Lars Brusberg

3-D Thin film interposer based on TGV (Through Glass Vias): An alternative to Si-interposer

Interposers for SiP will become more and more important for advanced electronic systems. But through substrate vias are essential for the 3-D integration. Being a standard for laminate based materials this is much more complex for Si-wafers: High speed etching has to be combined with complex electrical isolation, diffusion barriers and void-free Cu-filling. Without doubt this can be solved in lab-scale but for high production scale cost is a tremendous barrier. Glass wafers with W-plugs have been intensively investigated in this paper. A new acronym has been posted to high-light this technology: TGV for Through Glass Vias. The results of modeling and simulation of TGV at RF/Microwave frequencies showed a very good compromise between wafer thickness, TGV-shape and via diameter for vertical metal plugs with 100 μm diameters in 500 μm thick glass wafer still very stable for thin film wafer processing without costly temporary wafer bonding processes. Therefore the HermeS® from Schott was chosen as the basis for a prototype of a bidirectional 4 × 10 Gbps electro-optical transceiver module. Thin film RDL and bumping of these wafers was possible without any modifications to Si-wafer. First thermal cycles showed very promising results for the reliability of this concept.

glassPack — A 3D glass based interposer concept for SiP with integrated optical interconnects

We introduce thin glass for electrical-optical integration on module level. Glass is regarded as promising material for high frequency wiring to drive the e/o components having additional advantages in terms of transparency, waveguide and lens integration capability and PCB integration. Modeling results of vertical and horizontal electrical interconnects show the suitability for certain configurations. The integration schemes will be discussed and experimental results from thin film deposition, laser drilling of through vias and ion exchange for optical waveguides will be presented.

Thin glass based packaging technologies for optoelectronic modules

The novel packaging approach glassPack is introduced as System-in-Package (SiP) technology. Wiring length can be reduced and integration density can be increased by stacking different assembled substrate layers and interconnecting them with one another resulting in 3D-SiP. Glass is an excellent material because of matched coefficient of thermal expansion (CTE) to silicon, high thermal load, dielectricity and high optical transparency over a wide wavelength range. Commercially available thin glass foils can be used as substrate material for electronic and optoelectronic modules. The goal of our ongoing development is making glass based packaging competitive with polymer based (e.g. chip-in-polymer) or silicon based packaging (e.g. silicon-through-via, stacked dies by wire bonding). Our work is focused on conductor trace and through-via realization as well as optical lightwave circuits integration using glass as substrate material. For through-vias in glass, holes were drilled in glass wafers by different laser technologies or etched using photosensitive glass and evaluated. Conductor traces and through-via interconnects were deposited on glass. Also, optical waveguide and fluidic channel integration in glass substrates were investigated. This paper presents the first demonstrator of our glass based packaging technology targeting sensor applications. Two silicon dies, a laser diode, two photodiodes and a fluidic-optical chip were mounted on a glass substrate and interconnected by 3D electrical wiring.

Pluggable Electro-Optical Circuit Board Interconnect Based on Embedded Graded-Index Planar Glass Waveguides

Widespread adoption of electro-optical circuit boards based on embedded glass waveguide technology would enable seamless optical connectivity from external fiber-optic networks to system embedded optical interconnect architectures. In this paper, we report on the fabrication of planar multimode waveguides within thin glass foils based on a two-step thermal ion exchange process. Novel lamination techniques were developed to allow glass waveguide panels to be reliably integrated into a conventional electronic multilayer printed circuit board. In addition, a complete suite of optical connector technologies were developed to enable both direct fiber-to-board and board-to-board connectivity. We present the design, development, and characterization of a fully integrated connection platform, comprising a 281×233 mm2 multilayer electro-optical backplane with integrated planar glass waveguides, a pluggable connector system, and five pluggable test cards. Both on-card and externally generated 850 and 1310-nm optical test data were conveyed through the connector and waveguide system and characterised for in-system and system-to-system optical connectivity at data rates up to 32 Gb/s per channel exhibiting bit error rates of less than 10-12.

Glass carrier based packaging approach demonstrated on a parallel optoelectronic transceiver module for PCB assembling

Glass as a carrier material for electrical and optical interconnects has many benefits compared to conventional materials like silicon, ceramic or polymer based laminates because of its excellent dielectric and transparent properties that are becoming important for electrical high-frequency signal wiring as well as for optical wave guiding. Furthermore, the integration potential of glass is excellent because of the dimensional stability under thermal load and the coefficient of thermal expansion matching that of silicon ICs. A small pitch size of conductor traces, small scale through-vias and high alignment accuracy are the key requirements that will be achieved from glass carrier based packaging. Another outstanding benefit is the transparency of glass that allows the planar integration of optical waveguides inside the glass core material and the light transmission through the carrier between different optical layers. This paper presents a four channel bi-directional optoelectronic transceiver module that was designed and processed using the glass carrier based packaging approach called glassPack. The transceiver operates with 10 Gbps per channel and has an extremely low power consumption of 592 mW. The module is mounted on a printed circuit test board and the performance is characterized by bit error rate testing.

Photonic System-in-Package technologies using thin glass substrates

The novel packaging approach glassPack is introduced as a system-in-package (SiP) technology. Wiring length can be reduced and integration density can be increased by stacking different assembled substrate layers and interconnecting them resulting in 3D-SiP. Glass is an excellent substrate material because of matched coefficient of thermal expansion (CTE) to silicon, high thermal load, dielectric constant and high optical transparency over a wide wavelength range. Commercially available thin glass foils can be used as substrate materials for electronic and optoelectronic modules. The goal of our ongoing development is to make glass based packaging competitive with polymer (e.g. chip-in-polymer) or silicon based packaging (e.g. silicon-through-via, stacked dies by wire bonding). Our work is focused on conductor trace and through-via realization as well as optical lightwave circuit integration using glass as a substrate. For through-glass-vias, holes were drilled in glass wafers by different laser technologies and evaluated. Also, optical integration of waveguides and mirrors in glass substrates were investigated. This paper presents basic design rules and a selection of technologies for glass based SiP as well as a process flow for glass interposer applications.

Optical backplane for board-to-board interconnection based on a glass panel gradient-index multimode waveguide technology

Future bandwidth needs force the development of optical interconnects for data transmission at board level. The aim is to develop technology solutions for embedded optical architectures in data center and network systems to allow significant reduction in power consumption, increased energy efficiency, system density and bandwidth scalability, which is currently unfeasible in todays copper driven systems. A passive optical backplane comprising a printed circuit board (PCB) with integrated optical waveguides and standardized pluggable optical coupling interfaces to the line cards is proposed for future data communication systems. Our activities are focused on embedded glass-based electro-optical circuit boards (EOCB) with integrated gradient-index multimode waveguides, which exhibit very low propagation loss at key optical communication wavelengths. A pre-processed glass panel with planar integrated optical waveguides is embedded into a backplane by using proven industrial PCB processes. A pluggable optical connector and receptacle system is designed for connecting the optical fiber links of the line cards with the optical waveguide circuit of the backplane.

Glass panel processing for electrical and optical packaging

Glass is a perfect substrate material for electrical and optical packaging. The integration concept to bridge board and chip level using thin glass substrates by lamination in between of PCB base material will be presented. Different thin glasses are commercial available and will be reviewed. Furthermore the paper reviews glass panel processing in the area of display and electro/optical packaging focusing on integration advantages for photonic packaging. Ion exchange technology for large panel processing to integrate high-performing optical waveguides will be demonstrated for multi-mode beam propagation. Based on glass based photonic system-in-package (SiP) which is done on wafer level the up scaling on panel size of those processes is discussed in detail and experimental results are presented.

Single-mode glass waveguide platform for DWDM chip-to-chip interconnects

Due to high bandwidth potential, optical single-mode signal transmission is superior to electrical as well as optical multimode signal transmission. For years, optical single-mode fiber cables have been used in telecommunication networks. However, there is a lack of photonic system integration based on optical single-mode interconnects in printed circuit boards and modules for signal transmission between electro-optical components and optical fibers. Therefore, a thin glass-based photonic integration concept for single-mode signal transmission was developed. Optical waveguides and optical free space interconnects are integrated in a single or a stack of thin glass sheets for module and printed circuit board packaging. For light routing inside a thin glass sheet, a singlemode waveguide technology on wafer level (150 mm) was developed promising for scaling up on panel size (45 × 60 cm2). The waveguides show single-mode behavior, low propagation (0.05 dB/cm) and fiber coupling (- 0.3 dB) losses at wavelength of 1550 nm. Different waveguide structures such as 180°-bends, S-bends, splitters and crosses have been integrated in thin glass and characterized in detail. Coupling mechanism and misalignment loss has also been studied. Technologies for fiber laser joining on glass as well as laser structuring of an optical mirror are introduced and first results are presented. Generic module and board-based photonic packaging solutions can be put into practice by applying all introduced technologies and will be demonstrated for a chip-to-fiber module package platform.

Electro-optical backplane demonstrator with gradient-index multimode glass waveguides for board-to-board interconnection

First time an electro-optical circuit board (EOCB) is demonstrated with integrated planar glass multimode waveguides and with optical pluggable line card connectors. The waveguides are patterned inside commercially available thin-glass panels by performing a two-step thermal ion-exchange process. The resulting low-loss multimode waveguides possess a gradient-index profile. The glass waveguide panel is embedded within the layer stack-up of a printed circuit board (PCB) using proven industrial processes. Cut-outs inside the PCB are structured for assembling a pluggable optical connector and receptacle system for connecting optical fiber based waveguides on the line cards to integrated optical waveguides in the backplane. The demonstration platform comprises a standardized sub-rack chassis and five pluggable test cards with pluggable optical connectors and designed for housing optical engines. The test cards support a variety of different data interfaces for bidirectional signal integrity measurements. The evaluated demonstrator system performed with bit error free data transmission at 10.3 Gb/s for the tested wavelengths of 850 and 1310 nm.