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Laser soldering has attracted attention as an alternative soldering process for microsoldering due to its localized and noncontact heating, a rapid rise and fall in temperature, fluxless and easy automation compared to reflow soldering.

In this study, the metallurgical and mechanical properties of the Sn3.0Ag0.5Cu/Ni-P joints after laser and reflow soldering and isothermal aging were compared and analyzed.

In the as-soldered Sn3.0Ag0.5Cu/Ni-P joints, a small granular and loose (Cu,Ni)6Sn5 intermetallic compound (IMC) structure was formed by laser soldering regardless of the laser energy, and a long and needlelike (Cu,Ni)6Sn5 IMC structure was generated by reflow soldering. During aging at 150°C, the growth rate of the IMC layer was faster by laser soldering than by reflow soldering. The shear strength of as-soldered joints for reflow soldering was similar to that of laser soldering with 7.5 mJ, which sharply decreased from 0 to 100 h for both cases and then was maintained at a similar level with increasing aging time.

Laser soldering with certain energy is effective for reducing the thickness of IMCs, and ensuring the mechanical property of the joints was similar to reflow soldering.

The increasing complexity of microelectronic devices and the advent of surface mount technology has led to interest in alternatives to mass reflow soldering techniques. One method with advantages for rapid automation and minimal heat input, is laser soldering. Various laser methods are available for application to reflow soldering, the prime options being continuous wave CO2, continuous wave Nd/YAG and pulsed Nd/YAG. This paper presents the results of work to compare and contrast the three techniques. The paper concentrates on the soldering of leadframes and SMD (gull wing and J‐lead) to plated Al2O3 substrates, but also mentions soldering to FR4 PCBs.

With the ever‐decreasing size of electronic components, examines the use of laser soldering, particularly of fine‐pitch, high value devices. Discusses the advantages and disadvantages of using lasers and the applications to which they are suited. Looks at the different types of lasers and how their different wavelength of operation affects the soldering process. Describes an experimental laser soldering station and its ability to solder circuit boards. Concludes that modern electronic component packaging technology is demanding new techniques for the interconnection of devices, and that the application of lasers to the traditional technique of soldering will enable this tested process to be applicable to the very fine pitch devices now being introduced.

This study aims to review the effect of copper percentage in Sn-based solder alloys (Sn-xCu, x = 0–5 Wt.%) on intermetallic compound (IMC) formation and growth after laser soldering.

This study reviews the interfacial reactions at the solder joint interface, solder joint morphology and the theory on characterizing the formation and growth of IMCs. In addition, the effects of alloying and strengthening mechanism, including wettability, melting and mechanical properties are discussed.

This paper presents a comprehensive overview of the composition of tin-copper (Sn-Cu) solders with a potential to enhance their microstructure, mechanical characteristics and wettability by varying the Cu percentage. The study found that the best Cu content in the Sn-xCu solder alloy was 0.6–0.7 Wt.%; this composition provided high shear strength, vibration fracture life value and ideal IMC thickness. A method of solder alloy preparation was also found through powder metallurgy and laser soldering to improve the solder joint reliability.

This study focuses on interfacial reactions at the solder joint interface, solder joint morphology, modelling simulation of joint strength and the theory on characterising the formation and growth of IMC.

The paper comprehensively summarises the useful findings of the Sn-Cu series. This information will be important for future trends in laser soldering on solder joint formation.

Laser soldering, as a viable technique for surface mounting assemblies, is reviewed. The criteria for selection of a CO2 or a Nd:YAG laser are discussed. New data are given that quantify the beneficial effects of laser soldering on the solder fillet microstructure, and how this relates to in‐service performance.

This issue of the journal features the final part of a two‐part series which comprises Chapter 15 from Volume 1 of a recently published book ‘A Comprehensive Guide to the Manufacture of Printed Board Assemblies’^* edited by W.MacLeod Ross.Volume 1, containing 800 pages, and Volume 2, scheduled to be published in the Spring of 1997 and estimated to contain around 900 pages, will, as far as the publishers are aware, be the most comprehensive book ever published on the subject of printed board assemblies.

Laser soldering provides a useful tool for the electronics manufacturer and has found a number of successful industrial applications. The laser provides highly controllable localised heating in a manner similar to hand soldering and has distinct advantages over other soldering methods. However, the heating processes that occur in laser soldering are complex making it difficult to predict whether a particular operation will be successful. Numerical modelling provides a valuable tool in answering such questions but the modelling process and the assumptions upon which it is based must be understood if the results are to be reliable.This paper explains the assumptions made in deriving a suitable model and describes the use of a commercial finite element modelling package to aid the understanding of laser soldering processes, with a particular emphasis on single and multi‐pass scanned beam soldering operations.

Soldering techniques for surface mount technology are still in their early stages. Therefore, a survey is given of the main soldering methods which are currently used in research and production as well as those which are expected to come into use, such as wave soldering, infra‐red soldering, vapour phase soldering and laser soldering. These techniques are influenced by both the component and board design. Even in soldering surface mount components, a number of rules must be observed in order to produce a good solder joint.

The purpose of this paper is to investigate the laser soldering of fine pitch quad flat package (QFP) devices using lead‐free solders and solder joint reliability during thermal cycling.

QFP devices were selected as the test vehicles and were soldered with four alloy types, Sn37Pb, Sn3.5Ag, Sn3.8Ag0.7Cu and Sn3.8Ag0.7Cu0.03Ce. The experimental samples were QFP‐256 devices with lead‐free solder paste on the printed circuit boards. The packages were dried for 24 h at 125°C prior to reflow soldering. Soldering experiments on the QFP devices were carried out with an infrared (IR) reflow soldering oven and a diode laser (DL) soldering system. Reflow soldering was performed at peak temperatures of 210°C (SnPb), 240°C (SnAgCu and SnAgCuCe) and 250°C (SnAg), as determined on the boards. Pull testing was adopted to evaluate the tensile strength of the four solders using an STR–1000 micro‐joint strength tester.

The tensile force of the QFP micro‐joints increased as laser intensity increased when it was less than an “optimal” value. The maximum tensile force of the QFP micro‐joints was gained when the laser intensity had increased to 2,165, 2,127, 2,165 and 2,064 W/cm², depending on the alloy used. The thermal fatigue performance of three lead‐free solder joints, SnAgCuCe, SnAgCu and SnAg, was determined to be superior to that of the eutectic SnPb alloy. After soldering without thermal cycling tests, the fracture morphology of soldered joints exhibited characteristic toughness fracture with both of the soldering methods. After 700 thermal cycles, the fracture mechanism was also toughness fracture, nevertheless, the dimples became large. The fracture morphology of the soldered joints subjected to 1,500 thermal cycles indicated brittle intergranular fracture on the fracture surface and no intense plastic deformation appeared before fracture with IR soldering. For DL soldering, the pull fracture model of the SnAgCuCe was completely ductile in the soldered joint with 1,500 thermal cycles.

The paper usefully investigates the influence of laser intensity on the tensile strength of different soldered joints and the solder joint reliability during thermal cycling.

Laser soldering has become a viable method for the assembly of surface mounting components on printed circuit boards. This paper discusses the techniques both in terms of the physics involved and the practicalities of a production facility.