Brian, I was following with great interest the subject. Right now, I am in the middle of trying tosolder CSP's with "Flux underfill", and I see similarities in the problems that could arise. Could you give me some hints for the reliability of the process? Gaby ----- Original Message ----- From: "Brian Ellis" <[log in to unmask]> To: <[log in to unmask]> Sent: Thursday, February 28, 2002 9:10 AM Subject: Re: [TN] No No-clean? > OK, there are three issues at stake here. > > 1) The residues from "no-clean" products (and yes, there are residues - > always) may impede adhesion of the coating layer to the substrate > > 2) Many of the "no-clean" products rely on a slow sublimation of the > residues from the surface, requiring a few weeks to achieve optimal > performance. Sealing these in will prevent this from happening. > > 3) By definition, all soldering fluxes are ionic. Some may be slightly > hygroscopic, as may also the metal salts formed by the reaction between > the oxides and the flux acids. Some of the rheological additives to > pastes may leave slightly hygroscopic residues. This is an open > invitation to promote vesication, with a potentially very serious loss > of reliability. At the very least, a good "pressure cooker" test is a > must both in qualifying the process and at frequent intervals to check > that it stays on the rails. > > I am not saying that coating should never be applied over flux residues. > What I am saying is that anyone who does it without a really thorough > qualification and process control is being professionally irresponsible, > if the products must be reliable. After all, conformal coating is really > a high-rel process and "no-clean" chemistry started as a low-rel > process, creeping up to its present status of medium-rel. It is > therefore really a paradoxal conflict to try and combine the two, likely > to present the disadvantages of both processes with none, or few, of the > advantages. > > Brian > > -------------------------------------------------------------------------- ------- > Technet Mail List provided as a free service by IPC using LISTSERV 1.8d > 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 delivery of Technet send e-mail to [log in to unmask]: SET Technet NOMAIL > To receive ONE mailing per day of all the posts: send e-mail to [log in to unmask]: SET Technet Digest > Search previous postings at: www.ipc.org > On-Line Resources & Databases > E-mail 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 1.8d 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 delivery of Technet send e-mail to [log in to unmask]: SET Technet NOMAIL To receive ONE mailing per day of all the posts: send e-mail to [log in to unmask]: SET Technet Digest Search previous postings at: www.ipc.org > On-Line Resources & Databases > E-mail 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 ---------------------------------------------------------------------------------