Glued PCB component removal

Thread Starter

letsfixitgarage

Joined Dec 30, 2020
6
Got so frustrated with one repair that decided to register in this forum to look for help..

Have a HP docking station with shorted MOSFET.. thought it will be an easy job heat it up with a hot air station and remove the component.. but was I wrong.. first resoldered the legs and started heating up with 360 degrees C and 20% airflow after some time of nothing happening steadily increased it up to 400 C and 100% airflow still nothing then tried to move a capacitor next to the MOSFET and it didn't move either.. only then I got the idea that it could be glued with some kind of epoxy.. anyone with this kind of experience? What would be the possible, non destructive, ways of removing it..

Attached is the picture of the nice guy.. even scratched it trying to move it..
 

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jpanhalt

Joined Jan 18, 2008
10,963
Is it adhered with "hot goo" or "hot snot?' If so, isopropyl alcohol is a miracle release agent for that. Just a drop or two, and the snot removes easily.
 

Thread Starter

letsfixitgarage

Joined Dec 30, 2020
6
Probably not hot enough yet. It most likely is soldered with lead free solder and the takes more heat around
217°C/422°F from, https://www.digikey.com/en/maker/blogs/rohs-vs-non-rohs-soldering Also not sure about that component but many big things like that also have a coppr pad under them as a heat sink that my also be soldered to the board.
Thanks for your reply. I applied 400 C and yes the MOSFET has quite big surface on the bottom and the trace where it is soldered on is quite big too but as I mentioned at the same time when I was heating the MOSFET I tried to move a much smaller capacitor (in the picture up from the MOSFET) and it didn't move either that's why I thought that there must be some kind of epoxy glue.. that withstands 400C heat..
 

Thread Starter

letsfixitgarage

Joined Dec 30, 2020
6
Is it adhered with "hot goo" or "hot snot?' If so, isopropyl alcohol is a miracle release agent for that. Just a drop or two, and the snot removes easily.
Hi, no the board is beautifully clean as if nothing is there.. didn't notice even protective coating on top.. you can check the attached picture in previous post..
 

jpanhalt

Joined Jan 18, 2008
10,963
1) Get some good solder wick. I use Chemtronics. I have tried other brands, and have found nothing better.
2) Get a "hot-air" desolder-er. It is the only way to heat multiple pads to soldering temperature. I have tried some options, but none work as well as the cheapest hot-air station. My current one netted out to about $70.
3) A cheap HF propane or butane torch can work m a pinch.
 

Thread Starter

letsfixitgarage

Joined Dec 30, 2020
6
1) Get some good solder wick. I use Chemtronics. I have tried other brands, and have found nothing better.
2) Get a "hot-air" desolder-er. It is the only way to heat multiple pads to soldering temperature. I have tried some options, but none work as well as the cheapest hot-air station. My current one netted out to about $70.
3) A cheap HF propane or butane torch can work m a pinch.
1 will not help in this case as the SMD has big pad underneath it that is soldered to the board track as heatsink and a small area of glue between it and the board.. I have an advanced hot air station and was applying 400C with a lot of air flow. With this setting I usually lift off even stubborn components but this time it didn't move at all.. i assume that there is some kind of epoxy applied by the manufacturer to not lose any components in the reflow procedure.. read that some use acetone/paint remover to soften the glue as nothing else effects the epoxy.. although that would damage the board too..
 

jpanhalt

Joined Jan 18, 2008
10,963
If the solder doesn't melt at 400°C, it is either a very unusual solder, or it is not at 400°C (pure tin melts at 232°C). The fact that your advanced hot air station could not move a small capacitor would make me lean toward the latter. Can you remove that capacitor with your regular soldering iron? When you are heating the component, does the exposed solder seem to melt?

There are some extremely high temperature epoxies, but the highest I found was rated to only 343°C and also required curing at high temperature. I think it is unlikely such epoxies or even ceramics are used in assembly.
 

Thread Starter

letsfixitgarage

Joined Dec 30, 2020
6
If the solder doesn't melt at 400°C, it is either a very unusual solder, or it is not at 400°C (pure tin melts at 232°C). The fact that your advanced hot air station could not move a small capacitor would make me lean toward the latter. Can you remove that capacitor with your regular soldering iron? When you are heating the component, does the exposed solder seem to melt?

There are some extremely high temperature epoxies, but the highest I found was rated to only 343°C and also required curing at high temperature. I think it is unlikely such epoxies or even ceramics are used in assembly.
Thanks for your thoughts. Decided to check my "advanced" air station :) it's a Chinese brand "bst 863" quite happy with it, but never checked is it accurate.. so multimeter temperature probe at 300 set shoved 230 actual and at 400 set 280-290 actual.. so not the 400 but should be enough for the job.. as said with other boards this setting was lifting anything..

I added leaded solder to the legs and it melts without problem.. haven't checked the neighbor components to be sure but I think it flowed too will check one more time..

I will try to put the board on the preheater to heat it up completely to 100-150C and then apply heat to the MOSFET.. if this will struggle too I think next step will be exacto knife..
 

jpanhalt

Joined Jan 18, 2008
10,963
I have a cheaper model 8582D hot air station from China. Its hot air temp with a thermocouple is right on. I would set the air temp a bit higher. Temperature control is up to you. Before my hot air station, I used a much hotter blower and even a small propane flame. You just have to keep the flame moving to control temperature.

Will you be using the scalpel to pry it or cut the legs off? Before I would use a scalpel to pry anything, I would use solder wick on the pins, then cut them at the IC's body. That way, only the heatsink is holding it. Good center heat and it should slide right off. A pre-heat plate will help, and/or apply the hot air to the back too.
 

andrewmm

Joined Feb 25, 2011
909
Epoxy fitting is used, but not in my experience on commercial stuff,

Looking at the picture, it also looks like the board has been conformably coated,
so you will have to scratch that off first, else it will go brown and be horrible to re solder !

looking at the PCB picture,
Those chips have large planes attached to them,
so I bet they also have a large plane underneath the chip ( see if on the bottom of the board there are vias in the middle of the chip area.


If it is like that , The amount of soaking at temperature you have to do is tremendous,
Think like 30 minutes soak before you put the boost on, which could be another 15 minutes,

measure the board temperature about 1cm away from the chip,
if that's not above 200 C , you are no where hot enough.
 

Thread Starter

letsfixitgarage

Joined Dec 30, 2020
6
Thank you for your tips and suggestions!

Got the chip off, a replacement on and as was suggested problem was heat, not somekind off epoxy.. wanted to preheat it to ~200C but problem with this board (docking station) that it has a lot of connectors (don't know much they can take before melting) so I set the preheater to ~100C so the board was at ~80C and then set the hot air to 450 so real was around 350.. and then I chose a test point/ connection point next to the MOSFET as a test point as it was on the same pcb track as the MOSFET and the same lead free solder as under the MOSFET. So I was heating both of them and when the solder point weakened the MOSFET came off without any problem..

So yes these boards take in a lot of heat.. was quite a surprise for me as I worked first time on this kind off board.

Wanted to share it, maybe it will be helpful to someone.
And thank you everyone for your help!
 
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