ALTERNATIVE PCB LAND PATTERNS
The standard PCB land pattern of the INMP621 has a solid rectangle around the edge of the footprint that can make routing the
microphone signals more difficult in some board designs. This rectangle is used to improve the radio frequency (RF) immunity
performance of the INMP621; however, it is not necessary to have this full rectangle connected for electrical functionality. If a design
can tolerate reduced RF immunity, this rectangle can either be broken or removed completely from the PCB footprint. Figure 18 shows
an example PCB land pattern with no enclosing rectangle around the edge of the part, and Figure 19 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 18. Example PCB Land Pattern with No Enclosing Rectangle
Figure 19. 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 pattern like one of these two examples is used on a PCB, take care that the unconnected rectangle on the bottom of the
INMP621 is not placed directly over any exposed copper. This ring on the microphone is still at ground, and any PCB traces routed
underneath it must be properly masked to avoid short circuits.
.
PCB MATERIAL AND THICKNESS
The performance of the INMP621 is not affected by PCB thickness and 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-INMP621-00
Revision: 1.1
Rev Date: 05/21/2014
