Browse Prior Art Database

Method for Rapid Verification of the Presence of Electronic Components using Laser Distance Sensing

IP.com Disclosure Number: IPCOM000109194D
Original Publication Date: 1992-Aug-01
Included in the Prior Art Database: 2005-Mar-23
Document File: 2 page(s) / 141K

Publishing Venue

IBM

Related People

Singletary, A: AUTHOR

Abstract

Measurement of three-dimensional geometrical information from printed circuit board assemblies (PCBs) can be a valuable tool for defect detection and process control. Several commercial systems which implement this concept using laser distance sensors are currently available. In most cases, the geometrical information is used to determine precise positioning of either electronic components or solder paste. If the desired result is reduced to confirmation that a component is in fact present in each location where one is expected, significant simplification in system design is made possible. Such a system has been implemented with high throughput as a major goal.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 51% of the total text.

Method for Rapid Verification of the Presence of Electronic Components using Laser Distance Sensing

       Measurement of three-dimensional geometrical information
from printed circuit board assemblies (PCBs) can be a valuable tool
for defect detection and process control.  Several commercial systems
which implement this concept using laser distance sensors are
currently available.  In most cases, the geometrical information is
used to determine precise positioning of either electronic components
or solder paste.  If the desired result is reduced to confirmation
that a component is in fact present in each location where one is
expected, significant simplification in system design is made
possible.  Such a system has been implemented with high throughput as
a major goal.  Disclosed in this article are some of the concepts
employed to reduce the time required to gather the information needed
to make an accurate decision regarding component presence.

      In the implementation to be described, three significant
enhancements have been employed to make the system more efficient in
the application of component presence verification.  These are: 1)
reduction in the amount of geometric information to be collected at
each component 2) simplification of the movement path for the data
collection device, and 3) generalization of the algorithms used to
determine component presence.  Each of these will be described
separately.
REDUCTION IN THE AMOUNT OF INFORMATION COLLECTED

      If component positioning information is desired, numerous
geometric measurements must be taken, usually resulting in a number
of movements of the sensing element over each component. If the only
requirement is the verification of component presence, a much smaller
and more flexible subset of measurements will suffice.  In the most
extreme case, one measurement from the top surface of the component
and one measurement from the surface of the circuit board could be
compared to the expected component height and used to make a decision
on component presence.  In the described implementation, a series of
measurements is taken during a continuous linear move.  Positioning
of the sensor is such that the edge of the component to be verified
should fall approximately in the center of the series of
measurements.  Various software algorithms are used to detect the
measurement gradient associated with this edge and interpret the
geometric results.  Inaccuracies in positioning of the component or
sensor head result only in the shifting of the component edge within
the data series and do not degrade the ability of the system to
verify component presence.
SIMPLIFICATION OF THE MOVEMENT PATH

      The nature of this implementation requires that a single-point
sensing element be physically positioned over a large number of
component locations, with a series of measurements taken at each
location.  Any reductions in the number of movements needed to
perform the d...