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Tin and solder coatings interact with substrates commonly used in the electronics industry to produce layers of intermetallic compounds at temperatures above and below the melting point of the coatings. Observations on the rates of compound growth at room temperature for durations of up to 12 years are reported and related to the published results for shorter times at higher temperatures. Recent results concerning the effect of intermatallic compound growth on the solderability of coatings and on the strength of soldered joints are presented. In both cases it is apparent that retarding the rate of compound growth could be useful and the use of barrier layers for this purpose is considered.

Introduction The International Tin Research Institute has approximately 80 staff working at the Headquarters and Laboratories of the organisation near London. Half of these are directly engaged in research into existing and potential uses for tin and the work is organised into two main Divisions. One of these, the Metallurgy and Tinplate Division contains a section devoted to tinplate research and additional support is drawn from the Analytical Chemistry and Metallography Sections as it is required.

The effect of tin, copper, nickel and molybdenum on the mechanical properties and corrosion resistance of sintered stainless steel (AISI304L). The industrial use of sintered stainless steel is restricted by the poor corrosion resistance of the materials in comparison with the wrought counterpart. It has been shown in the literature that the addition of tin and copper can bring about improvements in the corrosion performance of certain alloys and this paper reports a systematic study of the use of these and other alloying additions. In this work, elemental additions of Sn, Cu, Ni and Mo singly and in combinations were made to 304L stainless steel powder. The mechanical properties and corrosion resistance to salt spray and immersion in saline solution of the sintered compacts have been measured and compared with samples made from 316L powder and wrought stainless steel. It was found that 304L containing additions of either 2% Sn or 2% Ni + 2% Cu + 1% Sn had the most improved corrosion resistance but with some loss of strength following sintering under conditions suitable for 304L powder. Increasing' the sintering time of the alloys with elemental additions from 45 minutes to two hours at 1180°C increased the strengths of the compacts to the same level as 304L and 316L while retaining the improved resistance to corrosion. ITRI Publication No. 650, is by S. K. Chatterjee, M. E. Warwick, and D. J. Maykuth, and is available from ITRI, Fraser Road, Perivale, Greenford, Middx UB6 7AQ.

Joints made to the Surface Mount configuration for a chip capacitor using either 60Sn40Pb or 62Sn36Pb2Ag solders were found to weaken substantially during storage at room temperature. This loss in joint strength is attributed to microstructural changes in the solder, particularly precipitation of the β phase and recrystallisation of the matrix, i.e., the two solid solutions (α + β), and the subsequent coarsening of the microstructure.

The introduction of high density surface mount technology may lead to a number of metallurgical problems. This paper considers two aspects which are currently being actively discussed. Firstly, incompatibility in expansion properties of the materials used and severe thermal cycling may induce creep and fatigue stresses on soldered joints, and the merits of different alloys are considered. Secondly, the necessary thermal treatments such as burn‐in and elevated service temperature can lead to intermetallic compound layer growth between the solder and the metallised layer on components which may be considered a potential source of joint strength reduction. Mention is also made of the different visual appearance of joints to chip components compared with conventional soldered joints.

In an electronic manufacturing environment, rework of pin‐in‐hole components on printed circuit boards is an essential process. Rework enhances product yield and through‐put efficiency by allowing device repair to occur quickly and at significantly reduced costs in comparison with complete board reconstruction. However, current rework techniques are not without their shortcomings, most notably enhanced dissolution of copper in plated‐through holes. This paper discusses a new methodology using polymer films as barrier layers, resulting in negligible plated‐through‐hole copper dissolution when conventional rework technologies are practised.

In Part 1, background information on mechanical properties and metallurgy of solder alloys and soldered joints has been presented. In Part 2, mechanisms of damage and degradation of components and soldered joints during soldering, transport and field life have been discussed, the most important mechanism being low cycle fatigue of the solder metal. In this third part, the determination of the fatigue life expectancy of soldered joints is discussed. Accelerated testing of fatigue is needed, as the possibilities of calculations are strongly limited. A temperature cycle test under specified conditions is proposed as a standard. A model is worked out for the determination of the acceleration factor of this test. A compilation of a number of solder fatigue test results, generated in the author's company, is presented.

The accuracy of severability measurements using the wetting balance depends on a number of parameters, some of which will be studied and discussed. Particular attention will be given to the influence of temperature, standard test pieces for measuring the wetting ability of fluxes, calibration of the measuring apparatus and the composition of the alloy used. Where necessary, tolerance limits will be given.

In Part 1, background information on mechanical properties and metallurgy of solder alloys and soldered joints has been presented. In this part, mechanisms of damage and degradation of components and soldered joints during soldering, during transport, and during field life are discussed. Thermal shock damage of components and excessive dissolution of metallisations are the major effects during soldering. During transport, fatigue of leads and fracture may be caused by vibration and mechanical shocks respectively. During field life, degradation is governed primarily by low cycle fatigue of the solder and incidentally also by formation of intermetallic diffusion layers between solder and base metals. This article contains an extended illustration of solder fatigue of joints on a variety of component and board types. Finally, the influence of the variety of soldered constructions in electronic circuits on solder fatigue is discussed.

Damage to components during soldering and degradation of soldered joints is determined to a large extent by the mechanical properties and the metallurgy of solder alloys and soldered joints. Knowledge of these properties is required for understanding of the mechanisms of damage and degradation. A compilation of this background knowledge is presented in this first article. It comprises the elastic, strength, creep and fatigue characteristics of tin/lead solders. Further, the metallurgy of tin/lead solders and soldered joints is discussed in terms of solidification structures, formation of intermetallic compounds, ageing of structures and effects of different solderable metallisations and soldering technology.