Most of the time you can find the problem by yourself from some simple case.
For your case, the simple way to find out the problem is just apply a uniform heat source (flux) to the system and look at the steady-state response, which you should expect correct solution. Also you should understand the physics of the problem before running any simulation. For instance, what does following sentence mean?
板件周围的热对流系数我设定了8W
you put wrong unit for convective coefficient...