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Glass Core Technology: Integration Leads to Innovation
Keywords: glass interposer, laser micromachining, package integration
Glass Core Technology: Integration Leads to Innovation Steve Groothuis, Samtec Microelectronics Introduction The advent of glass interposers and glass-based Integrated Passive Devices (IPDs) has continued to aid in the miniaturization of semiconductor, MEMS, sensors, and biomedical packaging and products. To create disruptive technologies and products, companies must investigate new materials, processes, and equipment sets. Samtec is developing a new technology called Glass Core Technology (GCT), which provides avenues for new electrical, electro-optical, microfluidic, and biomedical applications. We will explore several of these applications and why they are so game changing for future device and package technologies. Samtec’s Glass Core Technology process leverages the performance benefits of glass to enable performance optimized, ultra-miniaturized substrates for next generation designs. Next generation microelectronics require increased performance and integration, advanced chip technology and miniaturization. Samtec’s extensive microelectronics and high-speed interconnect expertise, along with our proven methods for package integration, product miniaturization, wafer level processing, and signal integrity optimization, enable us to provide a unique level of support for advanced microelectronics applications. There is an increased requirement for advanced packaging technologies. In this presentation we will discuss a number of glass wafer-to-wafer bonding technologies. Development programs are focused on using glass wafers as a material for wafer level packaging of devices and to keep the thermal budget during the assembly and packaging process as low as possible. In addition to discussing these wafer level packaging (WLP) processes, several examples will be given to demonstrate applicability and pros/cons of the selected Glass Core Technology concepts will be discussed. Design for Manufacturability The lessons-learned from semiconductor wafer microfabrication have been leveraged in Glass Core Technology assembly and packaging. Semiconductor device substrates are facing increased requirements regarding substrate warpage, thermal expansion as a function of processing and operating temperature, total thickness variation (TTV), and RF device performance. Typically, glass-based substrates have superior electrical, thermal, and thermomechanical properties over organic glass fiber substrates, which makes it a promising alternative platform technology for advanced semiconductor substrates [Sawyer 2017]. The application of ultra-short pulse laser technologies is making the formation of Through Glass Vias (TGVs) significantly more economical and allowing glass to be considered as a more viable alternative than semiconductor packaging substrate. Through-Glass Vias (TGVs) enable Glass Core Technology (i.e., glass interposers, smart glass substrates, and microstructured glass substrates). TGV-enabled glass substrates permit the integration of glass and metal into a single wafer, while interposers promote more efficient package interconnects and manufacturing cycle times. The hermetically sealed TGVs are manufactured from both high-quality borosilicate glass, fused silica (aka quartz), and sapphire. Through the use of high-quality glass wafer material, combined with advanced interconnect technologies (e.g., Redistribution Layer (RDL)), Glass Core Technology enables a one-of-a-kind packaging product. Design for Performance The combination of borosilicate glass (BSG) and fused silica (FS) with lower dielectric constants and loss factors have enhanced the expected electrical performance for high-speed devices (e.g., radio frequency front end (RFFE) devices). Typical passive devices include band, low, and high pass filters, inductors, capacitors, and resistors networks, couplers, cross-overs, splitters, delay lines, attenuators, antennas, and 50ohm loads. Common active devices include VCO, amplifiers, tunable filters, and optics modules. Conventional RDL with its fine lines and spacings (<25 microns) has also contributed to superior electrical performance. RDL technology enables circuit formation on glass substrates for interfacing to TGVs via a unique thin-film approach. This provides for low loss fan-out of chip and package interconnects, and lower costs compared to traditional silicon-based interposers [Lu 2016]. Table 1. Comparison of Borosilicate Glass and Fused Silica Substrates. Borosilicate Glass (BSG) Fused Silica (FS) Excellent clarity & rigidity High-purity, transparent material High thermal shock resistance Low dielectric constant and loss factor Tunable Coefficient of Thermal Expansion Very low thermal expansion Wide operating temperature range Applications: Applications: 1. Biomedical 1. Biomedical 2. 2.5D/3D package platforms 2. Microfluidics and Lab-on-a-Chip 3. Displays 3. RF MEMS 4. Optoelectronics (Imaging) 4. Optics, Imaging, & Photonics Design for Reliability Glass appears to be an ideal candidate for interposers that addresses the limits of both organic and silicon substrates. Glass is an attractive material for interposers due to its silicon matched-Coefficient of Thermal Expansion (CTE), excellent surface flatness, dimensional stability, high electrical resistivity, and availability in thin glass wafers and large glass panels at a relatively low cost [Demir 2013]. In order to prove Design for Reliability principles worked, a suite of accelerated tests have been performed to meet the reliability requirements of a few market segments. The accelerated testing results to- date have been exceptional and glass interposer qualifications are being performed. Incorporating Microfluidics With a wide market reach and broad range of flow speeds, fused silica-based substrates are an ideal solution for micro fluidic devices, a growing market sector within the biomedical industry. Applications include: • Fluidic structures for electronics cooling designs • Microfluidic structures for biomedical devices and lab-on-chip application designs Through the use of ultra-short pulse lasers enable the microstructuring possibilities such as the formation of micro channels, cavities, larger cooling channels, mixing channels, 180-degree bends, as well as ferrule openings and v-grooves for optical fibers, among others. Glass Core Technology Market Segments Table 2. Vertical Market Segments and Their Applications. Vertical Market Segment Glass Core Technology Applications Connectivity Digital medical, Radar, Internet of Things (IoT), RF devices, Bluetooth LE, Microwave, and Millimeter Wave devices MEMS & Sensors CMOS Image Sensors, Digital Medical, Fingerprint Print Sensors, Solid State Radar, Inertial Measurement Units, Ohmic Switches, Ultrasound devices, and Automotive LiDAR Medical Technology Microfluidics, Imaging Diagnostics, Surgical Robots, Implantables, Digital Medical Wearables, Lab-on-a-Chip, and Medical Equipment Optics, Imaging, and Photonics CMOS Image Sensors, Automotive Cameras, Transceivers, Medical Imaging, Microfluidics, Photonics Platforms, Machine Vision, Wafer Scale Lens Array, and Electro-Optical Circuit Boards Summary In addition, our Through Glass Via (TGV) technology in BSG and FS will be presented, which in combination with processes specifically developed for multilayer redistribution layered structures, allows further device miniaturization and package integration. In summary, Glass Core Technology provides innovative solutions for interconnecting chips, packages, modules, and systems throughout the electronics industry. In order to address such a large range of applications, GCT is proof that “Integration leads to Innovation.”
Steve Groothuis, Chief Technology Officer
Samtec Microelectronics
Colorado Springs, Colorado

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