March 11, 2021

Packaging Demands For RF And Microwave Devices

RF and microwave integrated circuits (ICs), monolithic microwave ICs (MMICs) and systems in package (SiPs) are vital for a wide range of applications. These include mobile phones, wireless local-area networks (WLANs), ultra-wideband (UWB), internet-of-things (IoT), GPS and Bluetooth devices.

Moreover, RF-optimized packaging products and processes are essential to enabling the 5G ramp-up. RFICs, MMICs, and SiP (as well as MEMS, sensors and power devices) are all devices ideally suited to benefit from solutions such as quad flat no-lead (QFN) packaging – increasingly, one of the most popular semiconductor packages due to its low cost, small form factor and improved electrical and thermal performance.

Meeting a broad range of needs

Quik-Pak’s air-cavity QFN offering is our line of Open-molded Plastic Package (OmPP) technology. Our OmPPs were tested to support RFICs at around 40GHz and below – the sweet spot for 5G applications – and provide a lower-cost alternative than the ceramic packaging typically used for RF devices. We are packaging a wide range of devices, such as RFID chips, low-noise amplifiers, radio tuners, and RF switches.

Our off-the-shelf air-cavity QFNs come in a variety of sizes, are ideal for RF prototype, mid-volume or production-volume applications, and can be provided quickly in small to medium volumes. In addition, custom packages in various sizes, lead configurations, lead frame and/or mold materials can be designed and manufactured in just a few weeks, helping customers meet their time-to-market requirements.

Base station modules are a top application for which our standard air-cavity QFNs have been deployed. One customer has used it as a key component of its base station offerings, which are based on UWB radiating elements, combined with high-efficiency phase shifters and integrated remote electrical tilt (RET), to provide a range of advanced single- and multi-band antennas.

One notable recent example of a custom OmPP involves a project, currently in pilot production, that we developed for a tester company with very high-frequency performance requirements, i.e., at the top of the Ka band (27-40 GHz frequency). For this project, air-cavity capability allows the customer to attain the required performance on a custom lead frame, minimizing material loss and optimizing signal quality.

A flexible assembly processes can accommodate bonding of multiple components, including dies, passive SMT components, and discrete semiconductors, on a single substrate. This SiP capability utilizing air-cavity technology includes passives such as decoupling capacitors. These capacitors, which are used to maintain low dynamic impedance from the individual IC supply voltage to ground, are valuable for carefully designing decoupling schemes in SiPs to reduce impedance and avoid the parallel resonance in the chip-package connection.

RF assembly capabilities

Key to our RF capabilities is both flip-chip and wire-bond interconnect technologies. Flip-chip is critical for smartphones, mobile, automotive, medical, and other high-performance applications. However, wire-bonding remains an important technology for industrial, military, energy and other markets requiring robust, high-reliability solutions.

In addition to heavy wire-bonding, ribbon bonding is used for high-frequency applications. Ribbon bonding technology enables reducing the cross-section area of a gold bond while maintaining or increasing the surface area at the same time. Ribbon bonding utilizes rectangular rather than circular wire, offering more surface area across which current can flow and preventing loss of signal in the bulk of the material. Ribbon bonding is also a viable alternative to wedge bonding, which requires use of a bond loop to avoid putting pressure on the heat-affected zone used to create the ball. Using a bond loop lengthens the wire, which degrades interconnect performance.

For die attach, industry standard materials include non-conductive, conductive, super thermally and electrically conductive, and solder. Another, newer die-attach capability is silver sintering adhesives, which provides highly effective thermal and electrical conductivity. Silver sintering is becoming a popular alternative to lead-free bonding, as it can provide performance that is equivalent or superior to that of alloys such as gold-tin or gold-germanium typically used for this low-temperature process.(From Ken Molitor)

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