Experimental Test And Finite Element Simulation Of The Reliability Of Vertical Interconnection In Three Dimensional Assembly

As the electronic systems tend to develop more intelligent, functional and complex,the dimension of the system becomes larger and larger. In recent years, three-dimensional (3D) assembly technology receives more and more attention, due to itscapability of reducing the bulk of the electronic system and improving the density ofelectronics assembly. Besides, if people want to put this technology into the applicationof aerospace, more work should be done for the deep research of its reliability whenworking in severe working situations.In this work, the scheme of vertical interconnection for three circuit boards wasdeveloped. Three vertical interconnection technologies, transfer board bonding withbumps on both sides, thick copper wire bonding and fuzz button, were used to realizethe3D assembly of these three circuit boards. After that, some research was done toinvestigate the characteristic of the fuzz button. Besides, thermal shock test wasconducted to investigate the reliability of the3D assembly circuit board. In the sametime, the response of this3D assembly circuit board to thermal shock and randomvibration was explored through the method of finite element simulation.The results showed that the mechanical property of fuzz button possessednonlinear property. The relationship between its tangent modulus and compressivestrain could be divided into three stages. The interaction mechanism of metal wires infuzz button could be classified into rigid contact, frictional contact and squeezed contact.The fuzz button also showed force hysteresis characteristics. The loss factor decreasedbut the average stiffness increased with the deformation amplitude increasing. Also theresistance-strain curve showed nonlinear property. In the first stage, the resistancedecreased rapidly when the compressive strain increased. After that, the resistance offuzz button almost kept unchanged. When the strain reached0.15, the fuzz buttonshowed both good electrical conductivity and mechanical stability. After theexperimental test of thermal shock, some crack occurred in the inner part of the solderjoint, and adjacent to the interface of solder and pad. The thick copper wire bondingshowed strong thermal shock resistance. Au/BeCu based fuzz button could work stablyunder the condition of high temperature. However, Au/Mo based fuzz button did notown this property. Both of these two kinds of fuzz button can work properly in therandom vibration test. In the simulation of thermal shock test, the von Mises stress ofsolder joints adjacent to the edge of the circuit board is larger than that of solder jointsnear the center of the circuit board. In addition, more stress concentrated at the interfacebetween the solder joint and Cu pad. For thick copper wire bonding, stress concentration occurred near the bonding interface and inside the copper wire. For fuzzbutton, the response acceleration of the center area to the random vibration was muchless than that in the region near the pad. However, the von Mises stress in the centerarea was larger than that of other areas. In the random vibration test simulation, thelifetime of the transfer bonding with bumps at the both sides was estimated to be185s,and the working life of thick copper wire bonding was estimated to be151s.