[Elecraft] Re: OT: Removing Solder Through Plated Through Holes

[Mel Farrer]

I would like to add a comment on removing solder from SMT via holes.  There are three methods and the first two have been discussed.  I have found as the technology gets better, smaller, the plated through holes also get really small.  Like 0.020 or smaller.  Solder suckers have a very difficult time pulling the solder up. 

Let me explain, consider the mass of the solder pad on the side you are going to apply heat.  If you get the solder liquid and don't destroy the pad, the bottom pad, MAY be liquid and come up with the sucker type.  It works good on larger pads but not so good as the holes get smaller.  Too much air leakage and you are trying to pull cold solder.  Not always successful.

Using the solder braid has also the same problem as it is a heat sink and usually requires you to put additional heat to suck the solder up.  Works great on larger holes and traces that are large like 50 ohm strip line.  

OK, so what is left?  I use a solder "pusher".  Back before someone invented the solder sucker, we used a small hollow rubber ball with a small entrance teflon tube that we had and it had replaceable tips of different sizes to accommodate hole size.  This allows exact pressure of the right size on the hot side of the PCB and "blows" hot solder out against the colder solder on the other side and effectively cleans the hole without over heating the pad.........

>From someone who is long in the tooth,

Mel K6KBE



--- On Tue, 12/30/08, Don Wilhelm <w3fpr at embarqmail.com> wrote:
From: Don Wilhelm <w3fpr at embarqmail.com>
Subject: Re: [Elecraft] Re: OT:  Removing Solder Through Plated Through Holes
To: jimimaxi2 at comcast.net
Cc: elecraft at mailman.qth.net
Date: Tuesday, December 30, 2008, 3:32 PM

Jim,

You look at the schematic and find *all* the paths connected to that component
location - then you check for continuity from the potentially damaged pad to all
the other locations.  Even if you don't know how to "read" a
schematic sufficiently to identify the circuit function, it can still tell you
'which is supposed to be connected to what', and that is what you must
check.

With 2 sided boards, sometimes you can tell by looking at the board and see the
traces coming from the potentially damaged hole - if the circuit is not complex,
all the wiring may be all on one side and all you need to do is to be certain to
solder that side containing the PC board traces.  Normally on 2 sided boards, an
effective repair is to solder the component lead both on the top and the bottom.

If you are dealing with a multilayer board - the process of using the schematic
is the same, but the process is more complex since there can be a path from each
layer.  To repair in this situation, one would run discrete wire point to point
for the entire network containing that hole (it is the only certain thing to do
other than replacing the board).

Bottom line (may be 20-20 hindsight) - use a drill *only* on single sided
boards or boards that are known to *not* have thru-plated holes.  Many holes are
used as a continuation of the circuit from one side of the board to the other
(known as "via holes" and those holes can serve double duty as a
mounting place for a component lead.

All such damages are repairable with the possible exception of carefully laid
out VHF/UHF circuits - even if the repair is a PITA.

73,
Don W3FPR

jimimaxi2 at comcast.net wrote:
> 
> If I have done what you say I shouldn't , meaning take a hobbyist
drill to widen a solder-filled hole, how do I check if I have broken the
connection between top side and bottom side?
> 
> 
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