Brian,

I really opened Pandora's box with this one.  Not to rebut your statements, but I would like to comment for clarification or perceived results.

When adding liquid flux the visual appearance is far superior to core only and using the same soldering tip and temperature the dwell time of soldering iron contact seems to be less.  Can I measure it?  No, but I'm much happier with the results.

Mixing fluxes does sound bad.  In both cases where this has been done it was mixing Kester Core 44 solder with Kester 1544 and Alpha Metals Aqualine 6000 solder with Alpha Metals 825-70.

In the case of the Alpha Metals we are using the largest core available.  To correct my proposed method it sounds like if I want to use liquid flux I should switch to 63/37 solid wire solder.  My argument for using liquid flux is based upon the supposition that the low viscosity of the liquid better penetrates down into the barrel of the hole around the wire particularly if the hole/lead tolerance is tight. With cored solder I have seen more problems with poor solder joints due to poor flow through or poor wetting of the lead and excessive solder on the joint.  We do only through hole boards.

I do not have SIR capabilities nor can I micro-section a suspect solder joint.  So I can't confirm final quality of my solder joints.

Looks like some changes are in the wind.

Phil

-----Original Message-----
From: Brian Ellis [mailto:[log in to unmask]]
Sent: Thursday, February 27, 2003 9:13 AM
To: TechNet E-Mail Forum.; Phil Nutting
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
>>
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