SMTA International Conference Proceedings


Authors: Quan Qi, Ph.D., Curt Miller, Daryl Hollis, Kathleen Ullom, Jeff McDonald, Ken Vielmette, and Heidi Davis, Ph.D.
Company: Maxtek Components Corporation
Date Published: 10/11/2007   Conference: SMTA International

Abstract: For high performance RF & microwave applications, thinfilm circuits are frequently used. Trade-offs have to be made frequently to accommodate the requirements in performance, cost, materials availability, design flexibility, etc. Here we present an analytical, numerical and experimental investigation of a thin-film RF/microwave module that experienced assembly failures under thermally induced stresses and discuss a variety of approaches to mitigate the stress level and increase the bond strength. First, background for this module and characteristic failure modes are described, as well as typical assembly and test conditions; second, formulation of CTE mismatch induced stress analysis based on improved bi-metallic beam-plate theory is presented and mechanism & theory of de-bonding are then briefly discussed; the analytical approach is subsequently verified with an FEA; thirdly, several experimental investigations, guided by the analytical investigations, involving different base materials, bonding agents, processing conditions, pre-bonding cleaning, etc. were conducted to explore how to improve the bonding strength, reduce assembly stress and produce high-reliability assemblies.

While it is difficult to predict the interfacial bonding strength for dissimilar materials without resorting to calibrated test according to fracture mechanics, some experimental data may be used to infer the interfacial strength for given bonding agents. An effort to take advantage of the failure data based on different substrate sizes to predict the interfacial bonding strength is described.

Key words: RF/microwave modules, module assemblies, CTE mismatch, thermomechanical stress, reliability, thinfilm attach

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