Proper way to monitor temperature of a surface?
If you really want to know the temperature of the chip itself, the go-to method is to use a PN diode junction on that chip as a built-in temperature sensor. These temperature sensors have been built in to Intel i86 processors since at least the Pentium III days. The temperature measurement is done by forcing two different currents through the diode and measuring the two forward bias diode voltages. With a little math, a robust temperature measurement can be made. There are many temperature sensor chips that can use such a "remote sensor". Here is a nice explanation of how they work from Analog Devices:
Measuring temperatures on computer chips with speed and accuracy-a new approach using silicon sensors and off-chip processing