In the 21st century, polymers and their derivatives are ubiquitous in our daily lives. In particular, some composite materials have gradually replaced the wide application of steel and aluminum alloys in the past few decades. Composite materials are generally composed of glass fiber, carbon, aramid or natural fiber reinforced organic polymer matrix. It is understood that the output of glass fiber reinforced plastics in Europe in 2009 reached 815,000 tons.
Epoxy polymers for electrical and electronic (EE) applications account for approximately 12% of the glass fiber reinforced plastics market, and this is also one of the main applications of epoxy resin composites. In the printed circuit board (PCB), 80% of the composite material is rated as FR-4 by the National Electrical Manufacturers Association (NEMA). FR-4 is a glass fiber reinforced epoxy resin laminate that meets the required Flame Retardant standards (ie UL 94-V0).
We know that in the flame cycle, there are different ways to reduce the occurrence and damage of fire (the red mark in the figure represents the main way of extinguishing fire), and the most effective way is to improve the fire resistance of the cured resin by adding flame retardants.
Currently, halogenated flame retardants are still the majority of the flame retardant market for EE applications. However, with the implementation of new environmental regulations (such as REACH, WEEE and RoHS), some bromides will gradually be phased out, and most of the development of halogen-free flame retardants will focus on phosphorus-based products. This is because phosphorus-based flame retardants (organic and inorganic) are generally not harmful under high temperature conditions and do not form toxic gases, because the phosphorus element is mainly locked in the carbon. These products are expected to become a growing share of the flame retardant market.
With the rapid development of electronic information products today, the development and application of PCB put forward corresponding requirements for substrate materials:
①High speed and high frequency: Low dielectric constant (Dk) and low loss factor (Df) of substrate materials are required;
②High reliability: the substrate material is required to be resistant to ion migration and to resist the failure of the conductive anode wire (CAF);
③Multilayer number: high glass transition temperature (L), low coefficient of thermal expansion (CTE) and low water absorption are required for substrate materials;
④Environmentally friendly: the substrate material is required to be halogen-free and suitable for lead-free soldering processes.
Therefore, for the replacement of halogen-free flame retardants in PCBs, in addition to meeting the above 4 requirements, it also needs to meet:
①Achieve fire protection standards;
②Recyclability;
③No toxic substances will be produced during combustion, which is harmless to the human body and the environment;
④ After the replacement, it will have less impact on the performance of all aspects of the material;
⑤ Economical and applicable.
Regardless of economy, safety or material performance, high-efficiency halogen-free flame retardants have become the development direction of the flame retardant industry. Many halogen-free flame retardants are currently used in the PCB industry.
With the development of the times, electronic products have higher and higher requirements for environmental protection and performance. At the same time, it is very difficult to meet the many performance requirements of PCB materials, so it should be developed separately. Many researchers have made great contributions to the development of halogen-free PCB substrate materials, but there are currently few references to the failure and reliability of electronic products after using halogen-free substrate materials. Some studies have shown that the use of halogen-free PCB substrate materials is more likely to cause product failure, and the failure mechanism needs to be studied. This has also become the further work direction of the majority of researchers.
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