Here are some more EMI filter application examples for reference. The diagram on the left shows a DC motor application that an X2Y has been used in, whose purpose is to eliminate DC motor noise and to cancel the opposing voltage waveforms present on the power leads. On the right is a diagram of the heatsink example, parasitic coupling was introduced. The current propagates between the heatsink and µP device, and the heatsink becomes an antenna. The adoption of X2Y cancels the opposing voltage waveforms.