IPC APEX Expo, March 25-27, 2014, Las Vegas, NV

An Examination of Glass-fiber and Epoxy Interface Degradation in Printed Circuit Boards

Bhanu Sood, Michael Osterman, and Michael Pecht
Department of Mechanical Engineering, University of Maryland, College Park, MD 20742, USA


Conductive filament formation or CAF typically occurs in two steps: degradation of the resin/glass fiber bond followed by an electrochemical reaction. Bond degradation provides a path along which electro-deposition occurs due to electrochemical reaction. The path results from poor glass treatment, from the hydrolysis of the silane glass finish, or from mechanical stresses. Once a path is formed, an aqueous layer can develop through the adsorption, absorption, and capillary action of moisture at the resin/fiber interface. The path can be modeled as an electrochemical cell, in which the metal conductors are the electrodes, the driving potential for the electrochemistry is the operating potential of the circuit, and the electrolyte is the absorbed moisture.

Microscopic examinations of failure sites have shown that conductive filaments can be formed along debonded or delaminated fiber glass/epoxy resin interfaces due to breaking of the organosilane bonds. The organosilane bonds can be chemically degraded by hydrolysis (adsorption of water at the fiber glass/epoxy resin interface) or by repeated thermal cycling, which induces stresses at the interface due to coefficient of thermal expansion mismatches. This paper discusses the formation of pathways due to the degradation of organosilanes.

A complete article is available from the Publisher and to the CALCE Consortium Members.

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