Re: My A2 Hardware Projects

[Ed Eastman <noone@nowhere.net>]

Polymorph wrote:
> BTW, I do own a solder sucker, but I find it hard to use effectively.

Me too, but the desolding iron works really slick, you don't have to 
move the iron to suck the solder out!

> I tend to find that there is always some residual solder left that won't budge

No way around that, unfortunately.

> and in the cases where I have been trying to remove a component, I find that the
> residual solder is strong enough to prevent me (from removing it).

Ve haf ways to make you talk, er remove components.  Techniques, that 
you pick up as you go.

Warning soldering lesson ahead...

Knowledge: First off, the solder flows towards the heat so keep your 
contact short so the solder flows towards the iron. When you solder a 
component, you want to heat up the whole joint so solder flows in for a 
good connection, the opposite it true when desoldering.

Tip:  Use a heat sink on the leg of the component to help prevent 
sending too much heat into the component or board.

Warning:  Try not to overheat the board, this will cause the pad or hole 
to let loose.  (Not to mention the delicate traces that come up with 
them.)  There is a happy medium, it just takes practice/ experience to 
find it.

Practice:  I completely desoldered a scrap IIgs Ram card when I got my 
desoldering iron out the first time.  I bet I pulled a dozen through 
holes out, lifted two dozen more.  But by the end, I think I can use it 
fairly well with minimal damage to real boards.  Remember to take your 
time, if you start to get frustrated, take a break.

Use the right tool:  A solder sucker is really good at removing solder 
from a hole, especially around component legs.  A braid is good to 
remove solder where it can be seen and easily accessed, great for 
cleaning up pads when you expect to reuse them later or removing excess 
solder (blobs).  Toothpicks are good to clear holes and displace solder. 
 'Dental' picks are great for tiny manipulations necessary in soldering 
small components. (Ask your dentist to give you an old one.)

Tool tip: You need to melt the whole joint to be effective using a 
solder sucker, it can't pull out solder that is not melted.

Tool tip: When using the braid, you need to heat the braid and let the 
solder 'wick' into it. Move the wick each time you heat it to get a 
fresh area to fill with solder.

Technique to remove a surface mount chip:
Stick a dental pick under one leg, heat the pad and pull the pick across 
the pad, lifting the leg up just enough to free it.  Repeat 63 more 
times. Once component is removed, use a desolder braid to clean the pads.

Technique to remove a component with a through hole:
Desolder each pin/leg from the soldered side.  If it looks like solder 
is on both top and bottom, remove some of the top solder first using a 
solder wick.  You should be able to get most of the solder out of the 
hole.  When you have most of the solder out, wiggle the pin/leg using a 
dental pick or similar towards and away for the component, perpendicular 
to the hole.  There should be a slight 'snap' as it breaks the solder 
connection unless it moves freely.  If the leg fails to break free, move 
on and come back later after the area has cooled.  Resolder the leg and 
desolder it again.  The fresh solder should flow out of the hole better, 
bringing more of the 'old' solder with it.  If it fails the second 
attempt, try holding the iron for another half second to get a bit more 
heat through the solder.  (Remember: consider using a heat sink between 
the component and the hole/pad.)

Tip:  Do not try and pull a component out unless every leg is free, 
check each leg, twice.  To remove a component, push ends of the legs 
with your fingernail and it should pop out the other side.


> I've heard and read about the fluxed copper braid, and would like
> to try that in these instances. ...
> Maybe if I plan to do a lot of this kind of work, I might invest
> in a desoldering iron as suggested.

I would encourage you to get a desoldering iron, even for just one 
project, it can make a huge difference.  My radio shack desoldering iron 
was $10 and buy some spare tips too, I destroyed the intitial tip 
practicing.  Also get the braid if you plan on reusing the boards, it is 
very handy.

Technique for desoldering iron: Push bulb with tip low over trashcan or 
ashtray and beware as the solder splashes, count 5 wait for iron tip to 
reheat, apply iron to joint, count 4/watch for solder melt, release 
bulb, pull up iron.  Repeat on joint away from last one.  If it fails to 
clear the solder, try again or resolder the joint then try again.

Thankx,
Ed