DocID025706 Rev 1

13/18

AN4428

Customer manufacturing considerations

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2

Customer manufacturing considerations

2.1

Customer handling recommendations

The purpose of this section is to summarize, for typical failures that can occur in the

customer’s production line, an explanation of the issue first and then to propose a solution

or even give a recommendation to avoid these failures, usually caused by mishandling of

the device.

2.1.1

Contaminations

When the component provides a PDM output that when listened to or measured shows poor

SNR performance or very noisy output, the issue is typically due to contamination of the

MEMS membrane.

Contamination during PCB sawing, during PCB cleaning or washing can occur in a

customer’s production line. Further contamination can happen during device soldering if a

vapor phase soldering process is used for the reflow or some soldering paste accidentally

drops inside the sound inlet.

To avoid these types of contaminations, the sealing of the sound inlet with foam/tape before

sawing to prevent dust from entering the microphone is recommended. As a matter of fact,

using a vapor phase soldering process must be avoided to prevent membrane damage and

contamination.

2.1.2

Electrical overstress (EOS)

When the component does not show any signal at the output or the output is tied to GND (or

to Vcc), most probably the ASIC has been submitted to an electrical overstress.

Electrical overstress is an unexpected electrical phenomenon, like a high-voltage discharge,

that can cause irreversible damage to the ASIC such as burned areas or voids in the silicon.

Figure 11. Example of EOS

To avoid this issue, it is highly recommended to verify the supply voltage vs. microphone

operative and max absolute voltage specifications, or also to verify the voltage ripple when

doing hot plug to testing jigs. A diode (spike suppressor) can be included in the testing

equipment using the following configuration.