标题: Status of High Leaded Solder Use and Alternatives [打印本页] 作者: u1528428 时间: 2024-6-17 11:23 标题: Status of High Leaded Solder Use and Alternatives In order to protect human health and safety and to improve the environmental performance of electronic equipment, the European Union adopted the Restriction of Hazardous Substances (RoHS) Directive in 2006, which prohibits the use of certain hazardous substances, including lead, in electronic equipment. However, high-lead solder (i.e., lead-based alloys with more than 85% lead) is not regulated by the directive and can be used in any application.
The melting point of high-lead solder is up to 300°C or more, and the commonly used alloys are Sn5Pb92.5Ag2.5 and Sn5Pb95, which are widely used in high-temperature component connection, military manufacturing, medical devices and other specialized fields. These fields require high reliability and stability of the solder, which needs to be able to withstand high temperature, high pressure or high frequency of the working environment, while ensuring the performance and life of the components. High leaded solders are able to meet the needs of these fields due to their high melting point, low oxidation rate, good wettability, and excellent reliability and stability.
Due to the special properties and applications of high-lead solder, there is no completely reliable alternative. With the advancement of science and technology and the requirement of environmental protection, the RoHS Directive was revised in 2011 (RoHS), which stipulates the deadline for the exemption of high-lead solder and the conditions for applying for an extension. According to RoHS, the exemption for high-lead solder will expire on July 21, 2024, unless it can be demonstrated that there is no acceptable alternative. This means that users of high-lead solder must either find a suitable alternative before this date, or submit an application for extension to the EU, or face legal sanctions and competitive market pressure from the EU.
At present, the main alternatives to high-lead solder are as follows:
1. Gold-tin alloy solder
Au80Sn20 eutectic alloy, melting point 280 ° C, in the formation of solder joints with many advantages, such as high tensile strength, corrosion resistance, excellent thermal creep performance, good thermal and electrical conductivity, but its high cost makes only for some high-end optoelectronic components and military supplies.
2.Bismuth-based alloy
Bismuth-based alloy is another solution for high-temperature lead-free solder, based on bismuth alloy elements, adding enhanced micro-nanoparticles, such as the addition of 2.5% wt Ag BiAg eutectic alloy, melting point in 262. C, in line with RoHS environmental standards. However, Bi-based alloys have brittle solder joints with poor toughness and are not suitable for environments with high reliability requirements.
3. Sintering
Sintering is a technique of heating and bonding metal powder particles into a dense solid, which improves the thermal, electrical and mechanical properties of the material. The temperature of sintering is lower than the melting point of the material, so it does not change the phase state of the material, but rather the bonding between the particles is achieved by solid-state diffusion. Since the sintered materials are more compact than the original powder, they have better properties. Sintered silver and sintered copper are the main applications of sintering technology at present, but the cost of sintered silver is high, and the sintering process may produce porosity, which affects its densification and mechanical properties; the sintered silver layer may be cracked, which reduces its reliability; and the difficulty of sintered copper lies in the prevention of the oxidation of the copper powder, and therefore it is still under development.
Ag(Cu) powder - diffusion densification - sintered Ag(Cu) material
All of the above alternatives have their own advantages and disadvantages, and none of them can completely replace high-lead solder for all applications. Therefore, manufacturers need to choose the right alternative according to their specific needs, or continue to look for better alternatives. As environmental regulations continue to be improved and enforced, the use of high-lead solder will face more challenges and restrictions.
