Electronics > Repair

Desoldering advice

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I recently took on a repair and I am dealing with solder I have never encountered.  It is a scooter that quit working, error code states low motor voltage, even though the battery is good and fully charged.  I removed the controller, the mosfets appear fine, so I suspect the relay contacts.  Unfortunately, the solder that was used barely melts at the max setting on my soldering iron (480°C) and there are surface mount components including electrolytics all around the relay and underneath it.  To make things worse, the relay is soldered into plated vias.  So far, I have used an entire stick of ChipQuik with a solder sucker and managed to get the coil leads free and most of the solder off the contact legs, but I struggle getting the solder inside the vias to come out or even melt.  The relay won't budge.  I plan to keep going with the chipquik alloy, but I wonder how many rounds of getting them hot it can handle before I destroy other things.  Does anyone have advice for a situation like this?  I would try hot air, but there are SMD electrolytic caps and other chips right next to the relay and I fear hitting it that hard will do damage to them as well.

edit: another concern I have is whether or not the chipquik is getting in the via and that the relay is simply glued down, but given how many rounds of chipquik it took to get the bulk of the solder off the legs would suggest its just that high of MP.  I want to try to get under the relay and pry, but there are SMD resistors under it and I don't know what might peel off with the glue that may be there.  They built this thing to not be repaired.  I am tempted to decap the relay to check the contacts and cut it out if bad.

Any suggestions would be appreciated, thanks!

You need to yous a very large iron
300w 1/2" diameter tip
sumthing like this https://www.ebay.com.au/itm/295097210355
get it up to temperature and then turn it off
make a heavy copper wire bridge between all the pins that need to be desoldered  at least 2.5mm2
that way you can heat everything at once and pull the relay out.
The tip of the soldering iron should be at least 1/2" diameter and 2 > 3 inches long , including the bit inside the element.

For TH devices, use a solder wick or solder pump to remove the solder from each and every leg individually.
You can also try to place a heat plate beneath the pcb, and give it a preheat.
A large blower can also give a good preheat.

Another method (or rather an additional step) is to use low melting point solder, or simply Rose's alloy, by adding it to the joints and letting it mix with the old solder. The resulting mixture will melt much easier.

But after the job is done you will need to remove all the remains of this low melt mixture as thoroughly as possible: you don't want it to compromise the new solder joints you make when you reassemble the thing.

The chipquik is low melting alloy (around 80°C), but it does not like going in my solder wick (MG Chemicals SuperWick #453).  I do have a propane torch soldering iron tip that is a half inch diameter, I will try that route.  The problem with heating the whole thing to the necessary temp is the surface mount parts under and near the relay. I also worry about lifting the foil off the PCB. There are many SMD parts around and under the relay and I cannot risk them all falling off.


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