Soldering & Surface Mount Technology

Reliability test and failure analysis of high-density packages assembled with a low-temperature lead-free solder (SnBiAg) : Table of Contents

Sun Apr 13 14:15:03 BST 2008

Abstract:
Purpose The High Density Packaging Users Group Consortium has conducted a study of process development and solder-joint reliability of high-density packages on printed circuit boards (PCB) using a low-melting temperature lead-free solder. The purpose of this paper is to investigate the reliability tests (e.g. temperature cycling and shock and vibration) and failure analysis (FA) of high-density packages on PCB with the low-melting temperature lead-free solder (Sn-57?wt%Bi-1?wt%Ag). Design/methodology/approach The design for reliability, materials, and assembly process aspects of the project have been discussed in Design, materials, and assembly process of high-density packages with a low-temperature lead-free solder (SnBiAg) also published in this journal issue. In this study, reliability tests (e.g. temperature cycling and shock and vibration) and FA of high-density packages on PCB with the low-melting temperature lead-free solder (Sn-57?wt%Bi-1?wt%Ag) are investigated. Findings Lead-free solder-joint reliability of high-density packages, such as the PBGA388, PBGA256, PBGA208, PBGA196, PBGA172, PQFP80, and TSSOP56 were determined by temperature cycling, shock, and vibration tests. Temperature cycling test data for over 8,100 cycles between 0 and 100°C in a 44?min. cycle were statistically analyzed. Shock and vibration test data based on the HP Standard Class Bi-II Products SPEC have also been reported. Originality/value Currently there is a lack of experimental and simulation data and field experience in respect of one of the critical issues for industry that of solder joint reliability in lead-free soldering. The paper contains some important research results and recommendations.

Design, materials, and assembly process of high-density packages with a low-temperature lead-free solder (SnBiAg) : Table of Contents

Sun Apr 13 14:15:03 BST 2008

Abstract:
Purpose The purpose of this paper is to discuss the design, materials, and assembly process aspects of a study, conducted by The High Density Packaging Users Group Consortium, into process development and solder joint reliability of high-density packages on printed circuit boards using a low-melting temperature lead-free solder (Sn-57?wt%Bi-1?wt%Ag). Design/methodology/approach The components studied include several SMT package types and various lead configurations. The assembly process addresses the low-temperature lead-free assembly process, inspection and analysis of these boards and packages. Findings It was found that, the assembly process of the SnBiAg lead-free test boards is very robust and the assembly yield is almost 100 percent. Originality/value The paper is of value by presenting a description of the rationale and material set used for an experiment to test SMT assembly and reliability characteristics using the 57Bi-42Sn-1Ag alloy, which has a melting point of 139°C.

Reliability study of surface mount printed circuit board assemblies with lead-free solder joints : Table of Contents

Jeffery C.C. Lo, B.F. Jia, Z. Liu, J. Zhu, S.W. Ricky Lee — Sun Apr 13 14:15:03 BST 2008

Abstract:
Purpose The purpose of this paper is to evaluate the lead-free solder joint reliability of a variety of surface mount components assembled onto printed circuit boards (PCBs) under a number of different tests. Design/methodology/approach Lead-free solder with a composition of Sn96.5-Ag3.0-Cu0.5 was used in a surface mount reflow process. Different types of surface mount dummy components with a daisy chain, such as CBGAs, BGAs, PLCCs, CSPs, and QFNs, were assembled onto PCBs. Both the mechanical and thermo-mechanical reliability of the solder joints were evaluated by several tests. The experiments included package shear, package pull, three-point bending and accelerated thermal cycling testing for 2,000 cycles. The packages were examined by X-ray and C-SAM before the reliability tests were carried out. The maximum load and the corresponding load-displacement curve were recorded in the mechanical test. Findings The results from the mechanical tests show the major failure mode is on the copper pad. Weibull analysis shows that the characteristic lives of most packages are between 1,100 and 2,400 cycles. For the CBGA, the characteristic life of 96 cycles is relatively short, due to the serious CTE mismatch. Cross-section inspection shows failures occur at the solder joint. Copper pad failure is also observed. Originality/value This paper provides both the mechanical and thermal-mechanical reliability of lead-free solder joints. The experimental data are very useful in the lead-free SMT industries.

An investigation into the rheological properties of different lead-free solder pastes for surface mount applications : Table of Contents

S. Mallik, N.N. Ekere, R. Durairaj, A.E. Marks — Sun Apr 13 14:15:03 BST 2008

Abstract:
Purpose The purpose of this paper is to investigate the rheological behaviour of three different lead-free solder pastes used for surface mount applications in the electronic industry. Design/methodology/approach This study concerns the rheological measurements of solder paste samples and is made up of three parts. The first part deals with the measurement of rhelogical properties with three different measuring geometries, the second part looks into the effect of frequencies on oscillatory stress sweep measurements and the final part reports on the characterisation and comparison of three different types of Pb-free solder pastes. Findings Among the three geometries, the serrated parallel plate was found effective in minimising the wall-slip effect. From the oscillatory stress-sweep data with different frequencies; it was observed that the linear visco-elastic region is independent of frequency for all the solder paste samples. To understand the shear thinning behaviour of solder paste, the well known Cross and Carreau models were fitted to the viscosity data. Moreover, creep-recovery and dynamic frequency-sweep tests were also carried out without destroying the sample's structure and have yielded useful information on the pastes behaviour. Research limitations/implications More extensive research is needed to fully characterise the wall-slip behaviour during the rheological measurements of solder pastes. Practical implications The rheological test results presented in this paper will be of important value for research and development, quality control and facilitation of the manufacturing of solder pastes and flux mediums. Originality/value This paper shows how wall-slip effects can be effectively avoided during rheological measurements of solder pastes. The paper also outlines how different rheological test methods can be used to characterise solder paste behaviours.