Common PCBA lead-free plating technology features

Common PCBA lead-free plating technology features

    The EU WEEE and RoHS Directives were formally implemented on July 1, 2006, and have a direct impact on the electronics and electronics industry. The European Union's WEEE and RoHS Directive requires that producing countries and production companies must be responsible for the recovery of electrical and electronic products. At the same time, they also impose bans on harmful substances in electrical and electronic products.

    Due to the implementation of the EU WEEE and RoHS directives, various PCBA lead-free plating materials and technologies have appeared on the market. And generally have their own strengths and weaknesses. The following figure is a comparison of some of the most commonly used technologies in some important features. Readers can learn about the characteristics of various existing technologies and the reasons for their existence. For example, Ni/Au has good performance in terms of protection performance, but there are problems of high cost, low inventory life, and IMC affecting reliability. OSP has the advantages of cost, low processing temperature and easy process, but the stability of quality, inventory life and compatibility with Flux are users' concerns. Basically, no technology is absolutely superior. If viewed from a more balanced perspective, ImAg seems to have advantages. This is why the recent ImAg has been welcomed by users based in the United States. Especially when its cost has dropped, it has become a technology with great development potential.

    HASL Hot Air Leveling: Due to its low cost and usage habits, Japan is more optimistic about this technology and has more research investment. Mainly on SAC and SnCu alloys. However, Europe and the United States are not optimistic about its development. This is mainly based on considerations such as its flatness issues, high temperature processing issues, and process health risks to employees. HASL can provide a material that perfectly matches the solder alloy and has good wettability. However, it will have problems such as IMC growth and unfavorable PCB green oil. Therefore, the development situation is not very sure whether it will eventually be widely accepted. It depends on the sensitivity of most users to the process and quality, the cost competition status of OSP and ImAg, and whether users can abandon this traditional process.

    ImAg chemical silver: In the commonly used technology, ImAg is relatively new technology, and it is optimistic about the recent years. ImAg has performed well in all aspects and is a technology that shows "balanced". Coupled with improvements in its processing technology, the cost can be reduced. Although it is still higher than HASL and OSP technology, it is lower than ImSn and Electroless Sn, especially lower than Ni/Au. Many can handle Ni/Au at bonding and contact points. In application, this technology is optimistic about the industry and has great potential for development.

     ImAg technology benefits include high flatness, high electrical conductivity, IMC (Ag3Sn) is stronger than other coating materials IMC, processing temperature is low (generally 46 degrees), good wetting and long inventory life.

    Pure Sn Technology: The biggest benefit of using pure tin is that there is no IMC problem after soldering with PCBA lead-free solder, which typically contains high amounts of Sn. However, the SnCu layer formed after the pad (copper) plating process has grown rapidly, resulting in a short inventory life. In the early days, the quality of pure tin plating was very unstable and once unpopular. Recent technological improvements (using "white tin" and the so-called "FST") have made this technology acceptable again. Some suppliers even believe that it will become the mainstream of PCB plating technology in PCBA lead-free technology. However, this must happen after Whisker, IMC growth after plating, and tin crucibles are properly addressed.

    Pure tin plating technology occurs in all three common processes. Electroplating, electroless plating, and immersion plating techniques. Electroless plating technology replaces metal whiskers and uneven plating thicknesses in electroplated pure tin technology. With the new electroplating pure tin technology, it has been reported that the production of metal whiskers can be prevented by the use of a plating solution to create a larger polygonal crystal grain structure and the use of 'white tin'. Coupled with its relatively simple process, Electroplating technology has regained its head. ImSn is widely used in pure tin plating due to its low cost and simple process. ImSn is considered to have the closest performance to SnPb technology in the soldering process (all material processes in PCBA lead-free technology are not as good as traditional tin-lead materials), but the thickness of the plating is generally not as strong as the immersion plating technology is not able to control the thickness. Only 1.5um