Sunday, July 15, 2012

MEMS pressure sensor teardown - part 2

The sensor I studied in my last post was delivered to me in a partially disassembled state. After returning to the e-waste dumpster we were able to find a fully intact unit.

SiliconPr0n wiki page: http://siliconpr0n.org/archive/doku.php?id=honeywell_awm2100v

The part number is clearly visible, it's a Honeywell AWM2100V airflow sensor. Some of my analysis from earlier was a bit off - it turns out that there's two ports on the device and some of the resistors on the membrane are heaters. One of the resistive elements is driven with a constant power and the resistance of the other one is measured to determine the membrane's temperature. Given the power input and the temperature increase above ambient (compared to unheated regions of the die and board) one can compute the airflow rate.

I tore this one down to the bare board but no further, die/board photos from the other unit are in part 1 of the post.

Sensor on the PCB
The original unit was a multi-board Honeywell process control module containing this sensor, a solenoid valve, and a large number of through-hole ICs including a Z88 family microprocessor (which may be covered in a future post - I want to get it decapped but haven't had time to do so yet).

I removed the sensor from the board using hot air. It's a six-pin SIL package with a plastic case snapped around the sensor board.



Packaging of sensor after removing from board

After removing the snapped-on casing we're left with the ceramic sensor board and a hose fitting on top. Under the host fitting is the actual sensor die, studied in detail in the previous post.

Fully disassembled

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