Using the Surface Potential Decay Method to probe electrical conduction in epoxy resins used for packaging
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Using the Surface Potential Decay Method to probe electrical conduction in epoxy resins used for packaging 1
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Alain Sylvestre , Patrice Gonon , Jérôme Teysseyre , Christophe Prior 1 Lab. for Electrostatics and Dielectric Materials, University of Grenoble and French National Center for Scientific Research. LEMD-CNRS, BP166, 38042 Grenoble Cedex 9, France. (E-mail: [email protected]) 2 STMicroelectronics, Corporate Package development, BP217, 38019 Grenoble Cedex, France
ABSTRACT In this work we discuss the usefulness of the Surface Potential Decay (SPD) method to investigate electrostatic charges deposited on epoxy resins which are used for electronic packaging. Corona discharges were applied on epoxy resins with different degrees of Post Mold Curing (PMC). SPD studies were conducted at room temperature under a relative humidity of about 45%. In the first part of this study we analyze the flow of electrostatic charges as a function of time. Using the SPD method we evidence that 10% of the electrical charge is still present at the surface three hours after the corona discharge has been applied. We find that the surface potential decay is more important for samples with longer PMC duration. In the second part of this work we provide a physical interpretation of the surface charge decay. We suggest that it is related to polarization mechanisms within the bulk of the material.
INTRODUCTION Epoxies are the most popular polymers used for microelectronic packaging. Indeed, in comparison with other resins, epoxies show very low shrinkage, good adhesion properties, a better resistance to environmental stresses, and excellent electrical insulating properties [1]. High package reliability was obtained when epoxies are used as encapsulating material [2]. Although the process to produce packages is well controlled, little attention was paid to the problem of electrostatic charges that could deposit onto the surface of the resin. As epoxies are dielectric materials they have the major drawback to accumulate electrical charges. These charges can induce potentials up to several kilovolts (kV). This can lead to discharges and sometimes to malfunction or to degradation of the electronic circuit. Discharges induced by electrostatic charges always proceed in the same way: generation of charges, accumulation of these charges, and finally disruptive discharges. The generation of electrostatic charges is produced when two systems are brought into contact (solid-solid or solid-liquid). When the two systems are separated, electrons and (or) ions are accumulated at the surface. Therefore, in order to protect electronic devices it is important to quantify the surface charges deposited on the resin and to understand how surface charges are evacuated. Surface charge accumulation is likely to become a serious problem for today’s packages where the resin is more and more often found in close proximity of active electronic parts.
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Mat. Res. Soc. Symp. Proc. Vol. 682E © 2001 Materials Research Society
In this work we present
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