| With the rapid development of electronic industry,epoxy resin,as an important electronic packaging adhesive,will continue to improve in bonding strength,insulation and mechanical properties.However,due to the high cross-linking density and brittleness of the cured product,the irreversible degradation of mechanical properties in a long-term thermal oxygen environment and the difficulty of stress release during the thermal cycling limit its application in the field of semiconductor packaging.In order to overcome the above shortcomings,the flexible epoxy resin(epoxy resin active diluent,fatty acid epoxy resin)and flexible curing agent are used to modify the rigid bisphenol F epoxy resin.The intrinsic properties,thermal oxygen aging resistance and stress behavior of the blend system are discussed.In addition,through the evaluation of toughened epoxy resin,combined with material strength and stress test,a new research method is explored to quantify the failure of electronic packaging adhesive and evaluate the relationship between adhesive layer stress and strength.Firstly,the structure,curing behavior,Tg value and CTE value of epoxy resin system before and after toughening are characterized with FTIR,DSC,DMA,TMA and TGA.The results show that the bisphenol F epoxy has the best thermal properties(Tg value is 76?,Td5%is 325?);Due to the absence of benzene ring structure in the molecular chain segment of epoxy resin diluent system,the thermal performance is the worst(Tg value is 13?,Td5%is 301?);The Tg value of epoxy resin toughened system with diluent and fatty acid decreases from 76? to 37? and 44? respectively,and the CTE value increases from 240 ppm/? to 248 ppm/? and 269 ppm/? respectively;In addition,the analysis of mechanical properties shows that the peel strength and compressive shear strength of bisphenol F epoxy resin is 11.2 N/cm and 32.5 MPa respectively,while the peel strength and compressive shear strength increases by 10.1%and 8.6%respectively after toughening with fatty acid epoxy resin,the peel strength of the diluent toughened system increases by 20.2%,but the compressive shear strength decreases by 32.6%.The results show that the blending modification of rigid structure with flexible epoxy resin system can increase the bonding performance and effectively reduce the modulus,which is of great significance for the follow-up study on thermal stress accumulation.Secondly,five groups of epoxy resin systems are subjected to thermal oxygen aging test.The test results show that the blend system of fatty acid epoxy resin and bisphenol F epoxy resin has the best thermal oxygen resistance stability due to its dimeric acid structure and high benzene ring density,and it shows a good comprehensive performance,the mass loss rate after a 125?/100h aging and a 150?/100h aging is 1.8%and 2.7%respectively,the tan ? curve shows an obvious post chemical crosslinking reaction.After aging at 125? for 100h and at 150? for 100h,the Tg value increases from 44? to 60?and to 58? respectively,and the compressive shear strength increases from 35.3 MPa to 50.2 MPa and to 53.8 MPa respectively;The thermal oxygen resistance of bisphenol F epoxy resin is slightly poor.The mass loss rate after aging at 125? for 100h is 0.8%,and the mass loss rate after aging at 150? for 100h is 2%.After aging at 125? for 100h,the Tg value increases from 76? to 96?,but the Tg value after aging at 150? for 100h remains the same level as that of the unaged sample;Due to the absence of benzene ring structure,the epoxy resin diluent system shows the worst thermal oxygen resistance stability.The mass loss rates after a 125?/100h aging and a 150?/100h aging is 4%and 6.7%respectively,which are much higher than that of other systems.The Tg value and compressive shear strength decrease significantly.The Tg value after a 150?/100h aging is-6?,and the compressive shear strength reaches a maximum value of 15.2 MPa after aging at 150? for 20h and decreases to 14.3 MPa after aging at 150? for 100h.Finally,the intrinsic strength and residual stress of epoxy resin system under static and dynamic conditions are characterized with compressive shear test and TFSA,so as to verify the effect of stress on the static strength and thermal aging strength.The results show that bisphenol F epoxy resin has the highest heating stress(36.3 MPa-42.7 MPa),cooling stress(17.1 MPa-21.1 MPa)and cyclic stress(40.5 MPa-49.9 MPa)at different heating rates;The thermal stress accumulation of fatty acid epoxy resin is the least,with heating stress(3.7 MPa-4.8 MPa),cooling stress(1.2 MPa-2 MPa)and cyclic stress(3.2 MPa-3.7 MPa);The stress accumulation of the blend system of bisphenol F epoxy resin and fatty acid epoxy resin is between the two,and the heating stress(3.8 MPa-5.1 MPa),cooling stress(3.7 MPa-4.3 MPa)and cyclic stress(3.2 MPa-4.9 MPa)are much less than those of the rigid system.In addition,after toughening with fatty acid epoxy resin,it has a high strength(0.6 MPa-0.3 MPa)at high temperature of 200-250?,and compared with the rigid system,the residual stress significantly reduces.At the heating rate of 10?/min,the heating stress reduces by 37.6 MPa,the cooling stress reduces by 14.9 MPa,the first cycle stress reduces by 42.8 MPa and the fifth cycle stress reduces by 15 MPa;The above properties make the toughened system have the strength at high temperature and effectively reduce the accumulation of thermal stress during high and low temperature cycle,so that it has the widest reliable temperature range:static(R.T.-182?,101?-R.T.)and dynamic(R.T.-126?,81?-R.T.).Finally,the theoretical analysis is verified by the high and low temperature cycle test of actual bonding of three groups of epoxy resin system samples.In conclusion,the blending modification of rigid system with suitable flexible epoxy resin can improve the flexibility,bonding strength and thermal oxygen resistance stability,and significantly reduce the thermal stress accumulation,and make the semiconductor packaging adhesive have a wider application range and service life.The stress failure mode of adhesive under thermal aging condition can be effectively predicted with stress test combined with strength value.This research method is expected to be applied to the analysis of bonding interface failure of heterogeneous materials. |
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