Usage of Fusible Sewing Threads to Improve the Waterproof Property of Seam

In classical stitching process, needle holes occur during the penetration of the needle through the fabric. If the waterproofness of the sewn product is important, the water leakage from these holes must be prevented. To prevent this negative situation, different techniques such as sealing of seams with waterproof tapes, joining the textile materials by bonding or welding are used. Among these techniques, there is no needle damage in bonding and welding and all the seam area is covered by thermal or chemical bonding. In sewing technology, the water leakage is prevented by covering all the seam area with seam sealing tape. These three methods have different effects on the physical properties of the seams obtained. Instead of covering the whole seam area, covering just the needle damages is the focus of this research. With this aim, fusible sewing threads were used to cover the needle damages to increase the waterproof performance of seam line. The fusible sewing threads have not been used for obtaining waterproof seams before. In this research, the fusible sewing threads were used as lower thread in different combinations. Initial results of waterproofness test show that, melted fusible threads improve the waterproof performance of seams. In other words, the needle damages on sewn fabric can be covered by melted fusible sewing thread. However, unbalanced seam is the negative side of this research because of using different threads as needle and bobbin thread. Additionally, there is no variety of fusible threads to select an appropriate one for this method. The study is hoped to be a sample for the further studies on this method, using different fusible threads, fabrics, seam types and even improving new fusible threads for this waterproofing method.

Hermetic Sealing of Stainless Steel Packages by Seam Seal Welding

Welded stainless steel packages offer a number of advantages relative to those fabricated from kovar or aluminum metals and braze sealed. They are highly resistant to corrosion, especially in aqueous or elevated temperature environments, are mechanically stronger, dramatically so at temperatures above 100°C, exhibit lower outgassing rates, and have better vibration characteristics. Since welded stainless steel packages do not require over plating to facilitate braze sealing, combined material and fabrication costs are lower than kovar or aluminum packages. Also, unlike kovar, stainless steel is nonmagnetic, which is advantageous in many electronic applications. For sealing stainless steel packages, we elected to use seam sealing rather than laser welding for two reasons. Seam sealing subjects the package contents to lower thermal excursions than laser welding because less material is melted to achieve a weld in seam sealing. Second, seam sealing confines the molten material between the cover and package, where as laser welding produces a surface filet. Consequently, there is more opportunity for molten metal to splatter or react with the atmosphere in laser welding than in seam sealing. We successfully developed a process to weld a 2 millimeter thick cover onto a box with dimensions of 75 mm long by 50 mm wide by 15 mm deep using a seam sealer. The box walls were 1 mm thick and were penetrated by a dozen glass insulated feedthrus on one side. Both cover and box were fabricated from 316L stainless steel. A combination of analytical and finite element modeling were used in conjunction with a designed experiment to optimize the process variables of roller angle, speed and pressure, weld current, pulse shape, duration and spacing, number of weld passes, and sealing atmosphere. Weld quality and seal integrity were evaluated by leak testing before and after environmental stressing, mechanical testing and metallographic cross sectioning. The effects of component dimensions and tolerances on seal integrity were also investigated. Particular attention was paid to cover flatness, flange thickness, and tightness of fit between the cover and box. The process development was concluded by conducting a qualification experiment that used the optimized process parameters with controlled variation about their nominal values. A 100% yield of sealed boxes was obtained. These test articles were then subjected to various environmental screening tests, which were all passed with no failures.

Automated Assembly and Hermetic Packaging of MOEMS for Applications Requiring Extended Shelf-Lives

In this paper we describe two modular automated microassembly systems, along with a several packaging processes that have been integrated to produce reliable and cost-effective MOEMS devices. The automated and packaging systems consists of robotics such as pick and place, insertion and fastening, machine vision and controls, and processes such as die attach, solder reflow by laser, wire bonding and seam sealing. The target MOEMS devices are intended for applications requiring a minimum twenty year shelf-life.