Effect of fiber orientation in glass filled plastic enclosure on the performance of wire bonds in automotive electronic product under thermal cycling environment

Abstract

Typical automotive electronic product consists of housing, cover and a laminated printed circuit board (PCB) with several electrical components mounted on it. Hard mount electrical connector on PCB with integrated pins is sometimes replaced by wire bonds and insert molded terminals in plastic enclosure. Wire bonds provide the much needed flexibility for the movement between connector and PCB wire bond pads, mainly under thermal cycling environment which is critical for the reliability of wire bonds. An extensive literature survey indicated that most of the work related to wire bonds so far focused on wire bond formation, materials, manufacturability, loop optimization, etc. There is a scarcity of work related to the effect of fiber orientation in glass-filled plastic as per the injection molding process on the reliability of solder joints of electronic devices and wire bonds on the circuit board. In this paper, a unique work has been published on the effect of glass fiber orientation in plastic housing and cover on the reliability of wire bonds used in an automotive electronic product under thermal cycling load. Fiber orientations in the glass-filled plastic housing and cover during injection molding are mapped on the structural mesh using DIGIMAT software. Then, a coupled thermal cycling finite element analysis (FEA) has been performed between DIGIMAT-Ansys on the structural mesh of the product assembly. Number of survival thermal cycles of the wire bond from the finite element analysis is compared with the actual product test data. Results show excellent correlation on the displacement behavioral trend at different wire bond pad locations and the number of wire bond thermal cycles. The major highlight of this paper is the importance of capturing the right physics of glass-filled plastic in thermal cycling analysis as per the fiber orientation from the mold flow during injection molding process. Absence of capturing the right physics of glass-filled plastic particularly during thermal cycling load, would lead to incorrect results, conclusions and thereby early failures during product life cycle, including warranty returns.