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Old 04-16-2021, 03:02 AM   #1
dicky96
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Default Need to Replace small QFN very close to DIMM sockets - suggestions?

Hi guys
You can see the attached pic - the QFN is faulty and needs changing. It is closer than 1cm to the DIMM sockets and of course I must not damage these

So.... best suggestions and techniques please. Desolder and Resolder. I have some thoughts myself but don't want to distort the responses
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File Type: jpg IMG_20210416_092734.jpg (515.9 KB, 44 views)

Last edited by dicky96; 04-16-2021 at 03:03 AM..
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Old 04-16-2021, 05:25 AM   #2
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Default Re: Nood to Replace small QFN very close to DIMM sockets - suggestions?

shield the sockets with tin-plate
i use old tuner covers.
and consider heating the underside first.
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Old 04-16-2021, 07:05 AM   #3
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Default Re: Nood to Replace small QFN very close to DIMM sockets - suggestions?

You could Dremel the top off if you're worried about heat. I'd shield the ram socket with foil and kapton tape.
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Old 04-16-2021, 06:53 PM   #4
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Default Re: Need to Replace small QFN very close to DIMM sockets - suggestions?

Worried about heat? Use a QFN soldering iron tip
... don't bother to buy one: that qfn ic is so small that your everyday soldering iron will be enough:
just make a solder bubble and drag it to the unused space (top left corner on the picture)
or live life to edge and throw it off by quickly flipping the motherboard upside down.
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Old 04-16-2021, 07:09 PM   #5
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Default Re: Need to Replace small QFN very close to DIMM sockets - suggestions?

try hot air and iron at same time . crank both up and do it as quick as possible .oh add low melting solder to speed things up .
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Old 04-17-2021, 04:31 AM   #6
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Default Re: Need to Replace small QFN very close to DIMM sockets - suggestions?

@petehall
@megaraider

I normally add leaded solder to all the pins of an IC, or SMD cap/resistor before using hot air to desolder - It seems to help a alot, but I'm not sure how effective that would be on a QFN where most of the pads are underneath the IC

Are you suggesting if I add leaded solder as best I can then place a large tip (T12 BC3) to the top left corner of the QFN, hit Boost on the KSGER T12 and I can just lift it off with tweezers?

I can see that may work if, especially if I use my hot air preheater (Kada 853B) and a thermocouple to get that area of the board heated from below to around 100C first. Hmmm........... interesting.

Last edited by dicky96; 04-17-2021 at 04:35 AM..
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Old 04-17-2021, 06:41 PM   #7
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Default Re: Need to Replace small QFN very close to DIMM sockets - suggestions?

Quote:
Originally Posted by dicky96 View Post
@megaraider
I normally add leaded solder (...) a QFN where most of the pads are underneath the IC
Since it's a (very) small QFN IC package not only add leaded solder to the pins but also make a solder bubble covering all the IC.
Therefore, don't bother with the underneath, the leaded solder will reach there.
Quote:
Originally Posted by dicky96 View Post
Are you suggesting if I add leaded solder as best I can then place a large tip (T12 BC3) to the top left corner of the QFN, hit Boost on the KSGER T12 and I can just lift it off with tweezers?
Yes, but again since the IC is so small using tweezers will cool the solder before you manage to grab it.
Instead use the soldering iron tip to drag it.
Quote:
Originally Posted by dicky96 View Post
I can see that may work if, especially if I use my hot air preheater (Kada 853B) and a thermocouple to get that area of the board heated from below to around 100C first. Hmmm........... interesting.
imo there's no need to add complexity to the procedure using a hot air preheater below the motherboard.
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Old 04-18-2021, 03:21 AM   #8
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Default Re: Need to Replace small QFN very close to DIMM sockets - suggestions?

OK, thanks mate

I'll look for some small QFN on scrap boards to practice this method first. The 'solder bubble' method is something I already use with other SMD devices

Cheers
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Old 04-18-2021, 06:45 PM   #9
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Default Re: Need to Replace small QFN very close to DIMM sockets - suggestions?

You're welcome. Let us know how it went when done.
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Old 04-21-2021, 07:35 AM   #10
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Default Re: Need to Replace small QFN very close to DIMM sockets - suggestions?

Нужно залудить контакты сплавом розе или вуда если такового нет то свинцовым припоем .При условии что они открыты и пропаять их сначала паяльником с тонким жалом а потом феном .Использовать не активный флюс , каптоновый или алюминевый скотч ими закрыть пластмассовые детали чтобы вы не поплавили их случайно паяльником а тем более феном.Но учтите этот сплав используйте аккуратно им можно перепачькать всю плату. Для удаления используйте медную оплетку
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Old 04-21-2021, 07:36 AM   #11
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Default Re: Need to Replace small QFN very close to DIMM sockets - suggestions?

Сплав вуда или розе
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Old 04-21-2021, 09:31 AM   #12
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Default Re: Need to Replace small QFN very close to DIMM sockets - suggestions?

miayotto: English only in this forum please.
You can use Google translate if you need to translate something.
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