Brian, so we have three possibilities: deonized water, deweynized water and polariced water. Which is best in your offpinion? Inge ----- Original Message ----- From: "Brian Ellis" <[log in to unmask]> To: <[log in to unmask]> Sent: Thursday, May 07, 2009 4:51 PM Subject: Re: [TN] PB Surface Contamination > To understand this problem, you also need to understand what happens > when synthetic polymers are heated. What I am about to say applies > equally to solder masks and to the substrates under them. > > When a polymer is heated, it reaches a temperature where its > characteristics change, called the glass transition temperature. Above > this temperature, the surface of a polymer becomes very porous and opens > up like a sponge. To make things worse many of the chemicals that the > polymer comes in contact with contain surfactants or other molecules > which have a hydrophilic and lipophilic ends. If the molecule is > linear, or nearly so, such as most of the common detergents and > surfactants, another phenomenon occurs and the lipophilic end of > hundreds of molecules rush into the pores and are trapped there when the > polymer cools again. If, for example, the product is a flux, then some > activators will probably become co-trapped and these can be released, > not only with subsequent heating, but also at ambient temperatures over > a long period of time. > > This is obviously a danger for the reliability of any printed circuit in > critical applications. In addition, just to make things worse, many > thermosetting polymers have ionic salts in their molecular makeup. For > electrical applications, these salts are practically eliminated but > there is always a risk of small quantities remaining and these can also > leach out. > > Other posts have specifically mentioned HASL. This is because the > fluxes used for this process are not only highly activated but nearly > all the other chemicals in them are closely related to surfactants! > You've got the worst of both worlds! > > What can be done about them? Not a great deal if you have a batch of > circuits that leach enough to compromise the functionality. Perhaps a > good wash in DI water after having baked the circuits may improve the > situation if the problem comes from the fabricator. If it comes from > your own workshop, then a systematic tracing will find the culprit. > > Hope this helps! > > Brian > > Kane, Joseph E (US SSA) wrote: >> A cleaned bare PB is exposed to bake or reflow, and comes out with >> measurable ionic contamination. The board is dirtier at the surface >> after a heat excursion. >> >> The contamination isn't coming from the oven, handling, or anything >> external. >> Heat causes something to move from the inside of the board to the >> outside. >> >> We haven't done any ion chromatography or other testing yet to >> run this down, but has anyone heard of or experienced anything similar? >> >> In our normal process, we clean everything multiple times, but if the >> contaminant builds up under solder mask, or in other areas that are >> difficult to clean, we could have SIR or corrosion problems around fine >> surface features or in high voltage areas. >> >> And if this ionic contamination doesn't just move up to the surface, >> but is somehow moving around inside the board, could it collect in some >> places and lead to CAF or other problems? >> >> Joe Kane >> BAE Systems >> Johnson City, NY --------------------------------------------------- >> 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 -----------------------------------------------------