PCB design recommendations

AN4046

2/9

Doc ID 022792 Rev 1

1

PCB design recommendations

For optimum electrical performance and highly reliable solder joints, STMicroelectronics

recommends the PCB design guidelines listed in Table 1

.

Note:

A too thick gold layer finishing on the PCB pad is not recommended (low joint reliability).

1.1

Micro vias

An alternative to routing on the top surface is to route on buried layers. To achieve this, the

pads are connected to the lower layers using micro vias.

.

Figure 2.

Contact dimensions

Table 1.

PCB design recommendations

PCB pad design

Micros vias under pad are not allowed

PCB pad size (NSMD design)

Same pad size as micro battery (see Figure 2)

Solder mask opening (SMD design)

Same pad size as micro battery (see Figure 2)

PCB pad finishing

Cu-Ni (2-6µm max) or Cu OSP (organic substrate

protection)

Pink colour:

contact pad Pt

5.46

5.46

5.46

5.46

25.4

25.4

0.25

0.25

4.21

4.21

3.71

3.45

R 0.75

R 0.75

R 0.75

Dimensions in mm