OR3C80 datasheet(194/210 Pages) AGERE

194 / 210 page

194

Lucent Technologies Inc.

Data Sheet

June 1999

ORCA Series 3C and 3T FPGAs

Package Thermal Characteristics

There are four thermal parameters that are in common

use:

ΘJA, ψJC, ΘJC, and ΘJB. It should be noted that all

the parameters are affected, to varying degrees, by

package design (including paddle size) and choice of

materials, the amount of copper in the test board or

system board, and system airflow.

The data base containing the thermal values for all of

Lucent Technologies’ IC packages is currently being

updated to conform to modern JEDEC standards.

Thus, Table 76 contains the currently available thermal

specifications for Lucent Technologies’ FPGA pack-

ages mounted on both JEDEC and non-JEDEC test

boards. The thermal values for the newer package

types correspond to those packages mounted on a

JEDEC four-layer board. The values for the older pack-

ages, however, correspond to those packages mounted

on a non-JEDEC, single-layer, sparse copper board

(see Note 2). It should also be noted that the values for

the older packages are considered conservative.

ΘJA

This is the thermal resistance from junction to ambient

(a.k.a. theta-JA, R-theta, etc.).

where TJ is the junction temperature, TA is the ambient

air temperature, and Q is the chip power.

Experimentally,

ΘJA is determined when a special ther-

mal test die is assembled into the package of interest,

and the part is mounted on the thermal test board. The

diodes on the test chip are separately calibrated in an

oven. The package/board is placed either in a JEDEC

natural convection box or in the wind tunnel, the latter

for forced convection measurements. A controlled

amount of power (Q) is dissipated in the test chip’s

heater resistor, the chip’s temperature (TJ) is deter-

mined by the forward drop on the diodes, and the ambi-

ent temperature (TA) is noted. Note that

ΘJA is

expressed in units of °C/watt.

ψJC

This JEDEC designated parameter correlates the junc-

tion temperature to the case temperature. It is generally

used to infer the junction temperature while the device

is operating in the system. It is not considered a true

thermal resistance, and it is defined by:

where TC is the case temperature at top dead center,

TJ is the junction temperature, and Q is the chip power.

During the

ΘJA measurements described above,

besides the other parameters measured, an additional

temperature reading, TC, is made with a thermocouple

attached at top-dead-center of the case.

ψJC is also

expressed in units of °C/watt.

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:

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 so as 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/watt.

ΘJB

This is the thermal resistance from junction to board

(a.k.a.

ΘJL). It is defined by:

where TB is the temperature of the board adjacent to a

lead measured with a thermocouple. The other param-

eters on the right-hand side have been defined above.

This is considered a true thermal resistance, and the

measurement is made with a water-cooled heat sink

pressed against the board so as to draw most of the

heat out of the leads. Note that

ΘJB is expressed in

units of °C/watt, and that this parameter and the way it

is measured is still in JEDEC committee.

ΘJA

–

--------------------

ψJC

–

--------------------

ΘJC

–

--------------------

ΘJB

–

------------------

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