Search results

This paper presents analytical and computational models of adhesive joints constructed from anisotropic conducting materials. Such materials are becoming increasingly important in the construction of fine pitch interconnection, for example the assembly of surface mounted components to printed circuit boards, and are likely to find considerable application in silicon die attach as alternatives to current ‘flip chip’ technologies. The paper presents design models of the mechanical and low frequency electrical behaviour of typical materials and relates these models to manufacturing process parameters.

Thermal cycling tests for surface mounted components are usually taken around a mean temperature of approximately 35°C (e.g., −55°C to +125°C; −40°C to +110°C). To test the effect of different maximum temperatures thermal cycling tests using a lower temperature of −55°C have been conducted with alumina/thick film ‘zero‐ohm’ jumper chips with nickel barriers. These are connected in series chains and wave soldered on to FR‐4 test coupons (128 chips/coupon). The test regimes used were −55°C to +5°C; +65°C; +95°C, +110°C and +125°C. Resistance changes before and after cycling were observed at room temperature. After 100 cycles changes of approximately +200 mΩ were observed against a total resistance of 5·5 Ω. However, more detailed examination showed that a top temperature of +95°C gives optimum results with a total change over 100 cycles of +4·9%.

There is continued concern over the ability of SMD solder joints to survive in the harsh operating environments endured, for example, by automotive and aerospace products. This paper will review the techniques available for analysing solder joint fatigue behaviour and then describe a software tool designed to allow estimation and comparison of the thermal fatigue life of solder joints exposed to a complex operating profile. The modelling technique takes account of the large changes with temperature of the solder alloys stress/strain‐rate behaviour and also the complex geometry of the component/solder/PCB assembly, whilst avoiding the very high cost of non‐linear finite element analysis. This is achieved by first performing a linear stress analysis of the assembly in order to determine its compliance, and then using this compliance estimate in the solution of a non‐linear differential equation describing the relationship between temperature, stress and strain‐rate in the joint. The technique has been implemented as a software package known as ECLIPS—Electronic Connection Life Prediction System. This software package will run on a workstation or PC and has been shown to give results very close to those from non‐linear finite element analysis, but at approximately 1/20th of the cost.

The final geometry of the solder joints in surface mount technology (SMT) assemblies is dependant upon the design rules, the materials and the manufacturing processes used. An understanding of these dependencies should allow the design of assemblies that have satisfactory thermal fatigue strength, while minimising the probability of process defects such as shorts and opens. This paper presents preliminary results from the use of a computational modelling tool, the Surface Evolver, in the simulation of the formation and geometry of solder joints and in the understanding of solder wetting phenomena. The paper also identifies other application areas for Evolver relevant to SMT.

Increases in component packing density and the consequent decrease in feature size in electronics products continue to place ever more emphasis on process design to manage or predict the outcome of the inherent process/materials interactions. The most significant pressure is for improved first‐off process yields because of high cost and technical difficulty of rework processes and concerns about the life of reworked products. The current dominant process for the production of surface mount assemblies is the reflow soldering of stencil printed solder paste. This paper presents the results of work that begins to describe the sub‐processes of solder paste reflow. It is essential to understand and optimise these complex physical processes when aiming for the six‐sigma level quality demands of electronics manufacture.

Recently nanoparticles reinforced lead free solders are vastly developed in electronics packaging industry. Studies and investigations have been conducted to learn and investigate the types, properties, method, availability and importance of nanoparticles in this field.

Mechanical properties, melting temperature and microstructural conditions are taken into major considerations in any of the preparation on nanoparticles and being reviewed in this paper. Segregation of the types of nanoparticles being added together with their properties is summarized in this paper. High temperature reliability is crucial in providing a good viable solder and hence addition of nanoparticles have been seen to give a positive outcome in this particular property.

This paper reviews on the beneficial of the various nanoparticles addition in the solder. Briefed explanations and the factors are revealed in this review.

This paper reviews on the beneficial of the various nanoparticles addition in the solder.

In this paper, analytical modelling of heat distribution along the thickness of different printed circuit board (PCB) substrates is presented according to the 1 D heat transient conduction problem. This paper aims to reveal differences between the substrates and the geometry configurations and elaborate on further application of explicit modelling.

Different substrates were considered: classic FR4 and polyimide, ceramics (BeO, Al₂O₃) and novel biodegradables (polylactic-acid [PLA] and cellulose acetate [CA]). The board thicknesses were given in 0.25 mm steps. Results are calculated for heat transfer coefficients of convection and vapour phase (condensation) soldering. Even heat transfer is assumed on both PCB sides.

It was found that temperature distributions along PCB thicknesses are mostly negligible from solder joint formation aspects, and most of the materials can be used in explicit reflow profile modelling. However PLA shows significant temperature differences, pointing to possible modelling imprecisions. It was also shown, that while the difference between midplane and surface temperatures mainly depend on thermal diffusivity, the time to reach solder alloy melting point on the surface depends on volumetric heat capacity.

Results validate the applicability of explicit heat transfer modelling of PCBs during reflow for different heat transfer methods. The results can be incorporated into more complex simulations and profile predicting algorithms for industrial ovens controlled in the wake of Industry 4.0 directives for better temperature control and ultimately higher soldering quality.

The resistance, capacitance and inductance of anisotropic conductive film (ACF) connections determine their high frequency electrical characteristics. The presence of capacitance and inductance in the ACF joint contributes to time delays and cross‐talk noise as well as simultaneous switching noise within the circuit. The purpose of this paper is to establish an experimental method for estimating the capacitance and inductance of a typical ACF connection. This can help to provide a more detailed understanding of the high frequency performance of ACF assemblies.

Experiments on the transient response of an ACF joint were performed using a digital oscilloscope capable of achieving the required ns resolution. An equivalent circuit model is proposed in order to quantify the capacitance (C) and inductance (L) of a typical ACF connection and this model is fitted to the experimental data. The full model consisted of two resistors, an inductor, and a capacitor.

The capacitance and inductance of a typical ACF connection were estimated from the measured transient response using Kirchhoff's voltage law. The method for estimation of R, L, and C from the transient response is discussed, as are the RLC effects on the high frequency electrical characteristics of the ACF connection.

There was decay time deviation between the calculation and the experiment. It may have resulted from the skin effect in the high frequency response and the adhesive surrounding joint as well. The main reason may be the capacitance zctric lost. Further research work will be done to determine more accurately the dielectric losses in anisotropic conductive adhesive (ACA) joint.

This paper presents a new method to characterise the high frequency properties of ACA interconnections and will be of use to engineers evaluating the performance of ACF materials in high frequency applications.

Presents some experimental and theoretical results from research exploring the design rules and relevant process parameters in the assembly of electronic components using anisotropic conductive adhesive materials. The experimental configurations studies have geometries representative of flip‐chip and micro ball grid array chip scale packaging. Evaluates a range of materials combinations, including (random filled) adhesive materials based on both thermoplastic and thermo‐setting resin systems, combined with both glass reinforced polymer printed circuit board and silver palladium thick film on ceramic substrate materials. Also presents a summary of assembly experiments which have been conducted using a specially developed instrumented assembly system. This test rig allows the measurement of the process temperatures and pressures and their relationship with the consequent bondline thickness reduction and conductivity development. Finally summarizes the capabilities of models which have been developed of the assembly process and of the final joint properties.