Optics: measuring and testing – By configuration comparison – With comparison to master – desired shape – or reference voltage
Reexamination Certificate
2002-05-31
2004-09-21
Stafira, Michael P. (Department: 2877)
Optics: measuring and testing
By configuration comparison
With comparison to master, desired shape, or reference voltage
Reexamination Certificate
active
06795186
ABSTRACT:
FIELD OF THE INVENTION
The present invention generally relates to automated optical inspection systems, and more particularly to references used in the automated optical inspection of electrical circuits.
BACKGROUND OF THE INVENTION
Electrical circuits, such as electrical circuits found on printed circuit boards, ball grid array substrates, semiconductors and other similar electrical circuits, typically are inspected during various stages of their manufacture using automated optical inspection apparatus. Automated optical inspection (“AOI”) conventionally is performed for one or more of the following reasons: to ensure that various elements, referred to herein as features and described hereinbelow in greater detail, that should be in an electrical circuit according to a design do indeed exist in the electrical circuit being inspected; to ensure, that the features are appropriately placed and appropriately shaped; and to ensure that undesired features are not present.
It is well known to inspect electrical circuits for the existence and placement of features by identifying features in an electrical circuit being inspected according to their morphology, determining the location of each such feature, and then matching each feature in the electrical circuit to a corresponding feature in a reference. References may be generated from a “golden” electrical circuit which is an electrical circuit that is known to be good or alternatively from computer generated data such as computer aided design (“CAD”) data or computer aided manufacturing (“CAM”) data. Additionally, neighboring identical regions in an electrical circuit may be used as mutual references.
In conventional automated optical inspection systems, a global tolerance is applied to all features, or to all features of a particular morphological type. As used herein the term “tolerance” refers to a distance by which the respective locations of corresponding matching portions, such as matching features, in an inspection input and in a reference input may deviate from each other without the feature in the inspection input being considered defective. Thus, a feature in an electrical circuit being inspected does not have be located at the exact location as indicated by the corresponding matching feature in a reference. Rather the location of a feature in an electrical circuit being inspected may deviate from an exact location indicated by its corresponding matching feature in the reference within the limits of the tolerance. A conventional AOI system that applies a tolerance dictated by feature morphology is an Inspire™ 9000 AOI system available from Orbotech Ltd. of Yavne, Israel.
In some modern electrical circuit designs not all features require the same tolerance in the sense that some features require greater precision in location than other features, even for features of the same morphological type. Degrees of precision which determine a tolerance are typically provided as part of an electrical circuit design or are input by a user. The use of a global tolerance applying to all features, or a feature morphology dictated tolerance applying to all features of the same morphological type, in an electrical circuit being inspected generally leads to an undesirably large quantity of “false alarm” defects if the tolerance is set to be too low, or to an undesirably large quantity of undetected defects if the tolerance is set to be too high.
SUMMARY OF THE INVENTION
The present invention seeks to provide an improved system and method for inspecting electrical circuits for defects.
The present invention further seeks to provide an improved method for preparing a reference for use in inspecting electrical circuits.
A general aspect of a preferred embodiment of the present invention relates to a system for automatically optically inspecting electrical circuits by matching portions of an electrical circuit being inspected to corresponding portions in a reference, wherein various tolerances are provided for the portions as a function of a characteristic thereof Preferably, the characteristic is one or more of a spatial characteristic, an optical characteristic or a suspected shape aberration. The spatial characteristic preferably is one or more of separation between two portions, a spatial location in the electrical circuit, a density of features in an electrical circuit. The optical characteristic preferably is one or more of a color, an optical characteristic associated with a material from which a feature is formed, or a level of reflectivity associated with a feature. The characteristic may be any one single characteristic, any combination of the preceding characteristics, or any combination of the preceding characteristics in further combination with a morphological characteristic of a feature.
Another aspect of a preferred embodiment of the present invention relates to a method for generating a reference to be used in the automated optical inspection of electrical circuits. Preferably the reference includes various tolerances that are applied to features in the electrical circuit as a function of a spatial characteristic, an optical characteristic, a shape aberration, any combination of the preceding characteristics, or any combination of the preceding characteristics in further combination with a morphological type associated with a feature.
Still another aspect of the present invention relates to a method for applying adaptive tolerances to references employed in the automated optical inspection of electrical circuits. An image to be used as a reference during automated optical inspection is analyzed, preferably by computer, to identify various spatial or optical characteristics of features therein. Features are classified by their characteristic, marked and saved as a reference. Prior to automatically optically inspecting an electrical circuit, tolerances are provided independently of the classification applying to features. An inspection reference is generated by merging the reference and the tolerances and by applying the tolerances as function of the characteristics.
There is thus provided in accordance with a preferred embodiment of the present invention a system for inspecting electrical circuits comprising a proximity indicator for indicating the proximity of at least a first portion of an electrical circuit to at least a second portion of an electrical circuit; circuitry, responsive to an output of said proximity indicator, for providing a tolerance output based on the proximity of said at least a first portion of an electrical circuit to said at least a second portion of an electrical circuit; and fault detection circuitry operative in response to inspection inputs representing an electrical circuit being inspected to provide an output indication of faults in said electrical circuit being inspected based at least in part on said tolerance output.
Preferably, the first portion and the second portion are in a representation of an electrical circuit of the same type as said electrical circuit being inspected. Generally, the first portion and said second portion are features in the electrical circuit, typically an open end, a pad, or a junction.
Further in accordance with a preferred embodiment of the present invention, the proximity indicator is operative to indicate the proximity between two features having a same morphological type. Alternatively, the proximity indicator is operative to indicate the proximity between two features having a different morphological type.
Additionally, in accordance with a preferred embodiment of the present invention, the tolerance is a permitted spatial separation between a feature of a reference electrical circuit and a corresponding feature of an electrical circuit being inspected.
Moreover, in accordance with a preferred embodiment of the present invention, a feature is classified as being isolated or non-isolated with reference to a spatial separation threshold between neighboring features, and the tolerance for a feature that is classified as isolated is greater than the tolerance for a fi
Aspir Doron
Kraus Menahem
Nadivi Jacob
Orgad Dror
Ladas & Parry
Orbotech Ltd.
Stafira Michael P.
LandOfFree
Adaptive tolerance reference inspection system does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Adaptive tolerance reference inspection system, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Adaptive tolerance reference inspection system will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3229816