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Method and apparatus for locating, inspecting, and placing large leaded devices
| Details |
Inventors: Cullen, Christopher P.; Engel, Antonie J.;
Assignee: Cognex Corporation (Natick, MA)
Primary Examiner: Boudreau; Leo
Assistant Examiner: Tadayon; Bijan
Attorney, Agent or Firm: Stretch; Maureen
In a machine vision system capable of capturing an optical image of a semiconductor electronic component part and digitizing the optical image, a method for locating, inspecting and placing parts known as large leaded devices, by estimating a part's location; estimating the approximate location of a group of leads; computing the center and angle of a lead scan search rectangle within which the leads in a group of leads must be located; scanning a lead scan search rectangle to locate lead edges and compile a list of edges; extracting lead positions; updating the part location estimate; and repeating these steps for each lead set to find all leads and lead centerlines; then calculating an optimal part position estimate by matching found lead positions with expected lead centerlines; and finally, inspecting the leads. A statistical lead rejection procedure is included during lead extraction. |
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DETAILED DESCRIPTION The invention provides a method and apparatus for locating, inspecting and placing large leaded devices.
In a preferred embodiment of the invention, the leads are found in sets by estimating the approximate location of a group or set of leads; computing the center and angle of a lead scan search rectangle within which the leads in a set of leads must be located; scanning a lead scan search rectangle to locate lead edges and compile a list of edges; extracting lead positions, using a statistical lead rejection procedure for defective leads at the ends of a set; updating the part location estimate; and repeating these steps for each lead set to find all leads and lead centerlines.
Once the leads have been located according to the method and application of the present invention, the apparatus calculates an optimal part position estimate by matching found lead positions with expected lead centerlines; and, finally, the leads are inspected.
Any of a number of leaded device types can be handled.
It is an object of the present invention to improve the speed and reliability of the location of the entire leaded part.
Devices with few leads can be found more quickly and reliably according to the method and apparatus of the present invention while the speed and reliability of locating large leaded devices is significantly improved.
For purposes of illustration, and not by way of limitation, two general types of large leaded devices are discussed herein.
For example, a preferred embodiment of the invention works with large leaded devices called J-lead devices or PLCC or SOJ's, among other appellations.
A preferred embodiment of the invention also works with "gullwing" leaded devices, also known as QFP or SOIC devices.
In a preferred embodiment of the invention device information can be derived and stored in a device description.
In a preferred embodiment of the invention, a training step is used to create information about a new device.
It is an object of the invention that the information about a device which is gathered in this way can be done at a high-level, in which case, the user supplies less detail about the device and the method and apparatus of the present invention calculates the details from a good model, or the information can be supplied at a low-level
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Image Analysis 
