i960(R) Thermal Fundamentals

In an embedded system environment, the temperature of an i960® component is a function of the surrounding system and the package thermal characteristics. The i960® for commercial applications has been rated for an operating case temperature environment between 0° C and 100°C. The component must be operated with in this temperature range to guarantee functionality and reliability. Operation outside this range will yield unpredictable behavior and can cause permanent damage to the component. In an application where the operating temperature may exceeds the maximum operating range, a heat sink, fins or fan can be used to increase the heat dissipation rate hence keeping the case temperature with in the recommended operating range.

Thermal Parameters

The following parameters must be observed in order to ensure maximum reliability and proper functionality of the device.

Theta _JC: This is the thermal resistance from the junction to the case. This value can be found in the datasheets or in the device characteristics for the component. Theta _JC is a measurement of the package internal thermal resistance from silicon die to the package exterior. This value is strongly dependent on the packaging material, thermal conductivity and package geometry.

Theta _JA: This is the thermal resistance from the junction to the ambient. This value can be found in the datasheets or in the device characteristics for the component. Theta _JA is a measurement of the package internal thermal resistance as well as the conductive and convective thermal resistance from the package exterior to the ambient. In sum, this value is a function of the material thermal conductivity, package geometry and ambient conditions such as air flow rates and coolant physical properties.

Ambient Temperature(T_A) is the temperature of the undisturbed ambient air surrounding the package. In the laboratory test environment, ambient temperature is measured 12 inches upstream from the package.

Case Temperature(T_C) is the temperature of the package. This value is measured by using a thermocouples. The thermocouples are placed at the center of the top surface of the package, typically the hottest point on the package case. Great care should be practiced when measuring the case temperature to ensure accurate measurement. Before any measurements are taken, the thermocouples must be calibrated. In addition, when measuring the temperature of the surface which is at a different temperature from the surrounding ambient air, errors could be introduced in the measurement. For example, errors can be introduced as a result of poor thermal contact between the thermocouple junction and the surface, heat loss by radiation or conduction through the thermocouple leads.

Junction Temperature(T_J) is the average temperature of the die within the package.

The junction temperature for a given junction-to-ambient thermal resistance(Theta _JA), power dissipation and ambient temperature can be calculated by using the following formula:

T_J=Junction Temperature
Theta_JA= Junction-to-ambient thermal resistance
Theta_JC= Junction-to-case thermal resistance
T_A=Ambient temperature
P_D=V_cc*I_ss=Power dissipation

If instead of the ambient temperature, the case temperature is known, the following formula applies:

The Junction-to-ambient thermal resistance is:

If the operating temperature is above the recommended operation temperature, a heat sink,fins or fan should be used. Please call thermalloy Inc. at (214) 243-4321 or EG&G Div. at (617) 245-5900 for more details on heat sinks and/or fins.

The PGA package offers better heat dissipation due to the large ceramic surface area and the material which is built from. On the other hand, most of the heat in the PQFP package is dissipated through the pins alone. Please keep in mind that the functionality and the long-term reliability for the device is bound by the ambient and package temperature.

In the case a component failure is linked to temperature and further investigation during operation is desired, the component should be tested in a control environment where the temperature can be controlled. A heat chamber and a thermocouple is strongly recommended. Avoid using freeze spray on the component. Freeze spray creates a large temperature swing hence adding stress to the package. In addition, moisture can be introduced into the die due to condensation. Moisture can produce permanent damage to the component by causing shorts and/or corrosion internally.

Reference:
1994 Intel Packaging Hand book, Chapter Four. Literature # 240800-004

_{Note: all of the parameter to calculate the Junction Temperature(TJ) can be found in the datasheets for the device under Package Thermal Specifications. Literature number 272084 contains all of the datasheets for the entire i960® family.}

Last update: 1/6/95

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