Thermal Interface Materials (TIMs) have been used in the electronic industry for decades from CPUs to phone batteries. However, as electric vehicles (EVs) become increasingly prominent, the volume of TIMs required for adequate battery thermal management has increased dramatically. With this new volume, new problems are being encountered by both thermal adhesive manufacturers and adhesive dispensing groups.
In particular, particle sedimentation has proven to be a challenge for these groups. In order to increase the adhesive’s thermal conductivity, conductive fillers are added to the mixture. However, given enough time, these conductive particles will succumb to settling as gravity draws them out of suspension towards the bottom of their storage tank, causing drastically uneven thermal properties. This problem is magnified given the volume requirement of EVs, as well as the safety and liability risk of having poor thermal management.
The Modified Transient Plane Source (MTPS) technique is able to rapidly monitor particle settling for quality control applications. As conductive fillers settle towards the bottom of the storage tank, the thermal conductivity will increase from their presence. Consequently, the thermal conductivity at the top of the adhesive tank will diminish. The MTPS can be retrofitted for in-line process monitoring, using thermal conductivity and effusivity measurements. Data for this application can be seen below:
As can be seen, the MTPS sensor at the bottom of the adhesive sample shows a significantly higher thermal conductivity over time, increasing as the weight percentage of filler increases. This shows the effects that particle settling has on thermal adhesives, and how the MTPS sensor is able to monitor this for when the adhesive is out of spec.