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Old 14th November 2006, 02:18 PM   #1
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Default Right technique to desolder?

I'll be replacing/upgrading some resistors and caps on a copper clad pcb. My prior experience (as a beginner) was that this was difficult as I did not have a solder sucker and found it difficult to clear the throughole of solder with regular braid. I just bought a solder sucker.

I guess I have a few Qs:

1. I have a metcal variable temp station with 700 degree tips: thin (says for surface mount pcbs etc) and medium. With the thinner tip it seems to take forever (20 sec or more?) to heat the solder joint in order to remove the part. Should I use the medium tip? When am I at risk of damaging the board?

2. Now that I have a solder sucker, what is a good technique to quickly remove parts and clear the holes without damaging the board?
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Old 14th November 2006, 07:21 PM   #2
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Default Re: Right technique to desolder?

Quote:
Originally posted by riotubes

1. I have a metcal variable temp station with 700 degree tips: thin (says for surface mount pcbs etc) and medium. With the thinner tip it seems to take forever (20 sec or more?) to heat the solder joint in order to remove the part. Should I use the medium tip? When am I at risk of damaging the board?
You need to add new clean solder - it'll improve the thermal interace between tip & part+trace and give the solder sucker a bigger blob to pull up. Using a tip that's a better match for the lead+pad will get it hot faster so less heat leaks into the rest of the board.
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Old 15th November 2006, 08:50 AM   #3
AndrewT is offline AndrewT  Scotland
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Hi,
try standing the PCB vertically.
Apply the solder sucker to one side (usually the component side).
A little new clean solder on the tip, it helps quick heat transfer.
Try higher than normal tip temp (maybe <360degC).
Apply the chisel point ( big enough to touch the whole pad area) to the pad.
Heat the pad until the heat flows up the tube towards the component side (usually only 2 or 3 seconds, but longer on a ground plane).
Tilt/twist the chisel tip slightly to leave a gap for the solder to escape.
Release the sucker and watch the gap at the chisel empty.
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Old 15th November 2006, 11:27 AM   #4
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i use the barbarian method -- i clip the offending resistor, integrated circuit or capacitor in half and then tweeze out the legs.

the important thing is to NOT OVERHEAT the pcb trances -- when they lift they are easily broken.
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Old 15th November 2006, 11:43 AM   #5
Duo is offline Duo  Canada
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I use a fairly oversized soldering tip on my old weller WTCPT (the old cyan colored solder station) for just about everything.

I find that in any application, having a tip able to hold lots of thermal energy is essential to quickly heating a joint. I would rather have more than enough heat and be able to quickly heat a joint and get away from it than to use an undersized iron and have to sit on the joint for a prolonged period.

In my work desoldering parts, in most cases the desoldering of a single through-hole pin, like that of an IC, takes less than a half second to heat, suck, and remove heat. In some cases, I even heat the joint, remove the tip, and then suck. This all requires very fast technique; there's nothing but practice that will make you good at it.

My method of practice in the past has been to take boards out of old computer monitors and televisions and desolder every part on the board, no matter what, without doing any damage whatsoever. I got to the point of being able to do this within about 20 minutes to a half hour depending on the monitor. (If it's an early trinitron professional monitor... Give me three days
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Old 15th November 2006, 02:08 PM   #6
Nordic is offline Nordic  South Africa
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Have to admit those monitor PCBs are good practice, did it myself... good source of ferite beads, caps , microswitches etc...
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Old 15th November 2006, 08:10 PM   #7
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Thanks to all who took the time to post. There are some excellent suggestions here! I picked up some tips here from everyone. I gave it a go last eve, and yes I need to practice. Trying to hold that sucker proximate to the hole, moving the iron, and sucking the solder...difficult. I did find that once I increased the size of the solder tip, things went more smoothly. Look forward to trying more of these suggestions. Thanks
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Old 15th November 2006, 08:16 PM   #8
EC8010 is offline EC8010  United Kingdom
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Be warned that the recoil of a solder sucker can kick tracks off an old PCB. If in doubt, use braid and cut the component leads first. You can always replace components but you can't replace the board...
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Old 15th November 2006, 08:51 PM   #9
AKN is offline AKN  Sweden
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Hi,

Agree EC8010, dyring my past years working in a service shop I often used desoldering braid.
Why not desolder sucker instead?
Components who used to be broken were usually hot running components and corresponding copper pads were often "not so sticky" to laminate. Although using desoldering sucker was no problem at fresh good quality PCB's.

Edit: repaced gun with sucker, so no misunderstanding
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Old 15th November 2006, 09:11 PM   #10
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Quote:
Originally posted by EC8010
Be warned that the recoil of a solder sucker can kick tracks off an old PCB. If in doubt, use braid and cut the component leads first. You can always replace components but you can't replace the board...
As well as static electricity (with the solder sucker.)
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