Two very different approaches to MEMS packaging - I-Micronews

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I S S U E N ° 2 6 F e b r u a r y 2 0 1 3 Optical ASIC foor plan & packaging. (Courtesy of Luxtera) adding a limited number of TSVs for power and ground to the printed circuit board. The interposer wafer could be full thickness or thinned, depending on application requirements. A packager could then micro bump an advanced CMOS control die and a little glass connector component on to the photonic/interposer-- either chipon-chip or chip-on-wafer--then plug in and align the optical fiber bundle to that connector. “Very little new needs to be developed beyond the natural evolution of the mainstream 2.5D packaging processes,” argues Bergey. The vias would need to be made through SOI wafers for the photonics/interposer, but there don’t appear to be major issues there. Assembly equipment will need to be modified to very precisely align the glass plug to the photonics substrate, and then to align the fiber into the connector. The required precision is on the order of that of copper pillar bumping, more precise than that for flip chip. Bergey figures commercial die attach tools could be customized to do the job, doing first pass alignment by machine vision, then running light though the fibers for final optical alignment. Luxtera has been busy finding partners to help in its strategy of leveraging the existing semiconductor manufacturing infrastructure to ramp silicon photonics quickly to low-cost volume production, including for packaging, assembly and test. It has designed its photonics to use standard processes and tools, and is licensing its technology to encourage others to develop products to add to the volumes as well. The company is now producing on 200mm wafers at Freescale Semiconductor, and developing a 300mm process at STMicroelectronics. ST plans to design and manufacture its own products for its customers with the process, as well as fab devices for Luxtera. Luxtera also has supplied its process to OpSIS for an open foundry service with design kit and multi-product wafers run at IME in Singapore and at Luxtera’s own fab, to help bring down the cost of photonics development for other users. It’s working with an OSAT to build a standard process for optical attach and test. It has partnered with Tokyo Electron to customize a standard probe tool for high speed wafer-scale optical testing, with fast alignment using prober cameras. After developing the needed volume technologies with the first key partner, Luxtera expects that partner to sell to other users as well, while Luxtera rolls the technologies out to more suppliers to create a more robust supply chain. “There’s a whole ecosystem that has to be built out as systems move from copper to optical interfaces for 25Gbps and beyond—it’s a big transition,” says Bergey. Paula Doe for Yole Développement Chris Bergey, Vice President of Marketing, Luxtera Prior to joining Luxtera, Chris was a Vice president at Broadcom, responsible for establishing and managing Broadcom’s WLAN combo business, which he grew into one of Broadcom’s largest lines of business. Prior to spending nine years at Broadcom, Bergey worked for Multilink Technology Corporation and Advanced Micro Devices. Chris received his MBA from the University of Maryland and a BS in Electrical and Computer Engineering from Drexel University. 3 D P a c k a g i n g 9
F e b r u a r y 2 0 1 3 I S S U E N ° 2 6 INDUSTRY REVIEW – FOCUS ON POWER DEVICE PACKAGING New packaging technology and new business models impact power module design Potential volume markets in alternative energy applications have attracted investment into both new packaging technologies and new business models that could have a big impact on the power device market. We check in with International Rectifier on technology for replacing wire bonding with modular solderable components, and with iQXPRZ on the rise of the fabless/foundry option. The potentially high volumes and extreme performance demands of the hybrid and electric vehicle market will have significant impact on power device technology. One recent example of the innovation being driven by this market is International Rectifier’s new modular IGBT and diode co-pack building block that can be surface mounted in different combinations, simplifying power module construction and allowing systems makers to more easily create their own optimized power circuit topologies. IR has replaced the wire bonds with solderable metal on both sides of the thin IGBT and diode dies, and attached both to a direct bonded copper substrate. These pre-assembled and pre-tested building blocks are then attached to a DBC—singly or in multiples, either face up, or face down flip-chip style for shorter connections and flexible design. Eliminating the wire bonds improves reliability and makes a more compact device, while the IGBT and diode dies with solderable metal on both sides can be easily assembled into co-packs and modules. (Courtesy of International Rectifier) double-sided cooling signifiantly improves thermal performance. After attaching the leadframe, this compact unit is then overmolded. Compared to a conventional module wirebonded in a gel-sealed plastic package, this process adds a top layer of DBC, but eliminates the wirebonds, gel and base plate, although a base plate can be added as an option. Jack Marcinkowski, Sr. Technical Marketing and Applications Manager for International Rectifier’s Automotive Business Unit, says this buildingblock approach significantly reduces overall system cost, by improving mechanical, electrical and thermal performance, but especially by providing a standardized and tested building block that simplifies power module customization and assembly and improves yields. IR will both use the technology in its own modules and sell the devices to outside customers. “This intermediate co-pack fills the gap between discretes and modules,” he says, noting that the compact modules can replace a number of discrete packaged devices. “There’s no precedent in the industry. Manufacturers can use the co-pack like a surface-mounted component to create their own optimized custom topology, instead of trying to design their system around an existing commercial module.” The compact module is reportedly roughly half the size and a quarter of the weight of a similarly-rated wire-bonded gel package, opening design possibilities such as putting the inverter inside the electric motor housing, for example. Key to the development was selecting proper device metallization, die attach, materials with well matched thermal expansion properties, and devising a high yielding manufacturing process. The company says the payoff is major improvements in performance for EV/HEV inverter demands. Marcinkowski reports the devices have held up through some one million thermal cycles so far in company tests, while wirebonds—the most common failure mechanism for power devices— may start to crack or delaminate at 100,000 cycles. 10 3 D P a c k a g i n g
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Two very different approaches to MEMS packaging - I-Micronews

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