Apparatus for determining the internal stress within electrodeposited metals is disclosed. The apparatus includes an improved spiral contractometer wherein the spiral substrate is coupled directly to a dial indicator without the use of a gear system. A rod, passing between the dial indicator and the lower end of the spiral substrate, causes a dial indication for changes in the radius of curvature of the spiral substrate. To determine the internal stress that is created within metal electrodeposited from a particular electrolytic plating solution, the spiral contractometer is submersed in that plating solution and connected as the cathode of a galvanic cell. An anode, consisting of the type of metal being electrodeposited, is supported in a precise position relative to the spiral substrate and a constant current is supplied between the anode and the spiral contractometer for a precise period of time to electrodeposit a controlled amount of metal on the spiral substrate. At the conclusion of the electrodeposition period, the deflection of the spiral contractometer is read on a vernier readout of the dial indicator and referenced to a calibration curve or multiplied by a known factor to provide the internal stress of the electrodeposited metal. Because the improved spiral contractometer is relatively free of frictional forces that change with time and a controlled amount of metal is deposited on the spiral substrate, the contractometer need not be calibrated prior to each use but is generally calibrated only when it is necessary to replace the spiral substrate.
An internal stress testing device for high speed electroplating is disclosed. The testing device comprises: a tank to be filled with a plating solution; a metal plate for anode disposed within the tank; a metal rod for cathode disposed within the tank and rotatably held by a motor at a position opposite to the metal plate for anode; a metal plate for cathode in the shape of a thin plate mounted on the metal rod; and a DC power supply connected to the metal plate for anode and the metal rod for cathode.
Internal stress on an object being electroplated is monitored continuously with a gauge. The gauge includes a metal receptor which is employed as a second cathode in the electrodeposition process. A separate plating current is supplied between the anode and second cathode, distinct from the separately controllable current between the anode and object being plated or electroformed. The stress on the second cathode is measured with a strain gauge, and a stress deviation from a desired plating stress is determined. The currents between the anode and first and second cathodes are adjusted in accordance with the measured internal stress on the metal receptor to achieve a desired stress condition. The internal stress is advantageously monitored with a foil resistance strain gauge. The strain gauge is connected to a carrier disposed in parallel with the metal receptor. The carrier is rigidly connected at opposite ends to the metal receptor. A stress transmission link centrally located between ends of the metal receptor and the carrier transmits the force applied by the electroplating material on the receptor to the carrier. The strain gauge provides an indication of the stress which results from the electroplating. The currents between the anode and first and second cathodes may be controlled in accordance with this stress measurement.
Apparatus and method for monitoring stress in a coating of material. The apparatus has a fluid-filled chamber and a deformable diaphragm on which the coating is applied forming a wall of the chamber, the fluid, which is generally incompressible, having a pressure due to pressing of the diaphragm against the fluid which is indicative of stress in the coating. The apparatus also includes a pressure transducer in communication with the fluid for sensing the fluid pressure and converting the fluid pressure to electrical signals whereby the electrical signals are indicative of the stress in the coating of material.
