Q
We would like to know if there are any limitations regarding the cleaning of
boards with your MEMs devices fitted, specifically with regard to the use of
aqueous/non-aqueous cleaning solutions and ultrasonics.
A
Aqueous washing shouldn’t be an issue with any of our products but you should
ensure that any solvents used in the PCB cleaning process are safe to use on
semiconductor devices. With regards to the aqueous washing process, this is the
feedback that I got:
“Aqueous cleans are not part of our qualification process, so, as such, we
cannot say whether they are OK or not. SMT companies use many different types
of cleaning processes and ADI has no way to control these cleaning processes
and cannot ensure that they do not affect device reliability. Because of this
the SMT companies take responsibility for ensuring that devices are not damaged
during SMT.”
Performing an ultrasonic clean is something that we do not recommend as it can
be very bad for MEMs devices.
The input-g’s increase as a result of the square of frequency. For example, 1mm
of displacement at 10Hz results in 4g’s. however, 1mm of displacement at 100Hz
results in 400g’s! The frequency increased by a factor of 10, but the g’s
increases by a factor of 100.
An ultrasonic clean will vibrate the device at frequencies over 20kHz. This can
cause many THOUSANDS of g’s of acceleration, and the customer is likely to
cause permanent damage to the MEMs element as a result.
In short, we do not recommend ultrasonic cleaning for MEMs devices!
(By the way, ultrasonic soldering should also not be used with MEMs devices for
the same reason).
