We didn't have the weld problem with our cleaning machines, as the welding rods were 18-8-2-1 alloy (expensive but was chosen for that reason). Welding 18-8 or 18-8-2 (or lower Cr/Ni SS) with 18-8 (or lower Cr/Ni SS) rods is a sure fire way of having the weld problem. However, we had one customer who coupled the machine to the water from their semiconductor plant and the 18-8-2 alloy of the sheet metal developed a thin coating of a loose very fine red powder, known as rouge, despite the molybdenum. See http://www.corrosionlab.com/Failure-Analysis-Studies/rouging.htm for more details. This caused a long-lasting complaint from the customer but I kept telling him to use a less pure water. We never saw this with other customers who used DI water from a mixed-bed column. Brian Douglas O. Pauls wrote: > Along these lines, but slightly different, when my esteemed colleague, Jim > Maguire, formerly of Boeing, now with Intel, was doing SIR testing at > Boeing, he told me an interesting story. All of their SIR chambers had > been plumbed with 18 megohm-cm water to make it as pure as possible. After > a while (don't remember the time frame) he started seeing very fine metal > needles on his test samples. The high purity DI water had attacked the > stainless steel of the chambers and the needles resulted. He had them > plumbed with 8-10 megohm-cm water thereafter. > > I know that ultrapure DI water is not desired for use in microelectronics > because it can attack aluminum bond pads, interfering with wire > bondability. In most cases, a microelectronics facility may start with 18 > megohm water, to get out the impurities, but will then mix carbon dioxide > back in to bring the resistivity down to the 2-6 megohm-cm range. > > For the cleaning of circuit boards, yes, I imagine that some people have > been able to clean with tap water. Keep in mind that what comes out of > the tap in your area may not be the same as what comes out of mine. Tap > water quality varies greatly as you move geographically. My biggest > problem with tap water cleaning is that most industrial water supplies are > coming from the municipal water supply. They add chlorine and sulfur > compounds to cut down on bacteria growth. What two ions are death to > electronics? Sulfur and chlorine. That is why I have always recommended > that people at least use RO quality water (500 kilohm-cm or higher) in > cleaning electronics. If you are using a saponifier, as we do here, tap > water has a large load of minerals that reduce the effectiveness of the > saponifier and can result in shorter saponifier bath life. Again, with RO > or DI water, I improve cleaning efficiency and extend chemical life which > is more cost effective. > > On the other side of the coin, I have never really seen the need to have > the ultrapure (15-18 mgeohm-cm) water for cleaning either. Purity of 2-8 > megohm-cm resistivity is easily achievable with standard industrial DI > column setups. > > Doug Pauls > Rockwell Collins > > > > > Richard Kraszewski <[log in to unmask]> > Sent by: TechNet <[log in to unmask]> > 03/07/2008 07:20 AM > Please respond to > TechNet E-Mail Forum <[log in to unmask]>; Please respond to > Richard Kraszewski <[log in to unmask]> > > > To > [log in to unmask] > cc > > Subject > Re: [TN] Effects of rinsing with high purity water. > > > > > > > I've heard the reason is that high purity water is a rather unstable > substance and as such is "ion hungry". > > Recall a story (urban "technet" legend?) which recounted how years ago > Wang (?) had a custom SS cleaning system that used ultra pure DI. Over > time the welded seams were eaten away and the system dumped on the > floor. > > Rich K / Kimball > 847-621-7310 > > -----Original Message----- > From: TechNet [mailto:[log in to unmask]] On Behalf Of Brian Ellis > Sent: Friday, March 07, 2008 4:27 AM > To: [log in to unmask] > Subject: Re: [TN] Effects of rinsing with high purity water. > > I'll offer you a guess, without any scientific knowledge to back it up. > If the Au is porous, the Ni could be attacked with OA residues diluted > during the first wash, leaving nickel halides in the pores. The high > surface tension of the final rinse water may prevent them from being > removed but the Au/Ni couple with the damp residues could make a nice > corrosion cell. Plausible? > > Brian > > Peter Barton wrote: >> Hello Technetters, >> >> There has been some comment on this forum recently implying that > cleaning or >> final rinsing of assemblies with high purity DI water can have a > detrimental >> effect on solderability. We very occasionally see a solderability > issue when >> processing second side surface mount after first side population and >> cleaning. Because of product build times and the use of paste with an > OA >> flux that must be cleaned soon after soldering we have to wash the > first >> side before continuing with the second side. >> >> The surface finish of the PCB concerned is ENIG. We have had various >> analyses carried out on the surface finish but have never had any > conclusive >> evidence that the finish itself contributes to the problems seen. >> >> Can one of the gurus please explain how high purity water could affect > >> solderability and, if there are any circumstances in which variation > in ENIG >> could be susceptible to degradation in solderability if cleaned this > way. >> Best rgds, >> >> >> >> >> >> >> > ----------------------------------------------------------------------- >> Peter Barton >> Senior Process Engineer >> ACW Technology Ltd >> Dinas Isaf West >> Tonypandy >> Mid Glamorgan. CF40 1XX Wales >> >> Tel: 01443 425275 (direct) >> Fax: 023 8048 4882 >> International Tel : +44 1443 425200 >> International Fax : +44 23 8048 4882 >> Website/URL: www.acw.co.uk >> >> --------------------------------------------------- >> 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 > ----------------------------------------------------- > > --------------------------------------------------- > 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 > ----------------------------------------------------- > --------------------------------------------------- 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 -----------------------------------------------------