Status of High Leaded Solder Use and Alternatives

�*** · 发表于 2024-6-17 11:23:24

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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.

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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.

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会员158306 · 发表于 2024-6-20 12:00:24

为了保护人类健康和安全并改善电子设备的环境性能，欧盟于 2006 年通过了有害物质限制（RoHS）指令，该指令禁止在电子设备中使用某些有害物质，包括铅。然而，高铅焊料（即铅含量超过85%的铅基合金）不受该指令的约束，可用于任何应用。
高铅焊料的熔点高达300°C以上，常用的合金有Sn5Pb92.5Ag2.5和Sn5Pb95，广泛应用于高温元器件连接、军工制造、医疗器械等专业领域。这些领域对焊料的可靠性和稳定性要求很高，需要能够承受高温、高压或高频的工作环境，同时保证元件的性能和寿命。高铅焊料具有熔点高、氧化速率低、润湿性好、可靠性和稳定性好等特点，能够满足这些领域的需求。
由于高铅焊料的特殊性能和应用，没有完全可靠的替代品。随着科学技术的进步和环保的要求，RoHS指令于2011年进行了修订（RoHS），规定了高铅焊料豁免的截止日期和申请延期的条件。根据 RoHS 的说法，高铅焊料的豁免将于 2024 年 7 月 21 日到期，除非可以证明没有可接受的替代品。这意味着高铅焊料的用户必须在此日期之前找到合适的替代品，或者向欧盟提交延期申请，否则将面临来自欧盟的法律制裁和竞争性市场压力。
目前，高铅焊料的主要替代品如下：
1.金锡合金焊料
Au80Sn20共晶合金，熔点280°C，在焊点的形成中具有诸多优点，如抗拉强度高、耐腐蚀性好、热蠕变性能优异、导热性和导电性好，但其高成本使得只能用于一些高端光电元件和军用用品。
2.铋基合金
铋基合金是高温无铅焊料的另一种解决方案，在铋合金元素的基础上，加入增强的微纳米颗粒，如加入2.5%wt的Ag BiAg共晶合金，熔点在262。C、符合RoHS环保标准。然而，双基合金焊点脆，韧性差，不适合可靠性要求高的环境。
3.烧结
烧结是一种将金属粉末颗粒加热并粘结成致密固体的技术，可改善材料的热性能、电气性能和机械性能。烧结的温度低于材料的熔点，因此它不会改变材料的相态，而是通过固态扩散实现颗粒之间的键合。由于烧结材料比原始粉末更致密，因此具有更好的性能。烧结银和烧结铜是目前烧结技术的主要应用，但烧结银成本高，烧结工艺可能产生气孔，影响其致密化和力学性能;烧结银层可能会开裂，从而降低其可靠性;而烧结铜的难点在于防止铜粉氧化，因此目前仍在开发中。
高铅焊料的使用现状和替代品
Ag（Cu）粉末-扩散致密-烧结Ag（Cu）材料
上述所有替代方案都有其优点和缺点，它们都不能完全取代所有应用的高铅焊料。因此，制造商需要根据自己的具体需求选择合适的替代品，或者继续寻找更好的替代品。随着环境法规的不断完善和执行，高铅焊料的使用将面临更多的挑战和限制。

Status of High Leaded Solder Use and Alternatives

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