Steve, I agree that this is madness, unless the telecom supplier has an end use environment of 85/85 where power-on in humid conditions is a reality. Assuming that the equipment is not functioning in a steam environment, here is the "science" that you are looking for. Designers, when they have knowledge of the material characteristics, will design spacings dependent on the dielectric strength or dielectric withstanding voltage of the laminate. The values in the data sheets for the laminates specify these parameters, but only for lab ambient conditions, not after 85/85 conditioning. When you expose a hydrophilic material to a long exposure in hot/humid conditions, then you don't have that same dielectric strength (dramatically reduced) and you have violated the design assumptions. Polyimide is such a hydrophilic material. I believe Brian Ellis referred to it as blotter paper, in which I would concur. If you allow the circuit to dry out, then you return to the expected dielectric strength. You may already be at an unrealistic threshold with 2500 volts/mm gradient, as Brian also pointed out. Unless the designer had a firm value for dielectric strength of the substrate after 85/85 conditioning, which would change as the substrate rapidly dried out, then the design would not and could not work. Doug Pauls Steve Kelly <[log in to unmask]> Sent by: TechNet <[log in to unmask]> 06/25/2008 10:09 AM Please respond to TechNet E-Mail Forum <[log in to unmask]>; Please respond to Steve Kelly <[log in to unmask]> To [log in to unmask] cc Subject [TN] Bias voltage test in damp heat Good Day To All, Back in April I posted some queries on the tech-net about high voltage testing after 85C/85RH testing and was basically told this test was impossible and I agree with that assessment. But some things have a life of their own. To re-iterate: We are building a 4 layer flex circuit. All layers are 18 micron copper and all lines and spaces assuming perfect etch are 100 micron lines and 100 micron spaces. My customer for some reason signed up to pass a 250 volt test after 1000 hours of 85C/85RH damp heat test. My premise is being in this case a polyimide build if they dried the circuit after this test it should pass. They do not want to dry it and still have it pass. The previous threads in summary said this test was "madness" - I agree but what is the scientific explanation of why this is madness. Please note this requirement is being driven by very large telecom companies and the worlds largest provider of internet gear. Thanks again for the help. Regards Steve Kelly Steve Kelly (416) 750-8433 (work) (416) 750-0016 (fax) (416) 577-8433 (cell) --------------------------------------------------- Technet Mail List provided as a service by IPC using LISTSERV 15.0 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/contentpage.asp?Pageid=4.3.16 for additional information, or contact Keach Sasamori at [log in to unmask] or 847-615-7100 ext.2815 ----------------------------------------------------- --------------------------------------------------- Technet Mail List provided as a service by IPC using LISTSERV 15.0 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/contentpage.asp?Pageid=4.3.16 for additional information, or contact Keach Sasamori at [log in to unmask] or 847-615-7100 ext.2815 -----------------------------------------------------