tailieunhanh - Conductive Polymers and Plastics in Industrial Applications Part 13

Tham khảo tài liệu 'conductive polymers and plastics in industrial applications part 13', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Electronic Packaging 249 amines cause polycarbonate parts to crack or craze . A general rule for polycarbonate compatibility is that there be no serious crazing up to a 2000 psi stress level at 158oF. SURFACE RESISTIVITY AND STATIC DECAY Federal Test Standard 101C Method requires a static protective material to have a static decay time of less than 2 seconds. EIA 541 defines a static dissipative material as one which has a surface resistivity of between IE5 and 1E12 Ohms per square. These two requirements are correlatable only for monolayer and homogeneous films. Multi-layer coextrusion technology as well as laminated materials separate these two parameters. The conception persists that a low surface resistivity is required to dissipate a static charge and that a good static decay is sufficient to characterize a dissipative material. The dissipation of static charges may be accomplished by several means across the surface by volumetric conduction through a relatively thin high resistivity skin across a subcutaneous conductive or dissipative layer and out of the film again through the thin high resistivity skin. Metal laminates actually fool the static decay test. The reason for their seemingly instantaneous dissipation of charges is that the static decay time is dominated by voltage suppressed by the ground plane being capacitively coupled to the metal layer. For metal laminates with surface resistivities less than 1E12 Ohms square one can assume that the surface charges decay in less than 2 seconds. For those layers with resistivities above this level no assumption can be made from the results of the static decay test as described in Method . The application of laminations or coextrusion technology to ESD materials allows the separation of the parameters of surface resistivity and static decay for laminates that do not contain metal or metallized layers. Coextrusion is the process of forming multi-layer materials from several extruders directly out of