Through Glass VIAS using an Industry Compatible Glass Handling Solution

Abstract

Thin glass (≤ 200 μm) has ideal properties for electronic packaging and RF applications. In electronic packaging, a smooth, dimensionally stable surface allows high resolution line/space patterning, while through glass via (TGV) technology permits integration in many relevant packaging structures. These capabilities combine with a low loss tangent at microwave frequencies and robustness to temperature and humidity to yield high performance for RF applications. In this paper we discuss a thin glass handling solution coupled with recent innovations that give glass an entry point into these applications at large scale using existing fabrication infrastructure. Our new polymer-free bonding process allows glass to be temporarily bonded to a handle such as silicon or other glass substrates. The Viaffirm™ bonding material is non-outgassing and capable of handling temperatures in excess of 400°C while remaining temporary. When silicon is used as the handle, the opacity and form factor of the silicon substrate means that the resulting bonded stack is compatible with existing silicon processing equipment. We discuss the properties of our bonding system including temperature performance, tunability of the bond energy for different applications, and approaches to debonding. We also describe the formation and metallization of TGVs utilizing our proprietary process. When using a silicon wafer as the handle substrate, vias in the glass terminate on the silicon and are thus comparable to blind vias in silicon. We discuss the ability to make tapered TGVs while tuning their size and via profile, as well as results in metallization to produce fully filled, void free vias using a range of seed and plating approaches.