Characteristics of common PCBA lead-free coating technology

- Nov 17, 2018-

Characteristics of common PCBA lead-free coating technology

The European Union's WEEE and RoHS directive came into effect on July 1, 2006.The eu WEEE and RoHS directive requires producers and manufacturers to be responsible for the recycling of electrical and electronic products, and prohibits hazardous substances in electrical and electronic products.

Various PCBA lead-free coating materials and technologies have appeared on the market due to the implementation of eu WEEE and RoHS directive.And each has its own strengths and weaknesses.Here is a comparison of some of the important features of the commonly used techniques.Readers can learn about the features of various existing technologies and why they exist.For example, Ni/Au has good performance in terms of protection performance, but there are problems such as high cost, low inventory life and IMC impact reliability.OSP has the advantages of cost, low processing temperature and easy process, but the stability of quality, inventory life and Flux compatibility are what users are concerned about.Basically, no technology has an absolute advantage.ImAg appears to have an advantage if judged in terms of overall balance.That's why ImAg has been gaining popularity among U.S. users recently.Especially when its cost is reduced, it has become a technology with great development potential.

HASL hot air leveling: popular due to low cost and usage habits, Japan is more bullish on this technology and has more research investment.Mostly on SAC and SnCu.But Europe and the United States are not optimistic about its development.It is mainly based on the flatness, high-temperature processing and the health risk to the employees.HASL is able to provide materials that match the solder alloy perfectly and have good wettability.But it will have problems with IMC growth and bad for PCB green oil.So it's not clear that it will eventually be widely accepted, depending on how sensitive most users are to the process and quality, the cost competitiveness of the OSP and ImAg, and whether users will be able to abandon the traditional process.


ImAg chemical silver sink: among the commonly used technologies, ImAg is relatively new, and its popularity is expected in recent years.ImAg has done well in every way, and is a "balanced" technology.Combined with the improvement of its processing technology, the cost is reduced. Although still higher than HASL and OSP technologies, it is lower than ImSn and Electroless Sn, and in particular, it is lower than Ni/Au. Many applications that can handle Ni/Au in bonding and contact point make this technology attractive to the industry with great potential for development.

Advantages of ImAg technology include high flatness, strong conductivity, IMC(Ag3Sn) is stronger than IMC of other coating materials, low processing temperature (generally 46 degrees), good wettability and long inventory life, etc.

Pure Sn technology: the biggest advantage of using pure tin is that there is no IMC problem after soldering with PCBA lead-free solder with high Sn content.However, SnCu layer formed after the processing of welding pad (copper) plating is growing rapidly, resulting in short inventory life.In the early days, pure tin plating was very unstable and was once unpopular.Recent improvements in workmanship (using "white tin" and the so-called "FST") have made the technology acceptable again.Some vendors even think it will become the mainstream of PCB coating technology in lead-free PCBA technology.However, this is possible only after Whisker, IMC growth after coating processing, and concerns such as tin plague are well handled. 


Pure tin plating occurs in all three common processes.Electroplating, electroless plating, and dip plating.Electroless plating replaces Electroplated pure tin plating as a result of metal whiskers and uneven coating thickness.The new Electoplating pure tin electroplating technology has been reported to prevent the production of metal whiskers by making large polygonal crystal particle structures and using 'white tin' through the electroplating solution formula.Combined with its relatively simple process, Electroplating technology and raise its head again.ImSn has been widely used in pure tin coating due to its low cost and simple process.ImSn is considered to be the closest to SnPb technology in welding technology (all materials in the lead-free PCBA technology do not perform as well as traditional tin-lead materials), but due to the weak control ability of dip plating technology on thickness, coating thickness is generally only 1.5um or less.This poses a major threat to the inventory life of the technology