The advantages become apparent when the circuit board 1 is a control board that controls a power semiconductor element. The reason why the advantages become apparent when the circuit board 1 is the control board that controls a power semiconductor element is as follows: the control board that controls a power semiconductor element is often a product from the small volume production of many models. Thus, when the circuit board 1 is the control board that controls a power semiconductor element, positions at which electronic components are mounted often differ depending on the model of the circuit board 1. Consequently, the time required for determining the presence or absence of a faulty component in the circuit board 1 tends to be prolonged.

The first electronic component 101 is preferably a passive component. When the first electronic component 101 is a passive component, the temperature indicating resin 12 should be applied to only the passive component. This can shorten the time required to perform the operation of applying the temperature indicating resin 12, and reduce the amount of the temperature indicating resin 12 to be used. This also contributes to reduction of the cost of the circuit board 1.

FIGS. 2 to 4 are enlarged cross-sectional views each schematically illustrating a part of the circuit board according to Embodiment 1. FIG. 2, FIG. 3, and FIG. 4 illustrate the first example, the second example, and the third example of the temperature indicating resin, respectively.