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Simulation results higher than expected

Question asked by Stuart Gunn on Mar 19, 2014
Latest reply on Sep 2, 2014 by Murat Topac

Let’s start off with the basics, SW Premium 2014, Flow w/ electronic cooling package added.

 

The issue I have is that a simulated assembly of an electronic enclosure is not giving me the expected results, comparing with calculated temperature.

 

The assembly in question has numerous components from 2-resistor components, multiple PCB’s, volume heat sources and a bunch of different custom materials like thermal gap pads, aluminum for heat sinks, QFN's, FC PBGA and so on. The data for the custom materials and components are from the manufacturers data sheets. Radiation is on, heat transferred through solids, gravity on, ambient is at 40 (and materials are at 40) and modeled as internal with a sudo box that is environment pressue on all but the bottom (I have found this better in the past than loads of small 'filler' parts).

 

There are local mesh’s for the small components, contact resistance, boundary for the enclosure and the simulation itself runs.

 

It is modeled off a prototype unit that my company is trying to develop and the issues I have is that the temperatures I get from the simulation are mostly way higher than the model.

 

For example, I have a SSOP device that have a volume power of 0.57W that is matted to the PCB (setup as a 6 layer). The device should reach a temperature of around 102C in the 40C ambient, but the simulation is showing it to be 180C+.

 

The other reason I know it the simulation is wrong is that the unit was developed by another team in my company and they used a different simulation package than SW and got different results, which line up more with the calculated temperatures.

 

I have built the assembly twice, re-made the thermal project 3 times and still get the same answer.


Has anyone else had a problem where their simulation gives higher than expected temperature results? If so, what was the cause and solution?

 

I have attached a 3D PDF of the model, made the CAN and Heat Sink transparent, removed one side and as you can tell, it is very basic in design.

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