Electrodeposition without internal deposit stress

A method for electroforming a first electrodeposit onto a rigid mandrel with minimum internal stress during its formation, the mandrel and anode means immersed inside a metal-containing bath;

• comprising the steps of:
• (a) providing a deformable substrate for receiving a second electrodeposit, the deformable substrate immersed inside the bath and having the shape of a thin disk;
• (b) providing a strain gage attached to a back face of the deformable substrate;
• (c) providing a non-conductive coating over the strain gage and the back face of the deformable substrate;
• (d) providing a voltage controlled power supply means for supplying direct current through the bath from the anode means to both a front face of the mandrel and a front face of the deformable substrate;
• (e) controlling the current from the power supply means so that the current densities over the front faces of both the mandrel and the deformable substrate are substantially the same;
• (f) providing an insulated barrier inside the bath separating the anode means from both the mandrel and the deformable substrate, the insulated barrier having a pair of windows each positioned near to and sized slightly smaller than, respectively, the mandrel and the deformable substrate;
• (g) providing transducer-controller means for producing an output voltage generally proportional to a strain measured by the strain gage, wherein the transducer-controller means has an input connected to the strain gage and an output connected to the power supply means for changing the output current of the power supply means generally in proportion to strains measured by the strain gage;
• (h) beginning a simultaneous electroforming of electrodeposits onto the front faces of both the mandrel and the deformable substrate and adjusting the output of the transducer-controller means to a preselected setting corresponding to an estimate of a near zero internal stress in the first electrodeposit;
• and,
• (i) continuing simultaneous electroforming of electrodeposits onto the front faces of the mandrel and the deformable substrate so that an internal stress in the second electrodeposit will deform the deformable substrate, thereby producing a strain measured by the strain gage and a proportional change in the voltage to the power supply means to change its output current to cause the internal stress in the first electrodeposit to approach zero.