[time-nuts] I love the smell of tantalum in the morning

Bob Stewart bob at evoria.net
Sat Nov 5 15:49:14 EDT 2016


Hi John,

I've never used the hot tweezers.  I'm going to have to look into them.  Normally, for desoldering, I use a narrower nozzle with an elevated temperature - usually between 280C and 350C.  That blows the part completely off the pads just as soon as the solder flows, with little impact on adjacent components.  For soldering, since I use a 240C leaded solder paste, i use a larger nozzle with slower air flow at about 245C-260C depending on what I'm soldering.  Desoldering against a copper plane is always a problem regardless of the thermal pad's shape.  I'd think you'd need a pretty hot set of tweezers to get a big 1210 sized tantalum off the board if there's a ground plane.

Bob
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      From: John Ackermann N8UR <jra at febo.com>
 To: time-nuts at febo.com 
 Sent: Saturday, November 5, 2016 2:35 PM
 Subject: Re: [time-nuts] I love the smell of tantalum in the morning
   
Either hot tweezers or a hot air rework station are the best/easiest 
ways to remove dead parts.  But two fine-tip soldering irons will also 
work and are a lot cheaper.  The idea is to heat both ends of the part 
at once, and when the solder flows, lift or flip the part off.  Then, 
use some liquid flux and narrow solder wick to suck off the excess 
solder, and you should end up with nice smooth pads ready for the 
replacement part.

The key thing to avoid damage is to make sure the solder is really 
flowing on both pads before you try to lift the part.  Sometimes ground 
pads have enough thermal mass that it takes a while to get them hot 
enough.  Be patient.

Good luck!
John
----

On 11/05/2016 03:12 PM, Tom Van Baak wrote:
> See C13 in the attached photo. I need to replace some blown caps on a few boards [1]. In one instance the cap got so hot it melted itself off the board. Quiet convenient, actually -- it acts like its own fuse -- but I don't think the 5071 designers had that clever feature in mind.
>
> Having not done SMT before, how should I do it with minimal risk to the very precious PCB. Or, what equipment should I use this as a good excuse to buy?
>
> Thanks,
> /tvb
>
> [0] http://www.imdb.com/title/tt0078788/quotes
> [1] http://leapsecond.com/museum/hp5071a/A1-mother.htm
>
>
>
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