Method for determining accuracy of a circuit assembly process and machine employing the same

• US 6,047,084 A
• Filed: 11/18/1997
• Issued: 04/04/2000
• Est. Priority Date: 11/18/1997
• Status: Expired due to Term

• Current Assignee: Google Technology Holdings LLC (Alphabet Inc.)
• Original Assignee: Motorola, Inc. (Motorola Solutions, Inc.)
• Inventors: Kent, Kevin, Rahn, Gregory, Tarbell, Kenneth A.
• Primary Examiner(s): Lee, Thomas D
• Application Number:
  US08/972,554
• Time in Patent Office: 868 Days
• Field of Search: 382/145, 382/147, 382/149, 382/151, 382/141, 382/150, 348/125, 348/126
• US Class Current: 382/147
• CPC Class Codes: H05K 13/083 Quality monitoring using results from monitoring devices, e.g. feedback loops H05K13/084 takes precedence

Abstract

Accuracy of a circuit assembly process (100) is determined by capturing an image (306, 1008) of an assembly formed on a substrate by the circuit assembly process (100), calculating coverage (310, 1012, 1024) of the assembly from the image, and comparing the coverage (312, 1016, 1026) to a threshold.

Claims

1. A method for determining accuracy of a circuit assembly process, the method comprising the steps of:

capturing an image of an assembly of a substrate, the assembly formed by the circuit assembly process, the image comprising a first shape representative of a first component of the assembly and a second shape representative of a second component of the assembly;

identifying a first set of numeric coordinates defining a location of the first shape and a second set of numeric coordinates defining a location of the second shape;

determining coverage of the assembly by calculating overlap of the first and second components from the first and second sets of numeric coordinates; and

comparing the coverage to a threshold to determine accuracy of the circuit assembly process.

2. A method according to claim 1 wherein the step of determining coverage comprises the steps of:

modeling the first component of the assembly as a first polygon and the second component of the assembly as a second polygon;

calculating points of intersection of the first polygon and the second polygon from the first and second sets of numeric coordinates; and

calculating points of enclosure of the first polygon and the second polygon from the first and second sets of numeric coordinates.

3. A method according to claim 2 wherein the step of determining coverage comprises the step of sorting the points of intersection and the points of enclosure.

4. A method according to claim 3 wherein the step of sorting comprises the steps of:

selecting one of the points of intersection and the points of enclosure;

determining a distance between the one of the points of intersection and the points of enclosure and other ones of the points of intersection and the points of enclosure; and

reordering the points of intersection and the points of enclosure by placing a closest one of the other ones of the points of intersection and the points of enclosure next to the one of the points of intersection and the points of enclosure.

5. A method according to claim 2 wherein the step of calculating comprises the step of computing an area enclosed by the points of intersection and the points of enclosure.

6. A method according to claim 1

further comprising the step of placing solder paste at a site of the substrate to form the assembly, the site having a pad;

and

wherein the step of capturing an image comprises the steps of;

defining the solder paste as the first component; and

defining the pad as the second component.

7. A method according to claim 6 further comprising the step of outputting data regarding the overlap of the solder paste and the pad when the circuit assembly process is determined to be accurate.

8. A method according to claim 1

further comprising the step of placing an electronic part at a site of the substrate to form the assembly, the electronic part having at least one lead, and the site having at least one pad covered by solder paste;

and

wherein the step of capturing an image comprises the steps of;

defining the at least one lead as the first component; and

defining the at least one pad covered by solder paste as the second component.

9. A method according to claim 8 wherein the step of determining coverage comprises the step of detecting an amount that first and last leads in at least two rows of the at least one lead overlaps first and last pads in at least two rows of the at least one pad.

10. A method for determining accuracy of a circuit assembly process, the method comprising the steps of:

capturing an image of an assembly of a substrate, the assembly formed by the circuit assembly process;

calculating coverage of the assembly from the image, the step of calculating comprising the steps of;

modeling a first component of the assembly as a first polygon and a second component of the assembly as a second polygon;

determining points of intersection of the first polygon and the second polygon, the step of determining points of intersection comprising the steps of;

constructing a first line segment from locator points of the first polygon;

constructing a second line segment from locator points of the second polygon;

determining a slope of the first and second line segments;

determining an intercept of non-vertical ones of the first and second line segments;

calculating a first point of intersection of the first and second line segments; and

determining if the first point of intersection lies between the locator points of the first and second line segments; and

determining points of enclosure of the first polygon and the second polygon; and

comparing the coverage to a threshold to determine accuracy of the circuit assembly process.

11. A method for determining accuracy of a circuit assembly process, the method comprising the steps of:

capturing an image of an assembly of a substrate, the assembly formed by the circuit assembly process;

calculating coverage of the assembly from the image, the step of calculating comprising the steps of;

modeling a first component of the assembly as a first polygon and a second component of the assembly as a second polygon;

determining points of intersection of the first polygon and the second polygon; and

determining points of enclosure of the first polygon and the second polygon, the step of determining points of enclosure comprising the steps of;

selecting a locator point of the first polygon;

selecting a line segment of the second polygon;

selecting a reference point of the second polygon; and

determining if the locator point and the reference point are on a same side of the line segment; and

comparing the coverage to a threshold to determine accuracy of the circuit assembly process.

12. A method for determining accuracy of a circuit assembly process, the method comprising the steps of:

placing solder paste at a site of a substrate to form an assembly, the site having a pad, the assembly formed by the circuit assembly process;

capturing an image of the assembly of the substrate;

calculating coverage of the assembly from the image, the step of calculating coverage comprising the step of detecting an amount of overlap of the solder paste and the pad;

comparing the coverage to a threshold to determine accuracy of the circuit assembly process;

outputting data regarding the overlap of the solder paste and the pad when the circuit assembly process is determined to be accurate;

placing an electronic part at the site of the substrate, the electronic part having a lead overlying the pad and the solder paste;

receiving the data regarding the overlap of the solder paste and the pad;

capturing an image of the assembly of the substrate; and

calculating coverage of the assembly from the image, the step of calculating comprises the step of detecting an amount that the lead overlaps the overlap of the solder paste and the pad.

13. A method according to claim 12 further comprising the step of adjusting any of the steps of placing solder paste and placing the electronic part when the amount that the lead overlaps the overlap of the solder paste and the pad is below a threshold.

14. A method for determining accuracy of a circuit assembly process, the method comprising the steps of:

placing an electronic part at a site of a substrate, the electronic part having a lead, and the site having a pad covered by solder paste; and

inspecting the part according to the substeps of;

modeling the lead as a first polygon and the pad as a second polygon,

determining points of intersection of the first polygon and the second polygon,

determining points of enclosure of the first polygon and the second polygon,

sorting the points of intersection and the points of enclosure, and

computing an area enclosed by the points of intersection and the points of enclosure,

comparing the enclosed area to an ideal overlap area, and

determining the lead to be defectively placed when the enclosed area is less than a percentage of the ideal overlap area.

15. A measurement machine for determining accuracy of a circuit assembly process, the machine comprising:

a vision section to capture an image of an assembly of a substrate, the image comprising a first shape representative of a first component of the assembly and a second shape representative of a second component of the assembly; and

a processing section coupled to the vision section, the processing section to identify a first set of numeric coordinates defining a location of the first shape, identify a second set of numeric coordinates defining a location of the second shape, determine coverage of the assembly by calculating overlap of the first and second components from the first and second sets of numeric coordinates and determine accuracy of the circuit assembly process from the coverage.

16. A measurement machine according to claim 15

further comprising a memory section;

and

wherein the processing section calculates overlap according to software instructions stored in the memory section.

17. A measurement machine according to claim 15 wherein the vision section captures the image of the assembly using two-dimensional sensing or three-dimensional sensing.

18. A method for determining accuracy of a circuit assembly process, the method comprising the steps of:

placing solder paste at a site of a substrate, the site having a pad; and

inspecting the site according to the substeps of;

modeling the solder paste as a first polygon defined by a first set of numeric coordinates and the pad as a second polygon defined by a second set of numeric coordinates,

determining points of intersection of the first polygon and the second polygon, the points of intersection occurring where line segments defined by the first set of numeric coordinates intersect with line segments defined by the second set of numeric coordinates,

determining points of enclosure of the first polygon and the second polygon, the points of enclosure occurring where coordinates of the first set of numeric coordinates are located within the second polygon or coordinates of the second set of numeric coordinates are located within the first polygon,

sorting the points of intersection and the points of enclosure, and

computing an area enclosed by the points of intersection and the points of enclosure,

comparing the enclosed area to an ideal overlap area, and

determining the solder paste to be defectively placed when the enclosed area is less than a percentage of the ideal overlap area.