AN2035 - Application note

6/11

The beneficial effects of the 150°C bake can be seen in the whisker test results shown in

Figure 3. Regardless of the plating thickness none of the samples had grown whiskers after

400 days of storage at room temperature.

Figure 3.

Protection by post-bake treatment (1 hour at 150°C)

Figure 4.

Protection by thickness

The above whisker mitigation techniques have been agreed with all subcontractors and are

therefore applied to all ST products.

A “Whisker Risk Free” coating does not develop whiskers that can impact electrical

performance, or component reliability. The E4 have chosen 50µm as the maximum whisker

length at the end of the device life (at the end of whisker assessment tests).

Time (in days)

1.82µm

3.5µm

5.35µm

7.10µm

10.10µm

Time (in days)