Plating solution automatic control

An apparatus for automatically and continuously controlling a concentration of an electroless plating solution comprising:

• a plating tank containing an electroless plating solution therein,
• a make-up tank containing a replenisher therein,
• a supply means for supplying the replenisher in the make-up tank into the plating solution in the plating tank,
• a heater,
• a thermometer,
• a thermoregulator for controllably maintaining the plating solution at a predetermined temperature, said thermoregulator operatively connecting said heater and thermometer,
• an analyzer for measuring a concentration of a consumable ingredient in the plating solution,
• a detector for detecting whether or not a workpiece to be plated is introduced in the plating solution, and
• a control unit having a computer incorporated therein and operatively interconnected to a pump, thermoregulator, and analyzer,
• said control unit having stored therein a set of information bits A relating to a plating solution composition and the deposition amounts per unit time from the plating solution at varying temperatures and surface areas of a workpiece to be plated, or the amount of a consumable ingredient to be consumed, or the amount of a replenisher to be supplied, and receiving a set of information bits B relating to the surface area of a workpiece to be plated and a set of information bits C relating to the temperature of the plating solution from the thermoregulator in order that upon receipt of surface area information B and temperature information C, the control unit computes the amount of plating film to be deposited on the workpiece per unit time, or the amount of a consumable ingredient to be consumed, or the amount of replenisher to be supplied,
• wherein when the workpiece is dipped in the plating tank, the detector delivers a signal D1 indicative of the presence of the workpiece in the tank to the control unit and the control unit then supplies a signal E1 based on the result of the preceding computation to the supply means to actuate the supply means so as to provide a predetermined flow rate for a predetermined time, thereby making up the plating solution with a predetermined amount of the replenishment over a predetermined time, and when the workpiece is thereafter taken out of the plating tank, the detector gives another signal D2 indicative of the absence of the workpiece in the tank to the control unit and the control unit then supplies another signal E2 to the supplying means to interrupt the operation thereof,
• said control unit being connected to the analyzer whereby a set of information bits F relating to the concentration of consumable ingredient is delivered from the analyzer to the control unit in order that comparing information F with a previously stored set of information bits G relating to the permissible concentration range of the consumable ingredient in the plating solution, the control unit delivers a signal E3 to the supplying means to interrupt its operation for a predetermined time to thereby interrupt the supply of the replenisher for the predetermined time when the concentration of consumable ingredient in the plating solution exceeds the permissible concentration range, or the control unit delivers another signal E4 to the supplying means when the concentration of consumable ingredient in the plating solution is below the permissible concentration range so that signal E4 commands the supplying means to increase the flow rate therethrough by a predetermined quantity and/or extend the operating duration thereof by a predetermined time to thereby increase the supply of the replenisher by a predetermined amount,
• whereby a workpiece is electroless plated at a permissible concentration range of a consumable ingredient in the plating solution which is maintained by supplying the replenisher in an amount corresponding to the amount of the consumable ingredient determined from the surface area of the workpiece and by insuring whether or not the concentration is maintained within the permissible range by analyzing the consumable ingredient in the plating solution.