Reballing gpu and/or lga socket with leaded solder vs lead free

[lewbaseball07]

Hey guys,

I am really getting into bga rework. i repair graphics cards and motherboards with my bga rework station. i was wondering if lead free solder has less of a resistance than leaded solder and if lead free solder is actually better for overclocking. This is contrary to popular belief because in the industry rohs is frowned upon because lead free solder is weak and it inevitably fails. So, my question is, what solder alloy has the least resistance? Lead based(most of the time containing lead and tin) or lead free(most of the time contains copper, silver, and tin). Also how much of a difference you think it actually makes in overclocking? i was thinking about this in the shower this morning lol and i've been wondering ever since if there actually is a real down fall to leaded solder....

 

[pjmelect]

Lead free solder has a lower electrical resistance than lead based solder because the resistance of lead is about double that of tin. I don't think that it will make any difference to overclocking. More importantly the difference of thermal conductivity and the lower melting point of lead based solder is more important in making a good solder joint.

 

[lewbaseball07]

I agree, thats what i thought. But, isn't the less amount of resistance in the processor what you want? isn't that why we want to have the lowest temps? And isn't that why we reach those "walls" while overclocking, because of the high resistance from the heat?

 

[pjmelect]

Although reduced electrical resistance to the processor is important to reduce "ground bounce" the difference between lead solder and lead free solder is ignorable. Also the heat conducted away from the processor by the BGA is only a small fraction of the heat conducted away by the heatsink although every little helps, the thermal resistance of the solder is so small that it can be ignored. Simply the limits on overclockability are set by the capacitance of the transistors in the processor which reduce reliable switching times, this can be overcome by increasing the processors voltage however there is a limit on how high you can increase the voltage as increased voltage will shorten the life of the processor (on a log scale) as well as increasing heat dissipation.
I think that you should concentrate more on making good reliable BGA solder connections and improving your skills on reworking BGA faulty boards something that is very difficult to do.