Brian, Some of polyimide got Corona discharge problem... But the CR type solve the problem (Corona resistance). Nothing is perfect (otherwise, we would out of job ;-). jk >-----Original Message----- >From: TechNet [mailto:[log in to unmask]] On Behalf Of Brian Ellis >Sent: Thursday, April 24, 2003 4:44 AM >To: [log in to unmask] >Subject: Re: [TN] wire coatings > > >May I come back to the chemical safety problem? > >PVC will support combustion and will give off toxic fumes >(mainly hydrogen chloride and carbonyl chloride) if heated to >beyond decomposition temperature. Carcinogenicity is not a >valid reason as it is only by repeated exposure over a long >period (chronic toxicity) will it kick in. A single exposure, >such as in a fire, is a question of acute toxicity, where the >metabolic action of the toxins is different (in this case, >mostly from the HCL potentially causing damage to lung tissue). > >PTFE (Teflon (R)) also gives off potentially toxic fumes, in >the event of heating to decomposition temperature, such as in >a fire. However, because the molecule is perfluorinated, it >will not burn. The decomposition products, in conjunction with >other organic molecules or in the presence of water vapour are >actually more toxic than with PVC (hydrogen fluoride and >carbonyl fluoride) and deaths have been recorded due to a >small chip of PTFE landing on a lit cigarette end. > >So the major difference, from the chemical point of view, is >the higher combustibility of PVC. > > From the physical point of view, PTFE is an infinitely >superior insulator, provided it is well sintered (pure PTFE >does not melt before decomposition). It has a lower dielectric >constant, so that connections will have a different >characteristic impedance in high speed/frequency applications. >However, because it is less "plastic", as others have >observed, it's a bugger to strip off wires without damaging >the metal with nicks and breaking off strands. Obviously, the >thicker the strand, the less likely it will break, but there >is always a higher risk of mechanical weakening of the metal >where the insulation ends, than with PVC. Badly sintered PTFE >insulation is often a cause for reliability problems, as well. >Coloured PTFE is sometimes electrically inferior as some >pigments have poorer characteristics than pure PTFE. > >Polyimides (e.g., Kevlar) are sometimes a good compromise but >may cause insulation problems if mechanically stressed (sharp >bends) under wet conditions. > >Brian > >Genny Gibbard wrote: >> Do you remember my question regarding the midplane assembly? >Turns out >> that there was a reel of mislabelled wire in house, and a >whole bunch >> of assembly has been done using a PVC coated wire, instead of the >> teflon coated wire I spec'd. Apparently the wire in question is >> obsolete, but they like using it better than the teflon, and want to >> continue to use that. I don't know much about wire coatings >- what is >> the difference between these two coating types, and when would you >> want to or not want to use them. I need to decide whether >we need to >> force them to change out the wiring they've already done. >> Sigh... >> Thanks for your help in advance. >> >> >> Genny Gibbard (mailto:[log in to unmask]) >> >> --------------------------------------------------- >> Technet Mail List provided as a free service by IPC using LISTSERV >> 1.8e To unsubscribe, send a message to [log in to unmask] with >following >> text in the BODY (NOT the subject field): SIGNOFF Technet To >> temporarily halt or (re-start) delivery of Technet send e-mail to >> [log in to unmask]: SET Technet NOMAIL or (MAIL) To receive >ONE mailing >> per day of all the posts: send e-mail to [log in to unmask]: >SET Technet >> Digest Search the archives of previous posts at: >> http://listserv.ipc.org/archives Please visit IPC web site >> http://www.ipc.org/html/forum.htm for additional >information, or contact Keach Sasamori at [log in to unmask] or >847-509-9700 ext.5315 >> ----------------------------------------------------- >> >> >> >> > >--------------------------------------------------- >Technet Mail List provided as a free service by IPC using >LISTSERV 1.8e To unsubscribe, send a message to >[log in to unmask] with following text in the BODY (NOT the >subject field): SIGNOFF Technet To temporarily halt or >(re-start) delivery of Technet send e-mail to >[log in to unmask]: SET Technet NOMAIL or (MAIL) To receive ONE >mailing per day of all the posts: send e-mail to >[log in to unmask]: SET Technet Digest Search the archives of >previous posts at: http://listserv.ipc.org/archives Please >visit IPC web site http://www.ipc.org/html/forum.htm for >additional information, or contact Keach Sasamori at >[log in to unmask] or 847-509-9700 ext.5315 >----------------------------------------------------- > --------------------------------------------------- Technet Mail List provided as a free service by IPC using LISTSERV 1.8e To unsubscribe, send a message to [log in to unmask] with following text in the BODY (NOT the subject field): SIGNOFF Technet To temporarily halt or (re-start) delivery of Technet send e-mail to [log in to unmask]: SET Technet NOMAIL or (MAIL) To receive ONE mailing per day of all the posts: send e-mail to [log in to unmask]: SET Technet Digest Search the archives of previous posts at: http://listserv.ipc.org/archives Please visit IPC web site http://www.ipc.org/html/forum.htm for additional information, or contact Keach Sasamori at [log in to unmask] or 847-509-9700 ext.5315 -----------------------------------------------------