Progress and developments in the field of materials for transient liquid phase bonding and active soldering processes

Abstract

In the last decade, microsystem engineering has rapidly developed. Nowadays microsystems have a very broad scope of applications, which range from electronics and aerospace to chemistry, optics, biology and medicine. Within this framework, the joining technique plays a crucial role. Therefore the development of new concepts for joining hybrid microstructures is one of the main tasks within the collaborative research center, assembly of hybrid microsystems. Active soldering and transient liquid phase (TLP) bonding processes are two innovative and trend-setting technologies in the field of joining dissimilar materials and have been specifically adapted to the requirements of the microsystems. IntroductionThe use of innovative materials and the adaptation of manufacturing methods in the field of microcomponents has contributed vastly to the enormous success of microsystem engineering. Within this framework the fabrication of hybrid structures is receiving increasingly more interest.The joining processes used at present in microsystem engineering are strongly limited concerning the number of suitable joining materials, as well as their use at higher temperatures. The two processes active soldering and transient liquid phase (TLP) bonding are innovative and ground-breaking in the field of joining dissimilar materials [1,2,5].In order to overcome the restrictions of common joining processes of hybrid microcomponents, these bonding techniques have been transferred from the macro-into the microtechnology and adapted to the special requirements of the microsystems. For this purpose, new filler metals have been developed and produced, which are constantly optimised and modified according to the specific requirements of the microstructures being joined.Investigated filler metals have been evaluated and characterized with regard to fundamental parameters in the field of microsystem technology. One of these parameters is the process temperature, since too high soldering temperatures are disadvantageous for numerous applications in the microtechnology.Regarding the mechanical characteristics of the filler metals, not only the strength has been particularly considered but also the ductility of the joint. Moreover, the material behaviour regarding chemical attack has been examined and evaluated for possible areas of improvement. Objectives and methodology Active soldersActive solders are metallic alloys, which contain ''surface active'' elements (e.g. titanium, zirconium) in small quantities, able to reduce the surface energy between nonmetallic material and molten filler metal, thus improving the wetting behaviour.On the contrary to the usual active filler metals, which require a minimum process temperature of 850°C and must be used either under vacuum or in inert gas atmosphere, the active solders can wet metallic and nonmetallic substrates in an air atmosphere in a temperature range of 200°C-400°C.This extraordinary result is due to traces of rare earth metals (cerium, praseodymium, neodymium), which are alloyed in the matrix...

Microstructural and mechanical analysis on Cu–Sn intermetallic micro-joints under isothermal condition

“…1(a). Such sandwich structure was heated up to 533±1 K to allow Sn melting and reacting with surrounding Cu in a vacuum chamber with 93KPa absolute pressure, and followed by an isothermal storage process with different dwell time (10,30,50,70 minutes). Finally, the specimens were removed from the vacuum chamber and cooled down to room temperature (R.T.) in air.…”

“…The typical description of the metallurgical reaction during this soldering process is Solid-Liquid Interdiffusion (SLID) bonding [7][8] or Transient Liquid Phase (TLP) soldering [9][10]. As reported by references [11][12], the effect of process parameters (such as time, temperature, and pressure) on the microstructure of IMC joints can be significant which requires a further understanding as far as the reliability is concerned.…”

Microstructural Evolution of TLP Bonded Ti3Al-Nb Alloy Joints

“…Therefore, welding and joining of Ti 3 Al-Nb alloys have been a critical factor that will promote the use of them as components. Transient liquid phase (TLP) bonding takes place as a consequence of element diffusion, during which, isothermal solidification of a liquid phase containing melting point depressant occurs to form high melting point materials [13,14]. TLP bonding has been successfully applied for joining some metallic and ceramic systems owing to a number of technological and economical advantages.…”

Active-Transient Liquid Phase (A-TLP) Bonding of Pure Aluminum Matrix Composite Reinforced with Short Alumina Fiber Using Al-12Si-xTi Foils as Active Interlayer

“…[41] Lugscheider et al developed an active solder of Sn91.8/Ag4/Ti4/Ga0.1/Ce0.1 to a wet silicon substrate in microsystem fabrication. [42,43] Huang et al added Ti powder (<3 wt pct) into a mixed Al-Si-SiC powder as an interlayer to improve the wettability of the SiC powder by the liquid Al-Si alloy formed by eutectic reaction in the powder interlayer. They claimed that a dense joining layer was formed for connecting the two SiC p /6063 composites, and no obvious SiC segregation was found in the bond seam.…”