Desolder ic attached to big heatsink. need tips

Thread Starter

cmrincon

Joined Oct 25, 2017
40
Hi. Im trying to desolder the ic attached to this heatsink:

IMG-20180715-WA0016.jpeg IMG-20180715-WA0013.jpeg
I'm using a 35w solder with a 1 mm plane tip and a 30w solder with a 0.5 round tip.
i need tips because i can't suck the tin, even, i barely can heat the ground pin.
All help is welcome. Thanks
 

jpanhalt

Joined Jan 18, 2008
11,088
1: It looks like that heat sink is attached to a PCB that is soldered to the main board. You need wattage. I have a large Weller for that. Your 30W may just not be big enough.
2: I do not use a sucker (except very rarely). I generally use solder braid to get almost all of the solder out.
3: If #2 doesn't work, I use compressed air to blow the molten solder. The effective working distance for compressed air @ 40 to 60 psi is much further than for suction.
4: I would consider cutting the pins to get the PCB off the main board.
5: As a last resort , I try to get a corner pin loose with leverage, then work across the row. That is risky, as you may damage a plated through hole (i.e., pull the hole plating out with the pin).
6: If you cannot reach the pins, then I would consider back drilling the screw that is holding the heat sink to the PCB. That will, of course, destroy the threads in the heat sink. You will need a new heat sink or use a barrel nut or small nut to re-attach it. The heat sink may be attached to its PCB with adhesive. If that is the case, then removing the screws may not be adequate. Pick a drill smaller than the minor diameter of the screw. Then enlarge if necessary. Since it is the screw bottom, you may find that simply drilling the screw will back it out.

I have done only #1-#5. #6 is just a hypothesis. #4 is usually my goto method for large chips or pin headers that I am willing to sacrifice. #5 is tricky, particularly with PTH.
 

Thread Starter

cmrincon

Joined Oct 25, 2017
40
Thanks you!

Definetly my 2 solders are not enough. I tryed to remove all the tin with the 2 solders together, but even this way i am short of watts.
#4 is impossible, there is no way to reach to the pins.

I think that this is only possible adding more watts.
Regards
 

jpanhalt

Joined Jan 18, 2008
11,088
Thanks you!

Definetly my 2 solders are not enough. I tryed to remove all the tin with the 2 solders together, but even this way i am short of watts.
#4 is impossible, there is no way to reach to the pins.

I think that this is only possible adding more watts.
Regards
There are also very low temp solders made, e.g., ChipQuik (https://gokimco.com/chip-quikr-smd1...MIzfP4yYqh3AIVm4qzCh2JLguKEAQYAyABEgKFwPD_BwE). You don't need the entire kit. You add the solder to each pin in the usual way. Then proceed with #1 again. Hot air then works well for heating multiple pins at once.
 

dl324

Joined Mar 30, 2015
13,505
Im trying to desolder the ic attached to this heatsink:
Your pictures are about as clear as mud. Point out to us what you're trying to desolder and how those points are connected to the heatsink and how the heatsink is connected to the component.
 

Thread Starter

cmrincon

Joined Oct 25, 2017
40
IMG-20180715-WA0016.jpeg

1: It looks like that heat sink is attached to a PCB that is soldered to the main board.
Here can you see the pins which i want to desolder. I know that It's not the best image in the world but the pins are visible.
The component is connected to the pcb through solderings and the component is connected to the heatsink through screws.
 

jpanhalt

Joined Jan 18, 2008
11,088
Chip-Quik is relatively expensive (IMHO), but it does work. I have a short piece that is more than 10 years old that I have used infrequently to say the least. There are other vendors of mercury-free, low-temp solder. I corresponded with this gentleman years ago (http://www.indium.com/blog/a-guide-to-low-temperature-solder-alloys.php ). I have not checked prices, but upon further thought, I think making an alloy with a low-temp solder, removing excess with solder wick, and then using a hot air gun might be the best alternative. Raise one side and then the other. Do you have access to any of the very low-temp alloys, e.g., Wood's metal, from a local school?

John
 

jpanhalt

Joined Jan 18, 2008
11,088
Not the electronics lab. I am a chemist. I meant chemistry (or metallurgy). Woods metal is a bit of a curiosity. We had a 5# can of it that was being discarded. I saved it from the trash. It's even on eBay. If you search on it, be sure to use the "-Tiger" modifier.:D

Here's a link o another list of low-melting alloys: https://en.wikipedia.org/wiki/Wood's_metal You probably want to avoid the alloy with thallium. It is mildly radioactive.
 
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Thread Starter

cmrincon

Joined Oct 25, 2017
40
Not the electronics lab. I am a chemist. I meant chemistry (or metallurgy). Woods metal is a bit of a curiosity. We had a 5# can of it that was being discarded. I saved it from the trash. It's even on eBay. If you search on it, be sure to use the "-Tiger" modifier.:D

Here's a link o another list of low-melting alloys: https://en.wikipedia.org/wiki/Wood's_metal You probably want to avoid the alloy with thallium. It is mildly radioactive.
Thanks you! I think i can borrow a 200w solder station. If it doens't work, i will search for it. Thanks you again
 

shortbus

Joined Sep 30, 2009
8,952
Not the electronics lab. I am a chemist. I meant chemistry (or metallurgy). Woods metal is a bit of a curiosity. We had a 5# can of it that was being discarded. I saved it from the trash.
Had to look to see what "Woods metal" was. It's seems like it is the real name for Cerrobend. That I'm familiar with and over the years doing very intricate die making work have used. It is some amazing stuff, and was the way some very thin metal was machined before the advent of sinker and wire EDM.
 
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R!f@@

Joined Apr 2, 2009
9,751
I use to remove those big IC's on plasma TV panel driver PCB's.
I use a 60W hakko iron that has very good heat replenishing capability, plus desoldering wick and flux.
After absorbing all the solder using the wick, I then uses a heat gun to heat the PCB and then just lift the sink with the IC.
The trick is to heat the PCB slowly using low temp and then increasing the temp slowly as the pcb starts to heat up, flux is always used to help the remaining solder with in the vias to melt. Too much temperature and the PCB will warp. so need to be careful on the heat settings
Then again if you do not need the PCB then just a heat gun set at high will do.
 

R!f@@

Joined Apr 2, 2009
9,751
Another trick is aim a hot gun towards the desoldering pin from a distance with not so hot air setting and then use iron and solder braid to clean the vias.
The trick with the hot gun is to prevent the joint going cold. It is helpful if the iron is not so good in heat transfer to large copper areas.
 

mtripoli3

Joined Mar 1, 2016
35
For the most part, what R!f@@ says is about it... Heat the heatsink at the same time you heat the pins; this will prevent the heat "sinking" into the sink. Get the heatsink hot enough to melt solder and it'll slide out of the board...

Good luck!
 

LesJones

Joined Jan 8, 2017
3,570
Are you trying to remove the IC because it is faulty or do you need to remove it without damaging it ? If it is faulty then removing the heat sink may allow you to cut all the pins with side cutters then remove the pins one by one. If you need to remove the IC without damaging it then I suggest making a special bit to fit a large soldering iron (100 watt +) You may be able to just use a strip of copper (Say 3mm thick) that is long enough to heat all the pins on one side of the IC at a time and remove one side at a time. If the pins come out from the bottom of the IC rather than the edges you will need to make the bit so that all the pins on both sides are heated at the same time. Tin the edges of the copper that will come into contact with the pins so that there is good thermal contact.
This is a bit I made to remove a 28 pin NVram chip from a PCB without damage to either the chip or the PCB.
IMG_1520 (Medium).JPG

A picture of the IC with the heatsink removed may also help with a solution.
Les
 

bertus

Joined Apr 5, 2008
21,667
Hello,

@LesJones , The main problem seems to be that the heatsink was mounted to the chip before mounting it on the board.
Now the heatsink can not be removed.
The soldering is difficult because of the heavy goundplane of the PCB.

Bertus
 

Thread Starter

cmrincon

Joined Oct 25, 2017
40
Hi!

i'm not be able to remove the heatsink from the ic without desolder the ic first so...as mtripoli3 suggested heat the heatsink is a way to solve this...

Heat the pcb is unlikely as there are components below the heatsink and beside the ic so if i heat the pcb i take the risk of desolder those components.

I forgot to say that the ic if faulty so i don't mind if i shatter the ic. :)

This weekend i am going to meet a friend who has experience in the repairs field and has got a 100+ Watts solder iron.

Regards
 

jpanhalt

Joined Jan 18, 2008
11,088
Hi!

i'm not be able to remove the heatsink from the ic without desolder the ic first so...as mtripoli3 suggested heat the heatsink is a way to solve this...

This weekend i am going to meet a friend who has experience in the repairs field and has got a 100+ Watts solder iron.
You can back drill the two mounting screws -- probably even by hand given the cup on the end of the screws. However, a drill press would make it easier.
As for #2, the problem is not melting the solder around just a few pins, it is melting the solder around all (or almost all) of the pins on one side.
 
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