Research On Glass Reflow Preparation And Design Of Glass Substrate Embedded With Passives

System-level design, miniaturization and low cost integration are trends of MEMS (Micro-electro-mechanical System) packaging. Packaging substrate technology, which provides functions of environmental support, mechanical protection and electrical interconnection, is the key technology for 3D MEMS packaging. An effect way to minimize MEMS packaging volume is to embed passives into the substrate. As glass has the advantages of low CTE (coefficient of thermal expansion), large optical bandwidth, good airtightness, moisture insulation, airtightness, high resistivity, chemical stability and low cost, it is regarded as a potential substrate material for MEMS packaging. However, existing microfabrication technologies are difficult to be directly applied in glass substrate. Total solutions of glass packaging substrates are in urgent demand. In this paper, a novel reflow process was proposed to prepare glass substrate embedded with passives, and the design of embedded glass substrates is investigated.First, glass substrate embedded with various passives including conductive through holes, resistor, capacitor, inductor and filter is designed. Glass reflow process is implemented in the fabrication process of glass-embedded passives. This design makes full use of the inner space of glass substrate, releases much surface space for 3D integration and significantly reduces packaging size.Second, experiment validation is operated for embedded glass substrate design. Glass-embedded structures with a width of 50-200um, thickness of 200um and aspect-ratio of 2.5 can be successfully fabricated. Glass reflow process makes molten glass flux to cladding micro structures without voids. Thus, embedded glass substrate can be mass produced inexpensively. This uncomplicated process can produce structures with a thickness in hundreds of micrometers, which broadens the signal pathway and reduces the resistance, while traditional surface micromachining process can only produce structures with a thickness as high as 20-30um.Third, HFSS simulation validation is operated for embedded glass substrate design. The simulation results show that coplanar waveguide with TGV has low insertion loss and return loss. For inductors, thickness increase reduces return loss and insertion loss. A minor thickness increase results in a large Q increase and a small L decrease. Traditional surface manufacturing technology can only produce planar inductors with a thickness as high as dozens of micrometers, while glass reflow process can produce glass-embedded inductors with a thickness in hundreds of micrometers. Moreover, Cu inductor has low loss and high Q, while highly-doped Si inductor has large insertion loss, large return loss and low Q. However, when the thickness is too large, the thickness increase cannot effectively increase Q but leads to Q roll-off while L decreases continuously.Finally, conclusion about design, experiment and simulation and new research idea are presented.