Why do we care what the wetting angles are? (Indirect overhead question) SnPb on SnPb finish yields solder contact angles we expect, we infer that certain process outputs exist because of the appearance of the solder joint. With Pb free finishes and SnPb finishes we still expect the same appearance but is the inference still true? Now, add Pb-free solder to the mix. Why would we expect the contact angels and solder joint geometries to be the same. The process inputs are different. I feel the more important, and largely unanswered question, remains. Given the variety of lead and board finishes, and variety of Pb-Free solder alloys, changes in performance from small shifts in alloy composition . . . Can we expect to have a single visual acceptance criteria, acceptance criteria that are data driven and performance based. I have observed that SnAgCu solder wets Immersion silver plated leads quite differently than PdNi finishes. What looks "normal" on the latter would definitely be a defect on the former. And neither of these would come close to what we call "target" today. > -----Original Message----- > From: TechNet [mailto:[log in to unmask]] On Behalf Of > Dave Hillman > Sent: Wednesday, July 16, 2003 1:15 PM > To: [log in to unmask] > Subject: Re: [TN] High temp pastes for wave soldering... > > > Hi Mel and crew! Sorry for the lack of response - been > chasing alligators in the swamp and they seem bigger than > normal this week. Mike F. and Gebbard hit the nail on the > head - because of the higher temperatures of a Pbfree > soldering process the thermal stability of many of the > current fluxes is pushed to the limit (and/or over the > cliff). We are going to need to rely on the flux supplier's > expertise in reformulating our fluxes to have better thermal > stability and hopefully have the same level of > noncorrosivitivity. The NIST webpage/database has a good > listing of Pbfree surface tension values if anyone is > interested in alloys properties type information. One > industry concern which has been expressed in a number of > conferences is what changes in our expectations of "assembly > cleanliness" do we need to be prepared for as the flux > formulations are adjusted. If we expect to achieve the same > wetting angles and solder joint geometries we'll have to make > adjustments in our assembly materials. > > Dave Hillman > Rockwell Collins > [log in to unmask] > --------------------------------------------------- Technet Mail List provided as a free 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/html/forum.htm for additional information, or contact Keach Sasamori at [log in to unmask] or 847-509-9700 ext.5315 -----------------------------------------------------