| Micro-interconnection technology in electronic packaging is rapidly developing to the orientation of miniaturization, high-density, the solder joint not only plays the role of electrical and mechanical connection, also provides a way to heat dissipation, so the reliability of micro-interconnection solder joint is very important. The present paper study the change and evolution of interface microstructure, the growth rhythm of intermetallic compounds (IMC) and thermal fatigue proformance under limiting conditions for ball grid array (BGA) lead-free micro-solder joint by rapid thermal fatigue. In addition, light-emitting diodes (LED) was appliedly researched by rapid thermal fatigue, too. The influences of LED property and interface microstructure of lead-free micro-solder joint in its chip were studied, and compared with results of conventional thermal fatigue experiment, the results shows that rapid thermal fatigue can obviously affects ther preformance and microstructure of micro-solder joint, so it can be used to evaluate reliability and life of micro-solder joint.In this present paper, a rapid heating experimental device was designed. Lead-free Sn3.0Ag0.5Cu (SAC305) solders were used to preparate SAC305micro-solder joints with single/double substrates, respectively. The influence of interface and surface profermances and microstructure of BGA micro-solder joints were investigated by rapid thermal fatigue. In addition, high-power LEDs were tested by rapid thermal fatigue. The influence of microstructures of lead-free micro-solder joint (Au/Sn and Ni/Au) in LED chip were researched except for the influence of LED properties, which results were compared with results of conventional thermal fatigue experiment.The main research results are listed as follows:The study on the single-base substrate SAC305solder joints revealed the influence of rapid thermal fatigue on microstructures of at0hour and rapid thermal cycle12hours at55-125℃and55-180℃. It was found that the intermatellic (IMC) between interface of solder joint starts from the scallop shape to a big wave, and its thickness increases with time, and IMC is only single Cu6Sn5firstly, later a new Cu3Sn layer is generated in the between Cu6Sn5layer and Cu layer, and it is also gradually thickening, and Ag3Sn grain start from short stick shape to elliptical granular. In addition, it was also found that Kirkendall holes appear in the IMC Cu3Sn layer, and it is bigger and bigger with the temperature. According to Fick diffusion law, the growth of the relationship of IMC thickness and the square root of cumulative test time is roughly linear, so the diffusion coefficient, and the diffusion constant and activation energy are calculated by the means of fitting. The single-base plate SAC305/Cu solder joint was tested at extreme temperature60-200℃by rapid thermal cycle24hours and36hours respectively, it was found the IMC grow by the zigzag shape, and fatigue cracks appear at the interface of IMC/Cu, they are initiating and propagating along the boundary, and thread through the cross section of solder joint in the end, which lead to the failure of solder joint.The study compared the influence of rapid thermal fatigue on the interface microstructures of two solder joints with double-base substrates of Cu/Sn3.0Ag0.5Cu/Cu and Cu/63Sn37pb/Cu at cyclic temperature60-200℃and55-180℃and test time for0hour,12hours,24hours,36hours and72hours, respectively. It was found the IMC in SAC305solder joints only haves Cu6Sn5, then evolves into Cu6Sn5and Cu3Sn. After36hours, the interface of solder joint appears recrystallization phenomenon, which causes stress concentration and crack generation. After72hours, it was also found that cracks have filled the entire section, and formed a network. However, the solder in Cu/63Sn37Pb/Cu solder joints happen remelting and deformation, the solder didn’t happen a recrystallization phenomenon, but the tin oxide film exist on the solder surface later, and the reasons of dismatch coefficient of thermal expansion (CTE) and frangibility of tin oxide urge cracks to form corrosion grooves. At last, according to the thermal simulation analysis and thermal deformation theory, the cracking process was explained with a schematic diagram.The study on LED revealed the influence of rapid thermal fatigue on the changes of performances under operating life test and non-operating life test onditions and compared the results of conventional thermal fatigue contidion. It was found that a luminous flux is ones of LED optical properties, as an example, and quickly fell down30%when it was tested24hours in the operating life test and achieve a failure standard, and it fell down15%after440hours in non-operating life test, but it only dropped to4%after552hours test. At the same time, their spectrogram also were studied, the relative spectrum of LED blue light is increased36%in the operating life test, it is increased17%in non-operating life test, and it is only increased7%in the constant humidity and temperature conditions. In addition, the color purity and radiation power appear similar declines, its amplitude are gradually reduced. But color temperature and forward working voltage is increased, and their increasing amplitude in operating life test is the highest among three states and conditions and it is minimum in the constant humidity and temperature conditions. This results show that rapid thermal cycle on LED reliability is remarkable, but the test in the constant humidity and temperature condition effects a little about LED reliability, so it must pay attention to heat dissipation for LED. |
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