Characterization of Surface Mount Package Effects with the TLM Method

Giampaolo Tardioli, Mario Righi, Lucia Cascio, Mario Righi, and Wolfgang J.R. Hoefer

A typical problem facing designers of integrated circuits is to determine the effect of the package on the performance of a monolythic microwave integrated circuit (MMIC) it contains. The presence of leads, bond wires and grounding pins affects the MMIC behavior. These effects must be included in the early design stages. In order to avoid costly design cycles, an electromagnetic approach becomes attractive to predict accurately the performances of a packaged circuit. We have performed the full wave time-domain analysis of a surface mount plastic package containing a simplified MMIC (a thru connection and a microstrip spiral inductor). Problems such as poor grounding terminations and crosstalk with neighboring lines are also considered as they can occur at relatively low frequencies. Finally, we propose an approach to isolate the package effects. The whole structure is segmented and the package is characterized by its scattering parameters. In this way the package needs only to be modeled once for a given configuration. The package effects are extracted and combined with the MMIC parameters to predict the performance of the packaged circuit at a fraction of the computational costs. In addition, the MMIC circuit can be optimized by including the package effects from the design stages, thus significantly reducing costly cut-and-try cycles. TLM Analysis of the SOIC-8 Package The described critical issues appear in the analysis of the SOIC-8 surface mount package. The structure comprises 8 leads which allow the IC to be soldered onto the mother-board. Some of the leads are extended to the paddle to provide grounding to the MMIC, while other leads are connected by bond wires to the MMIC providing input and output to the circuit.

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Further details can be found in: M. Righi, G. Tardioli, L. Cascio, W. J. R. Hoefer, "Time Domain Characterization of Packaging Effects via Segmentation Technique" to be published on the Special Issue on Packaging Effects and Interconnects of the MTT-S IEEE Transactions, September 1997.

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