New-Tech Europe Magazine | Q3 2020

Extending the Performance and Frequency Envelope for QFN Packaging Technology

Erick Olsen, Radha Setty and Chris Simmonds

High-performance, millimeter- wave (mmW) Monolithic Microwave Integrated Circuit (MMIC) products and cost-effective surface mount lead-frame-based packaging typically don’t come up in the same conversation, and for good reason. Just two to three years ago, it was difficult to conceive of operating at frequencies above 20 GHz without an expensive, open cavity, High Temperature Co-fired Ceramic (HTCC) package or resorting to more bespoke chip and wire assemblies. Why the need for these expensive solutions? The answer is simple. At mmW frequencies, every dB of signal strength is hard won. Traditional low frequency materials, like FR-4 for printed circuit boards or epoxy for molded packages, have excessive losses at mmW frequencies. For example, even newer materials like Hemeixin’s Megtron 6 that operate

well up to 20 GHz have a dissipation factor (Df) of 0.04 at 12 GHz, compared to TLY-5Z from Taconic, which has a Df of 0.0015 at 10 GHz. Although these materials are cost effective, their lower performance above 20 GHz combined with the potential need for extra gain stages, accompanying support circuitry and more complex signal processing are an ineffective trade-off for the lower cost materials. Thus, more exotic and more expensive materials are needed to mitigate parasitic losses. Air cavity packaging also reduces losses. However, these types of assemblies often require manual manufacturing methods. The resulting cost of materials and manufacturing methods make up a significant portion of the solution bill of materials (BOM) cost, and therefore a natural target for optimization. Meanwhile the

growing attractiveness and demand for high volumes in the mmW bands is adding further cost pressure. In response, Mini-Circuits has developed innovative packaging techniques to push the frequency range of over-molded packaging (e.g. the compact “quad flat no- lead” or QFN chip) up to 50 GHz. These techniques have been used successfully to design passive components including fixed attenuators, equalizers, splitters and reflectionless filters, as well as for high-frequency active mixers, multipliers and amplifiers. This article will explore the methods used to achieve high-frequency over- molded packing solutions for active and passive components, including high frequency package synthesis through a multiphysics 1 simulation approach and manufacturing techniques.

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