Adhesives are widely used in electronic packaging and are of vital importance in the reliability of electronic systems. A deep understanding of the degradation mechanism of adhesives under corrosion load plays a key role in lifetime prediction. Unfortunately, most of the common reliability tests are destructive. The present approach combines the nondestructive methods, electrochemical impedance spectroscopy and the Fourier-transform infrared spectroscopy, as powerful tools in a complementary manner to describe the degradation mechanism and kinetics of two epoxy-based adhesives, which are commonly used in electronic packaging. It is demonstrated that the application quality is the dominating impact on the optimization of the lifetime.
The present work focuses on the investigation of the degradation of screenprinted epoxy coatings on printed circuit boards under multiple corrosion loads realized by the pressure cooker test (PCT). Since methods like the common mechanical shear strength tests are destructive and limited in information, the authors' approach used electrochemical impedance spectroscopy to study the change of their electrochemical behavior and the state of degradation. Complementarily, the Fourier-transformed infrared spectroscopy was used to investigate the possible molecular change of the polymer due to the exposition. The experiments were carried out after different times of load. It could be shown that the complex conditions of the PCT initiate a controversial mechanism. The harsh corrosion load already results in a degradation of the polymer after 8 h but simultaneously the enhanced test temperature leads to ongoing curing processes consuming the remaining parts of resin and curing agents. As a result, the degradation kinetic seems to be delayed and after the test time of 96 h, the epoxy is less degraded than it was expected based on the results after a shorter time exposition.degradation, EIS, epoxy polymer, FTIR, pressure cooker test
| INTRODUCTIONEpoxy-based polymers play an important role in electronic packaging, the multifarious material act, for example, as thermomold systems, attachment materials, or adhesives. Prime functions of the polymers are mechanical stabilization, insulation, joining, and corrosion protection of electronic components and bonds. [1][2][3][4][5] The reliability of electronic components depends among others, essentially on the degradation, the adhesion strength on polymer/
The mechanical machining and finishing of cemented carbides is associated with high abrasive wear of cutting tools. Electrochemical Machining (ECM) is the technical application of high rate metal dissolution and well established for steels and several non –ferrous metals. ECM is a priory free of mechanical tool wear. Recently the authors investigated the high rate dissolution of cemented carbides in ammonia containing alkaline electrolytes [1]. The electrolyte system is suitable for ECM of tungsten carbide as well as cobalt. A homogenous dissolution of the compound material was achieved. In industrial practice, Electrochemical Machining is used to realize high surface quality of work pieces. The existence of anodic films during the machining step is important in controlling the texture of the machined surface obtained [2]. If the dissolution process is controlled by material transport through a film of compact dissolution intermediate, precipitated products [3] or viscous product layer [4] the surface will occurs bright and shiny. The formation of viscous surface layers can be enhanced by surface active organic additives of the electrolyte [5]. In the present work the authors investigated the effect of different solvents on the surface roughness during ECM of tungsten carbide. The electrochemical experiments were carried out in a channel flow cell. Firstly, an aqueous solution containing 2M ammonia and 1.5M sodium nitrate was used as reference electrolyte. In a second step ethanol and glycol, respectively, were added. Both additives change the conductivity as well as the viscosity of the electrolyte. All samples were investigated by SEM after the ECM experiments. A decreasing surface roughness in the order of water, water/ethanol and water/glycol was achieved. A quantitative evaluation will be given by using laser scanning microscopy.
References
[1] N. Schubert, M. Schneider, A. Michaelis, Electrochemical Machining of cemented carbides, Int. J. Refractory Metals and Hard Materials 47 (2014) 54-60
[2] J. Bannard, Electrochemical Machining, J. Appl. Electrochem. 7 (1977) 1-29.
[3] T.P. Hoar, T.W. Farthing, Solid Films on Electropolishing Anodes, Nature 169 (1952) 324–325.
[4] P. A. Jacquet, The Electrolytic Polishing of Metallic Surfaces, Metal Finishing Vol. 47 (1949) 83.
[5] J. Bannard, The effect of a surface-active additive on the dissolution efficiency and surface finish in ECM, J. Appl. Electrochem. 7 (1977) 189–195.
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