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Originally Posted by Bob Ward
... do the FETs need to be soldered on both top and bottom? Does anyone have any tricks or advice to share on replacing the FETs? Thanks!
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Bob,
A good solder should go "though" the board and both sides will show a clean and shiny solder wick connecting pad and pin.
The higher the current, the wider and/or thicker the copper trace needs to be on the PCB. This larger copper will leach away any heat you are attempting to apply to the connection and frustrate your efforts.
About 3 years ago, I did a power electronics design PCB able to carry over 200 amps. The soldering process was to have two technicians simultaneously heat the pin/pad from both sides of the board and then to apply solder to one side and verify that it flowed through to the opposite side of the board and wicked to both pin and pad.
De-soldering was nearly impossible as a one person operation...
Based on my experience:
1. Cut all FET pins with a good pair of transverse cutters. You will be removing each pin individually...
2. Heat both sides of the PCB (a two person operation) and pull the pin out with a good pair of needle nose pliers or a small spring hook (recommended for low thermal mass). Note that most pad delamination happens at this step...
3. Note that there will probably be solder left in the hole... Heat from both sides with soldering irons with very thin tips.
4. Remove the soldering iron on one side and then place a vacuum solder sucker on the hole. Note that a professional desolder station is highly recommended as the solder sucker tip is also the heating element...
5. Remove the other soldering iron and engage the solder sucker.
This should clean the hole without lifting the PCB pad.
Note 1: The above is augmented if you have design information on the PCB (at what temperature will it delaminate?) and solder/desolder stations with adjustable temperatures (as design engineer, I had both).
Note 2: My experience is with 60/40 lead/tin solder. Newer "lead free" solders melt at an even higher temperatures...
At any rate, good luck...
Mike