Tin–lead solder alloys are widely used in the electronic industry. They serve as interconnects that provide the conductive path required to achieve connection from one circuit element to another. There are increasing concerns with the use of tin–lead alloy solders in recognition of hazards of using lead. Lead-free solders and electrically conductive adhesives (ECAs) have been considered as the most promising alternatives of tin-lead solder. ECAs consist of a polymeric resin (such as, an epoxy, a silicone, or a polyimide) that provides physical and mechanical properties such as adhesion, mechanical strength, impact strength, and a metal filler (such as, silver, gold, nickel or copper) that conducts electricity. ECAs offer numerous advantages over conventional solder technology, such as environmental friendliness, mild processing conditions (enabling the use of heat-sensitive and low-cost components and substrates), fewer processing steps (reducing processing cost), low stress on the substrates, and fine pitch interconnect capability (enabling the miniaturization of electronic devices). Therefore, conductive adhesives have been used in liquid crystal display (LCD) and smart card applications as an interconnect material and in flip–chip assembly, chip scale package (CSP) and ball grid array (BGA) applications in replacement of solder. However, no currently commercialized ECAs can replace tin–lead metal solders in all applications due to some challenging issues such as lower electrical conductivity, conductivity fatigue (decreased conductivity at elevated temperature and humidity aging or normal use condition) in reliability testing, limited current-carrying capability, and poor impact strength. Considerable research has been conducted recently to study and optimize the performance of ECAs, such as electrical, mechanical and thermal behaviors improvement as well as reliability enhancement under various conditions. This review article will discuss the materials, applications and recent advances of electrically conductive adhesives as an environmental friendly solder replacement in the electronic packaging industry.

Recent advances of conductive adhesives as a lead-free alternative in electronic packaging: Materials, processing, reliability and applications

An updated review of adhesively bonded joints in composite materials

A review : On the development of low melting temperature Pb-free solders

An Introduction to Composite Materials: Fabrication

The objective of this review is to study the effect of minor alloying and impurity elements, typically present in electronics manufacturing environment, on the interfacial reactions between Sn and Cu, which is the base system for Pb-free soldering. Especially, the reasons leading to the observed interfacial reaction layers and their microstructural evolution are analysed. The following conclusions have been reached. Alloying and impurity elements can have three major effects on the reactions between the Sn-based solder and the conductor metal: Firstly, they can increase or decrease the reaction/growth rate. Secondly, additives can change the physical properties of the phases formed (in the case of Cu and Sn, ɛ and η). Thirdly they can form additional reaction layers at the interface or they can displace the binary phases that would normally appear and form other reaction products instead. Further, the alloying and impurity elements can be divided roughly into two major categories: (i) elements (Ni, Au, Sb, In, Co, Pt, Pd, and Zn) that show marked solubility in the intermetallic compound (IMC) layer (generally take part in the interfacial reaction in question) and (ii) elements (Bi, Ag, Fe, Al, P, rare-earth elements, Ti and S) that are not extensively soluble in IMC layer (only change the activities of species taking part in the interfacial reaction and do not usually participate themselves). The elements belonging to category (i) usually have the most pronounced effect on IMC formation. It is also shown that by adding appropriate amounts of certain alloying elements to Sn-based solder, it is possible to tailor the properties of the interfacial compounds to exhibit, for example, better drop test reliability. Further, it is demonstrated that if excess amount of the same alloying elements are used, drastic decrease in reliability can occur. The analysis for this behaviour is based on the so-called thermodynamic–kinetic method.

Impurity and alloying effects on interfacial reaction layers in Pb-free soldering

Investigations of interfacial reactions of Sn–Zn based and Sn–Ag–Cu lead-free solder alloys as replacement for Sn–Pb solder

Effect of adding 1 wt% Bi into the Sn–2.8Ag–0.5Cu solder alloy on the intermetallic formations with Cu-substrate during soldering and isothermal aging

https://pearl.plymouth.ac.uk/bitstream/handle/10026.1/3513/Moisture_Diffusion-July-2015-Le.pdf?sequence=1&isAllowed=y

M.J. Rizvi

Papers

Investigations of interfacial reactions of Sn–Zn based and Sn–Ag–Cu lead-free solder alloys as replacement for Sn–Pb solder

Effect of adding 1 wt% Bi into the Sn–2.8Ag–0.5Cu solder alloy on the intermetallic formations with Cu-substrate during soldering and isothermal aging

Effects of hygrothermal stress on the failure of CFRP composites

3D FEA modelling of laminated composites in bending and their failure mechanisms

Effect of adding 0.3 wt% Ni into the Sn–0.7 wt% Cu solder: Part II. Growth of intermetallic layer with Cu during wetting and aging