Bonding apparatus

A bonding apparatus comprising a stage that supports a subject device and is grounded, a joining machine unit that joins a wire to the subject device, and a measurement unit that measures a connection state between the subject device and the wire;

• wherein the measurement unit comprises:
• a variable equivalent capacitance circuit that is a variable equivalent circuit which compensates for a capacitance component of the joining machine unit in order to measure a connection state between the wire and a subject device that has no electric conduction with the stage, said variable equivalent capacitance circuit selecting and setting a variable capacitance value equivalent to the capacitance component of the joining machine unit before bonding, said capacitance component of the joining machine unit being the capacitance between the wire and the stage;
• an alternating-current signal source that supplies an alternating-current signal to the equivalent capacitance circuit and the joining machine unit, respectively;
• a capacitance comparison circuit that compares the capacitance component of the joining machine unit after bonding and the capacitance of the equivalent capacitance circuit with a capacitance value equivalent to the capacitance component of the joining machine unit before bonding;
• and
• a judgment unit that judges the connection state between the wire and the subject device based on a digital output of the capacitance comparison circuit;
• wherein the capacitance comparison circuit is configured to comprise:
• a differential circuit (68) that generates a differential output signal of the difference between two input signals applied to the input terminals of the differential circuit simultaneously, said two input signals are the responses to the alternating-current signal source of the capacitance component of the joining machine unit (20) after bonding, and the capacitance of said variable equivalent capacitance circuit (64) with a capacitance value equivalent to the capacitance component of the joining machine unit before bonding, respectively;
• an amplifier circuit (70) that amplifies the differential output signal obtained from the differential circuit and thereby outputs amplified signal;
• a rectification circuit (72) that rectifies the amplified signal obtained from the amplifier circuit and thereby outputs rectified signal;
• and
• an A/D conversion circuit (74) that converts the rectified signal obtained from the rectification circuit (72) to the digital output signal.