The reason and treatment method of tin whisker when soldering station
Earlier we mentioned that the solder paste may grow tin whiskers after soldering. Whiskers are conductive wires that spontaneously grow on the pads of electronics or electronic products. For example: electronic device terminals, metal shielding shells, etc. The metals that are particularly prone to producing whiskers mainly include tin, cadmium, zinc, etc., and the most representative one is tin whiskers. Xiaopeng Motors once recalled more than 10,000 vehicles because the tin whiskers produced by the inverter could easily cause short circuits. . Today, solder paste manufacturers understand the causes of tin whiskers and how to deal with them:
1. The nature and cause of tin whiskers
Tin whiskers are surface defects formed spontaneously on some pure tin or high-tin content objects. The cause of tin whiskers has not yet been determined in the industry, but it is generally believed that it means that the stress of the inner tin . The most common research is that the growth of tin whiskers starts from the pure tin electroplating layer. If once the growth process starts gradually, the tin whiskers will gradually start to grow from the "bottom", and the material supply is provided by a larger area. The supply of tin atoms is diffused in the medium, so we have a reduction in the thickness of the layer that does not exist at the root of the tin whisker, and sometimes the direction of growth may change suddenly, thus causing the tin whisker to bend.
2. The hazards of tin whiskers
1. Residual pollution
Considering that mechanical shock or vibration will cause tin whiskers to fall off from the surface of the coating and generate debris. If these debris conductive material particles work randomly, it may interfere with the operation of sensitive human optical signals or micro-electromechanical system systems. In addition, the debris may also cause a short circuit.
2. Temporary short circuit
When the short-circuit current formed by tin whiskers has exceeded the current it can withstand (mostly 30mA), the tin whiskers will be fused, resulting in intermittent short-circuit pulses, which are mostly difficult to detect.
3. Permanent short circuit
When the tin whisker grows to a certain length, it can short-circuit two different conductors. Low-voltage, high-impedance circuits do not have enough current to fuse the whisker, creating a permanent short. When the whisker diameter is larger, higher currents can be transmitted.
4. Metal vapor arc in vacuum
Under the condition of vacuum (or low air pressure), if the tin whisker transmits a relatively large current (a few amperes) or a relatively large voltage (about 18 volts), the tin whisker will evaporate into ions and can transmit hundreds of amperes Current, the maintenance of the current arc depends on the tin on the surface of the coating until it is exhausted or the current is terminated. This kind of thing is easy to happen in devices such as fuses or when the line is disconnected. There was once a commercial satellite that caused this kind of situation, causing the satellite to deviate from the orbit.
3. Specific measures for the prevention and suppression of tin whiskers
Considering that it takes a long time for tin whiskers to appear and may cause serious harm after they appear, it is necessary to prevent and inhibit the growth of tin whiskers in order to solve the tin whisker problem. So far, the generally effective method is not very clear, but generally try to avoid compressive stress inside the solder plating.
