Do I have to apply more thermal paste to put the processor heat sink back into the laptop? OR, do I just need to make sure that the screws are tight, and it will work? What are the problems with not applying more paste?
Also, if I do need to do so, how do I apply it? Just put some on and stick it together? Thanks!
You need to be careful you don't over-tighten the screws, that could lead to a cracked heat sink or even CPU.
If the heat sink has come/been taken off your safest approach is to carefully clean the old paste off both parts an apply fresh.
It can't be stressed enough that there needs to be good thermal conductivity between the CPU and the heatsink as processors generate a lot of heat.
Applying thermal paste is not that hard, there are different application methods depending on if the CPU has a heatspreader built on it or if the core is exposed.
If the core is exposed I suggest using this guide from Arctic Silver: http://www.arcticsilver.com/pdf/appmeth/int/ss/intel_app_method_surface_spread_v1.1.pdf
If the core has a heatspreader on it: http://www.arcticsilver.com/pdf/appmeth/int/vl/intel_app_method_vertical_line_v1.1.pdf
The application is the same on AMD CPUs.
And to answer your other question, yes it is really necessary to use thermal paste, with thermal paste you make sure there is contact between the two surfaces leading the heat to the heatsink. Without thermal paste you might experience very high temperatures which in the worst cases can lead to breakdowns and permanent CPU damage.
Also remember to thoroughly cleaning your CPU die, I recommend using 90%+ alcohol and clean all the old paste of it using q-tips or some pads.
My question at this point is: what kind of processor chip do I have? Is it an exposed core or a heatspreader? what is the difference? How do I tell?
Speccy can help you to determine which processor chip you have and much more.
