PCB Design Perfection Starts in the CAD Library - Part 3

PCB Design Perfection Starts in the CAD Library - Part 3

The next most popular component family on a PCB design layout is the Molded Body Tantalum Capacitor (CAPM). The CAPM components have an “L-Bend” component lead form. Most Molded Body Tantalum Capacitors are metric by default including their standard EIA names –

• 3216 – 3.2 mm X 1.6 mm
• 6032 – 6.0 mm X 3.2 mm
• 7243 - 7.2 mm X 4.3 mm
• 7343 – 7.3 mm X 4.3 mm

The common component families that use the Molded Body package are -

• Non-polarized Capacitors
• Polarized Capacitors
• Diodes
• Resistors
• Inductors
• Fuses
• LED’s

See Figure 15 for the 6032 component and land pattern dimensions. I broke 1 rule to create this land pattern. Instead of a 1.0 mm Land Placement Round-off I used a 2.0 mm Land Placement Round-off to snap the land centers on a 0.5 mm grid from the center of the land pattern. When the land pattern is placed on a 0.5 mm grid, the land centers fall on a 0.5 mm grid. This improves the via fanout seen in Figure 17.

FIGURE 15

Figure 16 illustrates the silkscreen and placement courtyard rules and sizes. The illustration shows the component leads on top of the land for graphic representation.

FIGURE 16

Figure 17 illustrates the via fanout for a 6032 Tantalum Capacitor. If you are going to use the same size via to maintain trace/space compatibility with the rest of the PCB layout I recommend at least two vias. The placement of these vias is critical in accomplish reduced impedance and increased capacitance. It’s important that the vias be placed as close as possible to the capacitor terminal leads. In Figure 17, the 2 vias coming out the side are 0.15 mm away from the terminal lead. The vias coming out the ends on the land pattern are 0.75 mm away from the terminal leads. That’s 5 times farther away than the vias coming out the sides however some EE engineers will request all 4 vias. Since all the traces and vias are snapped to a 0.5 mm grid, this makes copy/paste much easier to manually fanout all of the 6032 Molded Body Capacitors. The dot grid display is 1 mm and the land pattern is placed on a 0.5 mm grid. All the vias in this illustration fall on a 1 mm snap grid.

FIGURE 17

FIGURE 18

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