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|Modelling the Influence of Coatings, Potting and Underfills on Thermo-Mechanical Fatigue of Solder Interconnects in Electronic Packages|
|Keywords: Pottings, Conformal coating, Underfills|
|This research provides an insight into the effect conformal coatings, pottings and underfills have on solder fatigue in bottom terminated components under thermal cycling. Conformal coating and general potting encapsulants are characterized to determined their temperature dependent mechanical properties. These mechanical properties such as the elastic modulus and Coefficient of thermal expansion have strong influence on electronic components under thermal cycling. Bottom terminated components have been shown to be particularly sensitive to changes in material properties of encapsulants at both high and low temperatures. As these encapsulants expand they apply mechanical loads on electronic components that influence the stress state of solder interconnects. Up to this study no comprehensive analysis has been performed to quantify a range of properties for such encapsulants that can be used in various applications without reducing the reliability of electronic components. Protecting electronic components at harsh environments and applications often requires the use of conformal coatings, underfills or potting compounds. The temperature dependent properties of these materials greatly depend on their chemical formulation. Conformal coatings and pottings for electronic applications are available in a variety of materials ranging from Silicones, acrylics, polyurethanes and epoxies while underfill materials are epoxy based compounds filled with ceramic particles. The glass transition temperature varies for each material and represents a phase change from a hard glassy to a soft rubbery state. Temperature fluctuations experienced by electronics can span a wide range of temperatures which can often include the glass transition temperature of coatings, pottings and underfills. The inclusion of coatings and pottings have shown to have a detrimental effect on solder interconnect reliability. To illustrate these behavior, a quad-flat no-leads (QFN) and a ball grid array (BGA) package were modelled with a combination of coating, pottings and underfills. Thermal cycling simulations were performed to assess the thermo-mechanical fatigue loads experienced by solder interconnects. From the thermal simulations of each coating configuration it is possible to observe the effect on solder joint fatigue. Results obtained from this analysis provide recommendations on selecting coating material type and application as well as mitigation strategies for pottings and underfills.|
|Maxim Serebreni, Graduate Student
Department of Mechanical Engineering, University of Maryland College Park
College Park, MD