Electronic sealing adhesive is a kind of electronic adhesive or adhesive used to seal electronic devices, which is used for sealing, sealing or sealing. After being encapsulated by electronic packaging adhesive, it can play the role of waterproof, moisture-proof, shock-proof, dust-proof, anti-corrosion, heat dissipation and privacy. Therefore, electronic packaging adhesives must have the characteristics of high and low temperature resistance, high dielectric strength, good insulation, environmental protection and safety.
Why choose epoxy resin?
With the continuous development of large-scale integrated circuits and the miniaturization of electronic components, heat dissipation of electronic components has become a key issue affecting their service life. There is a strong need for adhesives with high thermal conductivity and good heat dissipation. performance as packaging materials.
Epoxy resin has excellent heat resistance, electrical insulation, adhesion, dielectric, mechanical properties, low shrinkage, chemical resistance, and good workability after adding hardener. Therefore, at present, foreign semiconductor devices are mainly packed on epoxy resin.
With increasing calls for environmental protection and the ever-improving performance requirements of electronic packaging materials in the integrated circuit industry, epoxy resins are subject to higher requirements. Epoxy resins used in IC packages require high purity, low stress, heat resistance, and low water absorption.
With regard to issues such as high temperature resistance and low water absorption, research at home and abroad begins with the design of molecular structure, and mainly focuses on the modification of mixing and the synthesis of new epoxy resins. On the one hand, biphenyl, naphthalene, sulfone and other groups and The fluorine element is introduced into the epoxy framework to improve the moisture and heat resistance of the material after curing; on the other hand, by adding several representative curing agents, the curing kinetics, glass transition temperature, thermal decomposition temperature, and water absorption are changed to study the efficiency and other properties of the cured product, and strive to prepare a high-performance epoxy resin for electronic packaging materials.
Introduction to several specialty epoxy resins
The following mainly introduces a few special epoxy resins for electronic packaging:
Biphenyl type epoxy resin
Tetramethylbiphenol type epoxy resin synthesized by a two-stage method (its structure is shown in the figure), cured by DDM and DDS, has high temperature resistance, good mechanical properties and low water absorption.
Structure and 1H-NMR of tetramethylbiphenol type epoxy resin
Another researcher combined a new type of epoxy resin containing a biphenyl structure, the reaction formula is shown in the figure below. After the SDS hardens, the water absorption rate, measured by the boiling water absorption method, is 1.53%. The introduction of the biphenyl structure greatly improves the heat resistance and moisture resistance, which is beneficial for applications in the field of electronic packaging materials.
Another line of research in the field of electronic packaging is the introduction of silicon chain segments, which can not only improve the heat resistance, but also improve the strength after epoxy curing, and silicon-containing polymers have good flame retardant properties. the surface energy of the silicon groups causes them to migrate to the surface of the resin, forming a heat-resistant protective layer that protects the polymer from further thermal degradation.
Some researchers are using chlorine-terminated organosiloxane polymers to modify BPA-based epoxy resins and form Si-O bonds through the reaction of chlorine-terminated and hydroxyl groups in the epoxy backbone. The structural formula is shown in the figure below.
This method increases the crosslink density of the cured resin without wasting epoxy groups, which not only increases the toughness of the resin, but also improves its heat and impact resistance.
Fluoropolymers have many unique properties. Fluorine has the highest electronegativity, strong interaction between electrons and nuclei, high binding energy with other atoms, and low refractive index. Excellent heat resistance, oxidation resistance and chemical resistance.
Fluorine-containing epoxy resin has the properties of dustproof and self-cleaning, heat resistance, wear resistance, corrosion resistance, etc., and can also improve the solubility of epoxy resin. New materials.
A fluorine-containing epoxy resin synthesized at the US Naval Laboratory is liquid at room temperature and has an extremely low surface tension. After curing at room temperature with silicon amine or acid fluoride, an epoxy resin with excellent strength, durability, low surface activity, high Tg, and high stability of tensile strength can be obtained. His synthetic steps:
Epoxy resin containing dicyclopentadiene
Dicyclopentadiene-o-cresol novolac resin can be synthesized by the Friedel-Crafts reaction, the reaction formula is shown in the figure below. The resin is cured with methylhexahydrophthalic anhydride and polyamide 651 hardener respectively, and the cured product Tg is 141°C and 168°C respectively, which is about 20°C higher than that of the plain cured E51 resin.
Structure of dicyclopentadiene epoxy resin and 1H-NMR
There is a new type of low dielectric dicyclopentadiene epoxy resin (see the figure below), the performance is comparable to commercial bisphenol A epoxy resin, 5% thermal mass loss exceeds 382 ° C, glass transition. The transformation temperature is 140–188°. C, and water absorption (100°C, 24h) is only 0.9-1.1%.
Epoxy resin containing naphthalene
Some researchers have synthesized a new type of novolac epoxy resin containing the structure of naphthalene, the reaction formula is shown in the figure below. The DDS cured product exhibits excellent heat resistance with a Tg of 262°C and 5% thermal weight loss at 376°C.
Synthesis of bisphenol-A-naphthalene-formaldehyde novolac epoxy resin
Cycloaliphatic epoxy resin
Cycloaliphatic epoxy resin is characterized by high purity, low viscosity, good workability, high temperature resistance, low shrinkage, stable electrical properties and good weather resistance, especially suitable for high-performance electronic packaging materials. Requirements such as low viscosity, high temperature resistance, low water absorption and excellent electrical properties are very promising electronic packaging materials.
The diagram below shows the reaction process of a new type of heat-resistant liquid cycloaliphatic epoxy resin. It can be obtained by esterification of alicyclic olefin diols and halogenated hydrocarbons to form alicyclic triene ethers, followed by their epoxidation.
Mixed Modified Epoxy
Mixing is an important method for effectively improving the properties of materials. One or more epoxy resins are added to the epoxy matrix to improve one or more specific properties of the matrix material, thereby obtaining a new material with better overall properties. In epoxy molding compounds, mixing can achieve the goals of cost reduction, productivity improvement and processing productivity.
In future production research, to ensure the full use of epoxy resin in the domestic electronic packaging industry, improve the preparation process technology, study the curing system of high-performance epoxy resin resistant to heat and moisture, as well as environment and temperature. epoxy resin resistant to heat and moisture and the preparation of new additives modified with epoxy resin is the development direction of this research area.