New-Tech Europe Magazine | Q3 2020

Innovating the QFN Production Workflow The results of the aforementioned research provided valuable insights into the limitations imposed by the standard QFN production flow, and more importantly, uncovered multiple options to address these limitations. We used these insights to approach the task of over-molded mmW component packaging in a holistic way, focusing on three primary, interrelated factors: Die and wirebond improvements Leadframe optimization NonRF interconnects Each of these factors will be discussed in turn below with examples of recent QFN components exhibiting excellent performance up to 50 GHz. DieandWirebondImprovements The contribution of the IC circuit design to the overall solution performance cannot be understated, but the interface between the IC and the package is critical. Bondpad geometry and transition were both important factors in optimizing performance. There is always a

between modelled predictions and measured results. Package Components Even with luxury of an in-house IC packaging line, it can be easy to take the status quo as given. But the status quo was not going to deliver the needed mmW performance. Analyzing the packaging materials uncovered some basic assumptions that were limiting performance at high frequencies. Combining this detailed material analysis with targeted 3D EM simulations yielded new options to optimize performance in the mmW range. Manufacturing Techniques As with the packaging components, assembly techniques have a considerable effect on overall product performance. Specifically, the wirebond interconnects, their method of attachment and physical layout have the greatest impact on the frequency response of the package. Detailed analysis of these features of the MMIC assembly led to innovative bonding techniques that have shown IC performance preserve the intrinsic performance of the die itself.

tradeoff between the number of RF bondwires and the accompanying bond pad size. Simply adding more bondwires doesn’t reduce the series inductance as mutual inductance diminishes the benefit of additional wires. Also, a larger bondpad to accommodate the extra wires adds unwanted capacitance. Our solution was to develop bonding techniques that reduced effective bondwire inductance and simultaneously reduced parasitic capacitance to ground, resulting in an interconnect structure that better approximates a 50Ω transmission line. The better match of the bondwire structure provided flexibility to tune the transition on the die, again optimizing the frequency response. The KAT-series of precision attenuators is one example of Mini- Circuits’ patent pending bonding technique. Based on the YAT-series of 18 GHz attenuators, we were able to extend the desired frequency response to 43.5 GHz (released in late 2019 as KAT-x+). With further refinements, a new family of attenuators will be released in 2020 that will operate up to 50 GHz (Figure 3.) where both the

Figure 3: KAT-0+ Attenuator - Optimized bonding (RED) vs original Bonding (BLACK)

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