PCB Design Perfection starts in the CAD Library - part 6

Part 6 - PCB Design Perfection Starts in the CAD Library

Part 6 – SOT223 Components

 

The SOT223 is the second most popular part in the small outline transistor (SOT) component families. The SOT223 comprises 4, 5, and 6 pin variations as well as three popular pin pitches, which include 1.27 mm, 1.50 mm, and 2.30 mm pitch. 

 

  Figure 1 shows the 6-pin 1.27 mm pitch SOT223 land pattern. The particular land pattern shown is portrayed in the Nominal environment.

Figure 1: SOT 223 with 1.27 mm pitch (Nominal environment)

 

 

  Figure 2 shows the 6-pin 1.27 mm pitch SOT223 land pattern via fanout. This fanout uses a power via with a 1.00 mm land and a 0.50 mm hole snapped to a 1.00 mm grid. The signal trace/space rules are for this layout are 0.10 mm.

Figure 2: 6-pin, 1.27 mm fanout 

 

  Figure 3 shows the 5-pin 1.50 mm pitch SOT223 land pattern.

Figure 3: 5-pin 1.50 mm pitch land pattern 

 

  Figure 4 shows the 5-pin 1.50 mm pitch SOT223 land pattern via fanout. This layout also uses a power via with a 1.00 mm land and a 0.50 mm hole snapped to a 1.00 mm grid. The trace/space rules are also 0.10 mm.

Figure 4: 5-pin, 1.50 mm pitch fanout 

 

  Figure 5 shows the 4-pin 2.30 mm pitch SOT223 land pattern. 

  Figure 5: 4-pin, 2.30 mm pitch land pattern

 

  Figure 6 shows the 4-pin 2.3 mm pitch SOT223 land pattern via fanout using the same power and trace/space rules as the previous examples.

Figure 6: 4-pin, 2.30 mm pitch fanout

 

Component Leads

The SOT223 component family uses a Gull Wing component lead. All Gull Wing leaded components have four different sets of land pattern rules. These example rules 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 is shown in Figure 7.

Figure 7: Dimensions for Standard Gull Wing vs. Outward L-Bend

 

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 two most important items 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 add the top assembly lands to the padstack.

 

Here are some of the various assembly outlines for the SOT223 component family. See Figure 8 for the 4, 5 & 6 pin versions of the Assembly Outline, Ref Des, and Polarity Marker for pin 1 location and lands (pads).

 

Figure 8: Assembly outlines for 4-, 5-, and 6-pin SOT223

 

  Figure 9 illustrates some of the various silkscreen outlines for the SOT component families, including the SOT223 version of the Silkscreen Outline, Polarity Marker and 0.50 mm Post Assembly Inspection Dot for pin 1 location and Lands (pads).

Figure 9: 4-pin example silkscreen outline

 

Coming Up

Additional brief topical articles will appear in future newsletters. You can also read more detail in my blog, which can be found at:http://blogs.mentor.com/tom-hausherr/

 

Written by Tom Hausherr CID+

EDA Library Product Manager

Mentor Graphics Corporation

Reprinted by permission from iConnect007