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Old 07-19-2020, 04:01 PM   #1
LearningToRepair
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Default How to correctly desolder through hole IC?

Hi!

I tried to desolder through I had IC that I wanted to replace but failed. And now I came here to learn what's the correct way for doing this. I tried to use soldering wick but the capillary force kept solder in the hole. With soldering wick I only managed to remove the part of solder that was outside the hole. But the solder that was inside the hole never got out. And of course when I moved on to next pin the solder in previous hole hardened again so no matter how many times I did all the pins there was still solder in holes.

Question 1: what would have been correct way of desoldering this IC?
Question 2: I tried to pull the IC with pliers while heating the pins from the other side but it did not help either. And as a result, I now have some pins stuck in hole together with solder that came off from IC when I pulled it. what would be correct way to remove these?


Also attached here the image of IC (taken before desoldering attempt)
20200712_174625.jpg
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Old 07-19-2020, 04:50 PM   #2
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Default Re: How to correctly desolder through hole IC?

Ok

It depends on if you want to spend some money or not

If want to spend some money then buy a Desoldering Gun with a vacuum pump style

If you do not want to spend very much money at all use a good quality solder wick with some flux

Either one will work but you if you choose the second option you should have a temperature controlled soldering iron at a minimum 60 watt would be preferred but could get by with a 40 watt iron but you will have to be some what patient with this but you can stay on a one soldering joint for a real long time because you could have have the pads lift off the board
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Old 07-19-2020, 05:32 PM   #3
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Default Re: How to correctly desolder through hole IC?

most wick is pretty crap unless you add flux to it first.
if you dont want the chip, cut each leg and then pull them out with tweezers while melting the solder.
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Old 07-19-2020, 06:18 PM   #4
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Default Re: How to correctly desolder through hole IC?

Quote:
Originally Posted by stj View Post
most wick is pretty crap unless you add flux to it first.
if you dont want the chip, cut each leg and then pull them out with tweezers while melting the solder.
That is what I do, I rather cutout the chip than damaging the traces.
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Old 07-20-2020, 12:25 AM   #5
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Default Re: How to correctly desolder through hole IC?

Quote:
Originally Posted by stj View Post
most wick is pretty crap unless you add flux to it first.
if you dont want the chip, cut each leg and then pull them out with tweezers while melting the solder.
I already tried to add extra flux on wick.
Ok, I will try to cut the legs next time.

Quote:
Originally Posted by budm View Post
That is what I do, I rather cutout the chip than damaging the traces.
What do you exactly mean by damage? Heat damage? It looks like around holes where I tried too hard, the green coating came off a little bit and the copper trace got exposed like 1 mm or maybe a bit less due to heat. Can this and should this be fixed or should the entire thing be now thrown away? also on the other side where I pulled the chip there are few small scratches where copper is visible but not damaged. In that case it's just mechanical damage, not heat damage.
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Old 07-20-2020, 04:08 AM   #6
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Default Re: How to correctly desolder through hole IC?

if you pull a chip out without the pins being TOTALLY unsoldered from the holes, you can rip the through-hole plating out.
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Old 07-20-2020, 04:12 AM   #7
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Default Re: How to correctly desolder through hole IC?

you should get a solder sucker .. it should almost fall out after using one .
sometimes you need to add new solder to get the old solder to melt to remove it .
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Old 07-20-2020, 05:38 PM   #8
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Default Re: How to correctly desolder through hole IC?

Thanks,

I will try out solder sucker. Meanwhile I have few more questions:
1) Will solder sucker also getrid of broken legs in holes or is it only useful for future desolderings?
2) Do scratched traces (see attached image) need some sort of treatment?
3) If I managed to break one piece off of smd ceramic capacitor would I have to replace it and if yes then what would be the voltage rating (see attached image), I read from the internet that it is ok to replace it with capacitor with larger voltage rating, but is there any limit how much higher voltage rating capacitor can I use, for example if original capacitor were rated for 5V and and new one were rated for 500V, would it become a problem or would it be fine as long as capacitance is close enough?
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Old 07-20-2020, 06:06 PM   #9
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Default Re: How to correctly desolder through hole IC?

you could heat those broke pins and pull out whilst iron still on it .
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Old 07-20-2020, 07:29 PM   #10
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Default Re: How to correctly desolder through hole IC?

Since you got the IC remove, you should check that you still have connection between the top side and the bottom side of the board of each hole, just need to make sure the through-hole plating are not damaged.
500V rating cap will be so much Bigger size than 5V cap, you also need to use the same type of cap. Are you talking about MLC Capacitor?
BTW, you should use good IC socket so If you have to replace the IC again, it will be easier to replace the IC.

Last edited by budm; 07-20-2020 at 07:31 PM..
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Old 07-22-2020, 12:00 PM   #11
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Default Re: How to correctly desolder through hole IC?

The capacitor I am talking about is the yellow one on the picture I attached to my previous post. Not exactly sure if it is MLC.
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Old 07-22-2020, 02:05 PM   #12
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Default Re: How to correctly desolder through hole IC?

Quote:
Originally Posted by stj View Post
most wick is pretty crap unless you add flux to it first.
I've been soldering for years, and I have NEVER been able to use wick to clean holes and remove components like some videos show. I've tried both cheap and expensive wicks, with and without flux, with my 75-Watt temp-controlled soldering station. As such, I NEVER recommend wick to anyone, especially beginners. And for through-hole components, wick is a big waste of time IMO. I only keep a little bit now for BGA work, which I haven't done in years.

Otherwise for removing multi-pin components and ICs like this, I either use a regular soldering iron with a manual vacuum pump or I use my 40-Watt Radio Shack soldering iron that has a built-in bulb sucker. Both work pretty well. Generally I usually try the RS 40-Watt iron first, as it's quicker and less work. But when there are large solder joints that the RS 40-Watt iron can't tackle, I go for my 75-Watt soldering station and my manual spring-loaded sucker. With these two, I can remove just about anything.

I don't suggest buying an expensive iron with a built-in sucker just for this one job. If you're going to do DIP ICs a lot, then yes it makes sense. But since through-hole soldering is not so popular anymore, it's not going to be a very useful tool. If you're going to spend that kind of money, then better get a regular but good-quality temperature-controlled soldering station (probably one that use T12 tips) and a cheap-ish spring-loaded sucker.

Quote:
Originally Posted by budm View Post
BTW, you should use good IC socket so If you have to replace the IC again, it will be easier to replace the IC.
That's a good idea, but not always applicable.
Some ICs need to be soldered to a large ground plane for thermal management reasons (e.g. certain low-power audio ICs.)
So depending on what the IC is/does, an IC socket may or may not be used.
*EDIT*
Looking at the pictures and checking the datasheet shows it's an SMPS controller, so probably OK to put in a socket. Always check with datasheet of course.

Quote:
Originally Posted by LearningToRepair View Post
The capacitor I am talking about is the yellow one on the picture I attached to my previous post. Not exactly sure if it is MLC.
Yup, it's MLC.
What's the part number on the IC?
Looks like KA3525A from the picture, if I'm not mistaken.
Knowing what the IC is and finding its datasheet are the first two things to help determine the cap value. A lot of times, the circuit on the PCB may closely resemble an application circuit in the datasheet. This can help you find the value of that capacitor... or at least a ball park.

That aside, any reason for changing out this IC? If this is for troubleshooting a PSU, a lot of time, the IC is not the issue - at least not if it's just a PWM driver or voltage monitor. If it is one of those offline PWM-FETs/ICs, then those do actually go bad somewhat more often.

*EDIT II*
Looks like the cracked MLC is connected to pin 9 (and maybe ground - please check.) That's a signal IC pin, so probably a 16V-rated or higher MLC will do. As for the capacitance, I think that will depend on the circuit design, since it's connected to the inverting input of the PWM comparator. The test circuit in the datasheet suggests 10 nF. But again, that may not be the value that's in your circuit. It does give you an idea for a ball park, though (i.e. it's probably not over 1 uF and probably not lower than 1 nF... but that's still a huge range to guess.)

If you have a cap meter or capacitance measure setting on your multimeter, you can test that MLC (out of circuit.) If it reads open or infinite capacitance, it's probably bad. If it does show a good standard capacitance value, it's probably OK and you can leave it back in.

Last edited by momaka; 07-22-2020 at 02:24 PM..
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Old 07-22-2020, 03:14 PM   #13
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Default Re: How to correctly desolder through hole IC?

Quote:
Originally Posted by momaka View Post
I've been soldering for years, and I have NEVER been able to use wick to clean holes and remove components like some videos show. I've tried both cheap and expensive wicks, with and without flux, with my 75-Watt temp-controlled soldering station. As such, I NEVER recommend wick to anyone, especially beginners. And for through-hole components, wick is a big waste of time IMO. I only keep a little bit now for BGA work, which I haven't done in years.
I also never got it to work until I tried it with a really large tip (=large thermal mass).
Then it works absolutely amazing, I can sometimes even clear multilayer PCB's (Though that is unusual) but a board like here should be doable...
The tip in question is a "SMD" tip for my Weller soldering station, i.e. a tip that can reach both sides of a 0805 component for example.
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Old 07-22-2020, 03:15 PM   #14
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Default Re: How to correctly desolder through hole IC?

i only use wick for cleaning tinned tracks in combination with a blade-style tip.
but to be fair, i have an electric pump.
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Old 07-25-2020, 11:44 AM   #15
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Default Re: How to correctly desolder through hole IC?

Quote:
Originally Posted by Per Hansson View Post
I also never got it to work until I tried it with a really large tip (=large thermal mass).
Nope, still no success for me.

By default, I use a 5.2 mm bevel tip with my 75-Watt station. It has enough thermal mass and heat transfer to melt a large blob/pool of lead-free solder for flooding the pins on a D-SUB port on a motherboard (to pull it out) - and I've done it a few times now with no issue.
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Old 07-26-2020, 09:29 AM   #16
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Default Re: How to correctly desolder through hole IC?

https://www.chipquik.com/store/index.php?cPath=200
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Old 07-26-2020, 12:07 PM   #17
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Default Re: How to correctly desolder through hole IC?

If you're using wick, you need the really fine wire stuff and have plenty of flux on it.
Usually old wick is no good. If your wick is not shiny bright yellow copper colored and just red copper colored, it's probably no good anymore...

Don't store your wick in a humid environment, if you have fresh wick you might want to keep some desicant with it.
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Old 08-11-2020, 04:41 AM   #18
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Default Re: How to correctly desolder through hole IC?

Quote:
Originally Posted by momaka View Post

*EDIT II*
Looks like the cracked MLC is connected to pin 9 (and maybe ground - please check.) That's a signal IC pin, so probably a 16V-rated or higher MLC will do. As for the capacitance, I think that will depend on the circuit design, since it's connected to the inverting input of the PWM comparator. The test circuit in the datasheet suggests 10 nF. But again, that may not be the value that's in your circuit. It does give you an idea for a ball park, though (i.e. it's probably not over 1 uF and probably not lower than 1 nF... but that's still a huge range to guess.)

If you have a cap meter or capacitance measure setting on your multimeter, you can test that MLC (out of circuit.) If it reads open or infinite capacitance, it's probably bad. If it does show a good standard capacitance value, it's probably OK and you can leave it back in.
Yes, It goes to pin nr 9. When I took it out of circuit I was unable to get any reading. I think it was because the other side was broken off. Just asking to be sure: can I be confident that this is capacitor or are there also other components that are yellow like that?
I would also like to know where you got 10 nF? Did you use this datasheet?
https://www.onsemi.cn/pub/Collateral/KA3525ACN-D.pdf page 5? It doesnt have any units. Is it default to assume that numbers are in F and therefore 0.01 F = 10 nF?

Local hardware store sells 10nF*50V X7R 10% SMD 0805 is it good enough? Sadly they dont have any other info than just product name. Also what does MLC exactly mean? If my local store lists this as SMD capacitor, are they same thing or different?

Here is also macro photo of after removing it from the board in case it helps.
cap.JPG
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Old 08-11-2020, 06:47 PM   #19
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Default Re: How to correctly desolder through hole IC?

MLCC = Multi Layer Ceramic Capacitor.
Take caution when handling them, check the resistance after you install the cap to make sure it is not damaged and shorted out due to mis-handling.
Read the PDF attached.
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File Type: pdf TDK_MLCC_common_cracking_modes.pdf (2.00 MB, 22 views)
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Old 12-18-2020, 11:07 AM   #20
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Default Re: How to correctly desolder through hole IC?

It's a cinch with real quality braid and real flow and not cheap chinoiserie. I use Amtech flux, the real one, not the Chinese copies and the "BMJ" desoldering braid and it is very easy to remove the solder and unclog the holes with that. When we look at the inexpensive braid and the quality braid with a microscope or a binocular, they are not at all the same thing. In the quality braid there are many more filaments and they are much smaller, which increases the capillarity. There is no comparison in use
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