Abstract-The impact of chloride ion concentration on electrochemical migration (ECM) of tin and silver was studied by using an in-situ optical and electrical inspection system. It was found, that in both cases, dendrites grow not only in an electrolyte solution at low chloride concentration but also in an electrolyte at medium and high or even saturated chloride concentrations as well. According to the results, the migration susceptibility has decreased at low and medium concentration levels in both cases. However, the ECM susceptibility of Ag has increased, while the migration susceptibility of Sn was decreased at the saturated concentrations.
IntroductionOne of the key reliability issues of the electronics technology is carry about the solder joints testing. Usually, the different failures can lead back to the not adequate physical properties (e.g. wetting behaviour, mechanical strength, etc.) of the solder alloy and/or the not adequate applied technological processes (e.g. reflow temperature profile), which have to be improved. This challenge was updated in 2006, with the introduction of lead-free solder alloys governed by the RoHS directive of EU [1]. Due to the lead-free limitations, different solder types such as near-eutectic Tin-Silver, Tin-Copper, and Tin-Zinc alloys were produced as replacement for Tin-Lead solder materials. Furthermore, solders with more alloying elements, such as (Tin-Silver-Copper, Tin-Zinc-Silver, Tin-Zinc-Indium) and/or (Tin-Zinc-Silver-Aluminum, Tin-Silver-Bismuth-Copper, TinIndium-Silver-Antimony) were also investigated as replacements for Pb-free types [2]. While, the different qualifying studies of the Pb-free solder alloys are even active topics [3] and one of the issues is carry about humidity induced failures, like electrochemical corrosion [4,5]. Different results were also published related to novel Pb-free solder alloys in terms of reliability topics, such as solderability [6], intermetallic layer (IML) investigation [7], shear force tests [8], wetting investigations [9] or (solid state physics) migration tests [10]. On the other hand, the investigations of humidity induced failures (like corrosion) of Pb-free solder alloys are not deeply addressed in the scientific publications. In our former publication [11], various microalloyed Pb-free solders tested in terms of corrosion resistance using electroanalytical tests. In that study [11] different Pb-free solder alloys (four micro-alloyed and a Sn96.5Ag3Cu0.5 alloy as reference) were compared using potentiodynamic polarisation tests. During polarisation tests, the sample (working electrode) is scanned from a cathodic polarisation state, and after reaching the corrosion potential (Ecorr) it begins anodic polarisation. When the sample reaches the passivation potential, if possible a passivation film begins to form on the surface and the current density at this point is called the critical current density (Icrit). After this point the corrosion current density begins to drop to a much lower value. When a compact passivation film
My work is to improve the generation of 3-D flexible structures by laser micromachining. The purpose is to extract the material by an ablation of matter in order to achieve ''V'' shape for multi-bend structure. This multibend part will be the key for 3-D structures. For that, a frequency multiplied Nd:YAG laser provided with a marking trigger and equipped with a galvanometric head was used. For optimizing the laser irradiation time and power a thermal modeling of the laser matter interaction for a continuous laser impact case is presented. The paper models numerically the localized three-dimensional temperature distribution in a polyimide caused by a moving Gaussian laser beam by Finite element method (FEM) analysis. The beam's penetration depth, which can be described with an absorption coefficient, depends on the ambient temperature. The model examines the penetration depth and the influences of the laser motion on the transient temperature distribution. As the maximum temperature is mesh dependent we decided to choose 10 lm initial mesh with 1.01 mesh grow, so the laser beam diameter occurs 20 lm. The overall heat flux and temperature distribution on a macroscopic level are both accurate.
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