Hi Brian: To obtain good results during SIR testing the voltage should not exceed 100V/mm. Is that a true statement? This is for uncoated boards. For coated boards it should be higher, Shouldn't it? Regards, Ramon -----Original Message----- From: TechNet [mailto:[log in to unmask]]On Behalf Of Brian Ellis Sent: Tuesday, November 16, 2004 3:26 AM To: [log in to unmask] Subject: Re: [TN] Solder Mask expectations / pushing the envelope? I'm sorry, as I've said hundreds of times and few seem to think it important, it is not the test voltage that matters; it is the voltage gradient. When will this be understood? If a test pattern has spacings of 0.1 mm and you apply 5 V, the 50 V/mm is moderate. If you apply 400 V, you have to have an 8 mm spacing to achieve the same moderate conditions. Believe it or not, gradients as low as 5 V/mm still cause a significant and measurable ionic migration within FR-4 and other epoxies, even under room conditions, resulting in polarisation and electrophoresis. At 150 V/mm, the conditions are still just acceptable. Anything higher and the ionic forces within the epoxy will start to cause a slow breakdown, which can be accelerated by increased moisture absorption causing the ions to be more mobile. Note that this migration is not a conduction, at least until breakdown starts. You may remember in a recent post, I explained the prepolymerisation of epoxy resins between epichlorohydrin and bisphenol-A (or TBBPA) in the presence of sodium hydroxide. I mentioned that the NaOH was used to capture the chlorine atom of the epichlorohydrin. The resultant sodium chloride is partially removed by ion exchange in electrical grade resins and it is the residual quantities of this molecule that cause the migration I mention (and cause the hygroscopicity, high dielectric constant and poor power factor of the cross-linked resin). It is also possible that the sodium silicate in the glass may also play a minor role. I brought up all these points in various papers in the late 80s, early 90s, particularly with regard to SIR testing, where I suggested that true SIR can be measured only at very low voltage gradients without bias, because the very slow movement of ions within the resin falsified the results, even without conduction. Brian Robert Coburn wrote: > Hi T'Netters; > > One of my customers stated they were experiencing what sounded like a > shorting problem due to ionic contamination. > Can't tell if the problem originates beneath the mask or not. > The customer was testing assemblies at 85o C, 85% RH, 400 volts for 168 > hours. > > The question is: is the Customer expecting too much from a Solder Mask? > > TIA, > Rob > > --------------------------------------------------- > Technet Mail List provided as a 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/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 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/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 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/contentpage.asp?Pageid=4.3.16 for additional information, or contact Keach Sasamori at [log in to unmask] or 847-615-7100 ext.2815 -----------------------------------------------------