1*Not all tc's are exactly same or accurate
2*Not all machines are same or accurate
3*Not all climates are the same,slight breeze,humidity,ambient temp etc,etc
So how do we get around this, simples- nudge test,
A nudge test is where when working on a bga chip we very gently touch the bga being worked on too see when exactly the solder is molten!
Its a very simple process but, it takes practice as you do need to be very gentle or you risk moving the chip to far and breaking contacts
So heres what i did/do, set up your profile following the guide CLICK HERE, it takes time, read through as much as you can multiple times check out all relevant information for your machine.
Once you have a profile that is consistant upto 210c i then suggest that you consider nudge testing for the final steps, this way you ensure that the solder under the chip is actually molten.
You are looking for a tiny amount of movement so watch very carefully and tap the corner of the bga very gently,every second until the bga can be seen to move very slighty. If performed gently enough the surface tension of the solder will hold the bga in place(highly recommened you do this with scrap boards to get a feel for it)
So the bga moves at 217c, now what?- now you know the solder is molten at 217c on your machine and that you need not go any higher with the temps! I personally go 1-2c higher then shut the machine off and allow board too cool, Profile done
This varies from each machine for example i know my machine is nudging when it reads 226c,others may find it happens anywhere between 215-230 dependant on the machine etc etc
Hope this is of use to people, for the record once i had my profile i setup i only nudged 1 in 5 chips, this way i was ensuring the tc readings stayed accurate, others like to nudge every chip they do, as with most things its down to personal preference, my hands are shaky so i dont like to risk nudging chips too hard
