From Longman Dictionary of Contemporary Englishcircuit boardˈcircuit board noun [countable] 
TEEa board in a piece of electrical equipment that uses thin lines of metal to conduct (=carry) electricity between different points
TEEa board in a piece of electrical equipment that uses thin lines of metal to conduct (=carry) electricity between different pointsExamples from the Corpus
circuit board• Just another chip on the dense circuit board of Santa Clara County.• They regarded its motherboard, the main circuit board, as a beautiful work of art.• Their many satisfied customers include gas and electricity companies, motor manufacturers, circuit board makers and steam railway maintenance organisations.• The brain is not a printed circuit board.• The disadvantages are that the batteries are inconvenient to change and severe battery leakage can be disastrous to the circuit board. 