

From the IRF1404Z data sheet:
Calculated continuous current based on maximum allowable junction temperature. Bond wire current limit is 120A. Note that current limitations arising from heating of the device leads may occur with some lead mounting arrangements.
You need to design the PCB so that the heat from the legs can be properly dissipated, or they won’t live up to the rated current.
Also, traces on a PCB are much thinner than those legs. A trace with the same cross-sectional area would be impractically wide.
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