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Reaction kinetics and mechanical properties in the reactive brazing of copper to aluminum nitride
Abstract
Aluminum nitride (AlN) is an attractive substrate material for electronic packaging applications because of its high thermal conductivity and electrical resistivity. However, improved metallization of aluminum nitride is required for reliable conductivity and good adhesion to the ceramic substrate. In this study, the kinetics, microstructure, and mechanical strength of Ag–Cu–Ti/AlN reaction couples have been studied in the temperature range of 900–1,050°C and hold time range of 0–1.44×104s using a eutectic silver–copper filler alloy containing titanium within the range of 2–8wt%. The product layer thickening kinetics has been observed to change from a linear to non-linear thickening mechanism with the increase in holding time and temperature. At shorter hold times at a fixed temperature, the interfacial product layer followed a linear thickening kinetics. With the increase in the hold time, the thickening kinetics of the interface followed a non-linear thickening behavior. The non-linear thickening mechanism has been approximated as a parabolic thickening mechanism. The interface has been found to be rich in the reactive metal (Ti) content. The mechanical strength of the brazed joints has been analyzed using four-point bend tests. The strength of the brazed joints initially increased and then decreased with an increase in the hold time at a fixed temperature. A maximum strength of 196MPa has been obtained for a brazed joint heated at 1,000°C for 2,700s containing 2wt% Ti in the filler alloy. It was observed that the sample with the maximum strength had a discontinuous interface.
... Ti would be released by TiH 2 when the temperature is higher than 723 K (450°C) in a vacuum condition. 29 The mixed fillers were dried in air for 24 hours and compacted into a 100 mg metal cylinder with a diameter of 3 mm for wetting experiments. ...
... Element Ti, released by TiH 2 at 723 K, dissolved into liquid droplets and diffused toward SiC ceramic under the influence of concentration gradient. 29 Owing to the neglectable effect of Ti-Sn reaction and the insufficient diffusion of Ti atoms, SiC could not be wetted by low Ti contenting droplets with almost no reaction products generation at the interface, as shown in Figure 10A 2 . With the addition of Ti, the wettability of liquid droplets on SiC was improved. ...
... When Ti content increasing to 0.5 wt%, sufficient interfacial reactions were guaranteed. Therefore, a high shear strength of [25][26][27][28][29][30][31][32][33][34][35] MPa was achieved and all the joints fracture at seam. ...
The wetting behavior of Sn0.3Ag0.7Cu (SAC) filler with the addition of Ti on SiC ceramic was investigated using sessile drop method. SiC/SiC was brazed by SAC‐Ti filler with different Ti content at 1223 K (950°C) for 10 minutes. The wettability of SAC‐Ti filler on SiC was significantly enhanced with the addition of Ti. The contact angle decreased at first and then increased with increasing Ti content. The lowest contact angle of 9° was obtained with SAC‐1.5Ti (wt%) filler. When Ti content further increased to 2.0 wt%, the contact angle increased, due to the intense reaction of Ti–Sn. The reaction between Ti and SiC controlled the wetting behavior of SAC‐Ti on the SiC substrate and the reaction products such as TiC and Ti5Si3 were formed. The wetting of SAC‐Ti on SiC was reaction‐controlled. Interfacial reaction products TiC and Ti5Si3 were observed. The wetting activation energy in spreading stage was calculated to be 129.3 kJ/mol. Completely filled SiC/SiC joints were obtained using the filler with Ti content higher than 0.5 wt%. The fillet height increased firstly then decreased with mounting Ti content. The shear strength of joints increased first with the addition of Ti then decreased with Ti content increasing to 2.0 wt%. The highest shear strength of 35.7 MPa was obtained with SAC‐1.5 Ti (wt%) filler.
... Aluminum nitride (AlN) ceramic has potential to be applied in electronic industries, such as substrate and packaging material for electronic devices, since it has high thermal conductivity, high electrical resistivity, good electrical insulation, and thermal expansion coefficient close to that of silicon [1,2]. This ceramic is a favorable candidate to replace the Al 2 O 3 and BeO in the manufacture of semiconductor devices [3,4]. Because of the covalent nature of its bonding, AlN ceramic has been sintered using sintering aids, such as alkaline and rare earth oxides, to achieve full densification by the liquid-phase sintering process [3,5]. ...
... For Al 2 O 3 substrates, a pre-oxidized copper foil is bonded to the substrate by a controlled heattreatment in an inert atmosphere between 1065 and 1080 °C, when the copper oxide melts and reacts with Al 2 O 3 to form a copper aluminate (CuAl 2 O 4 ) which results in the joining of both materials [7,8]. For AlN, the DBC process is not easy to apply, since it has poor wettability by metallic Cu and both materials have large difference in thermal expansion coefficient [4,9]. The DBC process can be improved by the surface oxidation of AlN substrate, but the oxidation treatment must be conducted in special conditions to avoid the occurrence of cracking [10,11]. ...
DBC is a process where copper foils are bonded to ceramic substrates for manufacturing hybrid electronic circuits and packages with high power-handling capabilities. For aluminum nitride (AlN) ceramics, a heat-treatment is required to grow an oxide layer to promote the bonding with copper. The oxidation treatment, however, must be conducted in special conditions to avoid the occurrence of severe cracking. In this work, an alternative method is proposed to form an intermediate oxide layers for DBC to AlN substrates. By this method, eutectic powder mixtures (CuO-CaO and CuO-Al2O3 systems) were applied to dense AlN substrates and then heat-treated at 1200 °C for 1 h in air. Different types of AlN ceramics sintered between 1650 and 1700 °C for 4 h in nitrogen atmosphere with additives of the system Y2O3-CaO-SrO-Li2O were investigated. The prepared oxide layers (thickness of ~25 m) presented good microstructural joining with the AlN substrates (characterized by SEM and EDS analysis), and did not affect significantly the thermal conductivity in the working temperature range of electronic devices (~100 to 50 W/m.K determined by laser flash method between 100 and 200 °C) compared to the AlN substrates.
... The active elements (Ti, Cr and Zr) are characterized by their high chemical affinity to oxygen, carbon or boron. In the metal/ceramic systems of Cu-Cr/C [8], Ag-Cu-Ti/AlN [9], Ag-Cu-Ti/SiC [10], Ni-Ti/ Al 2 O 3 [11], Cu-Ti/AlN [9], Cu-Ti/Y 2 O 3 [12], Cu-Ti/SiC [13], Cu-Ti/Al 2 O 3 [14], Cu-Cr/ZrO 2 [15], Cu-Cr/SiC [16] and Cu-Ti/B 4 C [17], the wettability can be significantly improved by the addition of active elements. The addition of Ti to Ag or Cu alloys involves the formation of Ti compounds (TiO x , TiC or TiN on oxides, carbides and nitrides, respectively) [11]. ...
... The active elements (Ti, Cr and Zr) are characterized by their high chemical affinity to oxygen, carbon or boron. In the metal/ceramic systems of Cu-Cr/C [8], Ag-Cu-Ti/AlN [9], Ag-Cu-Ti/SiC [10], Ni-Ti/ Al 2 O 3 [11], Cu-Ti/AlN [9], Cu-Ti/Y 2 O 3 [12], Cu-Ti/SiC [13], Cu-Ti/Al 2 O 3 [14], Cu-Cr/ZrO 2 [15], Cu-Cr/SiC [16] and Cu-Ti/B 4 C [17], the wettability can be significantly improved by the addition of active elements. The addition of Ti to Ag or Cu alloys involves the formation of Ti compounds (TiO x , TiC or TiN on oxides, carbides and nitrides, respectively) [11]. ...
Sessile drop technique was used to investigate the influence of Ti on the wetting behaviour of copper alloy on SiC substrate. A low contact angle of 15or Cu alloy on SiC substrate is obtained at the temperature of 1 100 . The interfacial energy is lowered by the segregation of Ti and the formation of reaction product TiC, resulting in the significant enhancement of wettability. Ti is found to almost completely segregate to Cu/SiC interface. This agrees well with a coverage of 99.8%Ti at the Cu/SiC interface predicted from a simple model based on Gibbs adsorption isotherm. SiC p /Cu composites are produced by pressureless infiltration of copper alloy into Ti-activated SiC preform. The volume fraction of SiC reaches 57%. The densification achieves 97.5%. The bending strength varies from 150 MPa to 250 MPa and increases with decreasing particle size.
... The active elements (Ti, Cr and Zr) are characterized by their high chemical affinity to oxygen, carbon or boron. In the metal/ceramic systems of Cu-Cr/C [8], Ag-Cu-Ti/AlN [9], Ag-Cu-Ti/SiC [10], Ni-Ti/ Al 2 O 3 [11], Cu-Ti/AlN [9], Cu-Ti/Y 2 O 3 [12], Cu-Ti/SiC [13], Cu-Ti/Al 2 O 3 [14], Cu-Cr/ZrO 2 [15], Cu-Cr/SiC [16] and Cu-Ti/B 4 C [17], the wettability can be significantly improved by the addition of active elements. The addition of Ti to Ag or Cu alloys involves the formation of Ti compounds (TiO x , TiC or TiN on oxides, carbides and nitrides, respectively) [11]. ...
... The active elements (Ti, Cr and Zr) are characterized by their high chemical affinity to oxygen, carbon or boron. In the metal/ceramic systems of Cu-Cr/C [8], Ag-Cu-Ti/AlN [9], Ag-Cu-Ti/SiC [10], Ni-Ti/ Al 2 O 3 [11], Cu-Ti/AlN [9], Cu-Ti/Y 2 O 3 [12], Cu-Ti/SiC [13], Cu-Ti/Al 2 O 3 [14], Cu-Cr/ZrO 2 [15], Cu-Cr/SiC [16] and Cu-Ti/B 4 C [17], the wettability can be significantly improved by the addition of active elements. The addition of Ti to Ag or Cu alloys involves the formation of Ti compounds (TiO x , TiC or TiN on oxides, carbides and nitrides, respectively) [11]. ...
Sessile drop technique was used to investigate the influence of Ti on the wetting behaviour of copper alloy on SiC substrate. A low contact angle of 15° for Cu alloy on SiC substrate is obtained at the temperature of 1 100 °C. The interfacial energy is lowered by the segregation of Ti and the formation of reaction product TiC, resulting in the significant enhancement of wettability. Ti is found to almost completely segregate to Cu/SiC interface. This agrees well with a coverage of 99.8%Ti at the Cu/SiC interface predicted from a simple model based on Gibbs adsorption isotherm. SiCp/Cu composites are produced by pressureless infiltration of copper alloy into Ti-activated SiC preform. The volume fraction of SiC reaches 57%. The densification achieves 97.5%. The bending strength varies from 150 MPa to 250 MPa and increases with decreasing particle size.
... During brazing, Al foil first melted during heating due to its low melting temperature of 660 • C. As the temperature was elevated to 779 • C, AgCu foil became liquid as well as Ti foil was dissolved. The element Ti was diffused toward the AlN substrates with the aid of concentration gradient, and reacted with them to produce TiN reaction layer, which has been widely reported [12,[19][20][21][22]. In fact, the chemical reaction between active Ti and AlN could take place according to following equation: ...
The aluminum nitride (AlN) ceramic is a underlying substrate material for high-voltage/power insulated gate bipolar transistors (IGBT), due to its excellent thermal conductivity and low coefficient of thermal expansion (CTE). The high-quality joining between AlN and Cu, which have a huge CTE mismatch and large residual stress remained in the joint, is the prerequisite for the application of AlN in IGBT. In this work, a AgCuTi-Al brazing filler was designed to connect the AlN and pure Cu. The element Al with a low melting point of 660 °C would decrease the brazing temperature, alleviating the residual stress level in the joints. In addition, Al could react with Cu and Ti in the liquid filler to in situ produce AlCu2Ti intermetallic compounds (IMCs), contributing to the mitigation of CTE mismatch and amelioration of joint bond strength. A heterogeneous structure in relieving the residual stresses would be driven based on the modulation of filler composition and joining condition, while the microstructural optimization and enhancement in mechanical properties could be achieved. Based on this, effects of Al content, brazing temperature, and soaking duration on the microstructure and mechanical properties of the AlN/Cu joints were investigated. The formation process and strengthening mechanism of the joints were also discussed. The work performed may provide useful strategies for the manufacture of high-performance packaged substrates in IGBT.
... In view of their brittleness and chemical inertness, engineering ceramics are hard to join with metals [1]. The good joining of these dissimilar materials often requires the use of high temperature and pressure [1,2], pre-processing of surfaces to be joined, and the use of brazing alloys [3][4][5][6][7][8]. ...
Ta/Ti/Ni/ceramic multilayered composites were successfully prepared by combustion synthesis. Laminated composites Ti–Ta–(Ti + 0.65C)–Ni–(Ti + 1.7B)–(Ti + 1.7B)–Ta–Ni-Ti and 3(Ti + 1.7B)–Ta–(5Ti + 3Si)–Ta–(Ti + 1.7B)–Ta–(5Ti + 3Si)–Ta–3(Ti + 1.7B) were combustion synthesized in an Ar atmosphere using (1) metallic foils (Ti, Ta, Ni) and (2) reactive tapes (Ti + 0.65C), (Ti + 1.7B), and (5Ti + 3Si), which, upon combustion, yielded ceramic layers as starting materials. The microstructure, crystal structure, and chemical composition of multilayered composites were characterized by SEM, EDX, and XRD. Their flexural strength was measured at 1100 °C. Upon combustion, Ta foils turned strongly joined with Ti ones due to the development of high temperature in the reactive layers yielding TiCx and TiBy. The formation of a liquid phase between metallic foils and reactive tapes and mutual interdiffusion between melted components during combustion favored strong joining between refractory metallic foils. Good joining between metals and ceramics is reached due to the formation of thin interfacial layers in the form of cermets and eutectic solutions.
... Therefore, brazing is widely used in the connection of two different metals, copper and aluminum, resulting in a joint with high strength and good airtightness [17,18]. Copper and aluminum brazing mainly use Zn-Al, Sn-Zn, and Al-Si brazing materials [19][20][21]. Al-Si brazing materials have good plasticity and are easy to be processed and formed. Compared with Zn-Al brazing filler metal, Al-Si brazing filler metal has better corrosion resistance, and the strength of the brazed joint is much higher than that of Sn-Zn brazing filler metal, so Al-Si brazing filler metal is more suitable for joining dissimilar metals of copper and aluminum [22,23]. ...
To meet the requirements of automatic production, a new type of green BAl88Si cored solder was developed. The lap brazing experiments were carried out with copper and aluminum as brazing substrates. The microstructure, phase composition, and corrosion behavior of solder joint interface were studied by field emission scanning electron microscopy, energy dispersive spectroscopy, transmission electron microscopy, electron backscattering diffraction, tensile testing machine, and electrochemical workstation. The results show that the brazing joint of Cu/BAl88Si/Al is metallurgical bonding, and the brazing joint of Cu/BAl88Si/Al is composed of Cu9Al4, CuAl2, a-Al, (CuAl2 + a-Al + Si) ternary eutectic. In addition, there is no obvious preference for each grain in the brazing joint, and there are S texture {123}<634>, Copper texture {112}<111>, and Brass texture {110}<112>. The interface of Cu9Al4/CuAl2 is a non-coherent crystal plane and does not have good lattice matching. The average particle size of CuAl2 is 11.95 µm and that of Al is 28.3 µm. However, the kernel average misorientation (KAM) value at the brazed joint interface is obviously higher than that at the brazed joint interface copper, so the defect density at the brazed joint interface aluminum is higher than that at the brazed joint interface copper. At the same time, due to poor corrosion resistance at the interface on the aluminum side of the brazed joint, serious corrosion spots and corrosion cracks occur at the same time, which leads to the shear performance of the brazed joint decreasing by about 75% after salt spray test for 240 h.
... Due to the chemical inertness of ceramics, conventional joining methods for metals cannot be used. To obtain adequate bond quality, high temperature and pressure are often required [3] and bonding media with reactive elements have been used [4]. The chemical phenomena occurring at interfaces determine the structure of the interface and hence, its properties. ...
Ceramics and metals are two of the oldest established classes of technologically useful materials. While metals dominate engineering applications, ceramics have some attractive properties compared to metals, which make them useful for specific applications. The properties of individual ceramics and metals can vary widely; however, the characteristics of most materials in the two classes differ significantly. Joints between a metal and ceramic are becoming increasingly important in the manufacturing of a wide variety of technological product. But joining ceramics to metallic materials often remains an unresolved or unsatisfactorily resolved problem. This chapter deals with problems of various studies in recent years on the joining between two materials.
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... This indicates that the phases present in the alumina interface are quite brittle than those belonging to the copper interface. Although based on the work of Ksiazek et al., the joint strength increased as the joint thickness 14) . From this study, for the type B nano-multilayer foils (the atomic ratio between Al and Ti is 3:1), when the thickness of react interface rose from 22 μm to 600 μm, the shear strength signi cantly increased from 9.25 MPa to 68.5 MPa. ...
In this paper, a series of Al/Ti multilayers with different modulation periods were used in copper and Al2O3 ceramic diffusion bonding. The reactive multilayer was deposited by DC magnetron sputtering, and the diffusion bonding experiments were performed at 900℃ for 10 min with a pressure of 5 MPa. The interfacial joints were inspected by scanning electron microscopy (SEM), energy dispersive x-ray spectroscopy (EDS), X-ray diffraction and tensile shear tests. As a result, no significant metallurgical defect was observed in the microstructures of the joints. The formation of several intermetallic compounds at the interface, such as Cu/Ti eutectic and Al2O3-X·TiO compound, has further confirmed the success of Cu-Al2O3 bonding as compared to the Al/Ni nano-multilayers, which use Al/Ti nano-foils as interlayer for diffusion bonding to bring more benefit to the quality of cermet joint.
... The bridging between the central zone of the interface and either SM or SS sample is promoted by the formation of a thin Ti-rich layer. The formation of a thin Ti-rich layer adjacently to aluminum nitride after joining either by active metal brazing ( Ref 6,7,9,10) In the present investigation, when brazing is carried out at 850°C, Ti-rich layer occasionally seems to present a layered morphology (see Fig. 3). However, it was impossible to assess the composition of each sublayer, since they were less than 1 lm thick wherever this apparent morphology was observed at the interface. ...
Shapal™-M machinable AlN-based ceramic and AISI 304 stainless steel were joined by active metal brazing, at 750, 800, and 850 °C, with a dwell stage of 10 min at the processing temperature, using a 59Ag-27.25Cu-12.5In-1.25Ti (wt.%) filler foil. The influences of temperature on the microstructural features of brazed interfaces and on the shear strength of joints were assessed. The interfacial microstructures were analyzed by scanning electron microscopy (SEM), and the composition of the phases detected at the interfaces was evaluated by energy dispersive X-ray spectroscopy (EDS). The fracture surfaces of joints were analyzed by SEM, EDS, and GIXRD (Grazing Incidence X-Ray Diffraction). Reaction between the liquid braze and both base materials led to the formation of a Ti-rich layer, adjacent to each base material. Between the Ti-rich layers, the interfaces consist of a (Ag) solid-solution matrix, where coarse (Cu) particles and either Cu-In or Cu-In-Ti and Cu-Ti intermetallics phases are dispersed. The stronger joints, with shear strength of 220 ± 32 MPa, were produced after brazing at 800 °C. Fracture of joints occurred preferentially not only through the ceramic sample but also across the adjoining TiN layer, independent of the brazing temperature.
... These properties make AlN an excellent material to replace alumina (Al 2 O 3 ) and beryllia (BeO) used for the manufacture of semiconductor devices [5,6]. AlN also has the potential to be used as heat sinks for high operating temperature applications, LED thermal management, laser diode heat spreaders, optoelectronic parts, cutting tools, ignition modules, and casting crucibles [5][6][7][8]. In order to translate the above mentioned thermal properties into demanding applications, it is necessary to net-shape AlN into fully dense microstructures. ...
The effects of nanoparticle addition on the pressureless sintering of injection molded and debound aluminum nitride (AlN) samples were studied. Variations in the densification, microstructure, and properties owing to the increased powder content and reduced particle size are discussed. The results indicate the formation of liquid phase at 1500 °C in the bimodal micro (μ)–nano (n) AlN samples, a temperature that is at least 100 °C lower than typically reported values in the literature. Consequently, a densification ≥ 99% was achieved by pressureless sintering at a relatively lower temperature of 1650 °C with ∼14% isometric shrinkage. Additionally, thermal and mechanical properties of the sintered bimodal AlN samples are presented and compared with sintering studies on conventional monomodal μ-AlN systems reported in the literature.
... These properties make AlN an excellent material to replace alumina (Al 2 O 3 ) and berilia (BeO) used for the manufacture of semiconductor devices. [1][2][3] An understanding of the nature of native defects in materials is needed for the applications because the defect-induced electronic states in the band gap significantly affect the thermal properties. ...
Calcium fluoride additive was used to produce high thermal conductivity AlN ceramics which has no grain boundary phase. Thermal conductivity of AlN is determined by the point defect, represented as oxygen related defect, within the AlN grain. The defect density characterization of high thermal conductivity CaF2 doped AlN ceramics after heat treatment was conducted by Raman spectroscopy. As measure Raman linewidth broadening, the point defect density variation after heat treatment and corresponding thermal conductivity change was investigated.
Refractory NbSS/Nb5Si3 composite has garnered significant attention for aeronautical applications owing to the exceptional high-temperature mechanical property stability. In this study, a novel Ti-Ni-Nb-Zr-Hf high-entropy filler alloy was designed for joining of NbSS/Nb5Si3 composite. The joints brazed at 1260 °C for 10 min revealed a multi-phase interfacial microstructure comprising residual low-melting-point NiTi2 intermetallic, (Nb,Ti,Zr)SS solid solution, and Nb5Si3 intermetallic. Remarkably, extending the isothermal holding duration to 60 min facilitated complete elimination of the NiTi2 phase through interdiffusion, concurrent with a phase transformation from α-Nb5Si3 to γ-Nb5Si3 within the joint region. The orientation relationship between NbSS and γ-Nb5Si3 phase was identified as [013] NbSS//[− 1101] γ-Nb5Si3, (200) NbSS//(1–102) γ-Nb5Si3. The diffusion of Ni into the NbSS/Nb5Si3 substrate followed the Arrhenius law as D = 5.463 × 10−2 exp(− 315,994/RT). Detailed atomic scale analyses revealed that Ni, Si, Zr, and Hf were enriched in the γ-Nb5Si3 phase, while Al, Nb, and Ti were segregated into the NbSS. Combined with first-principles calculations, the increase in Zr content gradually improved the ductility. The joints brazed at 1260 °C for 60 min exhibited three-point bending strengths of 349 MPa at room temperature and 150 MPa at 1200 °C.
The wetting behavior and mechanism of AgCu-Xwt.%Ti filler metal on AlN ceramic were investigated using experiments and first-principles calculations. The results indicate that the interfacial ideal adhesion work of wetting interface after interfacial chemical reaction is a crucial factor influencing the wettability of AgCu-Xwt.%Ti/AlN wetting system. This factor is controlled by the interfacial bonding characteristic. AgCu/AlN ceramic is a non-reactive wetting system, which has poor wettability with a contact angle of 22.9o. When 1.5 wt.% of active element [Ti] is added in AgCuTi filler metal, interfacial chemical reaction occurs, producing TiN. Therefore, the wetting interface is composed of AgCu-1.5 wt.%Ti filler metal after chemical reaction and TiN (ACTi-1/TiN interface), which exhibits a large interfacial ideal adhesion work of 9.908 J/m², leading to a small contact angle of 11.7o. When Ti content increases to 3.0 wt.%, the ionic bonding strength of wetting interface, composed by AgCu-3.0 wt.%Ti filler metal after chemical reaction and TiN (ACTi-2/TiN interface), becomes stronger than that of ACTi-1/TiN interface owing to the increasing residual Ti content. Consequently, the interfacial ideal adhesion work further increases to 9.711 J/m², and a decreasing contact angle of 8.2o is achieved. However, when Ti content reaches to 4.5 wt.%, although residual Ti content in AgCu-4.5 wt.%Ti filler metal after chemical reaction (ACTi-3) is further increased, both covalent and ionic bonding strengths of ACTi-3/TiN interface are closer to those of ACTi-2/TiN interface. This leads to an almost unchanged interfacial ideal adhesion work and contact angle of 9.753 J/m² and 8.1o, respectively.
This work reports on the bonding of Al2O3–Cu, AlN–Cu, and AlN–Ni by active brazing for the thermoelectric module support plate. Ag63Cu35.25Ti1.75 braze alloy in the form of paste and sheet was used for this purpose. Investigation of the microstructure using scanning electron microscope (SEM) attached with energy dispersive spectroscopy (EDS) showed that Al2O3–Cu brazed joint alone had an interface with a continuous reaction layer. On the other hand, AlN when brazed to Cu and Ni showed a relatively weak bonding due to the poorly developed reaction layer at the interface. The growth of reaction layer while brazing of AlN–Cu and AlN–Ni was impeded by the dissolution of the respective metals into the molten braze alloy. In AlN–Ni, the decrease in Ti activity due to such dissolution is so low that the interface reaction layer was absent. The temperature difference (ΔT) measured across the ceramic–metal joints showed little resistance to heat transfer in Al2O3–Cu. On the other hand, other joints have shown a significant ΔT, mainly due to the poorly developed and less thermally conductive (TiAl)1+xN interface reaction layer. Thus, this study demonstrates that a stable ceramic–metal joint with high thermal conductivity could be made with Al2O3 using Cu by active brazing.
Active elements play key roles in improving the interfacial bonding between Ag-based fillers and AlN ceramics. An understanding of the influence mechanism of active elements to interfacial adhesion can help us optimize the composition of active filler metals. In this paper, Ag(111)/AlN(0001) interfaces with different terminations and stacking sequences were constructed first. The N-terminated A-site interface was found to have the largest work of adhesion (Wad). Then, the effects of Si, Ti and V dopants on the Ag/AlN interfacial bonding were investigated via first-principles calculations. The results reveal that the Ti and V dopants can increase the values of Wad significantly. Electronic structure analysis reveals that the Si–N, Ti–N and V–N bonds formed at the interface are mainly ionic, and with some composition of covalent. Ti and V atoms can form strong bonds with not only the AlN slab, but also the neighboring Ag layers. It can be concluded that Ag–Ti and Ag–V active fillers are more suited to braze AlN. Ti–N and V–N compounds formed at the interface can greatly improve the interfacial bonding strength.
The joints with Cu and Al as base materials were brazed by a new BAl88Si filler metal. By using the field emission scanning electron microscope, energy spectrum analyzer and transmission electron microscope (TEM), the three-dimensional morphologies of intermetallic compounds in the brazed joint of filler metal were studied, and the lattice mismatch degree of each IMC interface was emphatically analyzed. The results show that the brazed joint of the filler metal has achieved good metallurgical bonding, and the interface micro structure of the Cu/BAl88Si/Al joint is Cu/Cu9Al4+CuAl2+CuAl2+ CuAl2-a-Al eutectic + α-Al/Al. Among them, Cu/Cu9Al4 has the best lattice matching, and it is a complete semi-coherent crystal plane. The interface of Cu9Al4/CuAl2 is a complete non-coherent crystal surface without. Based on the thermodynamic analysis, the formation and growth sequence of the intermetallic compounds in the brazing process was divided into four stages, and the formation of CuAl2 in the brazing seam was firstly confirmed by Gibbs free energy, followed by the formation of Cu9Al4.
The present contribution is dedicated to a coupling method mixing finite and discrete elements to simulate thermally induced stresses and local damage in composites. Investigations are focused on ceramic-metal materials which are characterized by a strong difference of properties and a coefficient of thermal expansion mismatch. Typically, thermal residual stresses are induced at the interface during a cooling process which can lead to dramatic effects on the local integrity of the joint. Some discrete approaches as the lattice beam model enable to simulate such effects but in some cases lead to prohibitive calculation costs which affect their relevance. As a result, a coupling method taking benefit of both continuous and discrete approaches with a lower computational cost is of great interest. In this work, we investigate the DEM-FEM coupling approach based on a domain decomposition with overlapping area which has already proved its flexibility and its reliability in a large context. However, be aware that what is commonly called DEM-FEM coupling is in fact a beam lattice-FEM coupling approach in which the lattice network is generated using the contact network of a granular assembly. Preliminary studies are first carried out to verify the ability of the coupling method to take into account the thermal expansion in homogeneous medium. In a second step, tests are performed in the framework of ceramic-metal fiber composites and compared to FE simulations in terms of stress and strain fields. Interfacial debonding effects are also studied. Finally, a classical ceramic-metal joint issue with local damage is simulated. In each case, results exhibit the relevance of the present approach to take into account thermal expansion and damage with a suitable accuracy. They also show a significant computation time decrease compared to FEM and DEM.
Direct bonding of copper and porous LaCrO3 without an extra filler interlayer was successfully completed using local and fast Cu‐infiltration through laser cladding. This significantly reduced the susceptibility of the ceramic to cracking. A high‐speed camera investigation into the wetting and infiltration behavior of a Cu‐melt into LaCrO3 with a porosity of ~ 63vol% was performed. By adjusting the focal distance with a constant laser power of 300W, the Cu‐melt was rapidly infiltrated into the ceramic preform in 10 seconds. This was completed under atmospheric air conditions, without added inert gas. The joining process developed can be used to fabricate ceramic/metal joints with targeted (micro‐)structure properties by adjusting the infiltrated melt and the infiltration depth, which would be suitable for many applications, such as multifunctional devices, solid oxide fuel cells or heating elements.
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Hard ceramic materials are used for a wide range of applications in diverse fields such as the automotive industry, machining and forming of metals, and power generation systems. Since most of these applications require complex shape components that cannot be fabricated in one forming step, and typically need to be in close contact to metal parts, the development of suitable joining methods has been essential and critical. Before 2010, several different joining techniques have been developed based on the application and harshness of the working environment. In this chapter, joining techniques for hard ceramics namely alumina, zirconia, silicon nitride, and silicon carbide are reviewed. In particular, solid-state diffusion methods, the active metal brazing technique and the liquid-phase bonding by inserting glass forming ceramic compositions are considered. Additionally, direct bonding and special joining methods such as the transient liquid phase are also discussed, and some examples illustrating joining applications for the specified materials are provided.
In this study, the AlN/Cu bonding was explored using the brazing technique. During AlN/Cu brazing, the temperature was set at 800, 850, and 900 A degrees C for 10, 20, 30, and 60 min, respectively. We studied the bonding mechanism, microstructure formation, and the mechanical characteristics of the bond. The reaction layer developed at the interface of AlN/Cu is observed to be TiN. The activation energy of TiN is about 149.91 kJ/mol. The reaction layer thickness is linearly dependent on the temperature and duration at 800 and 850 A degrees C for 60 min and 900 A degrees C for 30 min. However, the growth of the reactive layers decreases gradually at 900 A degrees C when the duration changed from 30 to 60 min. The strength of the specimens with thickness ranging between 1 and 1.5 mu m is 40-51 MPa.
Copper-AlN- and copper-Si3N4-composites are used as substrates for semiconductor modules in power electronics. Silver-based active brazing alloys are used for the fabrication of composites from copper foils and nitride ceramics. In this study the mechanisms during active metal brazing (AMB) of aluminium nitride and silicon nitride in combination with copper foils were investigated. Therefore the melting process of the braze filler metal, the chemical interactions between the braze filler metal and the raw materials and the influence of the processing parameters were studied in detail using thermo analytic and microscopic methods. Additionally, the fabrication process was tested under close to production conditions and application like samples were fabricated. The combination of lab experiments with low volume productions in industrial relevant processing equipment ensures the transferability of the developed processing models from lab into production. An increase of the AMB process reliability and an associated quality improvement as well as a significant reduction of the rejection rate during fabrication was achieved by optimisation of the active brazing alloys and the processing conditions during the active metal brazing.
Ti-Al system intermetallics and high-temperature ceramics or ceramic matrix composites, are the two kinds of light-mass heat-resistance structural materials with high potential in aerospace applications. According to the published literatures, the research advances on their welding and joining technologies, including the material weldabilities, joint properties with different welding processes and material combinations, and the progresses of studies on the application of the welding and joining technologies were reviewed, and some comments are made on the reporting advances especially in the past two decades. It is pointed out that, development of new high-temperature-tolerance welding consumables or brazing alloys, joining of dissimilar materials, and study on joint assessment and engineering application would be mainly important research areas in future.
Polycrystalline alumina and stainless steel were brazed at 900, 1000 and 1100°C. Microstructural and mechanical property of the interface have been correlated. Interface was characterized by scanning electron microscopy and transmission electron microscopy. SS interface consists of FeTi and Fe35Cr13Ni3Ti7 phase whereas TiO, Al2TiO5 and Cu3Ti3O phases have been found at the Al2O3 interface. Shear strength of the joints was evaluated for different samples and maximum strength of 94MPa has been obtained. Residual stress produced due to the coefficient of thermal expansion mismatch between the substrate and the reaction products at the interface, has been measured by X-ray diffraction technique. Thickness of the interface and the microstructural arrangements of the different reaction products at the interface play a vital role in determining the mechanical property of the joint. Optimum process parameters have been determined.
Engineering ceramics such as alumina, zirconia, silicon nitride and silicon carbide can now be manufactured reliably with reproducible properties. As such, they are of increasing interest to industry, particularly for use in demanding environments, where their thermomechanical performance is of critical importance, with applications ranging from fuel cells to cutting tools. One aspect common to virtually all applications of engineering ceramics is that eventually they must be joined with another material, most usually a metal. The joining of engineering ceramics to metals is not always easy. There are two main considerations. The first consideration is the basic difference in atomic bonding: the ionic or covalent bonding of the ceramic, compared to the metallic bond. The second consideration is the mismatch in the coefficient of thermal expansion. In general, ceramics have a lower coefficient of thermal expansion than metals and, if high tensile forces are produced in the ceramic, either as a consequence of operating conditions or from the joining procedure itself, failure can occur. The plethora of joining processes available will be reviewed in this article, placing them in context from both an academic and commercial perspective. Comment will be made on research reporting advances on known technology, as well as introducing ‘newer’ technologies developed over the last 10 years. Finally, reviews and commentary will be made on the potential applications of the various joining processes in the commercial environment.
AlN with 4wt.% Y2O3 or CaO were prepared by sintering in dilatometer and conventional furnace up to 1850°C. The aim of this work was to compare
the sintering behavior and mechanisms related with the densification of AlN with Y or Ca-containing additives. The sample
with Y2O3 approached 33% of total densification by solid-state sintering process preceding the liquid phase formation, which was near
1700°C. After the formation of liquid an overheating of only 50°C was needed for this sample to achieve full density. The
sample with CaO formed liquid-phase near 1400°C, but required a higher overheating (>300°C) in order to achieve full density.
The densification of the sample with CaO was retarded by: (i) high viscosity of the liquid-phase formed below 1600°C; (ii)
formation of large pores; and (iii) gas entrapped inside the pores.
AlN is used as high power LED package material because of its excellent thermal conductivity. But its poor adhesive with metal
is not compatible with the later processing sequence. The properties of the bonding between the deposited palladium, silver,
copper and the clean Al-terminated (0001) surface of wurtzite AlN are investigated by using the density-functional theory.
The results show that the sites of deposited metal atoms on N site are more stable than that on Al site. Relaxations are found
at all the studied interfaces. The bonding energies of Pd/AlN, Ag/AlN and Cu/AlN are respectively 2.75, 1.98, 2.26 eV. Hybridizations
of s orbit and p orbit of the deposited metal atoms are observed, which contributes to the bonding energy of interface. The
moving to lower energy state of the d orbit and the easier transfer of electrons to semi-empty d orbit in the case of deposited
Pd results in the higher bonding energy of Pd/AlN interface.
Keywordspalladium–silver–copper–AlN–clean Al-terminated (0001) surface–density-functional theory
Diffusion couples of AlN/V were experimentally examined after annealing in a temperature range of 1373 K1773 K for a bonding time range of 0.9 ks21.6 ks. The interfacial reaction, reaction mechanism, and bond strength of the bonded AlN/V couples have been explained on the basis of phase relations at different bonding conditions, making use of elemental analysis, XRD, and shear testing method. Formation of V(Al) solid solution and V2N nitride controls the interfacial joining of the AlN/V couples. A complete diffusion path between AlN and V could be predicted at 1573 K before 0.9 ks, following a sequence of AlN/V(Al)/V2N/V. This sequence can be discussed during the Al-V-N ternary phase diagram. At a high temperature of 1573 K, AlN decomposition at the interface took place. A maximum bond strength could be obtained for a joint bonded at 1573 K after 5.4 ks, having a structure of AlN/V(Al)/V2N + V.
Great progress in LSI (large-scale integration) has been made over the past 10 years, and more rapid progress is expected in the future. In recent years, the increased circuit density in LSI devices has led to remarkable heat generation, thereby creating thermalmanagement issues for microelectronics packaging. In order to develop highperformance LSI effectively, packaging and system-level configuration of the computer must be modified to handle the heat.
Brazing of aluminum nitride to copper was performed using Ag-Cu-Ti, Ag-Cu-Ti-Co and Ag-Cu-Ti-Nb brazing filler metals in an argon atmosphere. The reaction layer formed at the interface between AlN and braze layer in Aln-Cu joints was found to increase by increasing brazing time for all brazing filler metals used. In the case of the filler metal Ag-Cu-Ti-Nb, a thinner reaction layer was formed in comparison with the cases of using other filler metals. Form an EPMA analysis, it was found that not only Ti, but also Nb were concentrated in this thin reaction layer. From XRD analysis, it was found that TiN lattice was distorted by Nb addition. Shear strengths were measured for AlN-W joints at room temperature. The joint brazed at 1173 K for 0.3 ks using Ag-Cu-Ti filler metal showed a strength of 118 MPa. In the case of using Ag-Cu-Ti-co filler metal, almost the same shear strength, 116 MPa, was obtained after brazing at 1173 K for 0.6 ks. The joints brazed at 1173 K for 0.3 ks using Ag-Cu-Ti-Nb filler metal exhibited the maximum shear strength 147 MPa. The shear strength of the joints was discussed in relation to the thickness of the reaction layer.
We studied the reactions of Ti and Zr with AlN, 99.8% Al2O3 and 95% Al2O3. The substrates were chosen to represent a simple nitride (AlN), a simple oxide (99.8% Al2O3), and a simple oxide with a silicate grain boundary phase (95% Al2O3). The activities of the Ti and the Zr were varied by dissolving them at 1 and 5 wt% in the 72 Ag-28 Cu eutectic composition, which is otherwise unreactive with the ceramics. Reactions were studied by measuring the variation of the alloy contact angle on the ceramic with time at temperature and by determining the compositions of interfacial reaction products. Contact angles were lower for Ti alloys than for those containing Zr. Reaction products were primarily the nitrides of Zr and Ti for reaction with AlN and the respective oxides for reaction with Al2O3. Complex alloy phases were found in the metal away from the ceramic-metal reaction zone.
The joining of aluminum nitride by active metal brazing with a Ag–Cu–Ti foil has been investigated in cross section by transmission electron microscopy. The reaction of AIN with the braze alloy results in the formation of continuous TiN and (Ti, Cu, Al)6N (η-phase) layers at the interface. AIN grains at the interface often display arrays of dislocations, presumably arising from thermal expansion mismatch between the AIN and the TiN (the coefficients of thermal expansion are 43 ⊠ 10−7/°C and 80 ⊠ 10−7/°C, respectively). The adjoining TiN contains small Cu precipitates and may also contain numerous defects. Titanium preferentially penetrates the AIN grain boundaries, resulting in finger-like TiN intrusions into the substrate, which sometimes cover entire AIN grains in a TiN shell. On the other side of the TiN, a continuous layer of equiaxed, defect-free η–nitride grains is found. Beyond this η–nitride layer is the remaining mixture of metallic Ag and Cu. High-resolution electron microscopy demonstrates that the AIN–TiN and TiN–η boundaries are abrupt and contain no additional crystalline or amorphous intervening phases. Particular orientation relationships are occasionally observed at the AIN–TiN interface; these are not always the ones that produce the minimum lattice mismatch. The implications of the observed morphology with respect to the reaction sequence, transitional phases, and structural integrity of the joint are discussed.
Brazing of aluminum nitride (AlN), which is a good ceramic substrate in high power electronic applications, to copper was investigated using In-base active fillers. Compositions of brazing fillers were chosen as In–1 wt.% Ti (IT1), In–19 wt.% Ag–2 wt.% Ti (IAT2), In–15 wt.% Ti (IT15), and In–52 wt.% Ag–20 wt.% Cu–3 wt.% Ti (ACIT3). Brazing operation was performed in vacuum at temperatures of 650–900 °C. The brazing fillers showed good wetting on AlN and led to a strong bond between AlN and braze alloy. From the microstructural analysis, no evidence of reaction layer was clearly found at the interface under the experimental brazing conditions. The composition of brazing alloy layer changed into Cu9In4 phase due to the extensive dissolving of Cu from base metal. Bond strength, measured by 4-point bend test, was obtained as high as 23–30 kgf for the Cu/AlN/Cu joint brazed with IT15 and ACIT3 fillers, and shown to be nearly constant even when the temperature was varied within 700–800 °C. Most of the fracture appeared to proceed through the interior of the AlN ceramic. Based on the experimental results, it is believed that a strong bonding between AlN and braze alloy can be achieved without the apparent forming of a Ti-rich reaction layer at the interface.
Interdiffusion and reaction at the interface between titanium thin films and AlN have been studied by using Rutherford backscattering spectrometry and transmission electron microscopy. Ti2AlN is formed as a result of reaction with titanium and AlN at temperatures of 800°-950°C. The activation energy for Ti2AlN formation in the temperature range of 800°-850°C is 224 kJ/mol, which is similar to that of nitrogen diffusion in titanium. Therefore, the formation of Ti2AlN is believed to be controlled by the diffusion of nitrogen in titanium.
In: Principles of soldering and brazing, Ch 1–2
- G Humpston
- Dm Jacabson
In: Chemical kinetics
- Kl Laider
In: ART handbook of advanced ceramic materials
- Ptb Shaffer
- T J Mroz