In-circuit test fixture with integral vision inspection system

Abstract

An in-circuit test fixture performs both electrical tests on a Printed Circuit Assembly (“PCA”) and reads distinguishing features of a feature of interest of the PCA. The in-circuit test fixture physically supports an image sensor array. A light focusing means has a position relative to the distinguishing features and the image sensor such that a focused real image of the distinguishing features is imaged onto the image sensor. The image sensor outputs image information of the distinguishing features. A processor performs image analysis based on the image information of the distinguishing features to determine if defects exist.

Description

FIELD OF THE INVENTION [0001] The invention relates to the field of the automated testing of printed circuit assembly assemblies. BACKGROUND OF THE INVENTION [0002] A printed circuit assembly (“PCA”) is subject to many different types of defects during the assembly process. Accordingly, various test and inspection techniques are employed to locate these defects. Today, there are three general test methods used to find PCA defects: electrical test, optical (or visual) inspection, and x-ray inspection. Of these, electrical test, and in particular a technique known as “in-circuit test”, is the most mature and most commonly used technique. However, as physical access to nodes on the PCA via bed-of-nails probing decreases, in-circuit test is becoming more difficult. [0003] Some prevalent defects on PCA assemblies are missing, incorrect type or mis-oriented components. Missing components can occur when the components are either never loaded onto the board or they fall off during the assem...

AI Technical Summary

Problems solved by technology

A printed circuit assembly (“PCA”) is subject to many different types of defects during the assembly process.

However, as physical access to nodes on the PCA via bed-of-nails probing decreases, in-circuit test is becoming more difficult.

Some prevalent defects on PCA assemblies are missing, incorrect type or mis-oriented components.

Missing components can occur when the components are either never loaded onto the board or they fall off during the assembly process.

An incorrect type of component can occur when a component with the wrong electrical value is inadvertently loaded onto the board.

Improperly oriented components can occur when a component is loaded onto the board with a reversed polarity.

The above techniques each require at least some physical probing of the PCA nodes and are therefore ineffective for PCA assemblies with limited nodal access.

Although these methodologies can detect missing devices very effectively, they each suffer from their own limitation and disadvantages.

The major disadvantage of these techniques is that they require expensive manufacturing line equipment entirely separate from the in-circuit tester, and therefore also require an entirely new test step to be added to the manufacturing process.

The cost of adding such machines to the manufacturing process may be appropriate in some cases, but in other cases the need to do so represents a large disadvantage to these methods.

Additionally, some devices are electrically untestable even with probing.

While it is theoretically possible (e.g., on the bench with a single device under test (DUT)) to detect a single missing capacitor, in practice such detection is often not possible.

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