參數(shù)資料
型號: PC7457MGU1000L
廠商: Atmel Corp.
英文描述: PowerPC 7457 RISC Microprocessor
中文描述: 7457的PowerPC RISC微處理器
文件頁數(shù): 16/66頁
文件大?。?/td> 522K
代理商: PC7457MGU1000L
16
PC7457/47 [Preliminary]
5345B–HIREL–02/04
Thermal Interface Materials
A thermal interface material is recommended at the package lid-to-heat sink interface to
minimize the thermal contact resistance. For those applications where the heat sink is
attached by spring clip mechanism, Figure 5 shows the thermal performance of three
thin-sheet thermal-interface materials (silicone, graphite/oil, floroether oil), a bare joint,
and a joint with thermal grease as a function of contact pressure.
The use of thermal grease significantly reduces the interface thermal resistance. That is,
the bare joint results in a thermal resistance approximately seven times greater than the
thermal grease joint.
Often, heat sinks are attached to the package by means of a spring clip to holes in the
printed-circuit board (see Figure 32 on page 55). Therefore, the synthetic grease offers
the best thermal performance, considering the low interface pressure and is recom-
mended due to the high power dissipation of the PC7457. Of course, the selection of
any thermal interface material depends on many factors – thermal performance require-
ments, manufacturability, service temperature, dielectric properties, cost, etc.
Figure 6.
Thermal Performance of Select Thermal Interface Material
Heat Sink Selection Example
For preliminary heat sink sizing, the die-junction temperature can be expressed as
follows:
T
j
= T
I
+ T
r
+ (R
θ
JC
+ R
θ
int
+ R
θ
sa
)
×
P
d
where:
T
j
is the die-junction temperature
T
I
is the inlet cabinet ambient temperature
T
r
is the air temperature rise within the computer cabinet
0
0.5
1
1.5
2
0
10
20
30
40
50
60
70
80
Silicone Sheet (0.006 in.)
Bare Joint
Floroether Oil Sheet (0.007 in.)
Graphite/Oil Sheet (0.005 in.)
Synthetic Grease
Contact Pressure (psi)
S
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