MEMS pressure sensors and issues vapor-phase soldering? specifically regarding LPS35HW HLGA MEMS pressure sensor

[PRasm.1]

Hi, I am writing because after we changed our supplier we suddenly experienced a huge failure rate in our pressure sensors when our PCBA's arrived from our supplier.

Both us and our supplier are a bit lost in figuring out the cause of this. until our suppliers mentioned that perhaps these sensors are not suited for vapor-phase soldering even though they are "water resistant"

However we and they were not able to find ANY documentation on this, so is there an expert from ST who may be able to shed some light on this?

and if possible can you share some documentation on the issue with MEMS sensors and vapor-phase soldering?

best regards

P. Rasmussen

[Eleon BORLINI]

Hi P. Rasmussen @PR.4asmussen​ ,

when you changed the supplier, did he change also the soldering process?

As reported in the datasheet, the LPS35HW is compliant with the JEDEC J-STD-020D.1, i.e. the classification for Nonhermetic solid state surface mount devices. In the Solder equipment section (p. 9), it is reported that:

3.2 Solder Reflow Equipment

3.2.1 Full Convection (Preferred) Full convection reflow system capable of maintaining the reflow profiles required by this standard.

3.2.2 Infrared Infrared (IR)/convection solder reflow equipment capable of maintaining the reflow profiles required by this standard.

So basically the Vapour phase ovens are exluded. Consider in general that vapor phase soldering process is not recommended for open cavity devices. There is a potential for liquid to ingress into the cavity or possibility of condensation to form in cavity of the device.

Although the LPS35HW is water resistant, it is not hermetic and submitting the device to a "boiling" environment can damage the device.

-Eleon