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.