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Printed Circuit Board Cleanliness Testing
Improved molding process ensures consistency
Randy Frank, contributing editor -- Design News, March 19, 2007
Examining for contamination in a localized area of a Printed Circuit Board (PCB) assembly can be a critical part of process control in a manufacturing facility. Foresite Inc. makes a Localized Ionic Cleanliness Tester and Monitoring Tool called the C3 that simplifies the task. The C3 detects the presence of conductive or corrosive residues. To ensure consistent measurements, Foresite turned to Minnesota Rubber QMR Plastics for the test cell.
The C3 extracts about a 2.5 ml sample into a collection cell for testing from a localized area of 0.1 inch². With test results provided within minutes, users can detect cleanliness problems early in the manufacturing process. The small test area prevents diluting the sample and masking trouble areas. Accurate results in cleanliness tests start with the test cell.
The disposable molded test cell consists of two molded components (body and cap), an electrode and an end seal. Two slots in the cell body hold and align the electrodes and the cap snaps into the opening of the test chamber in the cell body. Microbursts of steam directed to the test area by a 1/16th-inch (1.6 mm) diameter flow path allow sample collection in the test chamber through a 3/8-inch (9.5 mm) diameter opening in the end seal. The system's computer analyzes and stores the measurements.
QMR was not the initial supplier for the test cell but Foresite challenged QMR to solve inconsistent vacuum reading and cleanliness problems. QMR engineers increased the cooling area in the mold to improve dimensional control, revised a portion of the molding operation for improved cleanliness and used a higher grade of medical grade polypropylene. With these modifications, the test cells have a 50 percent improvement in vacuum, testing consistently at 24 inches of Hg, and pass Foresite's molded part cleanliness specification.
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