Adesivos eletrônicos são uma de adesivos, usados ​​principalmente para selagem, colagem, envasamento, revestimento, colagem estrutural, filme coexistente e patch SMT de componentes eletrônicos e elétricos. Então, quais são a classificação dos adesivos eletrônicos? Como devemos escolher diferentes adesivos eletrônicos?

1. Classificação de adesivos eletrônicos

Electronic adhesives for microelectronic packaging can be divided into two categories: semiconductor IC packaging adhesives and PCB board-level assembly adhesives according to the packaging form. Adhesives for semiconductor IC packaging include epoxy molding compound (EMC), LED encapsulating glue (LED Encapsulant), die glue (Die Attach Adhesives), flip chip underfills (Flip Chip Underfills), cofferdams and fillers (Dam and Fill Encapsulant). PCB board-level assembly adhesives include: SMT Adhesives, COB Encapsulant, FPC Reinforcement Adhesives, CSP / BGA Underfills, camera module Image Sensor Assembly Adhesives, conformal coating, and thermally conductive adhesive.

Electronic adhesives can be divided into thermal curing, UV curing, anaerobic curing, moisture curing, UV curing + thermal curing, UV curing + moisture curing and so on. According to the material system, it can be divided into epoxy resins, acrylates and others.

Adhesives commonly used in electronic manufacturing include epoxy resin, UV (ultraviolet) glue, hot-melt adhesive, solder paste, anaerobic adhesive, double-group adhesive, etc. Epoxy resins are generally cured at high temperature, and the bonding force after curing is large. It is widely used in the bonding of functional devices, underfill and other processes. In the electronics manufacturing industry, the manufacturers of epoxy adhesives include Loctite, a subsidiary of Henkel, Fuji, Japan, Huahai Chengke, Huitian, etc. UV glue is cured by ultraviolet light, its pollution is small, and it cures quickly. It is the most widely used in some fields such as encapsulated dispensing and surface dispensing. Currently, UV glue manufacturers include Henkel Loctite, Xinyou, Debon, Huahai Chengke, Hestic Wait. In the chip packaging, the bonding power, thermal conductivity, thermal resistance and other requirements of the glue for the glue are all required. In the chip packaging, especially the LED chip packaging, the US Dow Corning glue is the most widely used. Changxin, Debang, Xindongbang and other companies are also investing in the development and production of special chip fixing glue to replace foreign products. Hot melt adhesives are structural PUR glues, which have the characteristics of low-temperature natural water vapor curing, fast curing, non-toxic and non-polluting. Due to their unique advantages, they are gradually replacing other types of glue. xinst etc.

2. Factors to be considered when choosing adhesives

Important properties of adhesives include rheological properties (viscosity, thixotropy, collapse resistance and tailing, storage period / condition and effective life) and mechanical properties (viscosity, mechanical strength and heat resistance, curing cycle, electrical properties) Stability, etc.).

(1) When choosing an adhesive, first ensure compliance with environmental protection requirements, and then consider the performance of the adhesive in three aspects: pre-curing performance, curing performance, and post-curing performance.

(2) Because the two-component adhesive needs to be mixed to the proper ratio at the right time, which increases the difficulty of the process, the single-component system should be preferred.

(3) It is better to choose a colored adhesive that is easy to distinguish from green oil and circuit board materials, because you can quickly find out whether there are missing parts, the amount of glue, whether the pads / components, empty glue, etc., are easy to control the process; Red, white and yellow.

(4) The adhesive should have sufficient viscosity and humidity to ensure that the components and circuit board are firmly bonded before the adhesive is cured. Both usually increase with viscosity. Highly viscous materials prevent components from moving during circuit board placement and transfer.

(5) Para o processo de impressão, o adesivo deve ter boa resistência ao colapso após o revestimento para garantir um bom contato entre os componentes e a placa de circuito. Isso é especialmente importante para componentes com grandes alturas de suporte, como SOIC e portadores de chip. Adesivos com boa tixotropia geralmente têm uma faixa de viscosidade de 60 a 500 Pa · s. A alta tixotropia ajuda a garantir boa capacidade de impressão e qualidade consistente de impressão do estêncil.

(6) Para o processo de impressão, o adesivo deve ser capaz de ficar exposto ao ar por muito tempo e não ser sensível à temperatura e umidade. Por exemplo, alguns novos adesivos têm uma vida útil de impressão de mais de 5 dias, e os adesivos restantes no processo de impressão O material é armazenado em um recipiente e pode ser usado novamente.

(7) Os adesivos que podem atingir a resistência de junta adequada em um tempo relativamente curto e a uma temperatura baixa devem ser preferidos. O tempo de cura e a temperatura de cura dos melhores adesivos são geralmente 30-40 s, 120-130 ℃. A força antes e depois da soldagem deve ser suficiente para garantir que os componentes estejam firmemente ligados e tenham boa resistência ao calor, e tenham adesão suficiente para suportar o efeito de cisalhamento da onda de solda. A temperatura deve ser inferior à temperatura na qual o substrato e os componentes da placa de circuito podem ser danificados e, geralmente, inferior à temperatura de transição vítrea do substrato. Esta temperatura é preferencialmente de 75 a 95 ℃. Se a força da conexão for muito grande, será difícil consertar, mas se for muito pequena, não será consertada.

The types and choices of electronic adhesives are as above. You can choose different characteristics of electronic adhesives according to different situations and different needs to make it play its greatest role.