Fabrication of Through Alumina Vias: An Alternative Approach Using Ultrasonic Machining and Electroless Deposition

This paper presents a cost-effective approach for fabricating through alumina vias (TAVs) using ultrasonic machining (USM) combined with electroless deposition. Alumina, with its superior electrical insulation and thermal conductivity, is a promising interposer material for harsh environment applications. While effective, traditional methods like laser-based etching and physical vapor deposition (PVD) are costly and require sophisticated infrastructure. The proposed USM technique, operating at room temperature, precisely machines alumina with no heat damage, facilitating the creation of microholes. Electroless copper deposition further enhances the process by providing conformal metallization of the vias, which is crucial for their performance in microsystem packaging. This approach significantly reduces the cost and complexity of TAV fabrication, making it accessible to a broader range of researchers. A 6 × 5 array of TAVs with an opening size of 415 μm and an aspect ratio of nearly 2.4 was successfully fabricated.