AN815

AN815
Vishay Siliconix
Single-Channel LITTLE FOOTR SC-70 6-Pin MOSFET
Copper Leadframe Version
Recommended Pad Pattern and Thermal Performance
INTRODUCTION
EVALUATION BOARDS SINGLE SC70-6
The new single 6-pin SC-70 package with a copper leadframe
enables improved on-resistance values and enhanced
thermal performance as compared to the existing 3-pin and
6-pin packages with Alloy 42 leadframes. These devices are
intended for small to medium load applications where a
miniaturized package is required. Devices in this package
come in a range of on-resistance values, in n-channel and
p-channel versions. This technical note discusses pin-outs,
package outlines, pad patterns, evaluation board layout, and
thermal performance for the single-channel version.
The evaluation board (EVB) measures 0.6 inches by
0.5 inches. The copper pad traces are the same as in Figure 2.
The board allows examination from the outer pins to 6-pin DIP
connections, permitting test sockets to be used in evaluation
testing. See Figure 3.
52 (mil)
BASIC PAD PATTERNS
See Application Note 826, Recommended Minimum Pad
Patterns With Outline Drawing Access for Vishay Siliconix
MOSFETs, (http://www.vishay.com/doc?72286) for the basic
pad layout and dimensions. These pad patterns are sufficient
for the low to medium power applications for which this
package is intended. Increasing the drain pad pattern yields a
reduction in thermal resistance and is a preferred footprint.
The availability of four drain leads rather than the traditional
single drain lead allows a better thermal path from the package
to the PCB and external environment.
96 (mil)
6
5
4
1
2
3
71 (mil)
26 (mil)
13 (mil)
0, 0 (mil)
18 (mil)
26 (mil)
PIN-OUT
16 (mil)
Figure 1 shows the pin-out description and Pin 1
identification.The pin-out of this device allows the use of four
pins as drain leads, which helps to reduce on-resistance and
junction-to-ambient thermal resistance.
SOT-363
SC-70 (6-LEADS)
D
1
6
D
D
2
5
D
G
3
4
S
FIGURE 2.
SC-70 (6 leads) Single
The thermal performance of the single 6-pin SC-70 has been
measured on the EVB, comparing both the copper and
Alloy 42 leadframes. This test was first conducted on the
traditional Alloy 42 leadframe and was then repeated using the
1-inch2 PCB with dual-side copper coating.
Top View
FIGURE 1.
For package dimensions see outline drawing SC-70 (6-Leads)
(http://www.vishay.com/doc?71154)
Document Number: 71334
12-Dec-03
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1
AN815
Vishay Siliconix
Front of Board SC70-6
Back of Board SC70-6
vishay.com
FIGURE 3.
THERMAL PERFORMANCE
Junction-to-Foot Thermal Resistance
(Package Performance)
COOPER LEADFRAME
Room Ambient 25 _C
The junction to foot thermal resistance is a useful method of
comparing different packages thermal performance.
A helpful way of presenting the thermal performance of the
6-Pin SC-70 copper leadframe device is to compare it to the
traditional Alloy 42 version.
Thermal performance for the 6-pin SC-70 measured as
junction-to-foot thermal resistance, where the “foot” is the
drain lead of the device at the bottom where it meets the PCB.
The junction-to-foot thermal resistance is typically 40_C/W in
the copper leadframe and 163_C/W in the Alloy 42 leadframe
— a four-fold improvement. This improved performance is
obtained by the enhanced thermal conductivity of copper over
Alloy 42.
The typical RqJA for the single 6-pin SC-70 with copper
leadframe is 103_C/W steady-state, compared with 212_C/W
for the Alloy 42 version. The figures are based on the 1-inch2
FR4 test board. The following example shows how the thermal
resistance impacts power dissipation for the two different
leadframes at varying ambient temperatures.
ALLOY 42 LEADFRAME
PD +
Rq JA
Elevated Ambient 60 _C
PD +
T J(max) * T A
Rq JA
o
o
P D + 150 Co* 25 C
212 CńW
o
o
P D + 150 Co* 25 C
212 CńW
P D + 590 mW
P D + 425 mW
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2
T J(max) * T A
T J(max) * T A
Rq JA
PD +
T J(max) * T A
Rq JA
o
o
P D + 150 Co* 25 C
124 CńW
o
o
P D + 150 Co* 60 C
124 CńW
P D + 1.01 W
P D + 726 mW
As can be seen from the calculations above, the compact 6-pin
SC-70 copper leadframe LITTLE FOOT power MOSFET can
handle up to 1 W under the stated conditions.
Testing
To further aid comparison of copper and Alloy 42 leadframes,
Figure 5 illustrates single-channel 6-pin SC-70 thermal
performance on two different board sizes and two different pad
patterns. The measured steady-state values of RqJA for the
two leadframes are as follows:
LITTLE FOOT 6-PIN SC-70
Power Dissipation
Room Ambient 25 _C
PD +
Elevated Ambient 60 _C
1) Minimum recommended pad pattern on
the EVB board V (see Figure 3.
1-inch2
2) Industry standard
PCB with
maximum copper both sides.
Alloy 42
Copper
329.7_C/W
208.5_C/W
211.8_C/W
103.5_C/W
The results indicate that designers can reduce thermal
resistance (RqJA) by 36% simply by using the copper
leadframe device rather than the Alloy 42 version. In this
example, a 121_C/W reduction was achieved without an
increase in board area. If increasing in board size is feasible,
a further 105_C/W reduction could be obtained by utilizing a
1-inch2 square PCB area.
The copper leadframe versions have the following suffix:
Single:
Si14xxEDH
Dual:
Si19xxEDH
Complementary: Si15xxEDH
Document Number: 71334
12-Dec-03
AN815
400
250
320
200
240
Thermal Resistance (C/W)
Thermal Resistance (C/W)
Vishay Siliconix
Alloy
42
160
Copper
80
150
Alloy
42
100
50
Copper
0
0
10-5
10-4
10-3
10-2
10-1
1
10
100
1000
10-5
Leadframe Comparison on EVB
Document Number: 71334
12-Dec-03
10-3
10-2
10-1
1
10
100
1000
Time (Secs)
Time (Secs)
FIGURE 4.
10-4
FIGURE 5.
Leadframe Comparison on Alloy 42 1-inch2 PCB
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