Re: gEDA-user: Surface mounted circuits in hobby projects

[Mark Rages <markrages@xxxxxxxxx>]

On Fri, Apr 10, 2009 at 2:58 PM, Steven Michalske <smichalske@xxxxxxxxx> wrote:
>
> On Apr 10, 2009, at 11:34 AM, Chris Albertson wrote:
>
>>> I tried to desolder a SMD component, a capacitor with solder remover
>>> wick (copper braid), and it's very hard to do it.
>>
>> The class setup is rework tweezers.   It's basically a double tipped
>> solder iron and you can just pick up the part off the PCB with
>> hot tipped tweezers.
>>
>> But us poor-folk just heat both ends
>> of the part at once with a larger tip solder iron then push the part
>> sideways off the pads with the iron.
>>
>> Also try lifting with normal tweezer while cycling the iron from
>> pin to pin.
>>
>>
>
> My motto when I teach interns to desolder components, you have to add
> solder to desolder.  This is because that solder wik removes solder
> but surface tension will always leave some behind.  forming a weak
> joint, that others here are suggesting you use something to pry off
> the parts.  It works a time or two before you tear off the pad you're
> reworking.
>
> like mentioned above.
> Flat wide tip that bridges the part and a large ball of solder to
> transfer the heat,  often it will cause the part to stick to the tip,
> or use the tip to lightly push the part off.
>
> I do reworks with two soldering irons, one in each hand, it offers
> more control,  as I often tombstone parts to do reworks.
> ( tombstoning is to stand the parts up on one pad. )
>

You can do it with one iron if you're quick.

1) Turn the iron temp up a little bit
2) Put a largish solder blob on each end of the part
3) Hold the board vertically
4) heat one end, then the other with the soldering iron.  Alternate
back and forth until both ends are melted at the same time.  The part
will fall off when the solder is molten.
5) clean the board (and the part, if desired) up with braid.

This works with other parts as well.  For a square IC, you add the
solder blob to all four sides and move the iron in a quick circle.
The part will fall off the board and can be cleaned up and reused.
(Hot air rework is faster though.)

This method is the gentle on the parts and board.  I don't think
mechanical stress or bending of SMT leads is helpful or necessary.

Regards,
Mark
markrages@gmail
-- 
Mark Rages, Engineer
Midwest Telecine LLC
markrages@xxxxxxxxxxxxxxxxxxx


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