smd components

[Josh Karnes]

> Someone asked about manually soldering smd components.
> It should be no problem, if you have very fine tip on your
> soldering iron. 
<snip>
> 
> If you wish to remove a faulty chip, just try to cut the pins first
> and then clean up the pads. 

Exactamundo.  Using a very very small wire cutter will work, or a 
dremel tool works better.  Sometimes the wire cutter will pull the 
pads too much, and lift them off the board.

> If you need to remove a chip without
> destroying it, use a thin isolated wire - put the wire under the
> chip, and then warm up one pin at a time simultaneously pulling the
> wire gently under the pin. This will work almost every time on SOIC,
> but PLCC package is another story.

PLCC requires, almost definitely, the use of hot air.  Solder-wick is 
the way to go with SOIC parts, IMHO, then use the wire like above.  
The solder-wick will pull off most of the solder.

> 
> To mount a component, put little solder on each pad,

Actually, you are better off only putting solder on one pad, then 
soldering that one to hold the part while you solder the rest of the 
part.  Remember to heat the joint between the pad and the pin, not 
just the pin, then apply solder to the joint, not the iron.  If the 
joint is not hot enough to melt the solder, then you will get a 
cold-joint.  It is pretty safe to re-heat all your SMT joints after 
the component is mounted.


> It is very easy to remove smd resistors etc by using two soldering
> irons, or by shortly warming both pads many times.

Careful because often times the parts are glued to the board as well 
as being soldered.  Dunno if this applies to car electronics, but 
certainly home electronics and computers.  Also, solder-wick is the 
way to go, no matter what type of part.  The less solder on the part 
when you prepare to remove it, the better.

BTW, destroying the part is always better than destroying the board:  
parts are generally replaceable.  This does not go for programmed 
parts however.  On any sirface mount part, it is much easier to 
crack, cut, or break the part to isolate the pins, then remove the 
remains one pin at a time, than it is to remove the part in tact.  
Attempts to save the part almost always result in destroying the 
board unless you have the right tools, or you are extremely skilled.  
Remember that the amount of heat required to extract a part are also 
likely to damage it.  They are not designed to be extracted, or 
soldered more than once.  Be sure to write down all the details of 
the part number, etc., before you remove the part, because it may not 
be in good enough shape to read when you get it off.

Happy soldering :)
_____________________________________________________________________________
Josh Karnes                                                 joshk at tanisys.com
Renaissance Man                        http://www.tanisys.com/~joshk/home.htm
Tanisys Technology                                     http://www.tanisys.com
Austin, Texas                      '78 BMW 530i | '72 Datsun 240Z | IZCC #308
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           *** opinions expressed herein are MINE, ALL MINE!! ***