Data Sheet

ADMP421

Rev. D | Page 9 of 16

ALTERNATE PCB LAND PATTERNS

The ADMP421’s standard PCB land pattern has a solid ring

around the edge of the footprint, which may make routing the

microphone signals more difficult in some board designs. This

ring is used to improve the RF immunity performance of the

ADMP421, but it is not necessary to have this full ring

connected for electrical functionality. If a design can tolerate

reduced RF immunity then this ring can either be broken or

removed completely from the PCB footprint. Figure 10 shows

an example land pattern with no enclosing ring around the edge

of the part, and Figure 11 shows an example pattern with the

ring broken on two sides so that the inner pads can be more

easily routed on the PCB.

Figure 10. Example PCB Land Pattern with No Enclosing Ring

Figure 11. 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 ADMP421 is not placed

directly over any exposed copper. This ring on the microphone

is still at ground and any PCB traces routed underneath it need

to be properly masked to avoid short circuits.