Soldering Technique

BobTPH

Joined Jun 5, 2013
3,502
Not sure it would work, but here is what i would try.

Clean up the solder off the pads and the central pad on the chip.

Put some solder paste on the center pad and position the chip.

Drag solder the pins. Look it up on Youtube if you don't know how.

Use a hot air gun fron the other side to melt the solder paste through the vias.

Bob
 
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Thread Starter

yoda.bear

Joined Jun 5, 2017
11
Thanks everyone. I can solder the pins my main concern was how to solder the pads underneath and how necessary they are. Based on mcgyvr post above it seems they serve a pretty important role in thermal dissipation
 

ian field

Joined Oct 27, 2012
6,539
Thanks everyone. I can solder the pins my main concern was how to solder the pads underneath and how necessary they are. Based on mcgyvr post above it seems they serve a pretty important role in thermal dissipation
You probably have to do both at once - surface tension pulls the pins into alignment if you do it right. If you solder the heat pad and find the pins are out - you're probably up a gum tree without a paddle.

The reflow oven looks like the best suggestion so far - at least one hobby magazine has done a series of articles for converting a low cost pizza oven.

A table top oven I had for experiments had some old scrap hard drives as trestles for test subjects (victims) - sometimes the SMD components fell off the logic boards, the MOSFETs I found all tested OK.

The thermostats on those are very crude - so don't blame me if you fry the new chip.
 

IMP002017

Joined Jan 28, 2017
192
First issue as I can't see really what is going on with the chip on the other side. So from what I can see there is 2 things I can see. One this is not a BGA chip and the part under the chip could easy flow in a few ways.

If I was doing this repair and the chip wasn't something that has to much issue with heat. I would first of all put some Solder on the board, This seems a redundant issue. However there is a reason. Then I would put my Blade tip in my Hakko FM-2027 and use some Goot Wick 3.5mm. Clean off the center and all pads around. Not that it would be needed if it was I would also use some Flux to help get it up..

Then i would Clean the board well with 99% Alcohol, Then first and easiest way would be using some Solder Paste. Then a Hot Air station and once the chip flows it will sink down to the board and all should be soldered with little clean up if paste wasn't over loaded.

Then next way I would take some solder and put it down on the center pads. Take the chip and lay on this mound that isn't to large in size but enough to make a good connection. Add some Amtech 559 Flux and add some hotair over the chip until it sinks down to the board and you know all solder has melted and making good connection to chip when the chip dances and not longer needs to be held with tweezers. I would cool off the board and clean up any of the extra flux if any that is still around. Then I would use my JS02 tip and drag solder the 4 sides of 16 pins using fresh Flux as well... Once all pins are soldered down I would double check to make sure they are all connected and fix any if any that may have been missed. Clean up the board, and test, Once it works it will go into the Ultrasonic cleaner, then 99% Alcohol bath for a short time and then let is dry.

That is how I would do it... Again this is assuming that I can use Hotair on the chip..
 

kubeek

Joined Sep 20, 2005
5,757
That really depends on what component that is. On some it is merely a heat sink, on some it is the only ground connection the chip has.
 

mcgyvr

Joined Oct 15, 2009
5,394
I "assumed" that the center pad was there for thermal reasons.. hence my comment about reflow (really about ensuring its sufficiently attached and putting the priority there vs the actual pins themselves..)
The pins will easily bend/deform some without issue and still offer electrical connectivity..
But the thermal performance of that center pad will be effected if its not properly attached and a large "gap" filled by solder may cause thermal issues later down the road (kind of unlikely but most certainly possible)..
 

kubeek

Joined Sep 20, 2005
5,757
It is not too hard to get the part soldered in the correct place with a blob under the thermal pad, and then use hot air to reflow it and a tweezer to push it flat on the pcb. Then remove excess solder and do the pins.
 
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