07-04-2009, 11:58 PM
Introduction
In power electronics, solid-state electronics is used for the control and conversion of electric power .The goal of power electronics is to realize power conversion from electrical source to an electrical load in a highly efficient, highly reliable and cost effective way. Power electronics modules are key units in a power electronics system. These modules contain integration of power switches and associated electronic circuitry for drive control and protection and other passive components.
During the past decades, power devices underwent generation-by-generation improvements and can now handle significant power density. On the other hand power electronics packaging has not kept pace with the development of semiconductor devices. This is due to the limitations of power electronics circuits. The integration of power electronics circuit is quite different from that of other electronics circuits. The objective of power electronics circuits is electronics energy processing and hence require high power handling capability and proper thermal management.
Most of the currently used power electronic modules are made by using wire-bonding technology [1,2]. In these packages power semi conductor dies are mounted on a common substrate and interconnected with wire bonds. Other associated electronic circuitries are mounted on a multi layer PCB and connected to the power devices by vertical pins. These wire bonds are prone to resistance, parasitic and fatigue failure. Due to its two dimensional structure the package has large size. Another disadvantage is the ringing produced by parasitic associated with the wire bonds.
To improve the performance and reliability of power electronics packages, wire bonds must be replaced. The researches in power electronic packaging have resulted in the development of an advanced packaging technique that can replace wire bonds. This new generation package is termed as 'Integrated Power Electronics Module' (IPEM) [1]. In this, planar metalization is used instead of conventional wire bonds. It uses a three-dimensional integration technique that can provide low profile high-density systems. It offers high frequency operation and improved performance. It also reduces the size, weight and cost of the power modules.
Features Of IPEMS
The basic structure of an IPEM contains power semi conductor devices, control/drive/protection electronics and passive components. Power devices and their drive and protection circuit is called the active IPEM and the remaining part is called passive IPEM. The drive and protection circuits are realized in the form of hybrid integrated circuit and packaged together with power devices. Passive components include inductors, capacitors, transformers etc.
The commonly used power switching devices are MOSFETs and IGBTs [3]. This is mainly due to their high frequency operation and low on time losses. Another advantage is their inherent vertical structure in which the metalization electrode pads are on two sides. Usually the gate source pads are on the top surface with non-solderable thin film metal Al contact. The drain metalization using Ag or Au is deposited on the bottom of chip and is solderable. This vertical structure of power chips offers advantage to build sand witch type 3-D integration constructions.
