Browse Prior Art Database

Component Placement Verification Through Height Discontinuities

IP.com Disclosure Number: IPCOM000062155D
Original Publication Date: 1986-Oct-01
Included in the Prior Art Database: 2005-Mar-09
Document File: 5 page(s) / 65K

Publishing Venue

IBM

Related People

Grossman, DD: AUTHOR [+3]

Abstract

Measuring component height by a light scanner and photodetector, and processing the height data by computer, allows automated verification of presence, position and orientation of electronic components after assembly on printed circuit boards. Most current electronic systems are packaged as printed circuit boards on which electronic components (integrated circuits, resistors, capacitors, etc.) are mounted using wave-soldering (for through-hole components) or vapor-phase soldering (for surface-mounted components). An increasing fraction of the cost of electronic systems goes into the assembly of components onto boards. Data-driven, automated machines reduce the cost and time of component placement.

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Component Placement Verification Through Height Discontinuities

Measuring component height by a light scanner and photodetector, and processing the height data by computer, allows automated verification of presence, position and orientation of electronic components after assembly on printed circuit boards. Most current electronic systems are packaged as printed circuit boards on which electronic components (integrated circuits, resistors, capacitors, etc.) are mounted using wave-soldering (for through-hole components) or vapor-phase soldering (for surface-mounted components). An increasing fraction of the cost of electronic systems goes into the assembly of components onto boards. Data-driven, automated machines reduce the cost and time of component placement. It then is necessary to verify the presence, position, orientation (polarity) and even the identify of components after placement to prevent costly rework after the components have been soldered. This automated method to verify presence, position, and orientation of electronic components does not address the problem of verifying component identity (e.g., SN7406 vs SN7404), since many automated placement machines have some capability for component-type verification. Many research laboratories and commercial companies have tried to develop systems for verifying component placement. In general, these systems have worked by processing two- dimensional images of components to extract component boundaries based on differences in reflectivity between components and the circuit board.

This approach is confounded by the complexity of the visual environment (underlying circuit patterns, markings on components, highly specular or transparent components, etc.) and by the photometric variability of the components themselves; for example, a dual-in-line (DIP) integrated circuit package from manufacturer A may be specular while one from manufacturer B may be matte, substantially changing its appearance under different lighting conditions. Fig. 1 shows the overall structure of the component verification system. The system includes range sensor 1, printed circuit board 2, transport mechanism 3, and computer 4, to verify components 5. 1.

Range Sensor: This measures the distance (relative to the sensor) to one or more points on the surface of the components or circuit board. The device must be capable of resolving range values to a fraction of the depth of the smallest component (e.g., O.1 milli meter for chip capacitors and transistors) over a range on the order of the depth of the largest component (e.g., 10 millimeters for double height DIPs.) In addition, it must be possible (through dead reckoning or calibration) to determine the position (in the plane of the board) of the point(s) whose range is being measured to an accuracy on the order of the component tolerances (e.g., 0.05 millimeter.) 2. Printed Circuit Board: This contains the components to be verified. The board must contain align...