Silicon Image, Inc.

Silicon Image, Inc.

19

Subject to Change without Notice

When a thermal land on the PCB is used to provide a means of improved heat transfer from the package to the board

through a solder joint, thermal vias are required to remove the heat from the PCB. It is recommended that these vias

connect to the ground plane of the PCB. These vias provide a heat transfer path from the top surface of the PCB to

the inner layers and the bottom surface of the package. An array of vias should be incorporated in the thermal pad at

1.2 mm pitch grid, as shown in Figure 13. Thermal Pad Via Grid. It is also recommended that the via diameter

should be around 12 to 13 mils (0.30 to 0.33 mm) and the via barrel should be plated with 1 oz copper to plug the

via. This is desirable to avoid any solder wicking inside the via during the soldering process which may result in

voids in solder between the exposed pad and the thermal land. If the copper plating does not plug the vias, the

thermal vias can be “tented” with solder mask on the top surface of the PCB to avoid solder wicking inside the via

during assembly. The solder mask diameter should be at least 4 mils (0.1 mm) larger than the via diameter.

8.00

8.00

Figure 13. Thermal Pad Via Grid

Board Mounting Guidelines

The following are general recommendations for mounting exposed pad leadframe devices on the motherboard. This

should serve as the starting point in assembly process development and it is recommended that the process should

be developed based on past experience in mounting standard, non-thermally enhanced packages.

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7.50