Soldering assembly recommendations

TN1200

10/16

DocID027277 Rev 1

5

Soldering assembly recommendations

5.1

PCB design recommendations for multi-pads Flip Chips

For optimum electrical performance and highly reliable solder joints, STMicroelectronics

recommends the PCB design guidelines for each bumps configuration.

Note:

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

To optimize the natural self centering effect of Flip Chip on PCB, PCB pad positioning and

size have to be properly designed (see Figure 9).

Figure 9. Footprint

Micro vias

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

the pads are connected to the lower layers using micro vias.

Table 3. PCB design recommendations example.

PCB pad design

Non solder mask defined

PCB pad size

80 µm / 100 µm maximum

Solder mask

clearance

25 µm minimum

PCB pad finishing

Cu - Ni (2-6 µm) - Au (0.2 µm max) or Cu OSP (Organic Substrate Protection)