Sensors

30

Freescale Semiconductor

MMA7455L

OVERVIEW OF SOLDERING CONSIDERATIONS

Information provided here is based on experiments executed on LGA devices. They do not represent exact conditions present

at a customer site. Hence, information herein should be used as a guidance only and process and design optimizations are

recommended to develop an application specific solution. It should be noted that with the proper PCB footprint and solder stencil

designs the package will self-align during the solder reflow process.

The following are the recommended guidelines to follow for mounting LGA sensors for consumer applications.

PCB MOUNTING RECOMMENDATIONS

1.

The PCB land should be designed with Non Solder Mask Defined (NSMD) as shown in Figure 21.

2.

No additional metal pattern underneath package as shown in Figure 20.

3.

PCB land pad is 0.9 mm x 0.6 mm which is the size of the package pad plus 0.1 mm as shown in Figure 21.

4.

The solder mask opening is equal to the size of the PCB land pad plus an extra 0.1 mm as shown in Figure 21.

5.

The stencil aperture size is equal to the PCB land pad – 0.025mm.

Figure 19. Incorrect PCB Top Metal Pattern Under

Package

Figure 20. Correct PCB Top Metal Pattern Under Package

Figure 21. Recommended PCB Land Pad, Solder Mask, and Signal Trace Near Package Design

Example of 2 layer PCB

Top metal pattern

under package area

Via structure under

LGA package w/ solder

PCB top metal layer

Top metal pattern

under package area

Via structure under

package area

0.8 mm

0.5 mm

PCB land pattern - NSMD

SM opening = PCB land pad + 0.1mm

= 1.0 x 0.7mm sq.

Cu: 0.9 x 0.6 mm sq.

Signal trace near

package: 0.1mm width

and min. 0.5mm length

are recommended.

Wider trace can be

continued after these.

Wider trace

Pad Dimension by Package