的限定区域将是最有益的。在碱性条件下的湿化学多孔化方法是一种新颖且最有利的方法，其可通过将空气局部嵌入到处于其烧制状态的LTCC表面中来应用于介电常数降低，对表面特性具有低影响。蚀刻工艺后的LTCC基板的所得孔隙率受到LTCC带组合物以及蚀刻参数的强烈影响。由于期望带的化学组成不变，因此优化蚀刻参数，即蚀刻剂浓度、蚀刻时间和浴温度是合理的程序，其允许定制用于处于其烧制状态的LTCC带的多孔化工艺。在这项工作中的LTCC基板的蚀刻行为和表面形态进行了研究，定性和定量，并进行了详细的重量和粗糙度测量，以及多孔化深度的调查。进行的分析表明，蚀刻过程中的主要反应控制机制。除了在表面附近区域中产生定制的孔隙率之外，还可以通过在限定的蚀刻条件下LTCC表面的整体溶解来减小LTCC的整体厚度。最后将实验结果拟合成非线性多项式模型，为确定实现定制孔隙率的最关键参数提供实验依据。
Outstanding material properties of low temperature co-fired ceramics (LTCC) make them the technology of choice when targeting the realization of robust, highly integrated substrates or packaging solutions for micromachined devices. However, the relatively high permittivity limits their utilization in high-frequency applications, as in addition defined areas with reduced permittivity in one single LTCC layer would be most beneficial. The wet-chemical porosification method under alkaline conditions is a novel and most advantageous approach which can be applied for permittivity reduction through locally embedding air into the LTCC surface in its as-fired state with low impact on the surface characteristics. The resulting porosity of the LTCC substrates after the etching process is strongly affected by the LTCC tape composition as well as the etch parameters. Since the chemical composition of the tape is desired to be unaltered, optimizing the etching parameters, namely etchant concentration, etching time, and bath temperature is a reasonable procedure which allows tailoring the porosification process for the LTCC tapes in their as-fired state. In this work the etching behavior and surface morphology of the LTCC substrates have been studied, both qualitatively and quantitatively, and detailed gravimetric and roughness measurements, as well as porosification depth investigations, were carried out. The conducted analyses suggest a dominating reaction-controlled mechanism for the etching process. In addition to generating a tailored porosity in the surface-near region, overall thickness reduction of the LTCC through the overall dissolution of the LTCC surface under a defined etching condition was also possible. The experimental results were finally fitted into a nonlinear polynomial model for providing an experimental basis in order to identify the most crucial parameters to achieve a tailored porosity.