Characteristics of tin whisker growth and prevention and control strategies in room temperature environment

Tin whisker growth has been a major concern in electronics manufacturing.At room temperature, thin, sharp whiskers often appear on the surface of tin coatings, which not only affect the appearance of the product, but can also cause short circuits and lead to equipment failure.In this paper, we will discuss the growth characteristics of room temperature tin whiskers, analyse the differences in their performance on different substrate materials, and propose effective prevention and control strategies.

I. Growth characteristics of room temperature tin whiskers

The growth of room temperature tin whiskers is mainly in a straight line, but sometimes in a curved form.Figure 1-1 shows the rapid growth of tin whiskers on a Cu-based surface tin layer without accelerating factors (only at room temperature of about 25°C).The formation of these whiskers is due to the reaction between the Sn layer and the Cu interface to form Cu6Sn5 compounds, which leads to volume expansion and increased pressure within the layer, which in turn contributes to the growth of the whiskers.In addition, the formation of conical Cu6Sn5 grains provides favourable conditions for the growth of tin whiskers.

图 1-1室温下 Cu 基表面锡镀层上的锡须

2. the growth of tin whiskers on different substrate materials differences

The reaction rate of Ni with Sn is much slower compared to that of Cu with Sn, so the probability of tin whisker growth for tin plating on Ni base is much lower than that on Cu base.However, it is worth noting that the growth of tin whiskers was also observed under high and low temperature cycling test conditions for layers formed by tin plating on Ni substrates.Figure 1-2 shows the tin whisker growth observed after 500 temperature cycling of the NiTin plating on chip capacitors at temperatures ranging from -55°C to 85°C.Although these whiskers are shorter, smaller, and less likely to occur than those on the Cu substrate, they still indicate a tendency to form whiskers on Ni-based coatings.In contrast, brass and alloy 42 have a difficult time reacting with Sn, and therefore tin whisker growth is generally not seen on these materials.

Fig. 1-2 Tin whisker growth of chip capacitor with Ni barrier layer

3. room temperature tin whisker prevention and control strategy

For the growth of tin whiskers on Cu substrates, heat treatment measures can be taken to prevent and control.By making the entire interface to form a layered compound, slowing down the diffusion of Cu, can effectively inhibit the growth of room temperature tin whiskers.This is done by heat treatment or reflow soldering at 150°C.This method can reduce the reaction rate between Cu and Sn and reduce the generation of Cu6Sn5 compounds, thus reducing the pressure within the plating layer and the risk of tin whisker growth.In addition, the use of alloy plating instead of pure tin plating, the addition of trace elements to form tin alloys to inhibit the growth of tin whiskers, such as the use of SnAgCu alloy plating.Finally, surface protection processes can be used, using organic coatings and metal barriers to isolate environmental moisture and mechanical stress and to block the diffusion path of tin whiskers.All of the above can inhibit the growth of tin whiskers measures.

4. CONCLUSIONS

Room temperature tin whisker growth is an important issue in electronics manufacturing.By understanding the growth characteristics of tin whiskers and the differences in their behaviour on different substrates, we can reduce the risk of tin whisker growth by adopting effective prevention and control strategies.In the future, with the continuous development of material science and process technology, we are expected to find more efficient and environmentally friendly tin whisker prevention and control methods, which will provide a better guarantee for the reliability and stability of electronic products.