AN814 Vishay Siliconix Dual-Channel LITTLE FOOTR SC-70 6-Pin MOSFET Recommended Pad Pattern and Thermal Performance INTRODUCTION This technical note discusses the pin-outs, package outlines, pad patterns, evaluation board layout, and thermal performance for dual-channel LITTLE FOOT power MOSFETs in the SC-70 package. These new Vishay Siliconix devices are intended for small-signal applications where a miniaturized package is needed and low levels of current (around 250 mA) need to be switched, either directly or by using a level shift configuration. Vishay provides these devices with a range of on-resistance specifications in 6-pin versions. The new 6-pin SC-70 package enables improved on-resistance values and enhanced thermal performance. PIN-OUT Figure 1 shows the pin-out description and Pin 1 identification for the dual-channel SC-70 device in the 6-pin configuration. SOT-363 SC-70 (6-LEADS) S1 1 6 D1 G1 2 5 G2 D2 3 4 S2 applications for which this package is intended. For the 6-pin device, increasing the pad patterns yields a reduction in thermal resistance on the order of 20% when using a 1-inch square with full copper on both sides of the printed circuit board (PCB). EVALUATION BOARDS FOR THE DUAL SC70-6 The 6-pin SC-70 evaluation board (EVB) measures 0.6 inches by 0.5 inches. The copper pad traces are the same as described in the previous section, Basic Pad Patterns. The board allows interrogation from the outer pins to 6-pin DIP connections permitting test sockets to be used in evaluation testing. The thermal performance of the dual SC-70 has been measured on the EVB with the results shown below. The minimum recommended footprint on the evaluation board was compared with the industry standard 1-inch square FR4 PCB with copper on both sides of the board. THERMAL PERFORMANCE Top View FIGURE 1. For package dimensions see outline drawing SC-70 (6-Leads) (http://www.vishay.com/doc?71154) Junction-to-Foot Thermal Resistance (the Package Performance) Thermal performance for the dual SC-70 6-pin package measured as junction-to-foot thermal resistance is 300_C/W typical, 350_C/W maximum. The “foot” is the drain lead of the device as it connects with the body. Note that these numbers are somewhat higher than other LITTLE FOOT devices due to the limited thermal performance of the Alloy 42 lead-frame compared with a standard copper lead-frame. Junction-to-Ambient Thermal Resistance (dependent on PCB size) 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 6-pin SC-70. This basic pad pattern is sufficient for the low-power Document Number: 71237 12-Dec-03 The typical RθJA for the dual 6-pin SC-70 is 400_C/W steady state. Maximum ratings are 460_C/W for the dual. All figures based on the 1-inch square FR4 test board. The following example shows how the thermal resistance impacts power dissipation for the dual 6-pin SC-70 package at two different ambient temperatures. www.vishay.com 1 AN814 Vishay Siliconix SC-70 (6-PIN) PD + Dual EVB Elevated Ambient 60 _C TJ(max) * TA Rq JA o o PD + 150 Co* 25 C 400 CńW PD + 312 mW PD + TJ(max) * TA Rq JA o o PD + 150 Co* 60 C 400 CńW PD + 225 mW NOTE: Although they are intended for low-power applications, devices in the 6-pin SC-70 will handle power dissipation in excess of 0.2 W. 400 Thermal Resistance (C/W) Room Ambient 25 _C 500 300 200 100 1” Square FR4 PCB 0 10-5 10-4 Testing LITTLE FOOT SC-70 (6-PIN) 1) Minimum recommended pad pattern (see Figure 2) on the EVB of 0.5 inches x 0.6 inches. 518_C/W 2) Industry standard 1” square PCB with maximum copper both sides. 413_C/W 2 10-2 10-1 1 10 100 1000 Time (Secs) To aid comparison further, Figure 2 illustrates the dual-channel SC-70 thermal performance on two different board sizes and two different pad patterns. The results display the thermal performance out to steady state. The measured steady state values of RθJA for the dual 6-pin SC-70 are as follows: www.vishay.com 10-3 FIGURE 2. Comparison of Dual SC70-6 on EVB and 1” Square FR4 PCB. The results show that if the board area can be increased and maximum copper traces are added, the thermal resistance reduction is limited to 20%. This fact confirms that the power dissipation is restricted with the package size and the Alloy 42 leadframe. ASSOCIATED DOCUMENT Single-Channel LITTLE FOOT SC-70 6-Pin MOSFET Copper Leadframe Version, REcommended Pad Pattern and Thermal Performance, AN815, (http://www.vishay.com/doc?71334). Document Number: 71237 12-Dec-03