The Chapter deals with solderability of ceramic materials by ultrasound and suitable selection of soldering alloy. The solderability issue of ceramic materials consists mainly in the fact that the ceramic materials are not wettable by the common solders, due to their ionic and covalent bond between the atoms. However, there exist several ways to ensure the wettability of ceramic material surface. One of them is for example coating of ceramic material by a metallic layer. Anyway, a more perspective solution seems to be the application of soldering alloys which are alloyed with a small amount of alloying elements which exert high affinity to some component of ceramic material. The basic group of such solders are the so-called active solders containing from 1 to 5 wt. % Ti. Another group of solders, which may wet the ceramic material, are the solders alloyed with a small amount of lanthanides, for example La, Ce etc. The content of lanthanides varies from 0.5 up to 2 wt. %. The last group consists of the solders containing indium in the amount from 20 to 100 wt. %. The aim of study was to compare these three groups of soldering alloys from the viewpoint of mechanism of bond formation. The interactions between the solder and ceramic substrate were analysed and shear strength of fabricated soldered joint was determined. To improve the solderability, the soldering in combination with an active power ultrasound was also employed.
Part of the book: Soldering Materials
The chapter deals with Sn and Bi-In-based lead-free solders. The term “active solders” is used for the solders which contain one or more elements with enhanced affinity to some element contained in the substrate material. Mainly, Ti, In, lanthanides, etc. belong amongst the active metals. The role of an active element is to ensure a good wetting by a reactive decomposition of the surface layer of substrate. The perspective solders for joining the combined materials, as ceramics/metal, are mainly the tin-based, lead-free solders, which are enriched with titanium (usually up to 4 wt. %). The advantage consists in the fact that they offers a sufficient plasticity reserve, by what they are capable to compensate undesired residual stresses formed in the joint. Titanium also reacts with carbon, nitrogen or oxygen of the ceramic material, eventually it forms the intermetallic phases, which increase the strength of joint interface. The Sn-Ti, Sn-Ag-Ti and Bi-In-Sn solders were selected for the experiments. These solders were applied for fabrication of Al2O3 ceramics/Cu joints. The phase composition and microstructure of solders and soldered joints was analysed. Interactions in the interface of ceramic/solder and Cu substrate/solder were determined. The shear strength of soldered joints was measured
Part of the book: Lead Free Solders