"When I add the heat sink to the schematic, and then the layout..." Do you mean add the symbol for the heatsink to the schematic and then do **Update PCB...** to pull the Footprint for the heatsink into the PCB?

Please post some screenshots to illustrate your point.

See attached, this appears to be the smallest heat sink I could find. I added it to the schematic and connected terminal 1 to ground. Then I imported changes to the layout, which as you can see, doesn't allow me to attach the heat sink to the underside of the IC. Also, there is no exposed copper pad for the heat sink to attach to. 

@samtylee, Your schematic is correctly constructed and so your conversion and updates to PCB work as expected but there's a problem with your choice of heatsink. This is the heatsink that you have chosen: [https://lcsc\.com/mobile/product\-detail/Heat\-Sinks\_XSD\-C116600\_C116600\.html](https://lcsc.com/mobile/product-detail/Heat-Sinks_XSD-C116600_C116600.html)<br> <br> [https://datasheet\.lcsc\.com/lcsc/1810010332\_XSD\-C116600\_C116600\.pdf](https://datasheet.lcsc.com/lcsc/1810010332_XSD-C116600_C116600.pdf)<br> <br> This is the datasheet for the LT3652: [https://www.analog.com/media/en/technical-documentation/data-sheets/3652fe.pdf](https://www.analog.com/media/en/technical-documentation/data-sheets/3652fe.pdf)<br> <br> The last paragraph of Layout Considerations on page 21 describes how to heatsink the device. It does not refer to any additional heat sinking other than through the structure of the PCB itself. Any external heat sinking would have to either; 1) attach to a copper area on the opposite side of the PCB from that on which the device is mounted and which would be thermally via'd through to the GND pad of the device footprint or; 2) would have to be bonded into the top of the IC package which, given the device is already optimised for dissipating heat through the exposed pad on the bottom of its package, would probably be of minor benefit. From this you can see that the heatsink that you have chosen is: A) unsuitable for use with the LT3652 (it seems to be for a vertically mounted TO-220 type of package); B) with suitable PCB design practices, not necessary anyway. For information about how to add thermal vias to Footprints and some guidelines for how to successfully create footprints please see: [https://easyeda.com/forum/topic/How-to-place-multiple-vias-in-a-PCB-footprint-a34cf68d58414138898a56de60abd8c1](https://easyeda.com/forum/topic/How-to-place-multiple-vias-in-a-PCB-footprint-a34cf68d58414138898a56de60abd8c1)<br> <br> For more information about finding, editing, creating Footprints using the Footprint Editor and assigning them to Symbols using the Footprint Manager, please see the Tutorial and (2.3) in (2) in: [https://easyeda.com/forum/topic/How-to-ask-for-help-and-get-an-answer-71b17a40d15442349eaecbfae083e46a](https://easyeda.com/forum/topic/How-to-ask-for-help-and-get-an-answer-71b17a40d15442349eaecbfae083e46a)<br> <br> <br> <br>

Thanks @andyfierman What if I just add a normal via to the ground pad of the IC, and then draw a rectangle roughly the same size as the ground pad on the bottom solder mask layer? Then I can add an external heat sink to the exposed copper via a stick on silicon thermal pad? Also it seems that irrespective of if I use the expose copper button, in the 3D view, the rectangle always shows as exposed copper? Or is the concept of adding thermal vias different? I had a quick read of the links you sent, and didn't quite quite understand. Are there any videos to show this?  

"What if I just add a normal via to the ground pad of the IC, and then draw a rectangle roughly the same size as the ground pad on the bottom solder mask layer?" That works but you should probably add more then one thermal via. Maybe you can place 4 small ones: one in each quadrant. If your copper areas are placed as - or converted to - Pads then they will automatically be exposed copper. If they weren't then they would not be Pads. "I had a quick read of the links you sent, and didn't quite quite understand. Are there any videos to show this?" There are no videos about this made by me. Just copy the examples that are given and play with them to see how they're made. Try making you own and putting them into a simple dummy project and then experiment with them compared with the originals. However, here are some questions you probably need to answer: 1. Why do you think you need an extra external heatsink? 2. What calculations have you done that show that you do need one? 3. If you need an external heatsink doesn't that imply that you are overstressing the device and maybe need a high current rated converter chip? <br> <br>