Datasheet Si3457CDV (Vishay) - 8

AN823 Vishay Siliconix Mounting LITTLE FOOT
R
TSOP-6 Power MOSFETs
Surface mounted power MOSFET packaging has been based on Since surface mounted packages are small, and reflow soldering integrated circuit and small signal packages. Those packages is the most common form of soldering for surface mount have been modified to provide the improvements in heat transfer components, “thermal” connections from the planar copper to the required by power MOSFETs. Leadframe materials and design, pads have not been used. Even if additional planar copper area is molding compounds, and die attach materials have been used, there should be no problems in the soldering process. The changed. What has remained the same is the footprint of the actual solder connections are defined by the solder mask packages. openings. By combining the basic footprint with the copper plane on the drain pins, the solder mask generation occurs automatically. The basis of the pad design for surface mounted power MOSFET is the basic footprint for the package. For the TSOP-6 package A final item to keep in mind is the width of the power traces. The outline drawing see http://www.vishay.com/doc?71200 and see absolute minimum power trace width must be determined by the http://www.vishay.com/doc?72610 for the minimum pad footprint. amount of current it has to carry. For thermal reasons, this In converting the footprint to the pad set for a power MOSFET, you minimum width should be at least 0.020 inches. The use of wide must remember that not only do you want to make electrical traces connected to the drain plane provides a low impedance connection to the package, but you must made thermal connection path for heat to move away from the device. and provide a means to draw heat from the package, and move it away from the package. REFLOW SOLDERING In the case of the TSOP-6 package, the electrical connections are very simple. Pins 1, 2, 5, and 6 are the drain of the MOSFET and are connected together. For a small signal device or integrated Vishay Siliconix surface-mount packages meet solder reflow circuit, typical connections would be made with traces that are reliability requirements. Devices are subjected to solder reflow as a 0.020 inches wide. Since the drain pins serve the additional test preconditioning and are then reliability-tested using function of providing the thermal connection to the package, this temperature cycle, bias humidity, HAST, or pressure pot. The level of connection is inadequate. The total cross section of the solder reflow temperature profile used, and the temperatures and copper may be adequate to carry the current required for the time duration, are shown in Figures 2 and 3. application, but it presents a large thermal impedance. Also, heat spreads in a circular fashion from the heat source. In this case the drain pins are the heat sources when looking at heat spread on the PC board. Figure 1 shows the copper spreading recommended footprint for the TSOP-6 package. This pattern shows the starting point for utilizing the board area available for the heat spreading copper. To create this pattern, a plane of copper overlays the basic pattern on pins 1,2,5, and 6. The copper plane connects the drain pins electrically, but more importantly provides planar copper to draw heat from the drain leads and start the process of spreading the heat so it can be dissipated into the ambient air. Notice that the planar copper is shaped like a “T” to move heat away from the drain leads in all directions. This pattern uses all the available area underneath the body for this purpose. 0.167 4.25 Ramp-Up Rate +6_C/Second Maximum 0.074 Temperature @ 155 " 15_C 120 Seconds Maximum 0.014 1.875 0.122 0.35 3.1 Temperature Above 180_C 70 − 180 Seconds 0.026 Maximum Temperature 240 +5/−0_C 0.65 Time at Maximum Temperature 20 − 40 Seconds 0.049 0.049 0.010 Ramp-Down Rate +6_C/Second Maximum 1.25 1.25 0.25
FIGURE 1.
Recommended Copper Spreading Footprint
FIGURE 2.
Solder Reflow Temperature Profile Document Number: 71743 www.vishay.com 27-Feb-04
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