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SBVS001D − OCTOBER 1992 − REVISED JULY 2004
The SOT-223 package derives heat sinking from
conduction through its copper leads, especially the large
mounting tab. These must be soldered to a circuit board
with a substantial amount of copper remaining, as shown
in Figure 5. Circuit board traces connecting the tab and the
leads should be made as large as practical. The mounting
Table 1. SOT-223 q for Various Board
JA
Configurations
SOT-223
THERMAL
(1)
TOPSIDE
TOTAL PC
BOARD
AREA
BACKSIDE
COPPER
AREA
RESISTANCE
JUNCTION-
TO-AMBIENT
COPPER
AREA
tab of both packages is electrically connected to VOUT
.
2
2
2
2500mm
2500mm
2500mm
46°C/W
47°C/W
49°C/W
51°C/W
53°C/W
55°C/W
58°C/W
59°C/W
67°C/W
72°C/W
85°C/W
2
2
2
2500mm
1250mm
2500mm
Total Area: 50 x 50mm
35 x 17 mm
2
2
2
2500mm
950mm
2500mm
2
2
2500mm
2500mm
0
0
2
2
2500mm
1800mm
2
2
2
1600mm
600mm
1600mm
2
2
2500mm
1250mm
0
0
0
2
2
2500mm
915mm
16 x 10 mm
16 x 10 mm
2
2
1600mm
600mm
2
2
2
900mm
340mm
900mm
2
2
900mm
340mm
0
q
q
≈
≈
_
Without backside copper:
With solid backside copper:
59 C/W
JA
JA
_
49 C/W
(1)
Tab is attached to the topside copper.
Figure 5. SOT-223 Circuit Board Layout Example
SOLDERING METHODS
Other nearby circuit traces, including those on the back
side of the circuit board, help conduct heat away from the
device, even though they may not be electrically
connected. Make all nearby copper traces as wide as
possible and leave only narrow gaps between traces.
Both REG1117 packages are suitable for infrared reflow
and vapor-phase reflow soldering techniques. The high
rate of temperature change that occurs with wave
soldering or hand soldering can damage the REG1117.
Table 1 shows approximate values of qJA for various circuit
board and copper areas for the SOT-223 package. Nearby
heat dissipating components, circuit board mounting
conditions, and ventilation can dramatically affect the
actual qJA. Proper heat sinking significantly increases the
INSPEC Abstract Number: B91007604, C91012627.
Kelly, E.G. “Thermal Characteristics of Surface 5WK9Ω
Packages.” The Proceedings of SMTCON. Surface Mount
Technology Conference and Exposition: Competitive
Surface Mount Technology, April 3−6, 1990, Atlantic City,
NJ, USA. Abstract Publisher: IC Manage, 1990, Chicago,
IL, USA.
maximum power dissipation at
temperature, as shown in Figure 6.
a
given ambient
MAXIMUM POWER DISSIPATION
vs AMBIENT TEMPERATURE
6
5
4
3
2
1
0
_
= 27 C/W
q
q
−
PD = (TJ (max) TA) /
JA
JA
2
(4in one oz copper
mounting pad)
_
TJ (max) = 150 C
DDPAK
SOT−223
_
2
= 46 C/W
q
JA
(2500mm topside and
backside copper)
_
q
= 65 C/W
JA
(no heat sink)
_
2
= 85 C/W
q
JA
(340mm topside copper,
no backside copper)
0
25
50
75
100
125
_
Ambient Temperature ( C)
Figure 6. Maximum Power Dissipation versus Ambient Temperature
10