TSI-2
Data Sheet, Revision 3
September 21, 2005
2k x 2k Time-Slot Interchanger
3.4 Thermal Parameters (Definitions and Values)
System and circuit board level performance depends not only on device electrical characteristics, but also on device thermal
characteristics. The thermal characteristics frequently determine the limits of circuit board or system performance, and they
can be a major cost adder or cost avoidance factor. When the die temperature is kept below 125 °C, temperature-activated
failure mechanisms are minimized. The thermal parameters that Agere provides for its packages help the chip and system
designer choose the best package for their applications, including allowing the system designer to thermally design and in-
tegrate their systems.
It should be noted that all the parameters listed below 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.
Θ
- Junction to Air Thermal Resistance
JA
Θ
Θ
is a number used to express the thermal performance of a part under JEDEC standard natural convection conditions.
is calculated using the following formula:
JA
JA
Θ
= (T – T
) / P; where P = power
amb
JA
J
Θ
Θ
- Junction to Moving Air Thermal Resistance
JMA
is effectively identical to Θ but represents performance of a part mounted on a JEDEC four layer board inside a wind
JMA
JA
tunnel with forced air convection. Θ
is reported at airflows of 200 LFPM and 500 LFPM (linear feet per minute), which
JMA
roughly correspond to 1 m/s and 2.5 m/s (respectively). Θ
is calculated using the following formula:
JMA
Θ
= (T – T
) / P
amb
JMA
J
Θ
Θ
- Junction to Case Thermal Resistance
JC
is the thermal resistance from junction to the top of the case. This number is determined by forcing nearly 100% of the
JC
heat generated in the die out the top of the package by lowering the top case temperature. This is done by placing the top
of the package in contact with a copper slug kept at room temperature using a liquid refrigeration unit. Θ is calculated using
JC
the following formula:
Θ
= (T – T ) / P
J C
JC
Θ
Θ
- Junction to Board Thermal Resistance
JB
is the thermal resistance from junction to board. This number is determined by forcing the heat generated in the die out
JB
of the package through the leads or balls by lowering the board temperature and insulating the package top. This is done
using a special fixture, which keeps the board in contact with a water chilled copper slug around the perimeter of the package
while insulating the package top. Θ is calculated using the following formula:
JB
Θ
= (T – T ) / P
J B
JB
Ψ
Ψ
- Junction Temperature to Case Temperature
JT
correlates the junction temperature to the case temperature. It is generally used by the customer to infer the junction
JT
temperature while the part is operating in their system. It is not considered a true thermal resistance. Ψ is calculated using
JT
the following formula:
Ψ
= (T – T ) / P
J C
JT
Table 3-4. Thermal Parameter Values
Parameter
Temperature °C/Watt
Θ
25.1
21.4
18.8
5.8
JA
Θ
Θ
Θ
Θ
(1 m/s)
JMA
JMA
JC
(2.5 m/s)
13.0
JB
16
Agere Systems Inc.
AGERE [ AGERE SYSTEMS ]
