Numerical Simulation And Integrated Method Of High Heat Flux Heat Sink Structure

In recent years,due to the GaN HEMT device will occur the self-heating effect and exist the uneven temperature of the hotspots in the work,the demand for heat dissipation is more and more urgent.Select high thermal conductivity material as a heat spreader to fast and efficient transfer heat to the heat sink structure.Choose the micro channel that the mainly way is forced liquid cooling to rapid exchange heat.Choose the appropriate ensemble approach to make the lowest contact resistance and good for heat dissipation.This paper combination of microchannel heat sink and diamond heat spreader diffuser,using the method of eutectic bonding integrated hotspots with high heat flux and high thermal conductivity of diamond and Si based microchannel,expected to more efficiently conduct heat and reduce the junction temperature of high heat flux chip.First,carrier out the numerical simulation to thermal structure,to determine the designed structure has good heat dissipation effect.Finally,experimental test on cooling effect of diamond,microchannel heat diffuser and eutectic bonding integration mode.The research work and results are as follows:(1)The ANSYS Icepak 15.0 software was used to simulate the heat dissipation structure,and the influence of the change of the structure parameters on the cooling effect was studied.The results showed that: the number of microchannel's channel has great influence on the hotspot temperature,with the number of channel increased,the rheat dissipation effect of the microchannel become better,however,with the increase in the number of channel,heat capacity will tend to saturation.The flow rate of the cooling fluid in the microchannel also has a great influence on the heat dissipation,the faster the cooling fluid flows,the lower the hot spot temperature.In addition,the heat dissipation effect of absolute ethanol is better than that of deionized water.The diamond heat spreader can significantly reduce the surface temperature of the hot spot and make the hotspot temperature distribution is more uniform,but also reduce the temperature difference of heat transfer on the path,let the heat more evenly distributed in the microchannel,so that the microchannel can play a better role.Diamond heat spreader thickness increases,the heat dissipation capability better.Moreover,with the increase of the load power,the difference of the heat dissipation capacity of the different thickness of the heat spreader is larger.Because of the high thermal conductivity,the AuSn material used in eutectic bonding has good thermal conductivity,which is favorable to the reduction of hotspot temperature and make the hotspot temperature distribution more uniform,making heat quickly transmitted to the diamond heat spreader and the microchannel.(2)The optimal process parameters of eutectic bonding mode are studied,which makes the bonding layer morphology optimal.The more uniform and compact the morphology of the bonding layer is,the more favorable for the heat dissipation of the hot spots,repeated experiments showed that the bonding temperature is increased,the solder can be fully fused,and the bonding layer is more uniform and dense.In addition,the appropriate increase of pressure can make the bonding layer more compact and uniform.But for most of the integrated devices,it is desirable to reduce the bonding temperature in order to invalid of the devices.It is found that the morphology of AuSn layer is excellent when the bonding temperature is 280 ? at the pressure of 1.05 MPa.At the same time,it can meet the requirements of bond strength and meet the requirements of heat dissipation,so it is selected as the best process parameters.(3)The test results verify the heat dissipation effect of diamond heat spreader,microchannel and eutectic bonding.The control samples were prepared,and the hot spot temperature was measured by the infrared thermal imager to verify their cooling effect.The test results show that the diamond heat spreader can reduce the hotspot temperature,and make the temperature distribution more uniform,when the power is 4.9 W,the highest temperature of hotspot can control to under 49.5 ?,lower than the hotspot temperature on the Si substrate about 8.5 ?,the temperature difference between the hotspots is not more than 1.2 ?.Regardless of whether the hotspots are on the Si or on the diamond,the heat dissipation effect of the microchannel is significant.When the power is 6.4 W,the microchannel can reduce the hotspot temperature on the Si substrate and on the diamond substrate about 9 ? and 5.8 ?,respectively.The flow rate change of the cooling liquid in the channel also has a great influence on the hotspot temperature,hotspot temperature will gradually reduce with the increase of the cooling liquid flow rate,until stabilized,100 mL/h flow can reduce the hotspots temperature of 28.3 ?.By adjusting the coolant flow rate,temperature would stable at 37 ?.In addition,due to the thermal conductivity of anhydrous ethanol is much higher than the deionized water,the heat dissipation effect is very prominent.The bonding layer of AuSn has a positive effect on the reduction of hotspot temperature,when the power is 6.4 W,the temperature of the sample integrated by eutectic bonding is lower than the sample integrated by silica gel,which is lower than 5.4 ?.It shows that it is necessary for us to study the eutectic integration mode for the thermal management of GaN HEMT.