Joints microstructure

The initial approach in this study was to demonstrate the use of metallic interlayers and/or coatings in the bonding procedure. For the first layer (intended for the metallurgical bonding of the ceramic), Ti and Cr were found to be the most promising metals. Here both coatings (by PVD, 1-10 0.m thick) and layers of foils (25 im thick) were used. The function of the second Ta layer of 25 im thickness was to suspend the diffusion of Ti between the foils. In all of the experiments the third layer of niobium of 2 mm thickness was applied for thermal residual stress relief. The multilayered joint microstructure is shown in Fig. lb [7]. 

Figure 1. The typical thermal cycle for diffusion bonding of AI2O3 ceramic to Ni-superalloy (a) and the joint microstructure with the optimised joint configuration using interlayers (b).

Consideration of all aspects of joint microstructure would require a scope that includes most of materials science. In this article, attention will be directed particularly to micro-structural features of adhesive and of substrate surface that can be altered to affect the performance of an adhesive joint. 

Fig. 9 Microstructure of Sn3.8Ag0.7Cu. (a) Solder joint microstructure (b) as soldered (c) after shear loading at 125 °C (257 °F) for ° 3 h (Ref 37)...

Solder joint microstructures were studied and failure mechanisms identified as component failure, design failure and alloy failure. Grains intrusion/extrusion and voiding were examined in the micro-structures and a final alloy selection was made on the basis of these results. 

Results of thermal-cycle analysis. Solder joint microstructures were studied after final polishing and without being etched using an optical microscope at various magnifications. Many (148) photomicrographs were taken and side-by-side comparisons were made. The evaluation of the solder joints was made using these photomicrographs. 

Sn-3.5Ag-0.7Cu Reflowing on NiAu-coated FR-4 boards, shear stress in joint, microstructure of joint (SEM) 46... 

The choice of the printed wiring board surface hnish has been shown to have significant effects on the joint microstructure in the interfadal regions. 

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