SMTA International Conference Proceedings


SOLDER PASTE INSPECTION FOR SCREEN PRINTING

Author: Jeff Woolstenhulme
Company: Cognex Corporation
Date Published: 9/12/1999   Conference: SMTA International


Abstract: In the printed circuit board (PCB) assembly process, excess solder paste, a lack of paste, misaligned paste on a pad may cause defective electrical connections between a component and the board once solder joints are formed.

Traditionally, many manufacturers have used some type of In Circuit Test (ICT) or X-ray technology to inspect solder joints. While they may help unveil defects caused by the printing process, these approaches do not monitor the printing process itself. Thus, misprinted boards are permitted to pass through various value-adding processing steps and ultimately to the placement stage of production. Manufacturers are then left with a faulty board that needs to undergo costly and time-consuming rework, and no clear answers as to what the root cause of the defects may have been.

Ideally, defects that occur during the screen printing process should be detected prior to the mounting of components to the board, in which case a board could be cleaned and reused. One method for detecting solder paste defects early in the PCB assembly process has been with machine vision technology.



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