Reliability Study Of A Remote Control Car Dirver Module Packaged By COB Technology

With development of the electronic package towards the miniaturization and high density,the multichip modules based on COB technology were widely used in the electronics industry.However, the increasing consumption of power has led to the significant increase in powerdensities of equipment, and thermal stress was caused as a result of the coefficient of thermalexpansion (CTE) mismatch between different materials. In addition, the polymer material iseasy to absorb moisture from external environment, resulting in hygroscopic stress. Hence,study of reliability of multichip modules based on COB technology becomes one of the mostimportant research topics of electronic packaging.In this thesis, a multichip modules based on COB technology was designed and it'sreliability was studied. This module mounted four bare chips directly on printed circuitboards(PCB), chips were connected to PCB by wire bonding. Compared to separate packageper chips, the cost was reduced.By using ANSYS FEA software, temperature and thermal stress distribution of the modelwere simulated under power load in the situation of actual die heat generation rate and airconvection. Results show that thermal stress of model is concentrated on the interface ofepoxy molding compound (EMC), die and die attachment (DA) materials. In order tooptimize structure stress, the influences of the material's thickness and CTE were investigatedby changing the thickness and the CTE of EMC and DA material. Results indicate that thethickness of DA and the CTE of EMC are the major factor to affect thermal-mechanicalreliability.The moisture and hygroscopic stress diffusion was simulated by employing the thermalanalysis module of ANSYS,through comparison of the governing equation of heat transfer.The moisture-mechanical fatigue reliability of the COB module was studied under hightemperature and high humidity load of JEDEC MSL-1(85℃/85%RH). Results show that themajor hygroscopic stresses were found at the corner or on the edge of die, which could lead tocrack damage at the interface between die and other materials.