DT0096
Design tip
LPS33HW digital pressure sensor:
hardware guidelines for system integration……….. ……… ......... …….. ……….. By Mauro Scandiuzzo
Main components
LPS33HWMEMS pressure sensor: 260-1260 hPa absolute digital output
barometer with water resistant package

Purpose and benefits
The purpose of this design tip is to introduce the integration guidelines of the LPS33HW
pressure sensor in the final application.

Description
The LPS33HW is capable of being integrated in a 10 bar water-resistant design. In order toachieve a good seal, it is important to properly design the final package.

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O-ring implementation
ST suggests using a commercial type O-ring with an inner diameter of 1.15 mm and a
thickness of 1.0 mm for the implementation.
Figure 1 shows how the O-ring is allocated around the LPS33HW, while a top view of thering is shown in Figure 2.
Figure 1. O-ring implementation

The O-ring used to seal the metal lid of the package against the plastic wall of the socket isa nitrile 70 Shore standard part.
Figure 2. O-ring top view

Commercial O-ring characteristics:


1.15 mm inner thickness
1.0 mm thickness

Seal implementation
The seal is achieved through the mechanical pressure applied between the O-ring and theinner socket walls. Figure 3 illustrates how the seal is implemented.

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Figure 3. Seal implementation

Integration tips
The recommendation for the integration of the LPS33HW in the final package is as follows:
1. Consider the tolerance of the device and at the PCB level such as thickness of theceramic base, metal lid, glue, solder paste on the PCB, alignment device on the PCB,and housing/case tolerance. Also consider a margin on the housing design. TheLPS33HW maximum height is 2.9 mm, as shown in Table 1.
Table 1. LPS33HW package dimensions
Item
Length [L]
Width [W]Height [H]Dimension [mm]3.3
3.3
2.9 max

Tolerance [mm]0.15
0.15
/

2. Avoid putting the LPS33HW too close to the external border to prevent the damage ofthe device.
3. Protect the device and avoid exposing it directly to any significant external lightsources.
4. An adequate air flow channel is required for the device to function properly (forexample: L-shape channel).
ST suggestions for the PCB design:

Refer to the TN1198: Surface mount guidelines for MEMS sensors in HLGA packages

LPS33HW is compliant with the standard JEDEC J-STD-020



Central pad (Figure 4) does not have electrical functionality but it has been designed as
an anchor to reinforce the adhesion to the PCB. Important for the drop test - STsuggests that it is connected to the ground.

Dust and contamination during the assembly process and any damage to the gel
during the handling must be avoided.

Pay attention to the cleaning process after soldering so as not to introduce dust anddamage the gel inside the cavity.

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Figure 4. LPS33HW bottom viewSupport material
Related Documentation
Datasheet: LPS33HW, MEMS pressure sensor: 260-1260 hPa absolute
digital output barometer with water resistant package
Technical note TN1198: Surface mount guidelines for MEMS sensors in HLGA packages

Revision history
DateVersion

07-Dec-2017

1December 2017

Changes
Initial release

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