In today’s power hungry applications the bare board is taking a more active role in dissipating heat from components directly through the PCB to a heat sink.
Dissipating heat through a PCB can be done with thermal vias or MCPCB ( Metal core PCB) but sometimes thermal vias are not sufficient and MCPCB is not an option due to layer count. That is where press fit Copper Coin can be the answer.
The concept is based on getting a copper coin press fit into a premade cutout in the board right under an area that is identified as a hot spot – MOSFET pad for example.
The copper coin can be pressed all the way up to layer 1 and act as the assembly pad and provide the ultimate heat transfer channel for a hot component. In other cases if the pad size is too small and there are routing considerations under a hot pad, the copper coin can be pressed fit only up to a designated layer and not through the whole PCB.
Stack up configurations
The copper coin is press fit into the PCB and can be incorporated in different forms and configurations as shown in figure 1.
The configuration chosen by the designer is reflecting the trade off between routing, power plane requirement and proximity of the copper coin to the component that needs to be cooled.
Image 1 shows the implementation of Option A above, providing solid copper path from L1 to L6
6 layer PCB (Rogers 4003 L1-L2 and FR-4 L3-L6)
Image 2 shows the implementation of option C type stack up with the addition of routing the copper coin with a control depth router. Copper coin is pressed from L6 all the way up towards layer 2 but is not reaching L1.
Type C stack up with Z axis routing
When the copper coin is used to make contact to a component pad it will be electroplated and will form a flat assembly surface as if it is a pad etched on a copper foil.
Image 3 shows the flatness of the surface after plating the border between copper coin and copper foil.