Thermal Resistance Model And Conductivity Enhancement Of Thermal Interface Materials

Thermal interface materials(TIMs)are commonly used in electronics to reduce the contact resistance arising from the incomplete contact between two solid surfaces.After inserting TIM between the solid surfaces,a solid-TIM-solid joint forms at the interface.Thermal resistance at the joint(Rj)has two components:the bulk resistance of TIM(Rbulk),the ratio of its bond line thickness(BLT)to thermal conductivity(kTIM),and contact resistance(Rc)at the TIM-solid interface arising from the incomplete wetting of the interface.Therefore,Rj is determined by three factors:(1)kTIM;(2)BLT;and(3)Rc.Currently,there are several reseach issues on the three factors.To increase kTIM,various new highly thermally conductive particles have been disvovered and introduced into the TIM fabrications.However,the conventional fabricating methods hardly take advantage of the excellent thermal properties of those particles.In addition,the values of Rbulk and Rc need to be estimated accurately in industry.But,good predictive models or measuring methods are still lacking.Reseaches on those issues have been conducted as follows:Since TIM belongs to composite materials,several composite thermal conductive models were investigated in detail.Those models domenstrate that the fillers microstructure(orientation and distribution)and interfacial thennal conductance(Gint)at filler/matrix interface are the key factores that influence the thermal properties of TIM.The following work focus on microstructure design and interfacial thermal transport manipulation to enhance kTIM.The microstructure design were achieved by using magnetically responsive particles as reinforcing elements and the specific magnetic field to organize the elements into the predefined structure.Magnetically responsive particles were produced by coating the hexagonal boron nitride(h-BN)particles with superparamagnetic iron oxide(Fe3O4)nanoparticles.Then the particles orientation or positions can be remotally controlled under low external magnetic fields in low-viscosity suspending fluids.Such fluids can be then consolidated to fix the magnetically imposed microstructure.The materials with controlled microstructure exhibit enhanced thermal conductive properties.We experimentally demonstrated an effective strategy to achieve interfacial thermal transport manipulation at particle/polymer interface.The proposed strategy relies on using a strongly bonding self-assembled monolayer(SAM)to covalently connect the soft polymer and particles.This strategy was applied on the copper-epoxy resin interface,the adopted SAM was 11-amino-1-undecanethiol hydrochloride,which has the thiol on one end to connect copper and the amino to connect epoxy on the other end.Gint for the SAM modified interface exibit more than 11-fold increase.A non-contact length measurment system was built to measure BLT.The resolution is about ±3.5?m.An analytical model was built to predict Rc at TIM-solid interface.To verify the modcl,we built a thermal interface testing system,coupled with the BLT measuring system.Rc at the TIM-aluminium interface was measured for comparison with the model results.The comparison shows that the model results matches to experimental data within 14.3%.