Electronics Forum / Basics / November 2005

Yes.  What is left is called a tinned copper surface and is perfectly
fine.  It will help the new solder to coat the copper easily.

No.  Once enough solder has been removed to easily remove the original
component and insert the new one, you have removed enough solder.

(snip)

That solder has a high melting point that will easily damage many
circuit boards, separating the copper from the substrate.  Must you
use lead free solder?  63% tin, 37% lead solder melts at a much lower
temperature.  62% tin, 36% lead, 2% silver melts almost as easily, and
gives a fine looking joint.

betwee

usin

ti

fo

littl

an

everythin

I do a lot of soldering on the kitchen table and I try to remember to
wipe it clean before making a sandwich there, but I don't worry too
much about it.  The lead in 63 37 solder is pretty well locked up in
the alloy as far as absorbing it in the body, compared to lead oxides
used in old paint, etc.  I think there is very little risk from
ingesting an occasional tiny solder ball

Make sure you have a good quality, activated rosin core solder
designed for electrical work.  For hand soldering, I have less succes

with the no clean solder.  The flux just doesn't do as good a job at
helping the solder wet the board and component leads.  Never use
plumbing solder paste flux on a circuit board.  It leaves a residue
that conducts electricity and corrodes metals it contacts

If the flux and temperature are right, the joints should have a brigh

shine, especially when eutectic alloys are used.  These do not go
through a pasty stage (crystals of the excess metal growing in the
eutectic liquid before the freezing temperature is reached) but
solidify very suddenly

Here is an interesting document on some flux choices
http://rocky.digikey.com/WebLib/Kester/Web%20Data/285%20RMA%20Solder.pd

no, only enough to get the new component in, if you're experimenting with
different components you can often temporarily mount them on the underside,
which can be easier, but through-hole mounting is mechanically stronger
and therfore reccomended for permanent replacements.

Bye.
  Jasen

On Sun, 27 Nov 2005 21:27:31 -0800, longjohnstuartmill wrote:

I have a suggestion for a thought experiment: If you've removed enough
solder that the old component falls out of the hole, what will happen
if you try to insert a new component lead into the same hole that the
old one has just fallen out of? :-)

Then, part 2: Once the new component is in place, what gets put back
into the hole? :-)

Should I leave spoiler space? ;-)

That's as clean as it gets. To get any more solder off of it, you'd
have to use sandpaper. The copper is _tinned_, that means "coated with
solder". If, after wicking, there are no more big huge lumps, then
your wicking job is done.

I apologize if I sound condescending and patronizing here; after all,
this is the basics group, and any question is acceptable.

But, I _do_ wonder, being a tech myself, I have to ask, haven't you just
tried it and see?

If, in fact, the question was, "am I leaving too much solder?", then the
answer is, "If the lead fits, no." :-)

On the other hand, if you're having trouble getting solder out from the
inside of the plated-through hole, then the answer could be a solder
sucker:
http://www.google.com/search?q=solder-sucker

Sorry it took this whole tirade to get to it! Shoulda signed it "Rich
the stoner." %-}

Good Luck!
Rich