AIS328DQ datasheet(39/43 Pages) STMICROELECTRONICS

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AIS328DQ

Soldering information

Doc ID 18160 Rev 3

39/43

Soldering information

The QFPN-24 package is compliant with the ECOPACK®, RoHS and “Green” standard.

It is qualified for soldering heat resistance according to JEDEC J-STD-020C, in MSL3 condi-

tions.

For complete land pattern and soldering recommendations, please refer to the TN0019

technical note TN0019 available on www.st.com.

9.1

General guidelines about soldering surface-mounted

accelerometers

As common PCB design and industrial practice when considering accelerometer soldering,

there are always 3 elements to take into consideration:

1. PCB with its own conductive layers (i.e. copper) and other organic materials used for

board protection and dielectric isolation.

2. ACCELEROMETER to be mounted on the board. The accelerometer senses accelera-

tion, but it senses also the mechanical stress coming from the board. This stress is mini-

mized with simple PCB design rules.

3. SOLDERING PASTE like SnAgCu. This soldering paste can be dispensed on the board

with a screen printing method through a stencil. The pattern of the soldering paste on the

PCB is given by the stencil mask itself.

9.2

PCB design guidelines

PCB land and solder masking general recommendations are shown in Figure 13. Refer to

Figure 12 for specific device size, land count and pitch.

●

It is recommended to open solder mask external to PCB land

●

It is mandatory, for correct device functionality, to ensure that some clearance is

present between the accelerometer thermal pad and PCB. In order to obtain this

clearance it is recommended to open the PCB thermal pad solder mask

●

The area below the sensor (on the same side of the board) must be defined as keepout

area. It is strongly recommended not to place any structure in the top metal layer

underneath the sensor

●

Traces connected to pads should be as symmetrical as possible. Symmetry and

balance for pad connection helps component self alignment and leads to a better

control of solder paste reduction after reflow

●

For better performances over temperature it is strongly recommended not to place

large insertion components like buttons or shielding boxes at distances less than 2 mm

from the sensor

●

Central die pad and “Pin 1 Indicator” are physically connected to GND. Leave “Pin 1

Indicator” unconnected during soldering.

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