Desoldering heavy modules

[MaxFrister]

I'm working on repairing a Keithley 2304A (https://xdevs.com/fix/kei2304a/) and came to suspect the DC to DC converter module.

I wanted to desolder it for testing.  I tried every trick in my book and still was just barely able to remove it -- and even then with significant damage to the module and PCB.

I'm curious what techniques others use to desolder heavy parts from PCBs -- hopefully with less damage than I did.

[joeqsmith]

At home, I have resorted to using a heat gun with the iron.  For actual work:

https://paceworldwide.com/st-1600-IR-preheater

[tooki]

I'm working on repairing a Keithley 2304A (https://xdevs.com/fix/kei2304a/) and came to suspect the DC to DC converter module.

I wanted to desolder it for testing.  I tried every trick in my book and still was just barely able to remove it -- and even then with significant damage to the module and PCB.

I'm curious what techniques others use to desolder heavy parts from PCBs -- hopefully with less damage than I did.

How can we say what other techniques we use when you haven’t listed what you did? “Every trick in my book” tells us literally nothing.

[MaxFrister]

How can we say what other techniques we use when you haven’t listed what you did? “Every trick in my book” tells us literally nothing.

Note that I didn't ask for "other" techniques, just successful ones.  I didn't think a list of my failed techniques would be particularly helpful.

It might be one of the techniques I tried was the right way and just done wrong.  If there is interest I can provide a list of "how not to desolder heavy modules" in a few days.

[TheMG]

It might be one of the techniques I tried was the right way and just done wrong.

That, and also knowing what tools you used and what you have available. Sometimes having the right tool for the job can make all the difference.

[DavidAlfa]

Preheating the board to 70-80ºC makes life *much* easier.
If the part is expensive, don't take the risk, you might damage the pcb, instead get some low melting temperature solder alloy, like sn42 bi58 ( Tin/ Bismuth) that melts at 138ºC.

I have some smd paste. One day I used it by mistake, after 20 seconds of cooling the parts were still moving!

You can get even lower melting with indium based alloys.

[MaxFrister]

For some reason, people wanted more information about what doesn't work to desolder large modules.

I have available to usual assortment of soldering/anti-soldering tools:



In addition I have a variety of items the could be pressed into service if necessary:



The module is attached to a pcb with SMD parts on both sides.  The holes in the pcb have very little clearance.  To desolder the module I tried:

• Soldering iron at 375 and 400c
• Air soldering station at 400c
• Adding new leaded solder
• Desoldering with Hakko 472B at a couple of different temperatures
• Solder wick
• Air soldering station and soldering iron at the same time

at that point I gave up trying to get it out in one piece and tried:

• Clipping the leads -- not enough clearance between the board and module
• Cutting the leads with a hack-saw blade.  Worked but scratched the PCB and could only be used on 1 end of the module because of clearance
• Heating the pins in sequence while slowly prying up the module.  Worked with the smaller pins but there is always the danger of damaging the PCB

In addition to the successful methods mentioned above, someone reported that they were able to remove one by turning up the heat on a desoldering tool and drilling out the end for the larger pins.    I've order some low-melting point solder and plan to try preheating next time I'm forced to try to remove a heavy module.

Thanks for the good advice.

[geggi1]

Have you tried using a hot plate?
Any of the tools you have in your pictures is probably no more than 100W i guess.
Heavy would normally mean a lot of metal that must be heated and you will require more power for that. As suggested in the post using a heatgun (1000W or larger) will heat up things very fast.
By using tools without enough you will not be able to heat everything at the same time and some of the solder will still be hard.

[abdulbadii]

This does not make sense




would edit it with image editor to circle it which exactly is 'heavy module' that cannot be desoldered ?

[nali]

Power modules are usually connected to hefty power planes - preheating is the only way to go really.

If it's lead-free solder then a couple of cycles of removing / refilling with 60/40 or if desperate some of the low melting point solders as mentioned above.

Also a proper powered desoldering pump helps a lot. Make sure the entire hole has reflowed, then suck out the solder but keep the pump running as you remove it - the airflow should cool both the lead & the hole plating reducing the possibility of sticking. Wiggle the pin if you can.

[MaxFrister]

This does not make sense




would edit it with image editor to circle it which exactly is 'heavy module' that cannot be desoldered ?

Bottom left, under the heatsink.

[james_s]

I have yet to find something that I couldn't desolder fairly easily with a combination of my Hakko 808, a soldering station and when I really need more heat, a heat gun for preheating the board. Usually for a joint that has a large thermal mass I'll crank up my soldering iron, add a bit of solder to the tip to get a good thermal connection, then place that on the joint at the same time has the 808 tip. Once it all gets nice and molten I pull the trigger and it sucks out the solder.

[abdulbadii]

Bottom left, under the heatsink.

What is bottom left, under the heatsink ?

[MaxFrister]

Bottom left, under the heatsink.

What is bottom left, under the heatsink ?

The module (shown in the first post of this thread) that you asked me to point to. 

[m3vuv]

ive had issues trying to desolder fets on ebike controllers with unleaded solder,i found the best way is to put the pcb on my cooker hob to preheat it then atack it with an old copper soldering iron heated with a blowlamp.

[abdulbadii]

It's not solder stuff but rivetted bolt/nail, isn't it ?

[tooki]

It's not solder stuff but rivetted bolt/nail, isn't it ?

Nope. Those are soldered in. Here’s the manufacturer’s soldering guide: https://www.vicorpower.com/documents/application_notes/rohssoldering.pdf


Edit, since you later edited in snapshots of the pins: those aren’t rivets. The one side had the pins sawed off to get them off the board, the other side shows the pins with blobs of solder on them.

[abdulbadii]

IMHO it turns to both or just either

• Hi power tweezer desoldering iron with idea avoid contact soldering iron tip to plate
  s.o. like https://www.amazon.com/Tweezer-Soldering-ZD-409-Circuit-Specialists/dp/B01M2YHJAB
  
• Mini drill just what we use to make component hole on PCB
  drill the pin's edges entirely patiently

[tooki]

IMHO it turns to both or just either

• Hi power tweezer desoldering iron with idea avoid contact soldering iron tip to plate
  s.o. like https://www.amazon.com/Tweezer-Soldering-ZD-409-Circuit-Specialists/dp/B01M2YHJAB
  
• Mini drill just what we use to make component hole on PCB
  drill the pin's edges entirely patiently

That is all terrible advice.

The problem is that the board is high-mass, the part is heatsinked, the pins are thick, and the pins are rigid, so you can’t melt one and tilt the part out.

The sensible options are to preheat the board thoroughly and then use a desoldering iron to suck out the joints, use low-temp solder to reduce the melting point of those joints (to make them easier to suck out), or to use low-temp solder on those joints to get it to where you can heat the entire board thoroughly, but at a temperature that only the joints with low-temp solder melt, letting you pull out the part.

[abdulbadii]

... avoid contact soldering iron tip to plate

didn't read ?

[tooki]

... avoid contact soldering iron tip to plate

didn't read ?

Of course I did. The advice to not touch the board is part of why I think it’s bad advice. What makes you think that not touching the board is desirable? The problem is huge thermal mass; the board needs to get hot.

[MaxFrister]

All finished. 

$6.00   NOS Power Module
$10.00 New fan and gasket
$8.00   Rear connector
$3.00   Replacement optical couplers (to reconvert to internal triggering)
$10.00 Front Binding posts

[DBecker]

I didn't see anyone mention desoldering needles.

These are thin walled stainless steel tubes.  The solder is melted and the tube is slid over the pin.  Solder doesn't wet the stainless steel, leaving the pin free.

High end versions have more sizes, some with very thin walls, but even the cheap sets fit almost everything and work amazingly well.

[David Hess]

I heat the pins on one side at a time and "walk" it out.

[SilverSolder]

I heat the pins on one side at a time and "walk" it out.

This - with judicious use of an old school Weller soldering gun (or modern equivalent, i.e. fairly high power iron), will take care of it.