The uncertainties associated with tin whisker growth make it extremely difficult to predict if or when tin whiskers may appear. Due to the difficulties in predicting tin whisker growth, it may not be possible to completely eliminate tin whiskers as a failure risk.
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Fortunately, various mitigation techniques are available. Utilization of procurement specifications that have clear restrictions against the use of pure tin plating is highly recommended. Most of the commonly used military specifications currently have prohibitions against pure tin plating.
In some of these instances, tin whisker growths were also discovered. Users are advised to analyze the plating composition of the products received as an independent verification. When pure tin plating cannot be avoided, other mitigations must be investigated. One such mitigation is the solder dip of lead-free component finishes with SnPb. A SnPb solder dip process may be used to recoat the component leads.
Precautions are required to prevent damage to the parts. Possible damage can include package cracking or loss of hermeticity resulting from thermal shock, popcorning of plastic packages, solder bridging between leads on fine-pitch packages, solder bridging between leads and the component body, and handling damage such as bent or non-coplanar leads and electrostatic discharge.
The success of solder dipping as a tin whisker risk-mitigation approach depends on coating the entire exposed tin plated surface. If portions of the tin are left uncovered by the SnPb solder, they can still grow whiskers.
A specialist sub-contractor compliant with these requirements will perform the operation using an automated robot system. Larger, more robust parts for axial or radial leaded parts, for example, can be dipped by hand and in house by the printed-circuit board PCB assembler. Just as the name implies, conformal coating is a coating with an inert material that can protect electronic circuit boards from the problems related to tin whisker growth: shorts, plasma arc, and debris. Four points should be considered while using conformal coating as a tin whisker mitigation technique:.
We acknowledge that tin whiskers cannot be stopped until we understand how they form in the first place. No conformal coating meets all these criteria. However, the Arathane coating seems promising when applied sufficiently thick, and the conformal coating does prevent shorts from debris. Thermal effects need to be considered if a conformal coating is used on parts that will need to dissipate heat when operating. If necessary, the device may need to be derated.
If the conformal coating fails to contain whisker formation, the effectiveness of a conformal coat in providing protection against electrical leakage and corrosion will be compromised. A puncture site may provide an increased opportunity for excessive leakage currents that can produce transient or permanent failures. Ashworth G.
NEMI Tin Whisker Test Method Standards
Wilcox Rebecca L. Higginson Richard J. Heath Changqing Liu. Tin whiskers are filamentary growths that are formed on the surface of electrodeposited tin, which is used extensively in the electronics industry. The presence of whiskers on electroplated finishes has been observed for more than 60 years, but, despite a huge amount of work in this area, a definite mechanism by which whiskers grow remains unidentified. Write a Review.
Basic Info on Tin Whiskers
Related Searches. Chemistry of Tin. In common with the editor of the first edition, my own personal involvement with tin In common with the editor of the first edition, my own personal involvement with tin chemistry began when I had the privilege of studying for a PhD degree under the supervision of Professor Alwyn G. View Product.
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Related Factors Governing Tin Whisker Growth
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