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Method-for-inspecting-solder-paste-in-printed-circuit-board-manufacture

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Method for inspecting solder paste in printed circuit board manufacture

Details

Inventors: Wasserman, Harold;
Assignee: Teradyne, Inc. (Boston, MA)
Primary Examiner: Ryan; Patrick
Assistant Examiner: Knapp; Jeffrey T.
Attorney, Agent or Firm: Gamache; Richard E.

A method is available for inspecting a printed circuit board and solder paste deposited upon the printed circuit board, whereby both systematic defects occurring during a solder paste deposition process and random defects are located. The printed circuit board is continuously scanned by an inspection head immediately following the solder paste deposition process. Images of the printed circuit board are then analyzed for random defects such as missing solder paste, improper solder paste coverage, and solder bridging. Next, heights of solder paste deposits are sampled. A pattern of light is projected upon selected solder paste deposits, and images of the selected solder paste deposits are captured. Light triangulation techniques are then used for determining the height of each selected solder paste deposit. Variations in the height of solder paste are systematic defects occurring in the solder paste deposition process.

DETAILED DESCRIPTION With the foregoing background in mind, it is an object of the invention to provide a reliable way of detecting faulty solder paste for connecting electronic components to printed circuit boards.
Another object of the invention is to provide a way of detecting missing solder paste and improper solder paste coverage on conductive pads on a printed circuit board surface, and solder paste bridging between closely-spaced conductive pads.
Still another object of the invention is to provide a manufacturing defect analyzer for detecting faulty solder paste on conductive pads on a printed circuit board surface that is compatible with typical assembly line rates.
The foregoing and other objects are achieved by providing a manufacturing defect analyzer for inspecting a printed circuit board immediately following a solder paste deposition process.
The manufacturing defect analyzer takes a two-pronged approach for inspecting the printed circuit board.
First, the manufacturing defect analyzer obtains an indication of whether the solder paste deposition process is "in-control," in accordance with statistical process control techniques, by sampling heights of solder paste deposited upon selected conductive pads on a printed circuit board surface.
Second, the manufacturing defect analyzer inspects solder paste deposited upon each conductive pad on the printed circuit board surface for proper coverage, and then inspects each pair of adjacent conductive pads for solder bridges improperly connecting the adjacent conductive pads.
One feature of the manufacturing defect analyzer includes an improved lighting system for measuring the heights of solder paste deposited upon selected conductive pads.
In the preferred embodiment, the improved lighting system incorporates a projector for projecting a "cross" pattern of light on the solder paste deposited on the selected conductive pads.
Still further objects and advantages will become apparent from a consideration of the ensuing description and drawings

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