Characterization Of Interfacial Thermal Resistance And High-Temperature Degradation Mechanism Based On Submicron Silver Adhesion

The miniaturization of electronic devices and the development of high-power density integration have posed new challenges for advanced packaging thermal management technologies.To increase the lifetime and reliability of electronic equipment,the heat generated by electronic components is usually directed to the heat sink through a high thermal conductivity thermal interface material.As a new type of thermal interface material,the thermal conductivity of submicron silver glue is much higher than that of ordinary thermal interface materials.However,the increase in thermal conductivity will decrease the material’s application performance,reduce the service life and pose a risk to the reliability of equipment operation.There needs to be a non-destructive test method for characterizing the thermal resistance of interfaces of thermal interface materials(TIM).The mechanism of degrading the interfacial thermal resistance of the Submicron silver adhesive interface in service is unknown.A mathematical model to accurately predict the degradation of the interfacial thermal resistance needs to be improved.Based on the above issues and existing research,the following research work has been carried out in this dissertation.First,we have designed and built an experimental system based on the principle of onedimensional thermal conductivity.A new interfacial thermal resistance test method was developed using a combination of front-side and back-side testing and various algorithms to strip the contact thermal resistance of the upper and lower interfaces between the sample and the device.The method is non-destructive and can be repeated for samples with a testing error of approximately 2.4%,enabling high-accuracy testing of the interfacial thermal resistance.The submicron silver adhesive bonding interface samples were made experimentally to study the submicron silver bonding interface’s degradation mechanism and degradation law.High-temperature degradation experiments were designed at 150℃,200℃,and 230℃.A newly developed front and back test method was used to test the change in interfacial thermal resistance during high-temperature degradation.The experimental results show that the interfacial thermal resistance varies with aging time in a bathtub curve and is divided into three stages:secondary curing stage,fluctuating stage,and degradation failure stage.X-ray scanning techniques,scanning electron microscopy,and Fourier transform infrared spectroscopy analysis characterized the changes in the microscopic morphology and degradation mechanism of the submicron silver glue interface.We found that the interfacial porosity increased by only 0.5%during the secondary curing phase and that the contact gap width at the heterogeneous interface increased by 200-300 nm.The decrease in interfacial thermal resistance is due to incomplete curing of the Submicron silver adhesive,"secondary solidification," and hygroscopic expansion phenomenon occurs,the bulk thermal resistance decreases.At the same time,the contact gap changes are not noticeable.The contact thermal resistance is almost unchanged.The difference in bulk thermal resistance dominates at this stage.The porosity of the interface layer in the fluctuating phase is close to 10%,and the maximum gap width of the heterogeneous interface is close to 7 μm.The fluctuation of the interfacial thermal resistance is due to the reduction of the thickness of the interface layer by the contraction of the interface and the increase of the contact thermal resistance of the heterogeneous interface by the widening of the contact gap,which together leads to the fluctuation of the interfacial thermal resistance.The increase in interfacial thermal resistance is due to the interface’s aging and the interface’s cracking,which increases the thickness of the interfacial layer and the volume of the pores,increasing the bulk thermal resistance.The contact gap becomes more significant,resulting in fewer micro-contact points,increasing the heterogeneous interface’s contact thermal resistance.In this combined effect,the interfacial thermal resistance increases sharply.Finally,an interfacial thermal resistance degradation model was developed by introducing a porosity parameter based on the classical heat transfer model of Maxwell-Eucken and Hasselman-Johnson.Based on the Cooper’s model,the original heat flow tube model is simplified,and a micro-contact point thermal resistance degradation model is established using a series-parallel connection.A heterogeneous interface contact thermal resistance degradation model is based on creatively introducing the coupling of gas tube thermal resistance and microcontact point thermal resistance.The result is an interfacial thermal resistance degradation model that incorporates both the bulk thermal resistance and the contact thermal resistance of the heterogeneous interface.