US 6,151,406 AGranted

Method and apparatus for locating ball grid array packages from two-dimensional image data

AssigneeCognex Corporation

InventorsYian Leng Chang, Nigel John Foster, Jane Alice Loizeaux

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Abstract

A ball grid array inspection and location method and apparatus includes a raw feature finding processor which uses a feature finding algorithm to find ball features (irrespective of number) and generate a list of raw features as an X and Y location for each feature located. An angle estimation processor receives the list of raw features, a user estimated orientation angle, and ball-to-ball pitch information and determines an estimated grid angle. An on-grid check processor receives the estimated grid angle, the list of raw features and the ball-to-ball pitch information and produces a set or list of on-grid features in the form of a list X and Y translation parameters for each feature/ball found on-grid. A correspondence processor receives the list of on-grid features and model grid information and searches for correspondence between the two dimensional array of found grid features and the two dimensional array of model grid features to yield a direct mapping of respective two dimensional spatial relationships between model features and found features, which is used to determine the spatial relationship between model space and physical space in order to position/align balls of the device in physical space in accordance with model balls in model space. A least square fit is effected to refine position of the device in terms of its translation and rotation.

Claims19

Dependent claims

A vision system for locating and positioning ball grid array features for placement on an electronic assembly, comprising:

a raw feature finding processor receiving as inputs model information of a ball grid array device, captured image information as a two dimensional image of said ball grid array device, and calibration information comprising a two dimensional transform relating image space to physical space, said raw feature finding processor finding ball features in said captured image and generating a list of ball features as an X and Y location of each ball feature in physical space;
an angle estimation processor receiving said list of ball features from said raw feature finding processor and receiving as additional inputs a user estimated orientation angle and ball-to-ball pitch information from said mode information, said angle estimation processor determining therefrom an estimated grid angle;
an on-grid check processor receiving said estimated grid angle, said list of ball features and said ball-to-ball pitch information and fitting said list of ball features to a grid to eliminate noise features and refining said estimated grid angle, said on-grid check processor producing a set of on-grid balls as a list of X and Y translation parameters for each ball found on-grid;
and
a correspondence processor receiving said set of on-grid balls and said model information of said ball grid array device, said correspondence processor searching for correspondence between said on-grid balls and model balls of said model information of said ball grid array device and providing a direct mapping of respective two dimensional spatial relationships between said model balls and said set of on-grid balls
wherein correspondence between said model balls and said set of on-grid balls provides a mapping of model balls to corresponding balls in image space which is used, along with said two dimensional transform relating image space to physical space to position/align balls of said ball grid array device in physical space in accordance with model balls in model space.

3 more elements

A method of determining a spatial relationship between a two dimensional grid of model features in model space and a two dimensional grid of found features in image space, for positioning said two dimensional grid of found features in physical space, said method comprising the steps of:

receiving at a processor, inputs including model information of a feature grid array device in model space, captured image information as a two dimensional image of said feature grid array device in image space, and calibration information comprising a two dimensional transform relating image space to physical space;
processing said inputs to find features in said captured image and to generate a list of features as an X and Y location of each feature in physical space;
processing said list of features and additional inputs including a user estimated orientation angle and feature-to-feature pitch information to determine therefrom an estimated grid angle;
processing said estimated grid angle, said list of features and said feature-to-feature pitch information to fit said list of features to a grid to eliminate noise features, to refine said estimated grid angle, and to produce a set of on-grid features as a list of X and Y translation parameters for each feature found on-grid;
and
processing said set of on-grid features and said model information of said feature grid array device to search for correspondence between said on-grid features and model features of said model information of said feature grid array device and providing a direct mapping of respective two dimensional spatial relationships between said model features and said set of on-grid features
wherein correspondence between said model features and said set of on-grid features provides a mapping of model features to corresponding features in image space which is used, along with said two dimensional transform relating image space to physical space, to position/align features of said feature grid array device in physical space in accordance with model features in model space.

4 more elements

Dependencies are inferred from the claim text.