Method and apparatus for performing automated circuit board solder quality inspections

Abstract

A method and apparatus for measuring structural characteristics of a manufactured circuit board containing solder joints by automated real-time digital X-ray radiographic inspection techniques. A circuit board under examination is automatically positioned by a digitally controlled multi-axis positioning system between an electronic X-ray source and an electronic X-ray imaging system, X-rays, in a beam of X-rays from the X-ray source, are directed towards the circuit board. The X-rays are absorbed, scattered and transmitted through the circuit board. The X-rays transmitted through the circuit board are directed upon the X-ray imaging system. The X-ray imaging system converts the transmitted X-rays into digital images which represent the radiographic density of the portion of the circuit board under examination. The digital images are stored within a digital image processor. A computer, under program control, performs calculational measurements on the digital images so as to measure the structural characteristics of the solder joints and components on the circuit board. The calculational measurements are compared to predetermined standards corresponding to acceptable quality standards programmed into the computer. In response to the comparison, the computer provides an accept/reject decision on the circuit board in addition to providing manufacturing process control information for correction of found defects. The questions raised in reexamination request No. 90/002,298, filed Mar. 15, 1991, have been considered and the results thereof are reflected in this reissue patent which constitutes the reexamination certificate required by 35 U.S.C. 307 as provided in 37 CRF 1.570(e).

What is claimed is: .[.1. An apparatus for measuring structural characteristics of selected portions of a circuit board having components disposed upon and electrically connected thereto at solder joints, comprising: 
     
        predetermined measurement parameter..].2. The apparatus of claim .[.1.]. .Iadd.49 .Iaddend.further comprising filter means for modifying the energy 
     
     
        spectrum of X-rays in said beam of X-rays. 3. The apparatus of claim .[.1.]. .Iadd.49 .Iaddend.wherein said imaging means comprises a solid 
     
     
        state detector. 4. The apparatus of claim .[.1.]. .Iadd.49 .Iaddend.wherein said imaging means comprises: optical imaging means for providing an optical image corresponding to the intensity of X-rays transmitted through said circuit board; and   electronic imaging means for converting said optical image into a   
     
     
        corresponding electrical image. 5. The apparatus of claim 4 wherein said optical imaging means comprises a scintillating screen positioned to 
     
     
        receive X-rays transmitted through said circuit board. 6. The apparatus of claim 4 wherein said electronic imaging means comprises: a video camera;   and reflecting means mounted adjacent said video camera for reflecting said   
     
     
        optical image from said optical imaging means to said video camera. 7. The apparatus of claim .[.1.]. .Iadd.49 .Iaddend.wherein said processing means 
     
     
        comprises a high-speed digital gray scale image processor. 8. The apparatus of claim .[.1.]. .Iadd.49 .Iaddend.wherein said multi-axis positioning system comprises: controller means responsive to instruction signals generated by said computational means for providing predetermined position signals; and   motion table means responsive to said position signals for moving said circuit board mounted thereupon in x, y and z orthogonal axis with   
     
     
        rotation in each axis. 9. The apparatus of claim .[.1.]. .Iadd.49 .Iaddend.wherein said X-ray means comprises an electronic X-ray source. 
     
     
            The apparatus of claim .[.1.]. .Iadd.49 .Iaddend.wherein said gray scale coded image generated by said processing means from said electronic image represents the radiographic density of said circuit board said beam 
     
     
        of X-rays are transmitted therethrough. 11. The apparatus of claim .[.1.]. .Iadd.49 .Iaddend.wherein said computational means further provides an output indication as to whether each resultant analysis value is within 
     
     
        said corresponding predetermined measurement parameter. 12. The apparatus of claim .[.1.]. .Iadd.49 .Iaddend.wherein said computational means provides said output an output signal indicative of measurement data for the measured structural characteristics of a manufactured circuit board 
     
     
        under test. 13. The apparatus of claim .[.1.]. .Iadd.49 .Iaddend.wherein said computational means further provides visual display of said output of measurement data for the measured structural characteristics of said 
     
     
        circuit board under test. 14. The apparatus of claim .[.1.]. .Iadd.49 .Iaddend.wherein each selected measurement algorithm corresponds to a certain structural characteristic of a respective one of an electronic device, a mechanical device, an electrical component, and a mechanical 
     
     
        component of said circuit board under test. 15. The apparatus of claim 14 wherein said computational means further provides an output indication as to whether each resultant analysis value is within said corresponding predetermined measurement parameter. .[.16. A method of determining the structural characteristics of a circuit board having components disposed thereupon and connected thereto at solder joints, comprising the steps of: supporting a circuit board having certain structural characteristics by a multi-axis positioning means adjustable for optimum exposure of said circuit board to a source beam of X-rays;   exposing said circuit board to a beam of X-rays having sufficient energy to penetrate said circuit board;   detecting X-rays transmitted through said circuit board and providing an electronic image thereof;   converting said electronic image into a gray scale coded image;   providing a library of measurement algorithms;   providing predetermined measurement parameters corresponding to said measurement algorithms;   selecting at least one measurement algorithm with each selected measurement algorithm corresponding to a respective one of said certain structural characteristics;   performing predetermined computational analysis on said gray scale coded image using each selected measurement algorithm;   providing a resultant analysis value corresponding to each computational analysis;   comparing each resultant analysis value with each corresponding predetermined measurement parameter; and   providing an output indicative of the variation of each resultant analysis   
     
     
        value from each corresponding predetermined measurement parameter..].17. The method of claim .[.16.]. .Iadd.25 .Iaddend.further comprising the step of providing an output as an indication of whether each resultant analysis value is within said corresponding predetermined 
     
     
        measurement parameter. 18. The method of claim .[.16.]. .Iadd.25 .Iaddend.wherein said output includes quantitative data corresponding to the structural characteristics of at least one inspected circuit board 
     
     
        component. 19. The method of claim .[.16.]. .Iadd.25 .Iaddend.wherein the step of detecting includes: disposing a scintillating screen in the path of X-rays passing through said circuit board, said scintillating screen generating an optical image of X-rays passing through said circuit board;   viewing said optical image generated by said scintillating screen with a video imaging system;   providing an electronic signal corresponding to the optical image observed   
     
     
        by said video imaging system. 20. The method of claim .[.16.]. .Iadd.25 .Iaddend.wherein the step of performing predetermined computational analysis further comprises the steps of: selecting at least one measurement algorithm from a pre-structured library of measurement algorithms;   controlling the detection of X-rays in accordance with said algorithms; and   recording each resultant analysis value in an electronic storage means.   
     
     
            The method of claim .[.16.]. .Iadd.25 .Iaddend.further comprising the step of providing an output indication whether each resultant analysis value is within said corresponding predetermined measurement parameter. 
     
     
        .Iadd.22.  A method of determining the structural characteristics of a circuit board having components disposed thereupon and connected thereto at solder joints, comprising the steps of: supporting a circuit board having certain structural characteristics by a multi-axis positioning means adjustable for optimum exposure of said circuit board to a source beam of x-rays;   optically identifying said circuit board;   automatically retrieving an inspection list corresponding to said circuit board;   exposing said circuit board to a beam of x-rays having sufficient energy to penetrate said circuit board;   detecting x-rays transmitted through said circuit board and providing an electronic image thereof;   converting said electronic image into a gray scale coded image;   providing a library of measurement algorithms;   providing determined measurement parameters corresponding to said measurement algorithms;   selecting at least one measurement algorithm with each selected measurement algorithm corresponding to a respective one of said certain structural characteristics;   performing predetermined computational analysis on said gray scale coded image using each selected measurement algorithm;   providing a resultant analysis value corresponding to each computational analysis;   comparing each resultant analysis value with each corresponding predetermined measurement parameter; and   providing an output indicative of the variation of each resultant analysis value from each corresponding predetermined measurement parameter.   
     
     
        .Iaddend..Iadd.23.  A method as claimed in claim 22, further comprising the step of selectively positioning said circuit board in accordance with said inspection list. .Iaddend..Iadd.24. A method as claimed in claim 22, wherein the step of selecting the at least one measurement algorithm is 
     
     
        performed in accordance with the inspection list. .Iaddend..Iadd.25.  A method of determining the structural characteristics of a circuit board having components disposed thereupon and connected thereto at solder joints, comprising the steps of: supporting a circuit board having certain structural characteristics by a multi-axis positioning means adjustable for optimum exposure of said circuit board to a source beam of x-rays;   automatically generating an inspection list corresponding to said circuit board;   exposing said circuit board to a beam of x-rays having sufficient energy to penetrate said circuit board;   detecting x-rays transmitted through said circuit board and providing an electronic image thereof;   converting said electronic image into a gray scale coded image;   providing a library of measurement algorithms;   providing predetermined measurement parameters corresponding to said measurement algorithms;   selecting, in accordance with said generated inspection list, at least one measurement algorithm with each selected measurement algorithm corresponding to a respective one of said certain structural characteristics;   performing predetermined computational analysis on said gray scale coded image using each selected measurement algorithm;   providing a resultant analysis value corresponding to each computational analysis;   comparing each resultant analysis value with each corresponding predetermined measurement parameter; and   providing an output indicative of the variation of each resultant analysis value from each corresponding predetermined measurement parameter.   
     
     
        .Iaddend..Iadd.26.  A method as claimed in claim 25 further comprising the step of evaluating a manufacturing process by performing statistical analysis on measurement data generated by executing said at least one measurement algorithm. .Iaddend..Iadd.27. A method as claimed in claim 25, wherein said inspection list comprises a sequence of operation for said positioning means. .Iaddend..Iadd.28. A method as claimed in claim 27, wherein said inspection list further comprises a sequence of selecting said at least one measurement algorithm. .Iaddend..Iadd.29. A method as claimed in claim 25, wherein said inspection list comprises a 
     
     
        classification of said joints. .Iaddend..Iadd.30.  A method as claimed in claim 29, wherein said library comprises algorithms for a plurality of joint types, and said selection of algorithm is made in accordance with said classification. .Iaddend..Iadd.31. A method as claimed in claim 29, wherein said inspection list further comprises a correction factor associated with a particular one of said joints for adjusting said selected algorithm. .Iaddend..Iadd.32. A method as claimed in claim 25, further comprising the step of identifying the circuit board. .Iaddend..Iadd.33. A method as claimed in claim 32, wherein the step of automatically generating said inspection list comprises the step of retrieving computer-aided design data corresponding to the identified circuit board. .Iaddend..Iadd.34. A method as claimed in claim 32, wherein the step of identifying the circuit board comprises scanning at least a portion of the circuit board. .Iaddend..Iadd.35. A method as claimed in claim 34, wherein scanning said circuit board comprises scanning a label 
     
     
        imprinted upon said circuit board. .Iaddend..Iadd.36.  A method as claimed in claim 35, wherein each type of circuit board from a plurality of circuit board types is imprinted with a different label. .Iaddend..Iadd.37. A method as claimed in claim 36, wherein each type of circuit board has a corresponding inspection list. .Iaddend..Iadd.38. A method as claimed in claim 25, wherein said inspection list comprises view information and algorithm selection information. .Iaddend..Iadd.39. A method as claimed in claim 25, further comprising the steps of: interpreting the inspection list; and   selectively positioning the circuit board in accordance with the inspection   
     
     
        list interpretation. .Iaddend..Iadd.40.  An apparatus for measuring structural characteristics of selected portions of a circuit board having components disposed upon and electrically connected thereto at solder joints, comprising: x-ray means for providing a beam of x-rays;   multi-axis positioning means for receiving and for selectively positioning a circuit board, said circuit board having components coupled thereto at solder joints, within said beam of x-rays;   imaging means for detecting x-rays from said beam of x-rays transmitted through said circuit board and providing an electronic image thereof;   processing means for converting said electronic image into a gray scale coded image;   means for optically identifying the circuit board;   means for automatically retrieving an inspection list corresponding to the circuit board; and   computational means for storing a library of measurement algorithms and predetermined measurement parameters corresponding thereto, for receiving said gray scale coded image, for analyzing said gray scale coded image by selecting measurement algorithms from said library of measurement algorithms with the selected measurement algorithms corresponding to certain structural characteristics of said circuit board, performing predetermined computational analysis on said gray scale coded image based upon each selected measurement algorithm, and providing a resultant analysis value corresponding to each computational analysis, for comparing each resultant analysis value with each corresponding predetermined measurement parameter, and for providing an output corresponding to the variation of each resultant analysis value from each corresponding predetermined measurement parameter. .Iaddend..Iadd.41. An apparatus as claimed in claim 40, wherein the computational means automatically selects the algorithms in accordance with the inspection list. .Iaddend..Iadd.42. An apparatus as claimed in claim 40, wherein the output from the computational means is designated as corresponding to the circuit board. .Iaddend..Iadd.43. An apparatus as claimed in claim 40, wherein the circuit board is selectively positioned by the positioning means in accordance with the inspection list. .Iaddend..Iadd.44. An apparatus as claimed in claim 40, wherein the retrieving means comprises a computer and   
     
     
        a device containing computer-aided design data. .Iaddend..Iadd.45.  An apparatus as claimed in claim 40, wherein the identifying means further comprises a display monitor and an input device. .Iaddend..Iadd.46. An apparatus as claimed in claim 40, wherein the identifying means identifies the circuit board as belonging to a particular manufacturing lot. .Iaddend..Iadd.47. An apparatus as claimed in claim 40, wherein the identifying means comprises an optical scanner. .Iaddend..Iadd.48. An apparatus as claimed in claim 47, wherein the optical scanner generates a signal for automatically identifying the circuit board as one of a 
     
     
        plurality of circuit board types. .Iaddend..Iadd.49.  An apparatus for measuring structural characteristics of selected portions of a circuit board having components disposed upon and electrically connected thereto at solder joints, comprising: x-ray means for providing a beam of x-rays;   multi-axis positioning means for receiving and for selectively positioning a circuit board, said circuit board having components coupled thereto at solder joints, within said beam of x-rays;   imaging means for detecting x-rays from said beam of x-rays transmitted through said circuit board and providing an electronic image thereof;   processing means for converting said electronic image into a gray scale coded image;   means for automatically generating an inspection list corresponding to said circuit board; and   computational means for storing a library of measurement algorithms for a plurality of joint types and predetermined measurement parameters corresponding thereto, for receiving said gray scale coded image, for analyzing said gray scale coded image by interpreting said inspection list, selecting, in accordance with said inspection list interpretation, measurement algorithms from said library of measurement algorithms with the selected measurement algorithms corresponding to certain structural characteristics of said circuit board, performing predetermined computational analysis on said gray scale coded image based upon each selected measurement algorithm, and providing a resultant analysis value corresponding to each computational analysis, for comparing each resultant analysis value with each corresponding predetermined measurement parameter, and for providing an output corresponding to the variation of each resultant analysis value from each corresponding predetermined measurement parameter. .Iaddend..Iadd.50. An apparatus as claimed in claim 49, wherein said generating means comprises a computer and a device containing computer-aided design data. .Iaddend..Iadd.51. An apparatus as claimed in claim 49, further comprising means for identifying the circuit board. .Iaddend..Iadd.52. An apparatus as claimed in claim 51, wherein a plurality of inspection lists corresponding to a plurality of circuit board types are resident in a storage device coupled to said computational   
     
     
        means. .Iaddend..Iadd.53.  An apparatus as claimed in claim 52, wherein said identifying means comprises a scanner for automatically identifying said circuit board as one of said plurality of circuit board types. .Iaddend..Iadd.54. An apparatus as claimed in claim 49, wherein said computational means comprises an imaging computer having a software module for interpreting said inspection list. .Iaddend..Iadd.55. An apparatus as claimed in claim 54, wherein said positioning means selectively positions said circuit board in accordance with said inspection list. .Iaddend..Iadd.56. An apparatus as claimed in claim 49, wherein the inspection list comprises, for each of the joints, a designation of a set of algorithms from the library of algorithms, and a designation of a 
     
     
        sequence of applying the set. .Iaddend..Iadd.57.  An apparatus as claimed in claim 49, wherein a plurality of inspection lists corresponding to a plurality of circuit board types are resident in a storage device coupled to the computational means. .Iaddend..Iadd.58. An apparatus as claimed in claim 57, wherein the computational means comprises an imaging computer having a software module for interpreting the inspection list corresponding to the circuit board. .Iaddend..Iadd.59. An apparatus as claimed in claim 49, wherein the library of measurement algorithms comprises algorithms for a plurality of joint types. .Iaddend.