Polyimide 1, designers 0

My first experience with environmental testing was when I worked for a small R&D firm that was developing radiation-measurement equipment. One project was a radiation-detection badge for the U.S. Navy. The military specs required that the plastic badge survive hot and cold storage, a 6-ft drop onto a concrete floor, and depth testing down to 100 ft. All these tests were easy to perform, and with the property data sheets from suppliers the designer easily pinpointed a suitable ABS resin. A more-difficult project also under development was a detection system that needed flexible sensors for monitoring radiation. Manufacturing the sensor required encapsulating various radiation-sensitive materials in an adhesive that could be silk-screen printed onto flexible, thin-film substrates. The radiation-sensitive materials were thermoluminescent (TLD) phosphors that when heated from between 120 and 240°C emit light if they have been exposed to radiation. The amount of light emitted by the phosphor was proportional to how much radiation the sensor saw. Once the signal is zeroed, or read out, TLD phosphors can be used again. Traditional ways of heating such phosphors include heated metal planchets or hot gas. Our method, however, employed a 15-W CO laser which sped up the heating process and let us design a system that could heat a printed array of TLD phosphor spots individually. By reading each spot and treating the corresponding signal as a pixel, an algorithm could then plot the readings as a two-dimensional contour map of exposure. For selection of the substrate and adhesive, supplier property data sheets were only helpful in rejecting materials that could not withstand high temperatures. With hindsight, it's easy now to see how some of the problems we encountered late in the design phase may have been avoided if we would have been more vigilant testing prototypes made with sample materials,