edfas.org ELECTRONIC DEVICE FAILURE ANALYSIS | VOLUME 26 NO. 3 28 RELIABILITY AND OPTIMIZATION OF WIRE BONDING IN POWER MICROELECTRONIC DEVICES Norelislam El Hami1, Aicha Koulou2, Abdelkhalak El Hami3 1Science and Engineering Laboratory, ENSA, University Ibn Tofail, Kénitra, Morocco 2EST, University Ibn Tofail, Kénitra, Morocco 3Laboratory of Mechanics of Normandy, INSA, Rouen, France abdelkhala.elhami@insa-rouen.fr EDFAAO (2024) 3:28-34 1537-0755/$19.00 ©ASM International® INTRODUCTION Bonding gold (Au) wire has been a mainstream semiconductor packaging process for many decades. The steady increase of raw materials prices has driven the electronic packaging cost up to where the cost contribution of the Au wire has become the largest component of packaging materials aside from the substrates. Gold wire bonding technology has been advanced to very fine wire diameters and bond pitches; the pitch of pads becomes less than 60 µm and the diameter of commercial ultra-fine Au wire is about 25 µm. Failure modes of bonding wires have been well documented. The bonding wires lifting and surface degradation in bonding pads are reported as the most important failures.[1-2] Wu et al.[3] reported that wire-lifting failures occurred in about 70% of the tested modules. Since then, several numerical and experimental studies have studied the thermomechanical behavior of wire bonds at low and high temperature (250°C).[4-6] The thermomechanical properties of gold wire are the most important factors in achieving a good computational model. A micro-tensile test method for bonding wire was designed by Brotzen et al.[7] to find the numerical values of the parameters of materials at different temperatures. The results of this study have also shown the relationship between mechanical properties and microstructure of ultra-fine gold bonding wire.[8] Finite element methods (FEM) are broadly used to numerically predict the thermomechanical behavior of power modules. The results from this simulation are coupled to a multi-parameter numerical optimization tool based on a sequential quadratic programming method to optimize the thermal reliability of wire bonds through minimization of the thermal stress. PROBLEM DEFINITION The device studied is an electronic package (wire bonding type) developed for engine environments and Venus planetary exploration applications in harsh environments. (The temperature at the surface of Venus is 450°C). This device is in a stack configuration. The silicon chips are soldered into insulating substrates typically made of a ceramic layer (Al2O3 or AIN) sandwiched between two thin copper layers, and the entire assembly of the die and the direct bond copper (DBC) is soldered to a copper base plate. Gold wire bonds and the bus bars interconnect the die, substrate and module terminals. Schematic drawings of the module construction are given in Fig. 1. Fig. 1 Structure of the electronic package (wire bonding type).
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