4 Replies Latest reply on May 10, 2011 8:39 AM by Alec Chalmers

    CircuitWorks and SolidWorks PCB do vias dissipate heat to ground plane

    Jake Ridden
      Hi. I was looking at the tutorial for Flow Simulation's 'First Steps - Conjugate Heat Transfer.' This is a great tutorial.
      In this tutorial you analyze cooling over a pcb using a fan. The pcb contains several ICs (chips) that generate a few Watts of
      power. One of the ICs has a heat sink on top of it, which will display some of the heat dissipation once you run the flow
      simulation.
      In this tutorial we only define the pcb as FR4. The tutorial doesn't take into account the heat dissipation through the ground
      plane (copper) of the pcb. Obviously this is just a tutorial so I don't expect this analysis and that's why I'm asking about
      this concern..to see if anyone else simulated this issue.
      I thought more about this and took a pcb I had and converted it to CircuitWorks and then to SolidWorks. This turned out great
      actually..the  pcb looks just like the one I built. The problem I had with the  CircuitWorks/SolidWorks assembly (pcb) I converted
      and created was that my design was 2 layers and when  CircuitWorks converts the pcb file it only converts the pcb to ONE material
      block (a rectangular prism).
      I think it should have converted to 3 rectangular material blocks (or 3 rectangular prisms). This would make sense because I'll
      need to define each layer of copper and each layer of FR4 that is between the copper. 3 material blocks is from: 2 layers of
      copper + 1 layer of FR4 (the material between the copper).
      I want to know if anyone has tried to model heat transfer of an IC on a pcb (like the tutorial..the heat sink on top of the IC
      isn't necessary), but in addition has made the IC connect to the pcb copper (bottom layer) through the vias from the circuit
      board. CircuitWorks is good for this because when you create the assembly for SolidWorks the vias are already imported.
      Is the following approach correct when trying to show how much heat is dissipated through the pcb using vias from the IC to the
      ground?   ..I attached my circuitBoard assembly file for view.
      I took the circuit works file and offset all components on the bottom side of the pcb. This let me add in a copper ground plane
      (shown in brown). I also offset the main IC (shown in checkered board color and defined as a heat source @ 5W). This allowed me
      to put a copper pad below the IC to resemble a ground pad (also shown in brown). I'm hoping that this will make a connection to
      the plated through hole vias, which will connect to the copper ground on the bottom layer.
      In flow simulation I defined all material as default 'Tutorial Component Package' and then I defined 3 other solid materials: 1
      for the FR4, and 1 for each copper (the copper IC pad and the copper ground plane).
      What I'm hoping is that the IC will radiate heat through the package then heats the copper pad below, this will heat the PTH
      (plated vias) then this will heat the copper ground plane below.
      My problem is that my vias are PTH ( which I think is plated through hole ) , but I need to define the pcb material as FR4
      ..will this change the plated via material? I don't even know what the plated material is? Do you ? I'm just not sure if my
      setup / approach is correct..will this even work ?  I'm also curious as to the mesh settings I'd need to set because the  vias are
      very tiny.
      After simulation I looked at the cut plot..it seems like the FR4 pcb as a whole is heating up and the heat isn't being
      dissipated through the vias. Can someone comment on this?
      Long post, but I wanted to be thorough. 
        • Re: CircuitWorks and SolidWorks PCB do vias dissipate heat to ground plane
          Mark Larson

          First, a couple of tips:

           

          1) for anyone to open your assembly, they will need the parts that comprise the assembly, so do a pack and go to a zip file icluding all parts of the assembly

           

          2) when posting a message that long, make sure it is formatted so it is easier on the eyes to read

           

          A PCB is not a part, it is a composite, so maybe it needs to be constructed as an assembly:

          so for a two layer board you would need a part representing the copper, and another representing the fiberglass core (the insulator)

           

          see attached part, notice that the vias are not solid copper, but rather cylinders, although they could be solid, if that was the way the board will be constructed

            • Re: CircuitWorks and SolidWorks PCB do vias dissipate heat to ground plane
              Jake Ridden

              Hi Mark.

               

              1. Sorry, I didn't understand that all the part files were necessary.

               

              2. I think the post wasn't indented and spaced properly because I pasted it from a .doc file I typed up. Sorry again.

               

              I hope this time I attached all the files correctly.

               

              As far as your attachment: PCBassy:

               

              I like how you made your vias for your 'copper' part. Is there an easy way to create all the vias? I think you must have started from the 'PCB' part and then used some sort of extrusion. Then you saved the part as 'Copper' . Is that right?

               

              I think from looking at your assembly and parts that I have the correct idea. I'm still trying to verify that the flow simulation yields results that are expected.

               

              Based on what you typed I need to properly define the copper..just like you did in your attachment. I guess I was hoping that solid works would make the PTH plated with copper so I would do less work. ha.

               

              Let me know if you have any other pointers. Thanks.

                • Re: CircuitWorks and SolidWorks PCB do vias dissipate heat to ground plane
                  Mark Larson

                  Jake,

                   

                  sadly, no, there is not an easy way to create the vias that I have found.

                  You are correct, My not so quick but dirty method is to start from the pcb part created from Circuitworks.

                  Then I can use the vias and board outline to extrude the shape.

                   

                  With some PCB CAD it may be possible to bring the copper plane shape into SolidWorks thru DXF, and extrude that.

                  I have tried that with PADS without luck, some other CAD may be possible.

                  But really, making the assumption that the entire plane layer is solid rather than like Swiss cheese is perhaps accurate enough.

                   

                  Something that may be a "gotcha" is that most pcb's have a soldermask, so don't forget that once you have worked out the via & copper problem.

                   

                  here is a copper shape I extruded from your files, only took a couple minutes

              • Re: CircuitWorks and SolidWorks PCB do vias dissipate heat to ground plane
                Alec Chalmers

                I usually model a PCB thermally as FR4 with orthotropic thermal properties that depend on the number of copper layers and the thickness of those layers (1 oz, 2 oz). There are calculators available that estimate the thermal conductivity based on these inputs. The thermal conductivity will differ in the inplane directions as opposed to the through plane direction (orthotropic). The only real method to dial this in is to run testing with thermo-couples to be able to check your analysis. Here is a link to a discussion of this problem

                 

                http://www.coolingzone.com/library.php?read=550