PCB Design Perfection Starts in the CAD Library - Part 4

PCB Design Perfection Starts in the CAD Library - Part 4

The SOT23 is the most popular of this component family. It has 3, 5, 6 and 8 pin variations and 3 popular pin pitches.

0.50 mm Pitch

0.65 mm Pitch

0.95 mm Pitch 

Note: All pictures are shown in the “Nominal Environment” land pattern.

Figure 19 illustrates 0.5 mm pitch SOT23 3-pin and 8-pin examples.

0.5 mm pitch SOT23 fanout examples. Figure 20 illustrates 4 different 0.5mm pitch 3-pin SOT23 land pattern via fanout techniques. The SOT23 parts are placed on a 0.5 mm grid system and all the vias snap to a 1 mm grid.

• There are two 0.1 mm trace/space technology on all layers.
• Via land size is 0.5 mm, hole size is 0.25 mm and plane anti-pad is 0.7mm

0.5 mm pitch SOT23 fanout examples. Figure 21 illustrates 4 different 0.5mm pitch 8 pin SOT23 land pattern via fanout techniques. The SOT23 parts are placed on a 0.5 mm grid system and all the vias snap to a 1 mm grid. This allows two 0.1 mm trace/space technology on all layers.

Figure 22 illustrates 0.65 mm pitch SOT23 3, 5, 6 and 8-pin examples.

0.65 mm pitch SOT23 fanout examples. Figure 23 illustrates 5 different 0.65mm pitch 3, 5, 6 and 8 pin SOT23 land pattern via fanout techniques. The SOT23 parts are placed on a 0.5 mm grid system and all the vias snap to a 1 mm grid. This allows two 0.1 mm trace/space technology on all layers with 0.5 mm via land.

Figure 24 illustrates 0.95 mm pitch SOT23 3, 5, 6 and 8-pin examples.

0.95 mm pitch SOT23 fanout examples. Figure 25 illustrates 5 different 0.95mm pitch 3, 5, 6 and 8 pin SOT23 land pattern via fanout techniques. The SOT23 parts are placed on a 0.5 mm grid system and all the vias snap to a 1 mm grid. This allows two 0.1 mm trace/space technology on all layers.

The SOT223 is the next most popular component family. It has 4, 5 and 6 pin variations and 3 popular pin pitches.

• 1.27 mm Pitch
• 1.50 mm Pitch
• 2.30 mm Pitch

Figure 26 shows the 6-pin 1.27 mm pitch SOT223 land pattern.

Figure 27 shows the 6-pin 1.27 mm pitch SOT223 land pattern via fanout using a power via with a 1 mm land and a 0.5 mm hole snapped to a 1 mm grid. The signal trace/space rules are 0.1 mm.

Figure 28 shows the 5-pin 1.5 mm pitch SOT223 land pattern.

Figure 29 shows the 5-pin 1.5 mm pitch SOT223 land pattern via fanout using a power via with a 1 mm land and a 0.5 mm hole snapped to a 1 mm grid. The trace/space rules are 0.1 mm.

Figure 30 shows the 4-pin 2.3 mm pitch SOT223 land pattern.

Figure 31 shows the 4-pin 1.5 mm pitch SOT223 land pattern via fanout using a power via with a 1 mm land and a 0.5 mm hole snapped to a 1 mm grid. The trace/space rules are 0.1 mm but the routing grid is 0.05 mm.

The SOT143 is the next most popular component family. It has 4 pins with a larger Pin 1. The pin pitch is 1.9 mm. See Figure 32.

Figure 33 shows the 4-pin 1.9 mm pitch SOT143 land pattern via fanout using a via with a 0.5 mm land and a 0.25 mm hole snapped to a 1 mm grid. The trace/space rules are 0.1 mm and the routing grid is 0.1 mm.

The SOT343 is the next most popular component family. It has 4 pins with a larger Pin 1. See Figure 34.

 

Figure 35 shows the 4-pin 1.3 mm pitch SOT343 land pattern via fanout using a via with a 0.5 mm land and a 0.25 mm hole snapped to a 1 mm grid. The trace/space rules are 0.1 mm and the routing grid is 0.1 mm. The via fanout direction depends on which layer you need more routing channels.

The SOT component family uses a Gull Wing component lead. All Gull Wing leaded components have four different sets of land pattern rules. These examples are for the “Nominal Environment”.

1.       Pin pitch less than 0.625mm (side goal is -0.02 mm) considered “fine pitch”

2.       Pin pitch greater than 0.625 mm (side goal is 0.03 mm)

3.       Outward Flat Ribbon with pin pitch less than 0.625mm (heel goal is 0.15 mm and side goal is -0.02 mm)

4.       Outward Flat Ribbon with pin pitch greater than 0.625mm (heel goal is 0.15 mm and side goal is 0.03 mm)

The formula that calculates the difference between Gull Wing and Outward Flat Ribbon (Mini Gull Wing) is shown in Figure 36.

We already discussed Chip and Molded Body assembly outlines and Ref Des. It’s important to note that the Lands (Pads) do not get added to the assembly drawing layer for small parts. The 2 most important things on the assembly drawing are the Ref Des and Component Outline. If the part is too small and the Lands interfere with the Ref Des, then do not add the Top Assembly Lands to the padstack. However, if the Lands do not interfere with the Ref Des then we should add the Top Assembly Lands to the padstack.

Here are some of the various assembly outlines for the 0.95 mm pitch SOT23 component family. See Figure 37 for the 3, 5 & 6 pin versions of the Assembly Outline, Ref Des, Polarity Marker for pin 1 location and Lands (Pads). Note that the polarity marker shape in a triangle in the corner because the component is too small for the standard circle polarity marker.

Here are some of the various assembly outlines for the SOT223 component family. See Figure 38 for the 4, 5 & 6 pin versions of the Assembly Outline, Ref Des, Polarity Marker for pin 1 location and Lands (Pads).

Here are some of the assembly outlines for the SOT143 component family. See Figure 39 for the standard and reverse pin versions of the Assembly Outline, Ref Des, Polarity Marker for pin 1 location and Lands (Pads). Note that the polarity marker shape in a triangle in the corner because the component is too small for the standard circle polarity marker.

Here are some of the various silkscreen outlines for the SOT component families. See Figure 40 for the SOT23, SOT223 and SOT143 versions of the Silkscreen Outline, Polarity Marker and 0.5 mm Post Assembly Inspection Dot for pin 1 location and Lands (Pads). Note that the SOT23 and SOT143 do not have a polarity marker inside the silkscreen outline because the component is too small. The Post Assembly Inspection Dot will be the Polarity Marker.

0.50 mm Pitch

0.65 mm Pitch

0.95 mm Pitch

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