OR4 Datasheet, PDF (143/152 Pages) Lattice Semiconductor – ORCASeries 4 FPGAs

Data Sheet
May, 2006
ORCA Series 4 FPGAs
ΘJC
This is the thermal resistance from junction to case. It is most often used when attaching a heat sink to the top of
the package. It is defined by:
ΘJC = -T----^J----^–----T----^C--
Q
The parameters in this equation have been defined above. However, the measurements are performed with the
case of the part pressed against a water-cooled heat sink to draw most of the heat generated by the chip out the
top of the package. It is this difference in the measurement process that differentiates ΘJC from ^ψJC. ΘJC is a true
thermal resistance and is expressed in units of °C/W.
ΘJB
This is the thermal resistance from junction to board (ΘJL). It is defined by:
ΘJB = -T----^J----^–----T----^B--
Q
where TB is the temperature of the board adjacent to a lead measured with a thermocouple. The other parameters
on the right-hand side have been defined above. This is considered a true thermal resistance, and the measure-
ment is made with a water-cooled heat sink pressed against the board to draw most of the heat out of the leads.
Note that ΘJB is expressed in units of °C/W, and that this parameter and the way it is measured are still in JEDEC
committee.
Lattice Semiconductor
143