just out of curiosity, why do the T4`s need the chips reballing, in other words why do the chips come away so much, is it heat, or just poorly made in first place
It's a big subject but I'll try and keep it brief.Background
The graphics and Southbridge (SB) chips are just over 1" square and are soldered to the motherboard with hundreds of tiny solder balls (the ATI 7500 chip has 692 I believe!), each 0.6mm diameter. The solder ball set is known as the Ball Grid Array or BGA.
Early T4x Thinkpads used solder balls made of leaded solder. From July 2006 all manufacturers had to switch to lead-free solder balls to comply with ROHSS (
These can be identified to a certain extent by the motherboard FRU's and descriptions - see this page
on the Board Room site and for instance T43 series boards in particular are classified as leaded and lead free.The Main Reasons for BGA Failure1. Flexing
The Graphics and SB chips are located towards the front of the motherboard. When users pick the laptop up by the front edge or one corner or by the open lid, the weight at the back of the laptop from the screen and battery flexes the motherboard causing the GPU and SB chip BGA to be strained to the point where some of the balls become detached.2. Hot and Cold Temperature Cycling
As the laptop is used over the years the GPU and SB BGA's are subjected to quite large changes in temperature from being cold when switched off to becoming very warm when in use.
This is particularly relevant for any solder joint made with lead-free solder since it's been found that subjecting lead-free solder to this kind of temperature change causes the individual metallic components of the solder to separate out. This in turn results in oxidisation around the ball which will destroy the solder bond onto the motherboard and cause an open circuit.Solving the Problem1. Flexing
Always carrying the laptop correctly by the sides will very greatly reduce this problem.
If there has been a failure with leaded solder BGA's, it is possible to heat up the chip to melt the solder balls and they can make good reliable joints again.
But this does still rely on the overall BGA being in good condition and I believe that individual solder balls can become loose, and reheating will not somehow get them to migrate back to their right positions.2. Hot and Cold Temperature Cycling
...and lead-free solder balls
Some users never turn their laptops off and put them into hibernation, thus reducing the temperature cycling change.
Many repair companies try to resolder the BGA by simply reheating the chip to re-melt the balls. This is usually ineffective with lead-free balls because once the solder mix has broken down it will not recombine properly to create a new sound joint. In fact at best it will often create a touch only connection which will quickly fail.
Also when trying to resolder lead-free balls, when the solder melts it mustn't exceed a temperature margin of 3 - 5 deg C beyond the melting point, or else again the solder mix will separate and again a bad joint is made.
This is a very complex subject of which I'm only giving a brief overview.
So the very best solution is to reball a failed chip. By doing this the state of the existing solder balls is unimportant, and if very high quality solder balls are used and the melting temperatures very carefully monitored at all stages of the reballing and reflowing processes, then it's virtually guaranteed that the resulting solder joints will be 100% sound for many years to come.
To complete the picture, there are other issues with any laptop (Thinkpad T61 series) using an Nvidia GPU and this article
gives the whole sorry story and more information etc.