Desoldering advice

[antenna]

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!

[indeterminate]

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.

[nvmR]

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.

[shapirus]

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.

[antenna]

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.

[Psi]

What soldering iron and iron tip are you using?
It sounds like one or both are not up to the task.

They make more of a difference than most people think.

[shapirus]

Photos of the board would be nice btw, to see what we're talking about.

[donlisms]

The description screams "Need more power!" to me, also. Just because you set your iron to 480 doesn't mean that's what you're getting!

[modoran]

Use a preheater or hot air simultaneously to get the whole board arena to at least 80C and the relay will be desoldered much easier.

No smd part will fell off even at 230C due to the surface tension. But however aluminium caps will not withstand that .

[antenna]

Using an X-tronic 5040-XTS-XR3.  Have not tried bigger propane soldering iron yet, just got home, will try tomorrow.  I will go out to the shop and get the board and take pics now.  I like the idea of preheating, will try that too.

[antenna]

I may have damaged one of the SMD resistors under the relay trying to pry as I heated as I didn't notice or expect them under there on my first try, but I think you guys are right and that I need more thermal mass and I will try the bigger soldering iron tomorrow.

[KrudyZ]

I would take a hacksaw and start cutting off the relay.
While it doesn't look like you can cut it very close to the PCB, it's probably sufficient to turn this into a one pin at a time problem.

[Smokey]

hot plate?

[djsb]

Have you got a replacement relay? If so, maybe you can remove the plastic casing to get access to some of the pins. If you have access to the pins on the other side of the relay, then you could  use another soldering iron at the same time. Also, it also helps to apply liquid flux from a flux pen when using desoldering braid. The best way is a vacuum desoldering iron and preheat.




PS Get yourself some GOOT-WICK or Techspray desoldering braid. You can get it in different widths. Good stuff.
https://en.goot.jp/products/detail/cp_3015_10

[antenna]

I don't have a replacement yet, I just wanted it out so I could energize it and test it without backfeeding the board or poking at it while the board is live.  I will be giving it another try tomorrow using a butane soldering iron.  If that don't work, I will get out the heavy copper one for the propane torch.  And if that don't work, I will dremel it out.

My only desoldering tool besides the wick I mentioned is one of those Engineer SS-02 suckers from mouser.  Works ok, some day I will get a legit vacuum one

[strawberry]

lead solder. 80W should be minimum
if relay do not operate and coil is not open then something is wrong with control circuit

[tooki]

You absolutely need auxiliary heat!

Think of it like this, assuming the original lead-free solder: you need to raise the joint temperature by over 200°C (ambient 20C, melting point 227C). Right now, ALL of that energy has to flow in through the soldering iron tip, and you’ve got a big board sucking heat away on all sides. Even if your iron can reach 450C at the tip, all this means is that you’re overheating one spot on the board, while still not heating the joint as a whole sufficiently.

Now suppose you use a small oven or a hot air gun at a gentle temperature (say, 150C) to heat the entire board to 100C. Now the iron only needs to increase the joint temperature by 130C. Or preheat to 150C and the iron only needs to add 80C to the joint. Those are MUCH more reasonable numbers, and mean you’re less likely to damage the board.

And for sure, use a bigger tip. Bigger tip = better thermal conductivity = lower tip temperature needed = less risk of board damage.