Thermal Management For Total-Acextreme - DDC Total-AceXtreme MIL-STD-1553 Design Manual

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THERMAL MANAGEMENT FOR TOTAL-ACEXTREME

Ball Grid Array (BGA) components necessitate that thermal management issues be
considered early in the design stage for MIL-STD-1553 terminals. This is especially
true if high transmitter duty cycles are expected. The temperature range specified for
DDC's Total-AceXtreme device refers to the case temperature. Any duty cycle is
acceptable as long as the case temperature is maintained within the industrial
temperature range specified for the –Exx parts. See below for an explanation of
thermal management requirements for high transmitter duty cycles with the military
temperature range components.
All Total-AceXtreme devices incorporate multiple package connections which perform
the dual function of transceiver circuit ground and thermal heat sink. Refer to the
pinout tables for thermal ball connection locations. It is mandatory that these thermal
balls be directly soldered to a circuit ground/thermal plane (a circuit trace is
insufficient). Operation without an adequate ground/thermal plane is not
recommended and extended exposure to these conditions may affect device
reliability.
The purpose of this ground/thermal plane is to conduct the heat being generated by
the transceivers within the package and conduct this heat away from the Total-
AceXtreme. In general, the circuit ground and thermal (chassis) ground are not the
same ground plane. It is acceptable for these balls to be directly soldered to a ground
plane but it must be located in close physical and thermal proximity ("0.003" pre-preg
layer recommended) to the thermal plane.
The temperature of each chip within the Total-AceXtreme must be maintained below
its respective maximum operating junction temperature as specified in Table 1. The
simplest method to ensure this is to attribute all internal power dissipation to the
transceiver, use the θ
rise at the transceiver, and ensure that the temperature at the transceiver never
exceeds the lowest maximum operating junction temperature allowed for any internal
component (135°C for the protocol chip).
The general equation for the heat rise from ambient to the source of heat inside a
component (typically the transistor junctions) is ∆T=P*θ, where P is the power
dissipation of the component and θ is the thermal impedance from the junctions to
ambient. Here there are two heat paths to the ambient, up through the top of the
case, and down through the PCB, so we have a pair of equations:
Data Device Corporation
www.ddc-web.com
numbers also specified in Table 1 to calculate the temperature
Jx
∆T = P
*(θ +θ ) = P *(θ
C JC CA B
104
+θ ) and P = P +P .
JB BA C B
DS-BU-67301B-G
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