The thermal resistance at saturation point (no heat sink) on an FR4 PCB is 283 ℃/W (reference value). Total power dissipation can be calculated from thermal resistance using the following formula.
Pd = (Tj(max) - Ta)/Rth
Pd: Total power dissipation; Ta: Ambient temperature; Rth: Thermal resistance
The total power dissipation at an ambient temperature of 60℃ is as follows.
(150 - 60)/283 ≒ 0.32 W
Since FR4 PCBs generally have inferior heat dissipation, the total power dissipation will likely not change much even if board area is increased.
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