Technical Article
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Lead-free Element-related Knowledge and Applications
Countries and companies are gradually paying attention to changes in the earth's environment in response to the changes in the earth's climate. Many products have begun to require a commitment to environmental protection, carbon reduction, etc. Today, we will discuss the impact of RoHS regulations on lead-free piezoelectric films with an introduction.
[Introduction to RoHS regulations]
RoHS is a mandatory standard established by EU legislation, its full name is "Restriction of Hazardous Substances". This standard has been implemented since July 1, 2006. Its main purpose is to standardize the material and technical standards of electronic and electrical products to protect human health and the environment.
The RoHS directive restricts the use of the following hazardous substances in electronic and electrical products:
(The use of these substances is usually limited to no more than 0.1% by weight)
Lead (Pb)
Mercury (Hg)
Cadmium (Cd)
Hexavalent Chromium (Cr VI)
Polybrominated biphenyl (PBB)
Polybrominated diphenyl ether (PBDE)
The RoHS directive has a wide scope of application, including various equipment with an operating voltage of less than 1000V AC or 1500V DC, such as household appliances, lighting equipment, electronic tools, toys, medical equipment, etc. Because it involves the environmentally friendly design and recycling of products, this regulation is one of the important indicators for products entering the EU market.
[Piezoelectric working principle and piezoelectric effect materials]
The main reason why the piezoelectric sheet can be deformed when energized is that there is a layer of composite material with a piezoelectric effect on the piezoelectric sheet as a piezoelectric ceramic, which will have an effect only after being polarized and energized.Common materials with piezoelectric effect are as follows:
1. Natural crystals: quartz, sucrose, potassium sodium tartrate, topaz, tourmaline, Berlin stone.
2. Artificial crystal: gallium orthophosphate, Lanxi (LGS)
3. Piezoelectric ceramics: barium titanate (BaTiO3), lead titanate (PbTiO3), lead zirconate titanate ( PZT), potassium niobate ( KNbO3), lithium niobate (LiNbO3), lithium tantalate ( LiTaO3 ), tungsten Sodium phosphate ( Na2WO4 ), sodium potassium niobate ( NaKNb ), bismuth ferrite (BiFeO3), sodium niobate ( NaNbO3), aluminum nitride ALN, zinc oxide ZnO
4. Biopiezoelectric materials: tendon, wood, silk, enamel, dentin, collagen
【Lead-free piezoelectric ceramics】One of the main composite materials mentioned earlier is lead zirconate titanate (PZT). The traditional PZT material originated around 1950. After years of development and improvement, the material system and performance have matured. , has become the mainstream material for piezoelectric ceramics, but because its composition contains too much lead, recycling will cause great harm and impact to the environment.
Suppose the lead of PZT is removed separately, and it is hoped that the original piezoelectric performance can be maintained. In that case, yttrium (Yttrium) can replace lead instead of lead or rare earth elements. Still, after many experiments, it has been proved that the lead-free formulation and piezoelectric performance will generally attenuate or have low mass production yield shortcomings. It is difficult to replace lead zirconate titanate.
In the past 20 years, the material potassium sodium niobate (KNN) from 1997 began to study the application of piezoelectric ceramics, in 2004 The KNN process adopted, has developed the electrical characteristics and PZT performance close to the standard, although the process is still complex, the cost is still high, but after years of continuous testing and improvement, the past one or two years have made significant progress, some models have begun to be applied to electronic grade materials.[Comparison of the differences between leaded ceramics and lead-free ceramics]
The traditional lead-containing piezoelectric film material is lead zirconate titanate (PZT), which usually has a lead content of more than 650,000 ppm. Lead-free bare chips use a new material, potassium sodium niobate ( KNN), with a lead content of less than 1,000 ppm. In addition, Judging from the table of piezoelectric coefficients representing performance, the difference between lead and lead-free is also very small.
Partially leaded and lead-free piezoelectric ceramics are the same, but the process parameters will be different due to different material formulas. The most important differences are as follows:
We have applied the acoustic characteristics to the KS experimental shell. The current lead-free characteristics are very close to those of traditional lead films.