Solid state relay is hottest during heating up. Over 90 ℃
Additional action, add plastic plate under heat sink seems not effective.
As shown above data, both oven has plastic and, do not has plastic reach to 80℃ during heat up.
Please check Spec of solid state relay, for temperature we cannot exceed at point1
We need 2 kinds of action same time.
One is to insulate heat sink from oven body to prevent heat transfer from oven body to heat sink
The other is to increase heat radiation from heat sink. --> need more air flow…