An interposer for being connected to piezoelectric elements of a two-dimensional acoustic module and to an integrated circuit chip, the interposer comprising: a circuit board stack in which a plurality of circuit boards are stacked, the plurality of circuit boards being arranged next to one another to form a first side portion (1111 a) and a second side portion of the circuit board stack, characterized in that the circuit boards comprise first conductive lines , each of the first conductive lines having a first end exposed through the first side portion of the circuit board stack and a second end exposed through the second side portion of the circuit board stack, the second side portion being opposite the first side portion ; and an outer board arranged on at least one of outer side surfaces of the circuit board stack, to form joined planes with a plane of the first side portion and a plane of the second side portion , respectively, the outer side surfaces of the circuit board stack extending between the first side portion and the second side portion , wherein the outer board comprises second conductive lines , each of the second conductive lines having: a first end exposed through a first side of the outer board that is different from the plane joined with the plane of the first side portion of the circuit board stack, and a second end exposed through a second side of the outer board that is located on a same side as the plane joined with the second side portion of the circuit board stack. a circuit board stack in which a plurality of circuit boards are stacked, the plurality of circuit boards being arranged next to one another to form a first side portion (1111 a) and a second side portion of the circuit board stack, characterized in that the circuit boards comprise first conductive lines , each of the first conductive lines having a first end exposed through the first side portion of the circuit board stack and a second end exposed through the second side portion of the circuit board stack, the second side portion being opposite the first side portion ; and an outer board arranged on at least one of outer side surfaces of the circuit board stack, to form joined planes with a plane of the first side portion and a plane of the second side portion , respectively, the outer side surfaces of the circuit board stack extending between the first side portion and the second side portion , wherein the outer board comprises second conductive lines , each of the second conductive lines having: a first end exposed through a first side of the outer board that is different from the plane joined with the plane of the first side portion of the circuit board stack, and a second end exposed through a second side of the outer board that is located on a same side as the plane joined with the second side portion of the circuit board stack. a first end exposed through a first side of the outer board that is different from the plane joined with the plane of the first side portion of the circuit board stack, and a second end exposed through a second side of the outer board that is located on a same side as the plane joined with the second side portion of the circuit board stack. <EOS>