Customer manufacturing considerations

AN4428

14/18

DocID025706 Rev 1

Figure 12. Spike suppressor configuration

A spike can also be caused by an electrostatic discharge. ESD can be a problem when

there is a wrong or poor connection of the operators or of the equipment to ground.

Additionally it must be carefully checked that ESD does not exceed the declared values of

the components. Improving ESD protection in the production line is highly recommended in

order to avoid this kind of issue.

2.1.3

Mechanical overstress

If the component sensitivity is excessively far from the specification value, most probably

the membrane has been damaged. Such damage is typically caused by a mechanical

overstress.

The ASIC in the component is working properly, but performing a visual inspection reveals

that the MEMS microphone membrane is damaged. The membrane can be affected by

cracks or voids due to heavy mechanical overstress. Such stresses can be caused by

multiple reasons. When the microphone is mounted on a module, it is important to control

the module assembly on the final equipment (typically a laptop). During the assembly the

screwdriver can hit the microphone damaging the membrane. In general, high shock events,

above 10,000 g, can happen at other instances during handling due to equipment design or

configuration. Mechanical shocks can also be caused by the pick-and-place equipment, for

example if the nozzle does not pick in the proper area or if the machine picks or places the

device with excessive force. Finally, also the usage of air to clean PCB can be dangerous if

the pressure is too high.

Figure 13. MEMS sensor crack example

To avoid the issues listed above, the customer must pay attention in setting the production

line parameters such as the path of the screwdrivers on the modules (if any) and carefully

set the equipment to avoid any kind of dangerous shocks. A further recommendation is

related to the pick-and-place equipment. ST strongly recommends using the nozzle with 4

vacuum holes specifically designed to minimize the issue related to mechanical

overstresses in production line. For the same reason, the forces involved in the pick-and-

AM17607v1

MEMS crack