This technical information has been contributed by
Minnesota Rubber & Plastics

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Redesign of Reshored Test Cell Solves Quality Issues

Sealing Assemblies

MINNEAPOLIS and KOKOMO, Ind.—Designing and molding complex sealing assemblies for intelligent electronic devices is a core expertise of Minnesota Rubber and Plastics, a Minneapolis-based company that provides components and assemblies for electronics, medical, water, and transportation markets. Typical of the company's expertise is a reshored test cell assembly that the firm redesigned and manufactured for use in a printed circuit board (PCB) contamination tester. By improving the test cell design over the offshore supplier's design, Minnesota Rubber and Plastics improved the vacuum seal of the device by 50 percent, allowing the device to test consistently at 24 In. Hg. As it turned out, Minnesota Rubber and Plastics' experience in molding, assembling, and packaging the cleanliness test cell provides valuable lessons not only in correct mold design, but also in how important logistics and responsiveness can be in a vendor-customer partnership.

The molded test cell is used in the innovative C3 by Foresite Inc. (www.residues.com), a localized cleanliness tester. Foresite, designer and manufacturer of the C3, is a process consulting company and analytical laboratory with a long-standing reputation for solving reliability issues involving electronic assemblies. Out of customer need, which includes numerous Fortune 500 companies and many governmental agencies, Foresite designed the patented C3, which is sold throughout the world.

Foresite's C3 is designed for real time cleanliness analysis in the manufacturing facility. Using a steaming process, residues in sensitive areas of printed circuit boards are extracted and then tested electrically for corrosivity. Within minutes, the test provides results on the cleanliness of the surface to allow problem remedies early in the printed circuit board's production. The C3 tests 0.1 sq. in. (0.1in2) every time, removing residue in this tested area rather than testing the entire surface of the sample, which can dilute test results and mask trouble areas.

The heart of the system is a unique test cell that consists of two molded components (body and cap), an electrode, and an end seal. The electrode fits into two slots in the cell body, which aligns and holds it securely in position. The cap is snapped into the opening of the test chamber in the cell body. One-sixteenth inch (1.6 mm) diameter flow paths direct microbursts of steam to the test area and the collected sample from the three-eighths inch (9.5 mm) diameter opening in the end seal into the test chamber. In the cell, the sample is then analyzed electrically and the information is transmitted to the system's computer for determination of the sample's cleanliness; data are stored for future reference. The test cells are disposable and are designed for one time test usage.

The outsourced molding and assembly of these test cells had proved challenging for Foresite's supplier. Although qualified in many respects, the overseas source had quality difficulties during the prototyping, pre-production, and early production stages, which slowed the introduction of the new cell. Foresite also added secondary operations to ensure clean, functional cells.

"Quality questions arose initially because of the mold design," said Steve Ring, director of new product development at Foresite. "The mold components weren't cooled properly, which influenced component fit when assembly was attempted. The effectiveness of the snap fit we designed was impacted. The result was that vacuum readings within each cell's test chamber were too low and too varied. These vacuum readings had to be consistently correct to ensure reliable operation of the system from one test to the next. In addition, molded part cleanliness, despite secondary cleaning efforts by the overseas supplier, did not meet our specifications. Making certain finish molded components were clean and fit together tightly was key. So we looked for a better way and found it through Bob Howard of Minnesota Rubber and Plastics while visiting an area trade show."

Identifying Need and Providing Fast Solution is Key to Successful Outcome

"Howard is a real pro who's been around the molding business for a long time and knows how to react to a prospect with a problem," said Rick Strand, director of engineering for Minnesota Rubber and Plastics. "With Howard's upfront help, we quickly put a team together headed up by John Fredrichs, manufacturing engineer, to analyze the molded assembly and make recommendations. From the molded parts Mr. Ring showed us and from the descriptions of the assembly and contamination problems, we knew the solution had to start with the mold components and their design. Mr. Ring was confident enough with our early recommendations to have the mold components shipped from his overseas source to our Minnesota facility for firsthand analysis and recommendations."

Onsite, the MR&P team observed that the mold components had cooling deficiencies for producing the critical test cell with its aligned pathways and snap fit design. Both the cell body mold and cell cap mold had cooling lines in them, but the lines were insufficient in certain critical areas. So the MR&P team increased these cooling areas to improve the molded part dimensions, the part's dimensional stability, and the machine molding cycle.

"A molded assembly's fit and cleanliness starts with the correct mold design," said Strand. "Without proper cooling and other features designed into the mold, all other steps in the mold/assembly process downstream can go awry."

At the same time, the MR&P team drew on its experience with medical grade polypropylene and went to a higher quality blend. With satisfactory mold cooling and a higher grade resin, sample parts were much improved as to fit, cleanliness, and function.

"As an added measure for cleanliness, Minnesota Rubber and Plastics integrated the use of a recirculating, filtering cleaning tank system, along with a parts drying oven, to follow the molding operation prior to assembly," said Ring. "Then we did some trial runs on the components and final assemblies. Tests showed the test cells had a 50 percent vacuum improvement, testing consistently at 24 In.Hg. Tests in Foresite's laboratory verified the cell cleanliness improvements, bringing the parts up to Foresite specifications and eliminating the cell cleaning at Foresite. When delivered, each test cell receives a final testing and approval by Foresite."

Molded on Automated Equipment in Class 100,000 Facility

As an EN ISO 13485:2003 certified supplier, Minnesota Rubber and Plastics is certified with quality management systems to serve the medical industry. Although not a medical device, Foresite's C3 has many similar quality disciplines required for medical manufacturing and therefore benefits from these processes.

Molding of the test cells, for example, is done in Toyo PLCS9 presses equipped with Yushin robots located in a class 100,000 clean molding environment. Following cleaning, drying, assembly, and inspection, the test cells are packaged in trays of 25 cells with 4 trays bagged and boxed with outer barcode labels to ensure material lot and part traceability. MR&P production is set up to handle all volume requirements on a just in time basis.

"Having Minnesota Rubber and Plastics handle the entire process made sense the further we got into each of the mold, assemble, and packaging steps," said Ring. "Good communication plus the time and distance advantages with MR&P really were important to the success of this project, but the overriding factors were their capabilities and responsiveness."

This technical information has been contributed by
Minnesota Rubber & Plastics

Click here to find suppliers

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