US 5,455,870 A · Apparatus and method for inspection of high component density printed circuit board

Abstract

An automated electronic module inspection system having illumination sources that produce digitized gray scale images that are then analyzed by a computer. The inspection system illuminates the module including solder joints, components and printed circuit board using a sequence of illumination that produce visual images which are used to identify defects. The inspection system inspects for all defects as specified in MIL-STD-2000A (Section 4.4) by using both surface reflectance properties as well as topological properties of objects. The system comprises two video cameras. A positioning table aligns a module-under-test with the optical axis of each camera thereby enabling the same field-of-view to be observed under different lighting conditions. A dark field illumination associated with a first camera preferentially illuminates non-flat surfaces, but not vertical surfaces. A bright field illumination associated with a second camera preferentially illuminates relatively flat surfaces. The flat-surface illumination light source is collimated with the optical axis of the camera using a conventional partially reflecting angled mirror that reflects the light along the camera's optical axis onto a circuit board of the module. The angled surfaces are illuminated using four ring-lights concentrically aligned with the optical axis of the second camera. The images observed by the camera are then analyzed by inspection programs for discrepancies between image model attributes and the images, and such programs provide compensation for nonuniformities of the light sources and cameras and compensation of shadows resulting from the dark field illumination light source.

Claims52

Dependent claims

Apparatus for inspection of surface mount solder joints of an electronic module comprising:

means for positioning and aligning said module during said inspection;
a first light source means for providing a dark field illumination to non-flat surfaces of said module on said positioning means;
a first sensing means disposed above said first light source means for sensing an intensity of reflected light from said first light source to obtain a first image;
a second light source means for providing a bright field illumination to flat surfaces of said module on said positioning means;
a second sensing means disposed above said second light source means for sensing an intensity of reflected light from said second light source to obtain a second image;
processing means for compensating said first image for nonuniformities resulting from said first light source means and said first sensing means and for compensating said second image for nonuniformities resulting from said second light source means and said second sensing means;
means included in said processing means for providing information describing predetermined shadows to said detecting and compensating means using a PCB module data base and said second compensated image to compensate for predetermined shadows;
means included in said processing means for differentiating between a low light intensity region of said first image and said predetermined shadows of said first image;
means included in said processing means for detecting and compensating for said predetermined shadows resulting from surface mount components attached to said electronic module and said first light source means, said shadows including omni-directional and uni-directional shadows;
means included in said processing means for performing a transposition on said first image and said second image for establishing a three-dimensional topography of said module;
and
means included in said processing means for analyzing said three-dimensional topography and said intensity of said first image and said second image to determine the condition of said module.

9 more elements

An automated vision inspection system comprising:

a computer means for controlling the operation of said vision inspection system;
a positioning table having a plurality of axes for positioning and aligning a module during an inspection in accordance with a command signal from said computer means;
a dark field illumination means positioned above said module for illuminating non-flat surfaces of said module;
a first camera disposed above said dark field illumination means for sensing an intensity of reflected light from said module to obtain a first image;
a bright field illumination means positioned above said module and adjacent to said dark field illumination means for illuminating flat surfaces of said module;
a second camera disposed above said bright field illumination means for sensing an intensity of reflected light from said module to obtain a second image;
processing means within said computer means for compensating said first image for nonuniformities from said dark field illumination means and said first camera and for compensating said second image for nonuniformities resulting from said bright field illumination means and said second camera;
means included in said processing means for providing information describing predetermined shadows to said detecting and compensating means using a PCB module data base to compensate for said predetermined shadows;
means included in said processing means for differentiating between a low light intensity region of said first image and said predetermined shadows of said first image;
means included in said processing means for detecting and compensating for said predetermined shadows resulting from surface mount components attached to an electronic module and said dark field illumination means, said shadows including omni-directional and uni-directional shadows;
means included in said processing means for performing a transposition on said first image and said second image for establishing a three-dimensional topography of said module;
means for comparing said established three-dimensional topography to a predetermined three-dimensional topography criteria;
and
expert system means for analyzing the results of said comparing means to detect a defect in said module.

11 more elements

A method for inspection of surface mount solder joints of an electronic module comprising the steps of:

positioning and aligning said module for said inspection with a positioning means having a plurality of axes;
illuminating non-flat surfaces of said module with a first light source having a dark field illumination means positioned above said module;
sensing an intensity of reflected light from said first light source with a first sensing means to obtain a first image;
repositioning said module for said inspection;
illuminating flat surfaces of said module with a second light source having a bright field illumination means positioned above said module and adjacent to said first light source;
sensing an intensity of reflected light from said second light source with a second sensing means to obtain a second image;
compensating in a processing means said first image for nonuniformities resulting from said first light source and compensating said second image for nonuniformities resulting from said second light source and said second sensing means;
providing information describing predetermined shadows to said detecting and compensating means with means included in said processing means using a PCB module data base to compensate for said predetermined shadows;
differentiating in said processing means between a low light intensity region of said first image and said predetermined shadows of said first image;
detecting and compensating in said processing means for said predetermined shadows resulting from surface mount components attached to said electronic module and said first light source means, said, shadows including omni-directional and uni-directional shadows;
performing in said processing means a transposition on said first image and said second image for establishing a three-dimensional topography of said module;
and
analyzing said three-dimensional topography and said intensity of said first image and said second image in said processing means to determine the condition of said module.

10 more elements

A method of inspecting surface mount solder joints of an electronics module with an automated vision inspection system comprising the steps of:

controlling the operation of said vision inspection system with a computer means;
positioning a module during an inspection in accordance with a command signal from said computer means to a positioning table having a plurality of axes;
aligning said positioned module to a first camera and to a second camera;.
illuminating non-flat surfaces of said module with a dark field illumination means positioned above said module;
sensing an intensity of reflected light from said module to obtain a first image using said first camera disposed above said dark field illumination means;
illuminating flat surfaces of said module with a bright field illumination means positioned above said module and adjacent to said dark field illumination means;
sensing an intensity of reflected light from said module to obtain a second image using said second camera disposed above said bright field illumination means;
compensating said first image for nonuniformities from said dark field illumination means and said first camera and compensating said second image for non uniformities resulting from said bright field illumination means and said second camera with a processing means within said computer means;
providing information describing predetermined shadows to said processing means using a PCB module data base to compensate for said predetermined shadows;
differentiating in said processing means between a low light intensity region of said first image and said predetermined shadows of said first image;
performing detection and compensation in said processing means for said predetermined shadows resulting from surface mount components attached to said electronic modules and said dark field illumination means, said shadows including omni-directional and uni-directional shadows;
performing in said processing means a transposition on said first image and said second image for establishing a three-dimensional topography of said module;
comparing said established three-dimensional topography to a predetermined three-dimensional topography criteria;
and
analyzing the results of said comparing means to detect a defect in said module with an expert system means.

12 more elements

Dependencies are inferred from the claim text.

Apparatus and method for inspection of high component density printed circuit board

Life of this patent

Apparatus and method for inspection of high component density printed circuit board

Life of this patent

Abstract

Claims52