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

David davidwhess at gmail.com
Sat Nov 5 19:38:01 EDT 2016

On Sat, 5 Nov 2016 20:57:11 +0100, you wrote:

>> 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?
>Now, for these caps, you can use a normal soldering-iron without too 
>much trouble, but I strongly recommend pre-heating the board with a 
>hot-air gun.
>The trick is to pre-heat the board widely so it becomes hot, but not 
>enough to melt any solder. As you now apply your soldering iron, the 
>heat-transfer won't be as large as if you had a room-temperature board, 
>simply because the lower temperature gradient.
>The effect is that your heating up goes quicker and that part of the 
>board won't experience excess heat for too long.

I have never had a problem removing surface mount parts like that with
just a single soldering iron.  If access is good so that a large heat
capacity tip can be applied, then each solder joint can be heated up
very quickly preventing damage to the board.

Through hole parts on multilayer boards which have a high heat
capacity are a different manner.

>Another trick I use is to solder new solder onto the joints. This breaks 
>through the oxide layer, which is a poor heat conductor. I solder onto 
>the joints and let them cool. Then I come back again and now the 
>soldering iron melts it all up nicely.

On newer boards this is also a great way to dilute the lead free
solder lowering the melting point making removal easier without
damaging the board.

Add some leaded solder and flux to each joint, then remove most of the
solder from each joint with braid, and then a little heat will allow
each side of the part to pop off.

>I still do SMD with my Weller WECP-20, but it's not optimal.
>At work we moved the otherwise so high valued (over-valued) Metcal to 
>the side as the new JBC stations is much better. Metcal's doesn't keep 
>the temperature good enough and the new JBCs is beeter. Metcal's also 
>have a failure-mode in their tips which makes them break way to early. 
>There exist replacement tips which is in fact better than the original.
>So, if you need an excuse to buy a new toy, look at the JBC-stuff:
>However, I would probably be able to replace that cap before your get 
>your new and shiny toy on the table.

I still use my ancient Weller Magnestat irons but have quite a
collection of tips including my overpowered vacuum desoldering head.

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