Results after the Tin Whisker Growth Investigations

Tin Whisker Growth Results comes after the investigations and thanks to the methods carried out by Alter Technology, we can reach some conclusions.

An important starting point must be stressed that NONE OF THE “AS RECEIVED” SMD DEVICES POSSESSED WHISKERS. It was confirmed by performing a visual inspection. This was repeated by the company, with the help of the SEM, on the three lots of devices after each of the four runs for conditions of Temperature Cycling, and the Ambient- and High-Temperature/Humidity Storage.

In contrast:

According to the JEDEC standard, any tin whisker having a length of more than 40μm is potentially harmful and must be identified and recorded.

Alter Technology has measured the length of the whiskers using the radial method, i.e., considering that the length is defined by the most distant point of the whisker to the point of the surface where originates.

How are the results?

Alter Technology detected and measured the first two whiskers with a length more than 40μm (100μm and 150μm, respectively) in one BDS4.6/3/8.9-4S2-Z part after two runs of 1000 hours or approximately 12 weeks. This means a LOW whisker density range according to JESD22-A121, Para. 6.7, Table 5.

Other samples of the same lot showed whiskers too but with lengths less than 40μm.

First lot (BDS3-3-8.9-4S-Z devices)

Three parts showed one whisker with lengths of 99.4μm, 57.1μm and 118.9μm, respectively.

Figure 12.SEM images representative of the Sn whiskers found when the samples were stored for more than 4000 hours (24 weeks approximately) at 55ºC and 80% RH

Second lot (BDS·/3/8.9-3S1-Z devices)

This lot had six parts with one whisker each with lengths between 44.6μm and 90.7μm. And also two parts with two whiskers (one per contact) with lengths between 46.8μm and 122.2μm.

Figure 13.SEM images representative of the Sn whiskers found when the samples were stored for more than 4000 hours (24 weeks approximately) at 55ºC and 80% RH.

Third lot (BDS4.6/3/8.9-4S2-Z devices)

In the last lot, whiskers were found in the 13 devices and in most of the contacts. In total, 41 whiskers were counted with lengths ranging from 43 to 192μm. And up to three whiskers were found attached to several contacts.

Figure 14.SEM images representative of the Sn whiskers found when the samples were stored for more than 4000 hours (24 weeks approximately) at 55ºC and 80% RH.

These results show that the amount number of long whiskers in the third lot was very high when compared to the previous two lots even though the three lots of SMD parts had been made with the same manufacturing process and dimensions of the contacts.

Figure 15. Whisker length distribution after 24 weeks of High Temperature/Humidity Storage.

Third lot (BDS4.6/3/8.9-4S2-Z devices)

In the last lot, whiskers were found in the 13 devices and in most of the contacts. In total, 41 whiskers were counted with lengths ranging from 43 to 192μm. And up to three whiskers were found attached to several contacts.