1 Reply Latest reply on Nov 1, 2017 11:17 PM by Mark Keown

    Big temperature difference between component and PCB

    聖堯 陳

      Hi all,

      Recently, I found a problem that the temperature difference between IC and PCB is too big, which almost 16'C.

      The component size is 2.9mmx1.5mmx1mm with heat generation 0.5W.

      1. The thermal conductivity of this component is 5W/mk.

      2. The thermal conductivity of in-plane of this PCB is 40W/mk and that of transverse is 1.5W/mk

      But I did not see such big temperature in other CFD software like Autodesk CFD or even in a real test.

      I do not know why case temperature can not conduct to PCB.

       

      My settings:

      1. The location mesh of both of PCB and this IC has been refined. (solid mesh and solid/fluid mesh adjust to LV6)

      2. Radiation has been calculated.

      3. External

      4. Natural convection

       

       

      Is there any setting I can use to deal this problem?

       

      Thanks.

       

       

       

        • Re: Big temperature difference between component and PCB
          Mark Keown

          Best thing is to post the file and give the component number or specification of the component and the PCB specification (thickness of copper and fr4 for each layer).

          Normally you would use the 'two-resister' method to represent an IC.  With this method you can get both the case temperature and junction temperature.

          If you are comparing CFD to a bench test attention must be taken to fully represent the setup on the bench.  In a room the air is allays moving from people, hvac system, solar heating from windows, the bench blocking air flow, the wall blocking air flow, temperature stratification other equipment - where in CFD at the domain limits the air will have an absolute 0.000 velocity and constant temperature (at the start).  Typically the EE will give you the worst case calculated power.  It is best to get the measured power from the bench test, log the exact ambient temperature, capture the physical reality....  For natural convection your domain needs to be large.