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 www.vishay.com 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 www.vishay.com 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 www.vishay.com 3