Electronic Solder Joints Research Articles

Solder Joint Creep and Stress Relaxation Dependence on Construction and Environmental-Stress Parameters

Creep strain is probably the most important time-dependent damage accrual factor affecting solder joint reliability. Under typical multi-hour loading conditions, creep-induced strain is a complex function of solder metallurgical structure, solder temperature, loading time per cycle, the applied stress, and the spring constant of the combined part/lead/board system. The complex system level creep-fatigue interactions involved in electronic part solder joints are shown to be a strong function of the relative stiffness ratio κ, which is the ratio of the stiffness of the combined solder-lead system to the stiffness of the solder element by itself. For a leadless chip package, κ is close to unity. For a compliant leaded package, κ is typically in the 0.01 to 0.0001 range. Important environmental stress dependencies, including the effects of operating temperature, displacement amplitude due to thermal and mechanical cycling, and cyclic frequency of loading are investigated for different levels of k. Understanding the sensitivity of solder strain range to relative stiffness and these key environmental parameters is important to understanding the behavior of alternative packaging concepts and to achieving robust electronic packaging designs and testiong approaches.

Transputer-based feature extraction and shape analysis

This paper describes computer vision software for a project, the aim of which is to develop a prototype of a fast, low-cost machine vision system for the inspection of surface mount electronic assemblies and solder joints. The system uses advanced edge detection and shape description software to analyse the board, taking data from a simple optical platform. This platform is used as opposed to more complex alternatives such as laser range-finding/profiling, structured light, thermal or X-ray techniques. Hence the sophistication of this system lies in the software and not in the data capture technology. Transputers are used to provide an economical means of attaining the necessary computational power for the image analysis. This leads to a low cost solution that would be attractive to surface mount manufacturers. This paper describes the software modules required to perform feature extraction and shape analysis for inspection and how the modules are parallelized to run on a transputer network.

In-Situ Tem Study of Copper-Tin Intermetallic Formation

AbstractThe formation and growth of Cu6Sn5 and Cu3Sn at the interface of Sn-Pb solder/copper substrate are factors which affect the solderability and reliability of electronic solder joints. The addition of particles such as Ni to eutectic Sn-Pb solder drastically affects the activation energies of formation for both intermetallics. This study was performed to understand the mechanisms of intermetallic formation and the effects of Ni on intermetallic growth. Cu/Sn and Cu/Sn/Ni thin films were deposited by evaporation and observed in the TEM in real time using a hot stage. The diffusion of Sn through Cu6Sn5 and Cu3Sn followed by reaction with Cu must occur for intermetallic formation and growth to take place. Ni is an effective diffusion barrier which prevents Sn from diffusing into Cu.