Smitty Two wrote:
In article ,
"Michael A. Terrell" wrote:
"Ron(UK)" wrote:
Steve wrote:
I've often found that in a pinch, you can wick the solder out, re-fill
the holes with new solder, re wick the holes. Sometimes the
re-filling process can reflow the whole joint instead of wicking out
the top half and the bottom never gets hot enough. Of course, not
perfect, and should be done on a scrap board.
That`s true. One of the things novices do wrong is to wick off most of
the solder, but leave a little behind deep in the hole, that wont be
drawn up into the solder braid. Then they get impatient and try to rip
the component out damaging the board in the process.
There needs to be enough solder to easily wick up into the braid, and
the iron need to be hot enough to melt all the solder in the joint
through the braid or there`s a chance that pulling the braid away takes
some of the pad with it.
There`s as much an art to desoldering as there is to soldering. (IMO)
Ron(UK)
The solder used for wave soldering is 80/20 and has a higher melting
temperature. By removing what solder you can, then adding fresh 60/40
you move the melting point to somewhere in between, which then can be
either vacuum desoldered or removed with solder wick and a drop of
liquid rosin flux.
80/20 is used for wave soldering, because it has a very narrow
temperature range where it is in a plastic state. this reduces cold
solder joints, by not giving the leads a chance to move while the solder
passes through this state.
80/20? 60/40? What kind of solder are you talking about? Eutectic
tin/lead is 63/37 and used in both hand and automated soldering.
Really? I want proof. If 63/37 is the only solder used, please
explain to everyone WHY there are so many different solder alloys sold
for electronics. I have NEVER seen a wave solder machine filled with
eutectic solder. 80/20 was used in all the wave solder machines I've
seen because it has a higher melting temperature and goes from liquid to
solid almost immediately.
I shouldn't have included the reflow process, because there is too
damn many low temp plastics used in SMD components these days. Earlier
boards only had the resistors, capacitors and semiconductors reflowed,
which could use higher temperature solders. Now there are lots of
crappy SMD connectors, pots and relays that require a lot more work to
create a workable reflow profile for the oven. Every board design has
to be evaluated, and a custom profile created for that assembly. We had
over three hundred profiles stored on the Heller oven when I left
Microdyne, all sorted by assembly/stock number.
They kept changing the paste solder for reflow, and replaced the two
original ovens with the computer controlled Heller so I couldn't keep up
with all the variations in alloys, ball sizes and fluxes. It seemed
like as soon as we found paste solder that worked right, we couldn't get
more of it, and had to start looking again. I know that the solder I
used for rework was .015" 60/40.
http://www.kester.com/en-us/technical/alloy.aspx is a chart of alloys
currently available from Kester. They list 13 various tin/lead alloys.
--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.
Michael A. Terrell
Central Florida