OK, there is another hole in my boat. What would be your recommendation for reworks or repairs to a board that cannot be washed or cleaned in a batch or inline machine. Spot cleaning will be required.
-----Original Message-----
From: Mel Parrish [mailto:[log in to unmask]]
Sent: Thursday, February 27, 2003 10:50 AM
To: [log in to unmask]
Subject: Re: [TN] Adding liquid flux when hand soldering
Use of external flux is different today than it once was due to variation in
flux chemistries from those of the past. Many of the fluxes today require
greatly elevated temperatures to volatize, polymerize, neutralize the active
ingredients. When liquid flux is placed on the assembly to be soldered or
reworked, some of the solution will locate in places where it does not see
reflow temperatures and therefore remains active. Cleaning cannot assure
removal of these types of ingredients, especially if it is localized
cleaning (usually the case with offline processes). In fact it can
additionally contribute to the issue by further disbursing the residual
activators. The consequences can be and often are significant for product
reliability long term.
Mel Parrish
Soldering Technology International
256 705 5530
[log in to unmask]
-----Original Message-----
From: TechNet [mailto:[log in to unmask]]On Behalf Of Shoda, Steve
Sent: Thursday, February 27, 2003 8:54 AM
To: [log in to unmask]
Subject: Re: [TN] Adding liquid flux when hand soldering
Our process teaches operators to add liquid flux before core solder. In my
opinion, it helps because the lower surface tension of the flux has better
wetting to the solder tip. This increases the cross sectional area of a path
the heat from iron can flow to the item being soldered. The resultant
solder joint is not different, but the smoothness, ease, and cycle time of
getting there is improved.
Steve
-----Original Message-----
From: Phil Nutting [mailto:[log in to unmask]]
Sent: Thursday, February 27, 2003 8:43 AM
To: [log in to unmask]
Subject: Re: [TN] Adding liquid flux when hand soldering
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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