How to create footprint for MEMS microphone

Hi

Have you ever created a library part before? or just having problems with this one? I wish manufacturers would wake up and provide footprints for Eagle.

This one looks tricky but I have had worse! I can help you, just need to know where you are with it at the moment!

Dave,

I've have quite a few parts in my library so I'm not a complete novice I've also used Altium and Ultiboard in the past. I've gone ahead and made the footprint with just a hole for the mic, I figure I'll fake the ground around it on the pcb with polygons. But it would be nice to know if there is a way to make custom pads, especially surface mount in Eagle.

Thanks in advance for any help or advise you can give.'

Regards,

kj

Hi

In Eagle it is possible to create arbitrary pad shapes, and its easiest with SMD as you only need to create the top layer. Start with an SMD pad and then using lines/circles or polygons draw the required pad shape around the SMD pad.

Make sure that the SMD pad is at the dead centre of your polygon, and it will be recognised as part of the pad. Then when you come to the device creation you can connect pins to your new pads as normal.

Not a perfect situation I know, definitely needs upgrading. The only mention is buried deep in section 8:13 of the manual. It works though, and I have so far managed to make any SMD pad shape with it.

Hi

In Eagle it is possible to create arbitrary pad shapes, and its easiest with SMD as you only need to create the top layer. Start with an SMD pad and then using lines/circles or polygons draw the required pad shape around the SMD pad.

Make sure that the SMD pad is at the dead centre of your polygon, and it will be recognised as part of the pad. Then when you come to the device creation you can connect pins to your new pads as normal.

Not a perfect situation I know, definitely needs upgrading. The only mention is buried deep in section 8:13 of the manual. It works though, and I have so far managed to make any SMD pad shape with it.

Dave,

I'll give it a try, thanks for the help

Regards,

kj

Due  to the small size of the ADMP401  part you will run into issues with

the polygon approach.

This is due to the clearances from holes and signals the DRC will use.

Holes keep the flood fills away from the hole and the polygon.

A further consideration is the need  to keep solder out of the microphone

hole so I rejected using a pad which is drilled out further with a HOLE

later as this brings copper to the hole edge and there is no way to prevent

the solder stop mask.

I was interested in the challenge this scale of device would provide and I

settled as per the attached library.

You will get DRC errors to approve.

Within a flood fill, for the pad 3 ring around the hole you will need to

fake the thermals.

Hope this is of help

Warren

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