As a materials engineer by trade and having worked in the high rel electronics (aero) industry since the early eighties, I feel qualified to comment on this particular thread. Firstly, I wouldn't expect anyone to disagree with the statement that you don't mix flux types, that is cast in stone. There are however compatible liquid and plasticized fluxes sold by all the usual suspects and we for instance use an RMA QPL listed product from Alpha and so my comments reflect this. In a practical hand soldering operation on an assembly with a reasonable thermal demand, the plasticized flux tends to degrade pretty rapidly during the initial stages of the hole fill operation and once you have a solder plug you cannot introduce additional flux to the still to form joint area, you are reliant on whatever plasticizes material managed to get there during the initial stages of joint formation. Now with the vagaries of any hand soldering operation you will get the occasional little bu**er of a joint that won't go right first time. The addition of a drop of compatible liquid flux to the joint area before the application of the iron and wire does go a long way to overcoming the poor fillers (for want of a better description). It is true to say that most joints can be adequately soldered with just the original flux core, but it is so much easier with the addition of a drop of liquid flux. Provided the two fluxes are compatible, provided the assemblies are properly cleaned and verified as such then the use of a small amount of liquid flux should not be an issue, although there are always occasions where it isn't recommended and the aforementioned switches is one such instance. Ian Fox Goodrich Engine Control Systems -----Original Message----- From: Brian Ellis [mailto:[log in to unmask]] Sent: 27 February 2003 14:13 To: [log in to unmask] Subject: Re: [TN] Adding liquid flux when hand soldering What do you mean by less heat? A lower temperature? A shorter time? Both? All that any of these means is that the conditions to form the optimal joint no longer exist. Please do not forget that the formation of a solder joint is a chemical reaction whereby (say) tin and copper react to form intermetallic compounds. The optimal conditions require a given combination of temperature of the tin AND copper over a given time. Reduce either, and the joint is no longer optimal. The functions of the flux are numerous, but its acidic activity is mainly to reduce metallic oxides so that the tin and the copper are clean enough for the metallurgical reaction to take place. This oxide reduction occurs mainly during the preheating phase, before the copper reaches soldering temperature, so the type or quantity of flux has relatively little influence on the speed of the reaction, although a highly reactive flux, such as a water-soluble organic hydrochloride type, may just reduce the overall time by a tiny fraction of a second. "In a quick poll of some of my fellow old-timers who worked on military stuff all agreed." I guess your "old-timers" must be quite old, from the days when soldering was a "seat-of-the-pants" art and not a science, like it is today. Any person mixing two flux types for a military application would be shot down in flames by the inspectors from the UK Ministry of Defence and, presumably, the US DoD or sent out to Iraq to make sure Saddam's famous WMD would fail from faulty electronics. What you are proposing is an antithesis of reliability. Please quote me a single MIL Spec since Julius Caesar's days that said, "Thou art permitted to make whatever mixture of fluxes you please." or words to that effect. In all my 50 years of experience in this industry, I have never, ever, seen it done: the only times I've seen liquid flux used for hand soldering, it was with coreless, solid solder wire. In the very unlikely event that there is insufficient flux in a cored solder wire, then I very seriously suggest that, before you jeopardise the reliability of your products, you consult the manufacturer of the wire and have it exchanged for one with a slightly greater percentage of flux, or you change suppliers. Brian Phil Nutting wrote: > Brian, > > I can't argue with your statements. I can only speak from personal > experience (including a test last night) that adding the liquid flux > makes a much better solder joint with less heat applied to the joint. > In a quick poll of some of my fellow old-timers who worked on military > stuff all agreed. > > Gee, what would Moonman say to this one? > > Phil > > -----Original Message----- > From: Brian Ellis [mailto:[log in to unmask]] > Sent: Thursday, February 27, 2003 3:17 AM > To: TechNet E-Mail Forum.; Phil Nutting > Subject: Re: [TN] Adding liquid flux when hand soldering > > > If you are using cored solder, you should never add flux. Because: > a) liquid flux will spread beyond where you need it and add to > contamination > b) the chances are the two fluxes will be incompatible with each other > c) there is a distinct possibility the residues will be impossible to > clean off correctly or, if they are both "no-clean", they will form a > dangerous flux porridge which could be ionically incompatible with > reliability > d) you are insulting the wire manufacturer who has determined the > quantity and type of flux, through scientific lab tests, to optimise > what you are trying to do. > > IOW, you will cause far more harm than good. > > Brian > > Phil Nutting wrote: > >>Is it a common practice to add liquid flux when soldering by hand or >>do you rely on the flux core of the solder? My 30+ years says add the >>liquid flux for the best solder joint, but that was back when I was >>involved with rocket science. >> >>Phil Nutting >> >>--------------------------------------------------- >>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 >>----------------------------------------------------- >> >> >> >> >> > > > --------------------------------------------------- > 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 > ----------------------------------------------------- > > > > > --------------------------------------------------- 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 ----------------------------------------------------- --------------------------------------------------- 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 -----------------------------------------------------