Data Sheet

ADMP621

ALTERNATIVE PCB LAND PATTERNS

The standard PCB land pattern of the ADMP621 has a solid ring

around the edge of the footprint that can make routing the

microphone signals more difficult in some board designs. This

ring is used to improve the radio frequency (RF) immunity

performance of the ADMP621; however, it is not necessary to

have this full ring 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 21 shows

an example PCB land pattern with no enclosing ring around the

edge of the part, and Figure 22 shows an example PCB land

pattern with the ring broken on two sides so that the inner pads

can be more easily routed on the PCB.

Figure 21. Example PCB Land Pattern with No Enclosing Ring

Figure 22. Example PCB Land Pattern with Broken Enclosing Ring

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 ring on the bottom

of the ADMP621 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 ADMP621 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.

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