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Old 2nd May 2019, 2:07 pm   #27
julie_m
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Join Date: May 2008
Location: Derby, UK.
Posts: 7,732
Default Re: Revox A700 - A15 Board layout (old Style)

Quote:
Originally Posted by stewartrose View Post
I have tried to remove ic's with a proper DE soldering machine, but tracking is lifting
It sounds a bit counter-intuitive, but what you need is more power!

It takes a certain fixed number of Joules of heat to turn a kilogram of solder from solid to liquid. (A typical solder joint will only be a fraction of a gram, but the published data always refer to whole kg.) Your (de)soldering iron is only putting a certain fixed number of Joules into the joint every second (aka its Wattage). And the solder won't even begin to melt until it reaches a certain temperature anyway. The problem is that the heat will also leak away at a certain rate to where it's not wanted; overheating sensitive electronic components, softening PCB track adhesive and plastic insulation and possibly even burning fingers.

Now, if you have a 15W iron and the leakage rate is 5W, that means there are only 10W available for warming up and melting the solder. If you used a 45W iron on the same joint, there would be 40J of heat going into the solder every second; so the job of melting would be accomplished in a quarter of the time. Therefore, the total amount of energy lost (and therefore, available for doing damage .....) would also be reduced by a factor of four.

You can prove this for yourself easily enough with two differently-rated soldering irons. Holding a component in position by hand is a lot less pleasant if you have only a low-power soldering iron.
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