Investigation On Reliability Of High Current Density Micro Solder Joints Under Extreme Temperature

Deep space exploration has become an important activity in the field of aerospace in various countries around the world,but the temperature environment suffered by electronic equipment is becoming more and more complex.Therefore,higher requirements are placed on the reliability of solder joints.But most countries use temperature control measures to ensure the solder joints work within the normal temperature range,which will inevitably increase the weight of the detector,which will greatly increase the cost.On the other hand,with the miniaturization of the solder joints,the current density experienced by the solder joints will increase.However the increasing current density will accelcrate the electromigration effect of the solder joint.Therefore,exploring the microstructure evolution and mechanical property changes of the interface after the solder joints are stored under cryogenic temperature conditions,and studying the microstructure changes of the solder joints under the conditions of cryogenic temperature and cryogenic temperature and large temperature change impact,are important scientific significance to the establishment of the theory of field solder joint reliabilityIn this paper,the storage test and shear mechanical test of Sn37Pb/Cu and SAC305/Cu solder joints under cryogenic temperature conditions were carried out.The test results show that the intermetallic compounds of the two solder joints exhibit columnar growth at-196 ? and-100 ?,which is different from the planar growth at high temperature of 150 ?.But the growth law of IMC is parabolic,and the IMC composition is always Cu₆Sn₅.And the IMC growth rate is faster at-196 ?,and it can be known from ANSYS simulation that this is due to the stress gradient at-196 ? being greater than the stress gradient at-100 ?.The shear strength of the two solder joints at-196 ? and-100 ? decreased with storage time,which was mainly due to the increase in IMC thickness.Secondly,electromigration tests were conducted on SAC305 solder joints in a self-made simple ball grid array?BGA?package structure with current density of 1.5×104 A/cm2 placed under cryogenic temperature conditions.The test results show that,unlike the electromigration effect on solder joints at room temperature,the electromigration effect does not occur on solder joints at-196 ?.But regardless of the change in current direction,the microstructure of the anode and cathode interface exhibits columnar growth.The COMSOL simulation shows that this is due to the stress gradient at-196 ? being two orders of magnitude greater than that at room temperature.Simultaneously,it is predicted by simulation that the solder joint at-196 to-30 ? at this current density will not trigger the electromigration effect.Regarding the change of resistance of the solder joint,the resistance of the solder joint first decreases and then slowly increases at-196 ?,and shows an overall increasing at room temperature.Finally,electromigration tests were conducted on SAC305 solder joints in a selfmade simple ball grid array?BGA?package structure with current density of 1.5×104 A/cm2 placed under cryogenic temperature and large temperature change conditions.The test results show that with the increase of the number of thermal shocks,the IMC at the anode of the solder joint grows planar in the early stage,but the composition gradually evolves into a double-layer IMC of Cu₆Sn₅ and Cu₃Sn.However the IMC at the cathode gradually becomes thinner.For the solder joints with the same direction of stress gradient and the electronic wind,the thickness of the IMC at the anode continues to increase rapidly,and the cathode is about to be fused.But for the solder joint with the opposite direction of stress gradient and the electronic wind,the thickness of the IMC at the anode decreases,while the thickness of the IMC at the cathode increases rapidly.It can be seen from the COMSOL simulation that this is due to the later stress gradient driving force being greater than the electronic wind driving force.For cryogenic temperature and large temperature changes,the failure mode of solder joints is mainly caused by cracks that penetrate through the IMC.As for the resistance changes of the solder joint,the overall trend is rising.