Bond wire design for eXtreme Switch devices

Freescale´s third-generation eXtreme Switch devices set performance standards for automotive lighting. They are tailored to drive high-intensity discharge (HID) xenon, halogen and light-emitting diode (LED) lamps. For example, a halogen lamp draws high levels of current when first turned on, but much less once it has stabilized. The ICs therefor allow the lamps to draw high levels of current when needed at turn-on but less during operation. Hence, these devices have to withstand the event of an inrush current each time a lamp is switched on. Package and wire bond design have to consider the transient characteristics of Joule heating and heat transfer. The authors developed an approach for the current carrying analysis of bond wires in power packages. It is based on closed form solutions of the heat equation at single current pulse, repeated current pulses or arbitrary inrush current profiles. This paper focuses on the analysis of Joule heating in bond wires. We will solve the initial and boundary value problem for the Joule heating at an inrush current pulse. The solution will be validated with thermo-electric finite element simulation. We will then draw conclusions for the wire bond design.