Electrolysis: processes – compositions used therein – and methods – Electrolytic coating – Involving measuring – analyzing – or testing
Reexamination Certificate
2001-01-12
2003-02-18
Nguyen, Nam (Department: 1741)
Electrolysis: processes, compositions used therein, and methods
Electrolytic coating
Involving measuring, analyzing, or testing
C118S689000, C118S690000, C205S082000, C205S101000, C422S105000, C427S008000, C436S055000
Reexamination Certificate
active
06521112
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates generally to systems for maintaining a predetermined concentration or balance of chemical constituents in a chemical bath, and more particularly, to a system that replenishes chemical components in accordance with historical replenishment rates that are modified in response to chemical analysis of the chemical bath.
2. Background of the Prior Art
Known arrangements and methods for maintaining a predetermined concentration or balance of chemical constituents in a chemical bath employ a control system that uses both, feed-forward (i.e., predictive) and feed-backward control. The feed-backward control relies on sensor inputs relating to constituent concentrations, plating efficiency, current output from the rectifier, drag-out rate, plating solution volume/liquid level, temperature and plating thickness.
The feed-forward control relies on a predictive model. In the context of an electroplating process, the changes in composition of the plating bath due to anode and cathode reactions are quantitatively modeled as a function of current-time. Additionally, the changes through drag-out are also modeled as a function of current-time. These are combined to obtain an overall system model. Oftentimes, materials or mass balance equations are applied to the model to calculate replenishment as a function of current-time to compensate for the losses and to maintain constant bath composition.
Known arrangements employ a microprocessor to compare the sensor signals obtained by the feed-backward control sensors against set points obtained by the predictive model and control/tolerance limits. If the values exceed the control/tolerance limits, the system can (1) recommend additional replenisher additions; (2) recommend postponing upcoming fee-forward additions for a determined period of ampere-time; and/or (3) assist the user in bringing the bath parameters back into their desired ranges via diagnostic screens.
The known systems are complicated and not very accurate. There is a need for a system that is effective at adjusting an historical trend in replenishment additions, and which does not rely on adjustment of a predictive model to effect the replenishment.
SUMMARY OF THE INVENTION
The present invention, in a first aspect thereof, is in the form of a method of controlling the content of a chemical bath. This method aspect of the invention includes the steps of:
first determining a rate of continued replenishment of a predetermined constituent of the chemical bath;
second determining a replenishment condition for the chemical bath; and
adjusting the rate of continued replenishment of the predetermined constituent of the chemical bath in response to the replenishment condition.
The rate of continued replenishment in the step of first determining is based on an historical replenishment rate. The step of second determining a replenishment condition includes, in one embodiment of the invention, the step of monitoring elapsed time. In other embodiments, the step of second determining a replenishment condition includes, for example:
monitoring the consumption of electrical energy by the chemical bath;
monitoring the number of products to be plated in the plating bath; and/or
monitoring the surface area of the products to be plated in the plating bath.
In a further embodiment of the invention, the step of first determining a rate of continued replenishment includes the steps of:
first establishing a quantum of a replenishment medium; and
third determining a replenishment frequency corresponding to a rate at which the established quantum of a replenishment medium is deposited in the chemical bath with respect to the replenishment condition. This embodiment may further include the further steps of:
defining units of the replenishment condition; and
counting elapsed units of the replenishment condition.
In this embodiment, there is further provided the step of defining a replenishment threshold corresponding to the product of the defined units of the replenishment condition and a predetermined number of units of the replenishment condition. The step of adjusting the rate of continued replenishment includes the step of comparing a counted number of units of the replenishment condition to the predetermined number of units of the replenishment condition. Additionally, the step of adjusting the rate of continued replenishment includes the step of determining a rate of adjustment of the rate of continued replenishment.
In accordance with a further method aspect of the invention, there is provided a method of controlling the content of a chemical bath, the method comprising the steps of:
determining a replenishment condition for the chemical bath;
defining a unit of the replenishment condition;
establishing a pacing factor corresponding to a replenishment volume of a replenishment medium per unit of the replenishment condition; and
defining a replenishment threshold corresponding to the product of a predetermined number of the defined units of the replenishment condition and the pacing factor.
In one embodiment of this further aspect of the invention, there is provided the further step of counting elapsed units of the replenishment condition. Other embodiments include the steps of effecting a replenishment of the chemical bath when the replenishment threshold is reached, testing the chemical bath to determine the content of the chemical bath, and adjusting the quantum of the replenishment of the chemical bath in the step of effecting a replenishment of the chemical bath. The step of adjusting the quantum of the replenishment of the chemical bath is effected in accordance with the relationship:
P
F
′=P
F
×[1+(
RA/T
)×
A],
which is described in greater detail hereinbelow. This embodiment may include the step of adjusting the replenishment of the chemical bath and includes the further step of varying the replenishment threshold. In still further embodiments of the invention, the step of adjusting the quantum of the replenishment of the chemical bath includes the further step of varying the replenishment volume of the replenishment medium per unit of the replenishment condition.
Replenishment
The replenisher aspect of the present invention is a combination of software, computer/controller hardware, and chemical dispensing hardware that is able simultaneously to:
Receive commands and send responses or status to a host computer.
Receive commands and send responses or status to a user keypad and display terminal.
Start, monitor, and stop multiple chemical deliveries independently to multiple destinations.
Some of the parameters monitored or tracked by the system are:
Chemical flow rate
Chemical usage, cumulative
Chemical supply status (OK, low, empty)
Pump status (on, off, disabled)
Pump calibration factors
The following are employed to achieve accurate, variable and verified delivery volumes:
flow rate is limited to an approximate, predetermined value;
flow volume is measured by summing pulses from a paddle wheel flow sensor in the flow path;
flow is stopped when the intended volume is delivered by means of a shutoff valve.
The advantages of this approach are: 1) By limiting flow rate, the flow sensor is kept in a linear and, more importantly, reproducible volume per pulse range, thereby ensuring a high degree of accuracy. 2) By summing pulses and stopping at the desired pulse count (or volume), a variable, predetermined amount may be delivered, this system being considerably simpler than a variable flow rate system. 3) By using a flow sensor in place of, for example, a volumetric metering pump, the volume delivered can be verified rather than assumed.
The foregoing, in combination with the flow rate limiting method shown below (FIGS.
16
and
17
), is less costly than other mechanical methods to deliver a variable volume. The use of a pneumatic pump with a constant pressure air supply provides feedstock at a constant pressure to a restricting needle valve or orifice. This method achieves the advant
Dj Parker Company, Inc.
Leader William T.
Nguyen Nam
Rohm & Monsanto
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