INMP421

ALTERNATIVE PCB LAND PATTERNS

The standard PCB land pattern of the INMP421 has a solid rectangle around the edge of the footprint (see Figure 14). In some board

designs, this rectangle can make routing the microphone signals more difficult. The rectangle is used to improve the RF immunity

performance of the INMP421; however, it is not necessary to have the full rectangle connected for electrical functionality. If a design

can tolerate reduced RF immunity, this ring can either be broken or removed completely from the PCB footprint.

Figure 15 shows an example PCB land pattern with no enclosing rectangle around the edge of the part.

Figure 15. Example PCB Land Pattern with No Enclosing Rectangle

Figure 16 shows an example PCB land pattern with the rectangle broken on two sides so that the inner pads can be more easily

routed on the PCB.

Figure 16. Example PCB Land Pattern with Broken Enclosing Rectangle

Note that in both of these patterns, the solid ring around the sound port is still present; this ring is needed to ground the microphone

and for acoustic performance. The pad on the package connected to this ring is ground and still needs a solid electrical connection to

the PCB ground.

If a land pattern similar to Figure 15 or Figure 16 is used on a PCB, make sure that the unconnected ring on the bottom of the

INMP421 is not placed directly over any exposed copper. The rectangle on the microphone is still at ground, and any PCB traces

routed beneath it must be properly masked to avoid short circuits.

PCB MATERIAL AND THICKNESS

The performance of the INMP421 is not affected by PCB thickness. The INMP421 can be mounted on either a rigid or flexible PCB. A

flexible PCB with the microphone can be attached directly to the device housing with an adhesive layer. This mounting method

offers a reliable seal around the sound port while providing the shortest acoustic path for good sound quality.

Page 17 of 21

Document Number: DS-INMP421-00

Revision: 1.0.