Conductive Adhesive Technology Research Articles

Progress in application and preparation of silver nanowires

Silver nanowires have attracted wide research attention for their excellent optical, electrical and chemical properties. Many researches were performed toward synthesizing and application of silver nanowires. The application of silver nanowires such as transparent conductive film electrode, conductive silver adhesive and nanowelding technology was introduced herein. Principles and characteristics of different synthesizing methods of silver nanowires were reviewed in this paper, including template method, liquid polyol method, self-assembly method, ultrasonic reduction method and wet chemical method. The liquid polyol method was the most available one to achieve efficient large-scale production.

導電性接着剤技術

導電性接着剤技術

Coalescence Characteristics of Fusible Particles in Solderable Isotropic Conductive Adhesives (ICAs)

A new hybrid soldering and conductive adhesive joining technology using a fusible lowmelting- point alloy (LMPA) have been developed. A numerical method for numerical analysis of fusible particles behavior is proposed to investigate coalescence characteristics of fusible particles in solderable isotropic conductive adhesives (ICAs). For finding out suitable conditions to obtain reliable conduction paths, the present study examines the influence of process-related parameters such as volume fraction and viscosity on coalescence characteristics of fusible particles.

Recent Advances in Developing High Performance Isotropic Conductive Adhesives

Recently, significant advances have been made to improve isotropic conductive adhesive (ICA) technology. This paper provides an overview of research achievements in both electrical and mechanical aspects including electrical conductivity improvement, contact resistance mechanism elucidation and approaches to stabilize the contact resistance, and mechanical impact performance enhancement.

Reliability aspects of electronics packaging technology using anisotropic conductive adhesives

Anisotropic conductive adhesive technology for electronics packaging and interconnect application has significantly been developed during the last few years. It is time to make a summary of what has been done in this field. The present paper reviews the technology development, especially from the reliability point of view. It is pointed out that anisotropic conductive adhesives are now widely used in many applications and the reliability data and models have been developed to a large extent for anisotropic conductive adhesives in various applications.

A general Weibull model for reliability analysis under different failure Criteria-application on anisotropic conductive adhesive joining technology

In this paper, a generic four-parameter model has been developed and applied to the anisotropic conductive adhesive (ACA) flip-chip joining technology for electronics packaging applications. The model can also be used to predict any minimum failure cycles if the maximum acceptable failure criterion (in this case, a preset electrical resistance value) is set. The original reliability testing from which the test data was obtained was carried out on flip-chip anisotropically conductive adhesive joints on an FR-4 substrate. In the study, nine types of ACA and one nonconductive film (NCF) were used. In total, nearly 1000 single joints were subjected to reliability tests in terms of temperature cycling between -40/spl deg/C and 125/spl deg/C with a dwell time of 15 min and a ramp rate of 110/spl deg/C/min. The reliability was characterized by single contact resistance measured using the four-probe method during temperature cycling testing up to 3000 cycles. A single Weibull model is used for two failure definitions defined as larger than 50 m/spl Omega/ and larger than 100 m/spl Omega/ respectively using the in situ electrical resistance measurement technique. The failure criteria are incorporated into this Weibull model. This paper shows the flexibility and usefulness of Weibull distribution in this type of applications.

Reliability investigations on conductive adhesive joints with emphasis on the mechanics of the conduction mechanism

The isotropic conductive adhesive (ICA) mounting technology is of growing interest, but reliability concerns are still preventing its broad application. Reports on environmental testing results are related to both high temperature storage and thermal cycling. Additionally, the influence of moisture has been investigated for both pressure cooker test and humidity storage with exposure times up to several weeks. In an ICA, the conductive particles are embedded in a polymeric matrix material, where they can form conductive paths. This mechanical part of the conductive mechanism was studied in more detail using a finite element (FE-) model, because only a little information is available on this subject. A joint of a chip resistor on an organic board was selected for the model. The conductive adhesive is not treated as a homogeneous material, but split into the polymeric matrix material and idealized conductive particles. A temperature dependent viscoelastic constitutive description has been used to model the epoxy behavior. Additionally, moisture diffusion analyzes of the adhesive joints were conducted. The contacting pressure of the particles is shown to depend on cure shrinkage, temperature changes, and moisture swelling effects.

ELECTRICAL CHARACTERIZATIONS OF ISOTROPIC CONDUCTIVE ADHESIVES (ICAs)

Isotropic conductive adhesives (ICAs) have been developed as an alternative for traditional tin/lead (Sn/Pb) solders for electronics interconnect applications. Low processing temperature, elimination of lead, no-flux, no-clean process and the simple processing are some of the advantages of using ICAs. However, compared to the mature soldering technology, conductive adhesive technology is till in its infancy, and as such, there are some limitations for current commercial ICAs. Besides the conductivity fatigue and poor impact strength, electrically conductive adhesives tend to have lower current carrying capability and higher contact resistance in comparison to the conventional Sn/Pb solder. This is mainly due to the difference in the electrical conductive mechanisms between ICAs and Sn/Pb solders. This study focuses on current capacity measurements and other electrical properties, such as inductance, capacitance and resistance with a LCR meter and a four-point probe both in the direct current (DC) and alternating current (AC) ranges of the ICAs.

PROPERTIES OF CONDUCTIVE ADHESIVES BASED ON DIFFERENT CURING AGENTS

Electrically conductive adhesives (ECAs) are an environmentally friendly alternative for traditional tin/lead (Sn/Pb) solders. As a new technology, conductive adhesive technology still has many concerns and limitations. In order that conductive adhesive technology achieves universal acceptance, ECAs with better properties must be developed. ECAs consist of a polymeric matrix and a conductive filler. Compositions of the polymeric matrix play a very important role in determining the overall properties of ECAs. The objective of this study is to investigate the effects of different curing agents on the properties, especially contact resistance of conductive adhesives. Five polymeric matrix formulations are prepared by mixing five different curing agents, selected from different categories, with an epoxy resin. Using these polymeric matrix formulations, five ECAs are formulated. The properties of these ECAs studied include: curing profile, glass transition temperature (Tg), coefficient of thermal expansion (CTE), moisture absorption, adhesion strength, and shifts of contact resistance of these ECAs on non-noble metals such as tin, tin/lead, and copper, during elevated temperature and humidity aging. Also, a corrosion inhibitor is used to stabilize contact resistance of these ECAs on Sn/Pb. It is found that (1) the curing agents do affect the properties including contact resistance of ECAs and (2) the corrosion inhibitor is effective to stabilize contact resistance on Sn/Pb in all of the five ECA formulations.

High performance conductive adhesives

Isotropic conductive adhesives (ICAs) have been developed as an alternative for traditional tin/lead (Sn/Pb) solders for electronic applications. Compared to mature soldering technology, conductive adhesive technology is still in its infant stage, therefore, there are some limitations for current commercial ICAs. Two critical limitations are poor impact performance and unstable contact resistance with nonnoble metal finished components. These limitations seriously hindered the wide applications of ICA's. No current commercial ICAs show both desirable impact performance and stable contact resistance. In this paper, novel conductive adhesives were formulated using mixtures of an epoxide-modified polyurethane resin and a bisphenol-F type epoxy resin and a corrosion inhibitor. Cure profiles, rheology, and dynamic mechanical properties of the conductive adhesives were studied using a differential scanning calorimeter (DSC), a rheometer, and a dynamic mechanical analyzer (DMA), respectively. Impact strength and contact resistance with several nonnoble metals (Sn/Pb, Sn, and copper) of these conductive adhesives were tested and compared to those of a commercial conductive adhesive. It was found that these in-house conductive adhesives showed superior impact performance and substantially stable contact resistance with nonnoble metal finished components during elevated temperature and humidity aging.

A reliable and environmentally friendly packaging technology-flip-chip joining using anisotropically conductive adhesive

There is an increasing demand to move the radio base station closer to the antenna for future mobile telecommunication systems. This requires a significant reduction in weight and volume and increased environmental compatibility. This work provides an evaluation of environmental impact and reliability when using anisotropically conductive adhesives (ACA) for flip-chip joining in radio base station applications. Conventional FR-4 substrate has been used to assemble a digital ASIC chip using an anisotropically conductive adhesive and flip-chip technology. The chip has a minimum pitch of 128 /spl mu/m with 7.8 mm in chip 8 and has in total 144 bumps with a bump size of 114/spl times/126 /spl mu/m/sup 2/. Bumping was made using electroless nickel/gold technology. Bonding quality has been characterized by optical and scanning electron microscopy and substrate planarity measurement. The main parameters affecting quality are misalignment and softening of the FR-4 substrate during assembly, leading to high joint resistance. Reliability testing was conducted in the form of a temperature cycling test between -40 and /spl plusmn/125/spl deg/C for 1000 cycles, a 125/spl deg/C aging test for 100 h and a 85/85 humidity test for 500 h. The results show that relatively small resistance changes were observed after the reliability test. The environmental impact evaluation was done in the form of a material content declaration and a life cycle assessment (LCA). By using flip-chip ACA joining technology, the content of environmentally risky materials has been reduced more than ten times, and the use of precious metals has been reduced more than 30 times compared to conventional surface mount technology.

Reliability assessment of isotropically conductive adhesive joints in surface mount applications

A study of conductive adhesive joining technology on printed circuit boards (PCB) was conducted. Six different isotropically conductive, silver-loaded epoxies were evaluated for the surface mount process. These adhesives were used to attach electrically and mechanically 160-lead, 25-mil pitch, quad flat package (QFP) and 0805 chip components on PCB's with hash gold, passivated copper, and tin/lead metallization. The reliability of the conductive adhesive joints was evaluated in two types of environmental test: constant humidity at 60/spl deg/C and 90% RH for 1000 h, and temperature cycling for 1000 h from -40/spl deg/C to 85/spl deg/C. Under these conditions, both the electrical performance, in terms of contact resistance and surface insulation resistance (SIR), and the mechanical strength of the adhesive bonds were evaluated. The results show that reliable conductive adhesive joining can be achieved for both chip components and QFP components on PCB's with all three metallizations tested. Under well-controlled conditions, and with the right choice of adhesive for the application in mind, no significant increase or variation in electrical resistance during the temperature cycling test was encountered. The humidity exposure test was found to have a minor impact on both contact resistance and adhesion strength of most adhesives tested. In general. There was little difference between the different PCB metallizations used (except for SIR measurements). No evidence of silver migration could be observed after the humidity exposure for any of the adhesives tested.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

A review of the impact of conductive adhesive technology on interconnection

This paper reviews the current state of conductive adhesive technology. Most work to date has been carried out with isotropically-conductive adhesives which conduct electricity in any direction. In this review, particular attention has been paid to recently-developed anisotropically-conductive adhesives which are electrically conductive along one axis only. Patents filed in this area have been surveyed and the key points relating to the technology employed are summarized. A survey of the market was carried out and is presented. Adhesive processing techniques were studied and reliability issues relating to adhesives in general and to conductive adhesives in particular investigated. Voids in the adhesive leading to reduced adhesion and stress concentration were seen to be an area of concern while the effect of moisture leading to increased joint resistance and reduced strength was concluded to be the key limiting factor in the long-term reliability of conductive adhesives.