The Study On Fast Thermal Fatigue Reliability Of Electronic Packaging

Thermal fatigue is a critical reliability issue which would bring failure to electroniccomponents. The standard of thermal cycling test has been widely used among electronicindustry or independent institutes to conduct research. The equipment for this test istemperature chamber and which is capable of heating and cooling the objects in itfollowing given temperature profile. And the time for one cycle ranges from15min to2h,which is too time-consuming. In order to fix the shortage of the traditional thermal cyclingtest, a new testing method namely fast thermal fatigue test has been proposed here. And afast thermal fatigue testing machine has been built based this idea. The final operationresult indicates that the machine is capable of heating the sample temperature to200oCwithin10s, and cooling it to desired temperature within10s as well.In the common thermal cycling tests, the primary solder damage mechanism is theinteraction of creep and thermal-mechanical fatigue which is caused by the CTE(coefficient of thermal expansion) mismatch between different layers. However, so farthere is no reported research focused in the metallurgical vibrations of solder joints (suchas grain size of solder, the structure and distribution of IMC) in the process of thermalcycling without the effect of thermal stress. So the idea of this paper is to test the solderwhich is reflowed on pad without components. The customized Sn3.0Ag0.5Cu/Cu solderjoints are tested on the fast thermal fatigue machine. The results indicated that IMCbetween the interface of solder and pad would grow gradually during the test, and thegrow rate is faster under a higher temperature condition. The grow rate is also linearlyrelated to the accumulated heating preservation time. The test result provides newpossibilities to modify the thermal cycling temperature profile.The impact of fast thermal fatigue on the reliability of light emitting diode is alsotested on the machine. The results indicate that the LEDs light output would decay as thetest carried on, and it would decay faster under a higher temperature condition. The peak wavelength of LEDs and forward voltage has increased slightly which can be neglectedcompared to initial value. This means the performance of LED chip has not been affectedby the test. After test, CCT of LEDs as well as the phosphor-related blue emission hasincreased. It can be ascribed to decay of the conversion efficiency of the phosphors.