System and Methods for Data-Driven Control of Manufacturing Processes

Abstract

Systems and methods for implementing hybrid, closed-loop control that generates control values for processes defined by a limited number of function evaluations and large amounts of process and measurement noise. The described control system is applied to a stencil printing process for applying solder paste to an electronic medium such as a printed circuit board or semiconductor wafer. The control system is defined by a hybrid approach. A first, coarse algorithm is used to rapidly produce the value of a stencil printer control value resulting in a solder paste deposit having a volume within predetermined acceptable limits. After the coarse algorithm no longer produces solder paste deposits closer to a desired volume, a second, more refined estimator is used to fine tune the process. An additional transitional algorithm may be added between the coarse algorithm and refined estimator. The coarse algorithm may be implemented with a constrained-conjugated gradient search, and the refined search may be a implemented using a least-squares affine estimator or a quadratic estimator. The transitional algorithm may be implemented using a block version of a least-squares affine estimator.

1 - 41 . (canceled)  
   
   
       42 . A closed-loop control method of controlling a volume of solder paste applied to an electronic medium: 
 incrementally adjusting a value of a stencil printer control parameter by a predetermined amount; and    fine tuning the value of the stencil printer control parameter by a second amount once a mean solder paste deposit measurement is within predetermined process limits.    
   
   
       43 . The method of  claim 42 , wherein the solder paste deposit measurement is a volume, an estimated volume, or a height of a solder paste deposit.  
   
   
       44 . The method of  claim 42 , wherein the step of fine tuning the value of the stencil printer control parameter further includes: 
 adjusting the value of the stencil printer control parameter by a smaller amount than the predetermined amount using an estimator selected from an affine estimator and a quadratic estimator.    
   
   
       45 . The method of  claim 42 , wherein the step of incrementally adjusting a value of a stencil printer control parameter by a predetermined amount further includes: determining the value of the stencil printer control parameter using a gradient search.  
   
   
       46 . The method of  claim 42 , wherein the step incrementally adjusting a value of a stencil printer control parameter by a predetermined amount further includes: 
 determining a search direction; and    continuing to incrementally adjust the value of the stencil printer control parameter by the predetermined amount in the search direction until the resulting difference between the measurement and a desired value of the measurement is not decreased.    
   
   
       47 . The method of  claim 42 , wherein the solder paste deposit measurement is a height of a solder paste deposit, and wherein the step of incrementally adjusting the value of the stencil printer control parameter by the predetermined amount comprises: 
 setting an initial printer control value;    printing a first plurality of solder paste deposits on the electronic medium using the initial printer control value;    determining the mean height of the first plurality solder paste deposits on the electronic medium;    ascertaining a search direction by determining if the mean height of the first plurality of solder paste deposits is above or below a desired height;    determining an updated value of the stencil printer control parameter by incrementally adjusting the initial printer control value in the search direction by the predetermined amount;    printing a second plurality solder paste deposits on a second electronic medium using the updated value of the stencil printer control parameter; and    determining if the difference between the mean height of the second plurality of solder paste deposits and the desired height is less than the difference between the mean height of the first plurality of solder paste deposits and the desired height.    
   
   
       48 . The method of  claim 42 , further including: 
 transitioning from the step of incrementally adjusting the value of the stencil printer control parameter by the predetermined amount to the step of fine tuning the value of the stencil printer control parameter by using a block form of a least-squares estimator.    
   
   
       49 . The method of  claim 42 , further including: 
 transitioning from the step of fine tuning the value of the stencil printer control parameter to the step of incrementally adjusting the stencil printer control value by the predetermined amount when the mean solder paste deposit height is outside of a predetermined operational band.    
   
   
       50 . The method of  claim 42 , wherein the stencil printer control parameter is any one of the print speed, the squeegee pressure, snap off speed, the stroke length, the downstop distance, and the separation distance based on the measured height of the solder paste deposit.  
   
   
       51 . The method of  claim 42 , wherein the mean solder paste deposit measurement comprises a weighted mean of a plurality of solder paste deposits.  
   
   
       52 . The method of  claim 51 , wherein the weighted mean of the plurality of solder paste deposits gives a larger weight to solder paste deposits associated with problematic components or to solder paste deposits associated with fine-pitch contact pads.  
   
   
       53 . A computer-readable medium having a computer program for implementing a closed-loop control method for controlling a volume of solder paste applied to an electronic medium, comprising: 
 logic configured to incrementally adjust a value of a stencil printer control parameter by a predetermined amount; and    logic configured to fine tune the value of the stencil printer control parameter by a second amount once a mean solder paste deposit measurement is within predetermined process limits.    
   
   
       54 . The computer-readable medium of  claim 53 , wherein the logic configured to fine tune the value of the stencil printer control parameter further includes: 
 logic configured to adjust the value of the stencil printer control parameter by a smaller amount than the predetermined amount using an estimator selected from an affine estimator and a quadratic estimator.    
   
   
       55 . The computer-readable medium of  claim 53 , wherein the logic configured to incrementally adjust a value of a stencil printer control parameter by a predetermined amount further includes: 
 logic configured to determine the value of the stencil printer control parameter using a gradient search.    
   
   
       56 . The computer-readable medium of  claim 53 , wherein the logic configured to incrementally adjust a value of a stencil printer control parameter by a predetermined amount further includes: 
 logic configured to determine a search direction; and    logic configured to continue to incrementally adjust the value of the stencil printer control parameter by the predetermined amount in the search direction until the resulting difference between the measurement and a desired value of the measurement is not decreased.    
   
   
       57 . The computer-readable medium of  claim 53 , wherein the mean solder paste deposit measurement comprises a weighted mean of a plurality of solder paste deposits.  
   
   
       58 . The computer-readable medium of  claim 57 , wherein the weighted mean of the plurality of solder paste deposits gives a larger weight to solder paste deposits associated with problematic components or to solder paste deposits associated with fine-pitch contact pads.  
   
   
       59 . A closed-loop control system, comprising: 
 means for incrementally adjusting a value of a stencil printer control parameter by a predetermined amount; and    means for fine tuning the value of the stencil printer control parameter by a second amount once a mean solder paste deposit measurement is within predetermined process limits.    
   
   
       60 . The system of  claim 59 , wherein the mean solder paste deposit measurement comprises a weighted mean of a plurality of solder paste deposits.  
   
   
       61 . The system of  claim 60 , wherein the weighted mean of the plurality of solder paste deposits gives a larger weight to solder paste deposits associated with problematic components or to solder paste deposits associated with fine-pitch contact pads.