ABSTRACT

Micromachining of alumina has gained a lot of interest due to unique combinations of electrical resistivity and good thermal conductivity, thus being a potential substrate for microsystems packaging in high-power electronics. Creating multiple through-holes simultaneously in alumina is difficult due to its hard and brittle nature. In this article, the formation of multiple through-holes in a 425 µm thick alumina substrate is demonstrated for the first time using the combined pulse-feed approach of the ECDM process with multi-tip array tool to improve productivity. Initial experiments are conducted with a single-tip electrode to understand the effect of duty factor, pulse frequency, and feed rate. A combined pulse-feed approach is adopted to create deep microholes (>600 µm). Later, multiple through-holes are formed using 3 × 3 multi-tip array tool to achieve an average etch rate of 24 µm/min using the combined pulse-feed approach. A duty factor of 70% and a pulse frequency of 20 kHz are suggested for stable electrochemical discharge. A low feed rate (<1 µm/s) is recommended to avoid physical contact between the tool and workpiece. These multiple through-holes can be filled with electroplated copper to form 3D interconnects for upcoming radio-frequency MEMS applications.

摘要

由于电阻率和良好导热性的独特组合，氧化铝的微加工引起了很多兴趣，因此成为高功率电子产品中微系统封装的潜在基材。由于其硬而脆的特性，在氧化铝中同时创建多个通孔是困难的。在本文中，首次展示了在 425 µm 厚的氧化铝基板上形成多个通孔，使用 ECDM 工艺与多尖端阵列工具的组合脉冲进给方法来提高生产率。最初的实验是用单头电极进行的，以了解占空比、脉冲频率和进给率的影响。采用组合脉冲进给方法来创建深微孔 (>600 µm)。之后，使用 3 × 3 多尖端阵列工具形成多个通孔，以使用组合脉冲进给方法实现 24 µm/min 的平均蚀刻速率。为实现稳定的电化学放电，建议使用 70% 的占空比和 20 kHz 的脉冲频率。建议使用低进给速率 (<1 µm/s) 以避免刀具和工件之间的物理接触。这些多个通孔可以用电镀铜填充，以形成用于即将到来的射频 MEMS 应用的 3D 互连。