ORLI10G datasheet(65/72 Pages) AGERE

65 / 72 page

Agere Systems Inc.

Data Sheet

October 2001

10 Gbits/s, and 12.5 Gbits/s Line Interface FPSC

ORCA ORLI10G Quad 2.5 Gbits/s

Package Thermal Characteristics

Summary

There are three thermal parameters that are in com-

mon use:

ΘJA, ψJC, and ΘJC. 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.

ΘJA

This is the thermal resistance from junction to ambient

(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 gener-

ally 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/W.

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 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:

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 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 mea-

sured are still in JEDEC committee.

FPSC Maximum Junction Temperature

Once the power dissipated by the FPSC has been

determined (see the Estimating Power Dissipation sec-

tion), the maximum junction temperature of the FPSC

can be found. This is needed to determine if speed der-

ating of the device from the 85 °C junction temperature

used in all of the delay tables is needed. Using the

maximum ambient temperature, TAmax, and the power

dissipated by the device, Q (expressed in °C), the max-

imum junction temperature is approximated by:

TJmax = TAmax + (Q •

ΘJA)

Figure 21 lists the thermal characteristics for all

packages used with the ORCA ORLI10G FPSC.

ΘJA

–

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

ψJC

–

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

ΘJC

–

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

ΘJB

–

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

ORLI10G Datasheet(PDF) 65 Page - Agere Systems

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