Author Topic: how to desolder/solder small SMD  (Read 7439 times)

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Offline codrutoctavian

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how to desolder/solder small SMD
« on: December 27, 2013, 09:29:21 am »
Hi All,

Here’s the story. I bought an AMD Radeon R9 290 video card which was very loud with the fan turned on, so I tried to change the default factory fan with an aftermarket Accelero Xtreme III. After changing the fan when I boot the computer the video card fried. Analyzing the card it seems that the piece which broke was an IRF6811 component from International Rectifier. You can see why I suspect this particular piece due to the following picture showing how smoke came out of it:



As this card was about 400 EUR I thought it is okay to try and fix it by replacing the piece, which is a power MOSFET. I ordered the piece and here’s how it looks like:



And this is the piece to be replaced:




The tools I have is a Weller WESD51, solder Multicore Sn62 0.46 mm from Multicore or 60/40 0.6 mm solder from Super Solder Wire, and the following Weller tips:


 
I don’t have big expectations in trying to fix this but I though it worth a shot.
I do have the following questions:

1.   How to remove the old piece from the board? As you can see it is soldered underneath the piece itself.
2.   What temperature to fix the Weller tip?
3.   Which tip to use?

Thanks,
Codrut
 

Offline MatCat

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Re: how to desolder/solder small SMD
« Reply #1 on: December 27, 2013, 09:33:29 am »
Your going to have to reflow it, you should be able to pretty easily replace it using a heat gun.
 

Online digsys

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Re: how to desolder/solder small SMD
« Reply #2 on: December 27, 2013, 09:49:54 am »
Wrap some heavy copper around the larger weller tip and shape the end like a small fork, so that it sits on both sides of the
chip solder pads. Apply flux to the pads ... IMPORTANT! Tin the copper wire. Using tweezers, heat up the tip, drop it onto the
pads and remove the IC with the tweezers. Should take only 1-2 secs.
To clean the pads, get some solder wick. Apply flux AGAIN, BOTH to the pads and the solder wick !! DON'T press hard.
DON'T try any shortcuts, make sure you do this as described. It's a lot of money to waste if you make a mistake.
To solder the new chip - apply flux to one pad, tack the pad with solder. Apply flux to the rest of the pads and solder as well.
Clean up with Iso-propyl alcohol soaked in a cloth. I usually wrap the cloth around my finger, dip it in alcohol, and "wipe"
the area. GOOD LUCK
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Offline flolic

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Re: how to desolder/solder small SMD
« Reply #3 on: December 27, 2013, 10:12:53 am »
Wrap some heavy copper around the larger weller tip and shape the end like a small fork, so that it sits on both sides of the
chip solder pads. Apply flux to the pads ... IMPORTANT! Tin the copper wire. Using tweezers, heat up the tip, drop it onto the
pads and remove the IC with the tweezers. Should take only 1-2 secs.

No, it will NOT work that way. There are two solder pads under the package and you simply doesn't have access to them with soldering iron of any kind.
The only way to desolder/solder this component is by reflowing with hot air or IR. Also, board must be preheated.
 

Online digsys

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Re: how to desolder/solder small SMD
« Reply #4 on: December 27, 2013, 10:56:57 am »
Quote from: flolic
No, it will NOT work that way. There are two solder pads under the package and you simply doesn't have access to them with soldering iron of any kind. 
If the chip is dead anyway, there a very good chance that the flux will seep under the pins and get enough heat to free it.
In fact, he can apply heat to the top of the IC as well ... it's dead Jim :-) My suggestion was based on what limited equipment I believe
the OP has available to him. If he grabs a hair dryer or paint stripper, he may end up with a WHOLE lot of spare parts !!
I've used this method on MANY occasions, when not near my w/shop.
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Offline TheBay

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Re: how to desolder/solder small SMD
« Reply #5 on: December 27, 2013, 01:52:29 pm »
I've put a coin on top of SMD devices and BGA when out in the field with minimal tools and used the flame on my gas iron to replace or reflow them...

Also please assess what caused the damage in the first place, did the cooler touch any parts on the PCB and cause a short. Did you do any soldering?
« Last Edit: December 27, 2013, 01:59:51 pm by TheBay »
 

Offline amyk

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Re: how to desolder/solder small SMD
« Reply #6 on: December 27, 2013, 07:15:37 pm »
Get a cheap hot air gun (like the Atten 858D Dave reviewed), it'll be very easy to remove and replace the part with it.
 

Offline peter.mitchell

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Re: how to desolder/solder small SMD
« Reply #7 on: December 27, 2013, 07:47:16 pm »
also, next time, make sure your tim covers all the fets, its there also to insulate the heatsink from the device electrically too in this application.
 

Offline M. András

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Re: how to desolder/solder small SMD
« Reply #8 on: December 27, 2013, 10:39:53 pm »
he shorted out the fets, the outer case is the drain terminal and as i see that heatsink didnt have any insulation between the fets and the aluminium piece. i bet the gate drivers is shot too, expensive lesson :)
 

Offline codrutoctavian

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Re: how to desolder/solder small SMD
« Reply #9 on: December 28, 2013, 02:41:39 am »
Thanks all for the replies. I think I'll try with a hot air gun.
 

Offline codrutoctavian

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Re: how to desolder/solder small SMD
« Reply #10 on: December 28, 2013, 12:26:50 pm »
he shorted out the fets, the outer case is the drain terminal and as i see that heatsink didnt have any insulation between the fets and the aluminium piece. i bet the gate drivers is shot too, expensive lesson :)

I really don't know what I did wrong. The same operation was done successfully here http://www.tomshardware.com/reviews/r9-290-accelero-xtreme-290,3671-3.html
Perhaps it was the fact that instead of the standard glue which was included with the new fan kit, I used Silver Arctic thermal adhesive which includes also silver particles and I caused a short.
 

Offline peter.mitchell

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Re: how to desolder/solder small SMD
« Reply #11 on: December 28, 2013, 02:48:20 pm »
he shorted out the fets, the outer case is the drain terminal and as i see that heatsink didnt have any insulation between the fets and the aluminium piece. i bet the gate drivers is shot too, expensive lesson :)

I really don't know what I did wrong. The same operation was done successfully here http://www.tomshardware.com/reviews/r9-290-accelero-xtreme-290,3671-3.html
Perhaps it was the fact that instead of the standard glue which was included with the new fan kit, I used Silver Arctic thermal adhesive which includes also silver particles and I caused a short.

To quote the article:
Quote
To avoid short circuits, apply insulating strips over the surface-mount components, since the VRM sinks are larger than they need to be and overhang.
 

Offline M. András

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Re: how to desolder/solder small SMD
« Reply #12 on: December 28, 2013, 10:05:59 pm »
he shorted out the fets, the outer case is the drain terminal and as i see that heatsink didnt have any insulation between the fets and the aluminium piece. i bet the gate drivers is shot too, expensive lesson :)

I really don't know what I did wrong. The same operation was done successfully here http://www.tomshardware.com/reviews/r9-290-accelero-xtreme-290,3671-3.html
Perhaps it was the fact that instead of the standard glue which was included with the new fan kit, I used Silver Arctic thermal adhesive which includes also silver particles and I caused a short.
if my memory serves me rigght that arctic silver is conductive, from the pictures from the tomhardware's site it looks like they used thermal adhesive tapes notice the uniform overhang on the components at the end of the aluminium fins?
 

Offline codrutoctavian

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Re: how to desolder/solder small SMD
« Reply #13 on: December 28, 2013, 10:26:25 pm »
Okay. My mistake. Expensive indeed. I bought a new video card and this one now hangs around and I think I will try changing the FETs even if just for fun. But it seems my Weller is not enough. If I am to buy a hot air gun station which one would you recommend? I have seen rework stations starting from EUR 100 but they seem cheap. However the Weller ones are EUR 1,000. Anything in between of decent quality?

Thanks
 

Offline amyk

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Re: how to desolder/solder small SMD
« Reply #14 on: December 28, 2013, 11:18:48 pm »
Below 100 EUR you can get a pretty good one already:

http://www.amazon.com/WEP-858D-Soldering-Station-Suitable/dp/B0055B6NGE
 

Offline M. András

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Re: how to desolder/solder small SMD
« Reply #15 on: December 29, 2013, 12:05:11 am »
carefully mask everything around the fets with kaptop or aluminium foil and dont try to pry the fets off if its not moving otherwise you lift the pads too
edit: this for removing via hotair, otherwise you need a decent high wattage iron to remove the fets via their metal cover which wont be nice, and the bigger l8 looking packages are expensive too around 4-7bucks/piece
« Last Edit: December 29, 2013, 12:11:21 am by M. András »
 

Offline codrutoctavian

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Re: how to desolder/solder small SMD
« Reply #16 on: December 29, 2013, 09:23:59 am »
I have found some Tenma (made in China) hot air rework stations available at Farnell (I live in EU). It should be perfect for desoldering the parts but my question is how to solder the new components back? They have contacts underneath the metal plate:

http://ec.irf.com/v6/en/US/adirect/ir?cmd=catProductDetailFrame&productID=IRF6811STR1PBF
http://www.irf.com/product-info/datasheets/data/irf6811spbf.pdf
http://ec.irf.com/v6/en/US/adirect/ir?cmd=catProductDetailFrame&productID=IRF6894MTR1PBF
http://www.irf.com/product-info/datasheets/data/irf6894mpbf.pdf

will this kind of hot air station be able to do the job?

http://uk.farnell.com/tenma/ss-952bc-f/rework-station-500w-110v-220v-uk/dp/2311402

Thanks
« Last Edit: December 29, 2013, 09:26:40 am by codrutoctavian »
 

Offline Stonent

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Re: how to desolder/solder small SMD
« Reply #17 on: December 29, 2013, 10:36:16 am »
I happened to see this in a datasheet of an unrelated product.



The design of the 2 pins in the middle and the solder around it has to do with keeping the signal clean.
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Offline M. András

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Re: how to desolder/solder small SMD
« Reply #18 on: December 29, 2013, 08:56:35 pm »
the same way you remove them, if you clean the pads off after removing the chip add back a little solder and decent amount of flux
 


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