Classifications

• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
  • C25D21/00—Processes for servicing or operating cells for electrolytic coating
  • C25D21/12—Process control or regulation
  • C25D21/14—Controlled addition of electrolyte components
• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
  • C25D21/00—Processes for servicing or operating cells for electrolytic coating
  • C25D21/16—Regeneration of process solutions
  • C25D21/18—Regeneration of process solutions of electrolytes

Definitions

• 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.
• feed-forward i.e., predictive
• 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.
• 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.
• 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.
• 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.
• 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.
• a method of controlling the content of a chemical bath 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.
• the further step of counting elapsed units of the replenishment condition includes 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:
• This embodiment may include the step of adjusting the replenishment of the chemical bath and includes the further step of varying the replenishment threshold.
• 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.
• the replenisher aspect of the present invention is a combination of software, computer/controller hardware, and chemical dispensing hardware that is able simultaneously to:
• the paced replenishment system of the present invention refers to replenishment at a rate that is proportional to some event, hereinafter referred to as the replenishment condition.
• Suitable events that constitute the replenishment condition include elapsed time, ampere-hours (or coulombs), number of product loads, product surface area, line speed over time, etc.
• the method of the present invention replenishes process constituents as they actually are consumed. It also prevents depletion (or buildup in the case of decanting a by-product) and the associated time delay related to detection and correction.
• replenishment is automatically initiated at the following replenishment conditions:
• the system permits the operator to set the replenishment delivery calculations, based on analysis result and amp-minute accumulation (or other replenishment condition listed above) for each parameter/chemical(s). Once these settings are established, the system will automatically adjust the replenishment amount based on amp-minutes by the analysis result(s) for that plating bath.
• a communications link is provided between the plating tool and the controller of the inventive system. This link will inform the system of amp-minutes(amperage), by plating cell/bath, so that it can initiate replenishment based on, for example, an amp-minute target.
• replenishment of a chemical bath proceeds at a predetermined rate that may be based on historical experience with the particular operating bath. Alternatively, the existing replenishment rate in effect in a given system may be predetermined based on experience with similar or related chemical systems.
• the rate of replenishment is carried out in small batches, or aliquots, of a user-defined volume at a frequency controlled by the time required for the pacing signal to reach the trip point.
• the trip point is a predetermined sum of paced unit(s), for example, 10.0 ampere-minutes or 3 product loads.
• the volume delivered after the trip point is reached is defined by the following relationship, which corresponds to the volume delivered on or after the real time paced units accumulate to equal or excess this paced units trip point:
• Replenishment volume P F x P
• P p Pacing factor, in units of replenishment volume per paced unit accumulated
• P - Paced units accumulated of the replenishment condition
• the paced units are continuously accumulated in real time.
• the chemical bath is sampled periodically to determine whether the rate of replenishment is adequate to maintain the desired balance of chemical constituents. In situations where the result of the sampling indicates that the chemical bath is under-concentrated, as would be the case where too much H 2 O is added or decanted, or replenishment is delayed or inadequate, the volume of the next single delivery of the replenishment material is increased. Alternatively, the replenishment volume is maintained the same, but the subsequent replenishment is caused to occur sooner, essentially by retaining unused but accumulated paced units.
• the replenishment ratio i.e., the pacing factor
• the replenishment ratio is adjusted in response to intermittent quantitative analyses. That is, the ratio of feedstock is replenished in proportion to the accumulated signal or pacing factor. Since the equipment of the present invention can perform accurate intermittent quantitative analyses on the content of the chemical bath, the results of such analyses are used intermittently to adjust the ratio of replenishment to accumulated pacing factor.
• the time interval for ratio adjustment, or tuning ranges from one half hour to several hours, depending on the extent to which the process is dynamic, and its predictability.
• P F Current pacing factor, in units of replenishment volume per paced unit
• R Replenishment amount calculated from current quantitative analysis result. This calculation is usually stoichiometric.
• T Total paced replenishment since last analysis result. This excludes any amounts replenished for other reasons, such as in response to an analysis or operator request.
• A Fractional adjustment rate, 0 ⁇ A ⁇ 1.
• A controls how fast the pacing factor is tuned. Processes which require a quick response and have high analytical certainty use a setting of A near 1.0.
• Processes which are less dynamic or have lower analytical certainty use a lower setting for A, such as less than 0.5.
• the method of the present invention recovers from integral error (a constant offset) by replenishing the total amount necessary to return to the process control set point after each analysis.
• Integral error is intentionally not taken care of by the ongoing paced replenishment alone, is to avoid subsequent overshoot and correction after the set point is reached and to accomplish more immediate recovery.
• Overshoot is corrected by pausing paced replenishment until a volume of delivery is bypassed (not delivered) equaling the calculated volume that would have caused the overshoot.
• the tuning equation is used as always, expect that the R term becomes negative. As is the case with integral error, this avoids subsequent undershoot and correction alter the set point is reached and to accomplishes a more immediate recovery.
• the implementation of the invention includes:
• pacing signal conditioning to convert or amplify the signal to an acceptable range
• Tuning Tuning is based on the following:
• Analytical Replenishment Factor is the multiplier used to convert an analytical result to a replenishment quantity. It is expressed in replenishment units over analytical units, such as liters replenishment per gram/liter below target.
• Tuning Rate is the rate of tuning, expressed as a percentage from 0 to 100.0.
• a typical operating value is 20.0. It depends on the analysis error, analysis frequency, and rate of process change. That is, the user will set it in proportion to (rate of change/ analysis error/analysis frequency).
• Paced Units 1 * Ideal Pacing Factor 1 * Analytical Replenishment Factor - Sum of All Replenishments Since Last Analysis + Sum of Paced Replenishments 1 Paced Replenishment Error 2 Paced Units 2 x Ideal Pacing Factor 2 * Analytical Replenishment Factor -
• E1 Paced Units 1
• E2 Paced Units 2
• X1 Ideal Pacing Factor 1
• X2 Ideal Pacing Factor 2
• C Sum of All Replenishments Since Last Analysis
• a text box for entering the rate of tuning for each factor This is a percentage, expressed from 0 to 100.0. The default for this is 100.0, which should be set lower only if the rate of consumption in proportion to the pacing factor is inconsistent.
• the default value is two, which is set higher when needed to smooth out more analytical error.
• the text box caption should be, for example, "Use average of current and previous results.”
• Durability (or reliability) is also a problem.
• the electronics associated with most sensors inherently have a limited temperature operating range beyond which the sensor can be destroyed.
• Another example is that maintenance becomes problematical when a solution coats or crystallizes on surfaces.
• space constraints often limit where a sensor can be installed.
• the sensor head or electronics package
• This "material flow” limits what space is available for locating equipment above the tank liquid surface.
• the present system employs a pneumatic level sensing technique in order to solve or prevent the aforementioned problems.
• this technique uses 1) a pressure regulated air or gas source, 2) a precision orifice or needle valve to limit the gas flow rate, 3) a pressure switch or sensor to detect the pressure within the tube and 4) a length of tubing of material inert to the process solution which is immersed in the solution and which internally takes on the pressure of the liquid at the depth where it terminates.
• the orifice restricts airflow such that the pressure to the right (downstream) of the orifice is limited to the pressure head of the liquid above the bubbling tube outlet.
• a change in level is detected by the change in gas pressure required to keep the gas and liquid in equilibrium at the tube outlet. After the level rises, the gas will build in pressure until it equals the liquid pressure at the outlet, after which it will vent (bubble) and remain at equilibrium.
• a low pressure gas for example less than 2 psi, to supply the system. This limits the maximum possible pressure and thus prevents damage to the low range pressure switch or sensor should the tube outlet become blocked;
• a tube or pipe section in contact with the solution can be further oversized, for example to Vi inch or even linch diameter, so that plugging of the outlet such as by dried material is much less likely. While plugging of the outlet has not been a problem in the practical embodiment, this technique may be useful in certain solutions.
• connection may be provided to convert from one tubing of standard material, such as nylon, polyurethane, or polyethylene to an inert material, such as Teflon®, prior to entering the solution.
• standard material such as nylon, polyurethane, or polyethylene
• inert material such as Teflon®
• the pressure readings may be corrected for changes in solution density before converting the reading to level or volume.
• this method only applies to continuous analog level sensing, not discrete point level switching.
• the software used in conjunction with this level measurement method accomplishes the following: 1. "Debouncing" of the wave action in the tank. Since the tank solutions being measured undergo agitation, either intentionally or by work flow, the level is not constant, but is actually wavy. The software removes this "noise" switch type level detection to give a consistent, useful reading.
• a user settable control also allows automatic overfill, if desired, so as to reduce switch and fill valve cycling and thus increase in mechanical component life span.
• each one is also used to confirm the proper operation of the other.
• the lower sensor When installed at different levels, the lower sensor is used as the process or target level; the higher sensor is used as an alert or warning level.
• the lower sensor reads anything less than 100%, the only valid reading for the higher sensor is 0%. It is only when the lower sensor reads 100% that the higher sensor may read more than this. Conditions outside of this are reported as errors to the operator and are interlocked in the software to prevent hazardous or overfull operations. (It is common in the industry to use two sensors where the signal from one is used to turn on a filling or emptying device and from the other to turn it off. Thus the second sensor cannot be used to back up the first because it must be employed in the level control operation. For protection or interlocks a third sensor is required.
• software timers are employed to stop filling and alert the operator if the level does not 1) measurably rise within a preset time or 2) reach target within a (longer) preset time. Automated filling is not allowed until after an operator initiated reset occurs or the level is restored to the target by some external means.
• the system is designed to eliminate the need for manual analysis and replenishment of the chemicals associated with the control parameters of the copper plating baths.
• the system of the present invention also provides automatic sensor calibration and internal system diagnostics maintain a high degree of reliability, repeatability, and throughput performance. In addition, efficient trouble shooting and reduced maintenance requirements are achieved.
• an automatic analyzer is provided for copper sulfate, sulfuric acid, hydrochloric acid and two organic agents/additives.
• the analyzer automates titrametric procedures and delivers sharp, distinct end-points in approximately five to seven minutes. With time spent for sampling, purging, sample preparation, redundant analysis, cleanup and trend checking, is included, the overall cycle time is therefore approximately between twenty and thirty minutes.
• this embodiment of the invention achieves automatic, chemical analysis of: and chemical replenishment of: copper copper sulfate sulfuric acid sulfuric acid chloride hydrochloric acid additive #1 organic agent additive #2 organic agent
• the analyzer of the present invention will also automate cyclic voltammetric stripping for the analysis of the organic components, as well as provide indication of the total organic contamination of the plating solution. These analyses, when selected to be performed for a particular tank, are programmed to run concurrently with the analysis for the inorganic components. Within the method (titration or CVS or CPVS), analysis will occur in sequence. Housing:
• the system of the present invention is, in a highly advantageous embodiment, housed in a fire retardant polypropylene cabinet with see-through front, hinged (locked) door.
• the system uses a pH electrode, an ORP electrode, a chloride-ion-specific electrode, and a cyclic voltammetric stripping unit to automate the necessary analytical procedures.
• This cabinet is equipped with leak detection and secondary containment and is designed to accept chemical samples from up to three (3) pressurized sample lines.
• the cabinet also houses a manager system that is provided with a viewing screen for monitoring various forms of activity, a CPU shelf, a pull-out keyboard locking drawer, printer stand and electrical panel for a local control unit (LCU).
• the overall approximate size of this cabinet in a practical embodiment, is 48"W X 72"H X 24"D.
• the analyzer is connected to the manager, in this embodiment, via a RS-422 data transfer arrangement.
• the LCU is a combination of software, computer or controller hardware, signal conditioning modules, sensors and actuators. It is used to monitor, control and report a variety of physical parameters including temperature, level, conductivity, pH, voltage, current, pressure, flow, and other parameters that can be measured by a sensor. It is employed where continuous monitoring and/or immediate control response is required.
• the Chemical Replenishment, storage and handling unit is manufactured of fire retardant polypropylene and is designed, in a specific illustrative embodiment of the invention, to accept five "NOW-PAK" four-liter containers.
• This unit includes the following:
• the packaging approach is designed for clean room type environments.
• a practical embodiment of the present design complies with ST-93, CE "Essential,” andUL electrical standards.
• the chemical replenishment, storage and handling unit manufactured of fire retardant polypropylene, can optionally be designed to accept five "NOW-PAK" 200 liter containers.
• the system may include: a manager/PC controller with G E M/SECS Host communications output; • a automatic chemical analyzer;
• Fig. 1 is a process flow diagram of a specific illustrative embodiment of the invention directed to copper plating operation and chemical control
• Fig. 2 is a schematic representation of a 200 liter "NOW PAK" automatic dosing system
• Fig. 3 a simplified plan view of a manager facility the employs RS232/422 data exchange paths in an amp-minute embodiment
• Fig. 4 is a simplified schematic representation of a mixing and filtering arrangement
• Fig. 5 is a simplified plan view of the exterior of a replenishment system constructed in accordance with the invention.
• Fig. 6 is a plan representation of a practical embodiment of a 200 liter replenishment system
• Fig. 7 is a representation of a computer screen of the manager system of the present invention, showing a line status screen
• Fig.8 is a representation of a computer screen of the manager system of the present invention, showing a parameter status screen of post treatment inorganic chemical maintenance;
• Fig. 9 is a representation of a computer screen of the manager system of the present invention, showing a further parameter status screen of chemical staging organic addition;
• Fig. 10 is a representation of a computer screen of the manager system of the present invention, showing a further parameter status screen of a plater;
• Fig. 11 is a representation of a computer screen of the manager system of the present invention, showing an incoming chemical inspection screen
• Fig. 12 is a representation of a computer screen of the manager system of the present invention, showing an analyzer control system screen
• Fig. 13 is a representation of a computer screen of the manager system of the present invention, showing a screen representing the replenishment of copper sulfate of a plater;
• Fig. 14 is a representation of a computer screen of the manager system of the present invention, showing a feedstock screen
• Fig. 15 is a representation of a computer screen of the manager system of the present invention, showing a copper sulfate settings screen
• Fig. 16 is a simplified schematic representation of an arrangement that achieves accurate delivery volumes
• Fig. 17 is a simplified schematic representation of an arrangement that achieves accurate measurement of the level of fluid material in a chemical bath.
• Fig. 1 is a process flow diagram of a specific illustrative embodiment of the invention directed to copper plating operation and chemical control.
• the system includes a plater 10 that receives material from a chemical staging organic addition tank 12.
• a carbon treatment tank 14 receives fresh solution from a fresh solution make up tank 16, and collected plating solution from a plating collection tank 17.
• the carbon treatment tank supplies treated solution to a post treatment chemical maintenance tank 18 that delivers solution to chemical staging organic addition tank 12.
• Fig. 2 is a schematic representation of a 200 liter "NOW PAK" automatic dosing system 20.
• the tanks are contained within a housing 27 that is provided with a spill drain 28.
• a pair of valves 29 for communicating with the tanks is shown schematically.
• Fig. 3 a simplified plan view of the exterior of a manager facility 30 that employs
• Fig. 4 is a simplified schematic representation of a mixing and filtering arrangement 40.
• Mixing of metal hydroxides, acid wastes, and an activating agent is performed in a mixing tank 41.
• the acid wastes can include acid Cu, CuCl, H4 persulfate, Na persulfate, and acid peroxide.
• the metal hydroxides are received at mixing tank 41 from waste water and an activating agent that are combined and subjected to first and second stages of pH adjustment 43 and44, respectively.
• the pH adjusted material is then subjected to a clarifier at tank 46 and a thickener 47 is then added.
• the output of mixing tank 41 is then subjected to a filter press 48.
• FIG. 5 is a simplified plan view of the exterior of a replenishment system 50 constructed in accordance with the invention.
• Replenishment materials are received at replenishment connections 51.
• Electromechanical devices (not shown in this figure), such as solenoids, pumps, and the like, are contained within a region 53 of the replenishment system, and electrical power and compressed air are received at inlets 55. The power is converted to a low voltage for powering the internal component of the system at a region 56.
• Fig. 6 is a plan representation of a practical embodiment of a 200 liter replenishment system 60.
• a plurality of 200 liter drums 62 are provided with respectively associated ones of pumps 63. Certain aspects of the process can be viewed at viewing windows 64. Operator control is effected via an operator keypad 66, which in this embodiment of the invention, is installed at high voltage station 67.
• Fig. 7 is a representation of a main system status computer screen 70 of the manager system of the present invention. The figure shows the various portions of a line status screen.
• Fig.8 is a representation of a computer screen of the manager system of the present invention, showing a parameter status screen 80 of post treatment inorganic chemical maintenance.
• Fig. 9 is a representation of a computer screen of the manager system of the present invention, showing a further parameter status screen 90 of chemical staging organic addition.
• Fig. 10 is a representation of a computer screen of the manager system of the present invention, showing a further parameter status screen 100 of a plater;
• Fig. 11 is a representation of a computer screen of the manager system of the present invention, showing an incoming chemical inspection screen 110.
• Fig. 12 is a representation of a computer screen of the manager system of the present invention, showing an analyzer control system screen 120.
• Fig. 13 is a representation of a computer screen of the manager system of the present invention, showing a screen 130 representing the replenishment of copper sulfate of a plater;
• Fig. 14 is a representation of a computer screen of the manager system of the present invention, showing a feedstock screen 140.
• Fig. 15 is a representation of a computer screen of the manager system of the present invention, showing a copper sulfate settings screen 150.
• Fig. 16 is a simplified schematic representation of an arrangement 160 that achieves accurate delivery volumes.
• a pneumatic pump 161 receives a supply of air at a constant pressure at an air inlet 162, as well as the feedstock of the chemical desired to be delivered at a feedstock inlet 163.
• the outlet of pneumatic pump 163 is conducted to a needle valve 164.
• the needle valve may be replaced with an orifice (not shown) of predetermined size.
• the rate of flow of the chemical at the outlet of the needle valve is monitored by a flow meter 166, and can be controlled by a shut off valve 167. This arrangement produces a highly controlled rate of flow of the chemical to be delivered.
• Fig. 17 is a simplified schematic representation of an arrangement 170 that achieves accurate measurement of the level of fluid material in a chemical bath.
• the pressure of a pressurized gas that has been passed through an orifice 171 is monitored by a pressure gauge 173.
• the pressurized gas is released at an outlet 174 that is submerged in a chemical bath 176.
• the pressure reading at pressure gauge 173 constitutes an accurate measure of the level of the chemical bath. There is therefore provided a simple and inexpensive level monitor.

Landscapes

• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Electrochemistry (AREA)
• Materials Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Automation & Control Theory (AREA)
• Control Of Non-Electrical Variables (AREA)

Applications Claiming Priority (3)

Publications (1)

Family

ID=22233781

Family Applications (1)

Country Status (5)

Families Citing this family (3)

Family Cites Families (6)

• 1999
  • 1999-07-13 EP EP99933935A patent/EP1099013A2/en not_active Withdrawn
  • 1999-07-13 JP JP2000559286A patent/JP2003527477A/ja active Pending
  • 1999-07-13 KR KR1020017000554A patent/KR20010053520A/ko not_active Application Discontinuation
  • 1999-07-13 AU AU49881/99A patent/AU4988199A/en not_active Withdrawn
  • 1999-07-13 WO PCT/US1999/015752 patent/WO2000003073A2/en not_active Application Discontinuation

Non-Patent Citations (1)

Also Published As

Similar Documents

Legal Events