No offence, RealBlackStuff, but I've seen you give this "give it to a pro" advice before, and I know you may be a tad biased
First to state my "professional" relationship with RBS - I'm the UK part of The Board Room, of which he's the USA part, and I do the actual board repairs.
I would like to categorically state that neither of us are saying people shouldn't try repairing their laptops with a hotair gun. There's no doubt that it does work as testified throughout this thread.
BUT it's a very risky process and should be left to people like Visionviper who understand the issues with it. It's not for beginners, and as has also been stated within the thread first timers often don't succeed, and this can result in more damage to the board than existed beforehand.
RBS (and myself) are coming from the angle that we are a viable and cost effective alternative to "The Heat Gun", or some (dubious) USA-based Reflow companies.
We actually don't mind if you want to try the heatgun, but please don't come to us afterwards because your damaged board is likely to be rejected as a swap out by us.
The reason for this is that in my experience as the Reballing side of the company, such boards will have permanently damaged chips which increases the cost of the repair and will result on us making a loss on that board and affects the long term viability of the Board Room.
The southbridge is just like any other BGA chip, so the reflow trick should still work. Perhaps ajkula66 knows more than I do about the specifics of the R51 southbridge issue and as to why reflow won't work. Placement perhaps? As far as I know the southbridge problems are caused by the same thing as the GPU problems on the T40s.
Southbridge (SB) chips are quite delicate heat-wise and it's quite easy to apply just too much and "blow out" the substrate.
What I mean by this is that the micro solder joints under the raised part of the chip (above the planar which has the solder balls underneath) melt too much and the joints "leak" solder out onto the top of the planar. This can be seen as minute drops of solder and the only place for that chip is the trash.
Because every step of the reballing process from removal of the chip, thru Infrared Reballing, thru final reflow (resoldering) of the chip back onto the mobo again, is closely temperature monitored, we know just how far we can push it temperature-wise. This compares with the sorts of temperature measuring equipment recommended with the heatgun process, which are nowhere near accurate enough, and so is why we've advising people not to heatgun SB chips.
Also I'm interested in what people, who heatgun, do about the coloured dots around the chip (whether GPU or SB).
Honestly, it's a complete waste of time doing any sort of reflowing whilst these are still in place,because the chip must be allowed to "move" freely when the solder balls melt so they can resettle and (hopefully) resolder to all the pads. Keeping the chip "immobile" with the dots prevents this from happening and so the joints will not properly reform - in fact there's a good chance some will separate.
I don't mind sharing how the dots should be removed - just heat the chip up to around 120C to soften them and pick them off, but unfortunately a few bits will always remain under the chip and keep it anchored to the board no matter how thorough you are. This leaves you with only one option - to remove the chip off the board, clean it up (including removing any dot residuals), reball it, and solder it back on again.
Also some chips with orange dots are often IBM refurbished and can have a second set of dots around the centre of the chip, which can only be removed after the chip has been lifted off the motherboard.
This then raises another problem in that such chips have to be gently prised off when the solder balls have melted. This is generally OK for ATI GPU's but with Intel SB chips this lifting usually breaks the internal micro solder joints between the internal layers within the chip so again we throw them away after removal and fit a new one.
Since we are looking at all the pitfalls of heatgunning, another important issue is lead-free (LF) solder balls used on chips made after June 2005 (I think). LF solder is tricky to melt because raising its temperature 3 - 5 deg C above melting point will result in the compounds making up the solder separating out, which in turn results in oxidisation within the ball. Over time this spreads to cover the whole ball and creates an non-conducting open circuit.
To avoid this, close monitoring of the melting point of the solder ball is essential, and again this can never be achieved with a heatgun - or with some cheaper Infrared Reflowing stations for that matter.
So I hope you can see that not only are "we" (RBS and I) NOT biased but we actually have you as forum members interests at heart.
We want you to succeed with the heatgun method. In the hands of VisionViper and others with the skill to do it, it undoubtedly works and I greatly admire anyone who can do it. But I personally wouldn't even dream of trying even with the years of experience in this field because I just don't have that skill, though after trying it on a good number of boards I would probably acquire it.
Apologies for the long post (again) but it's an important issue which needs to be aired in detail.