8 Replies Latest reply on Oct 24, 2016 7:59 AM by Daniela Coblas

    Heat sink with TO-247

    Travis Rowell

      Hello,

      I am having trouble accuratly modeling TO-247 packages in simulation. I was hoping to get some help on how best to set this up. My TO-247 package consists of three components, a copper case, a die(the transistor), and a plastic case. I modeled the die as silicon, the copper case as copper, and the plastic case as epoxy resin. For the insulator I used the manufactuer spec sheet to build a material (the spec sheet wasnt very good I had to leave a lot blank). I am still not getting accurate results. My prototype has far different values then simulation. I took a cross section of the temperature distribution and I found that the temp of my junction was the same temperature as my heat sink. I know this is not possible. Can anyone who has done this type of work before give me an accurate method for modeling this situtaion? I would much rather use the junction to case resistance, and insulator to heatsink resistance provided by the manufactuer then rely on material selection in simulation. I have upladed my heat sink model for extra clarification.

      Thank you,

      Travis

        • Re: Heat sink with TO-247
          Jared Conway

          To do what you want for setup, get the electronics cooling module. He 2r input method does exactly what you want. Or convert the values and make your own 2r.

           

          To understands why you sim may be different, you will have to elaborate on your test setup and conditions. The assumptions you think your analysis makes and some numbers from your test. Blindly looking at simulations is really difficult.

            • Re: Heat sink with TO-247
              Travis Rowell

              I do have the electronic cooling module. I tried to use it for this project. However I get an error message when trying to apply it to my plastic case. I get the message cannot find face between case and junction or something to that effect. I was told that the two parts I make the 2R must be the same height, width, and thickness. These TO-247 packages do not follow that model. I may be being a bit picky here I dont know, but I didnt want to change the shape of my package to fit the solidworks model of a 2R. As to my real world setup. It is exactly the same as the setup you see in the picture below. I have a fan in front of the heat sink, each TO-247 package should have 17.833 watts running across it. I use a thermal couple to measure the temp of my heat sink. The thermal couple measures 74C which is very close to what solidworks told me it would be. However my junction temp should be way hotter. Instead solidworks is telling me my junction temps match my heat sink. This is not correct. I applied the 17.883 watts to the small sliver of chip on my model. How does solidworks calculate the heat from that? Would I be better off putting a more realistic temp of 100 degrees on that chip instead of putting a wattage?

              snap shot sim.png

                • Re: Heat sink with TO-247
                  Jared Conway

                  "my package to fit the solidworks model of a 2R." > the method used by solidworks is the standard method for 2r

                   

                  "I have a fan in front of the heat sink, each TO-247 package should have 17.833 watts running across it." > what you've shown is 17.833 shared among all the units. not per. (default in flow)

                   

                  "It is exactly the same as the setup you see in the picture below." > please describe the details of both the physical test setup and analysis setup. there may be a small detail in here that is causing a difference. for excample you haven't said if you are using internal or external analysis, what your fan is, what the environmental conditions are, is there radiation, do you have gravity enabled...etc. if you have a heat problem already and are using17.xxx for all the components, it will probably be much hotter now which indicates more likely a setup problem to start with. IE you weren't just getting lucky that the heat sink temp was 100 and the rest was off.

              • Re: Heat sink with TO-247
                Mark Keown

                layer resistance.jpgYou will need the manufactures Rj-c (resistance junction to case) and Rj-b (resistance junction to board) for the device.  Adjust the thermal conductivity of the layers as done in the attached picture.  You can use two or three layers.  With two layers apply the power to the interface surface and with three layers apply power to the center solid.  Good that you have a model to check your simulation.

                OR adjust the thermal conductivity until it matches your bench test results.

                • Re: Heat sink with TO-247
                  Mark Keown

                  For the issue of applying power to the interface - for some reason you have to use a surface filter if the feature is not an assembly.

                  • Re: Heat sink with TO-247
                    Daniela Coblas

                    Hello, I have to do same simulation. Did you managed to get good results?

                    Can you explain to me better how you built your 3D model, how you defined your materials? It is very important for me