Solidification and interfacial interactions in gold–tin system during eutectic or thermo-compression bonding for 200 mm MEMS wafer level hermetic packaging

In this work, Au–Sn eutectic bonding and Au–Sn thermo-compression bonding are studied for applications in hermetic packaging at wafer level. Eutectic bonding experiments were performed under vacuum or pure nitrogen at temperatures between 300 and 350 °C while thermo-compression bonding experiments were performed under vacuum at 270 °C. During these experiments, the solidification of electrodeposited Au–Sn alloy as well as the interaction of this alloy with W₂N layers are studied. Some supplementary specific brazing experiments were performed using commercial sheets of eutectic Au–Sn alloy in order to understand the mechanisms of interactions between the Au–Sn alloy and the W₂N layer and of solidification of the Au–Sn eutectic alloy. The melting and solidification process of eutectic Au–Sn alloy were studied by differential scanning calorimetry under different geometrical configurations such as commercial eutectic Au–Sn sheets alone, brazing joints performed by commercial eutectic Au–Sn alloy and samples made by thermo-compression bonding. Bonded wafers with good mechanical properties were characterized by cross-section scanning electron microscopy using energy dispersive X-ray mode. Some samples were characterized by transmission electron microscopy. The mechanical strength of the seal was checked by shear tests.     

冷喷涂Zn粉后5083铝合金的中温钎焊研究

以添加了5%(质量分数,下同)CsF-AlF3共晶钎剂的Zn粉为原料,采用冷喷涂技术在5083铝合金表面制备涂层,喷涂后的5083铝板在530℃进行钎焊连接。采用扫描电子显微镜结合能谱仪对涂层的显微结构及钎焊后的接头组织形貌进行观察与分析。结果表明:涂层与5083基体连接致密,钎剂颗粒呈絮状存在于Zn粒子交界面处;由于涂层对5083基体的保护,钎焊时5083基体表面没有出现Mg元素上浮现象,表面未形成复杂的氧化膜,530℃喷涂后的5083与1060可成功实现连接;钎焊接头组织均匀,主要由α铝基固溶体和β富锌基固溶体组成,存在少量孔洞缺陷。     

Reactive brazing of Al alloy to Mg alloy using zinc-based brazing alloy

According to the feature of Mg–Zn eutectic reaction, Al alloy was bonded to Mg alloy by contact reaction brazing using a zinc-based brazing alloy successfully. The experimental observations showed that Mg–Al intermetallic compounds were avoided for the addition of the zinc-based brazing alloy. The Mg substrate and the remanent brazing alloy were bonded with the reaction zone that formed along the zinc rich and magnesium poor interface. Only a few Mg–Zn intermetallic compounds (MgZn2) existed homogeneously in the reaction zone. The substrate and the remanent brazing alloy were bonded with a thin Al–Zn solution. The average tensile-shear strength of the final joints was a little lower than that of the zinc-based brazing alloy owning to some pores at the interface between the reaction zone and the remanent brazing alloy layer.     

Microstructure and XRD analysis in the brazing zone of a new WC-TiC-Co hard alloy

The microstructure and phase constituent near the brazing interface of a new WC-TiC-Co hard alloy was investigated by means of a scanning electron microscope, X-ray diffraction and an electron probe microanalysis. Test results indicated that the brazing joint with the interface combined excellently and can be obtained by using a Cu-Zn-Ni brazing filler alloy and by controlling the technology parameters. The microstructure of the brazing filler alloy is α+β eutectic. The brazing interface consists of WC, TiC, CuZn (α phase), and α-Co phase. There are no micro defects (such as microcracks, inclusions, etc.) near the interface.     

Microstructure of brazed joints between mechanically metallized Si<Subscript>3</Subscript>N<Subscript>4</Subscript> and stainless steel

Brazing has been increasingly used to join metals to advanced ceramics. Brazing covalent materials requires either the use of active filler alloys or the previous metallization of the surface. To that end, a new and simple mechanical technique has been applied to metallize advanced ceramics, thus avoiding the use of costly Ti-based active filler alloys. The mechanical metallization of Si₃N₄ with Ti was employed as an alternative route to deposit active metallic films prior to brazing with stainless steel using 72% Ag--28% Cu or 82% Au—18% Ni eutectic alloys. The brazing temperatures were set to 40°C or 75°C above the eutectic temperature of each filler alloy. Ti-films of average thickness 4 μm produced adequate spreading of both filler alloys onto Si₃N₄ substrates, which were subsequently brazed to stainless steel. The interface of Si₃N₄/310 stainless steel basically consisted of a reaction layer, a precipitation zone and an eutectic microconstituent. Mechanically sound and vacuum-tight joints were obtained, especially upon brazing at relatively lower temperatures. Increasing the brazing temperature resulted in thermal cracking of the Si₃N₄, possibly due to increased thermal stress.     

A copper-base brazing alloy for electronics industries

A copper-based alloy with suitable additives has been developed. Major applications are envisioned in the electronics and vacuum-tube industries. The developed alloy with only half the quantity of silver is less expensive than the standard Ag-Cu eutectic alloy and possesses comparable brazing characteristics.     

LF2/LD7铝合金管板高频感应钎焊工艺研究

目的为高频感应钎焊在LF2/LD7铝合金管板焊接应用中提供理论基础。方法选取内径为8.6 mm、壁厚为1 mm的LF2铝合金管和厚度为5 mm的LD7铝合金板,采用高频感应钎焊焊接异种铝合金管板结构。焊接过程中对比添加或不添加碳棒辅助的情况,研究不同钎焊参数下的钎焊接头微观组织和显微硬度,分析碳棒辅助对高频感应钎焊的影响,利用EDS分析钎缝不同组织元素含量。结果最佳工艺参数为:距离D=7 mm,电流I=28 A,加热时间t=80~140 s。当电流增至I=35 A,其他焊接参数不变,添加碳棒辅助可以改变管板形貌,明显降低管烧损程度,组织低熔共晶体含量增多,晶粒细小。结论钎焊接头成形较好,钎缝区组织显微硬度高于母材区组织硬度,钎缝区元素出现偏聚现象。     

Vacuum brazing of NiTi alloy by AgCu eutectic filler

Abstract

Joining of NiTi alloy to itself has been realised by vacuum brazing process using AgCu28 eutectic as filler metal. Microstructures, mechanical and shape memory behaviour have been investigated. The shearing strength of the brazed joint exceeds 100 MPa, and rupture occurs at the diffusion layer of parent metal beside brazing metal. The brazed joint will be stronger than parent metal on condition of the specimen with a joint of lap length 10 times of plate thickness. The brazed specimen shows a good shape memory behaviour. From the point of view of practice, the brazing joint design principle and brazing quality improvement have been discussed.     

Brazing of SiC and SiCf/SiC composites performed with 84Si-16Ti eutectic alloy: microstructure and strength

The microstructure and strength of brazed joints for monolithic SiC and SiC_f/SiC composites are presented and discussed; the brazing technique is based on the use of the 84Si-16Ti (at%) eutectic alloy. The rather low melting point of the used alloy allows to avoid a degradation of the fibre/matrix-interfaces in the composite materials. All the joints did not show any discontinuities and defects at the interface and revealed a fine eutectic structure. Moreover, in the case of composites, the joint layer appeared well adherent both to the matrix and the fibre interphase, and the brazing alloy infiltration looked sufficiently controlled. High resolving electron microscopic investigations of the microstructure and of the nanochemistry (HREM, EELS, esp. ELNES) revealed atomically sharp interfaces without interdiffusion or phase formation at the interlayer leading to the conclusion that direct chemical bonds are responsible for the adhesion. The joints of SiC_f/SiC composites showed 71 ± 10 MPa shear strength at RT and nearly the same values at 600°C.     

Vacuum brazing of carbon nanotube bundles

We have investigated vacuum brazing of CNTs with a eutectic alloy (Ag_xCu_y) doped with Ti. Bonding is confirmed to involve formation of covalent bonds between Ti and C atoms. The brazing in vacuum leads to the interdiffusion of Ti and C atoms and reaction at the joining interfaces. This joining process is promising for volume production with low cost and a low contact resistance.     

Brazing of AlN to SiC by a Pr silicide: Physicochemical aspects

In view of their very different thermomechanical properties, joining of metals to ceramics by brazing is usually performed by means of one or more interlayers. In a recent investigation AlN was chosen as interlayer material for brazing SiC to a superalloy. The aim of the present study is to determine an alloy with a high melting point (close to 1200 °C) enabling brazing of AlN to SiC. Two types of experiments are performed with a Si-17 at.% Pr eutectic alloy (T_m = 1212 °C): sessile drop experiments to determine wetting and brazing of AlN and SiC plates to determine gap filling. Experiments are carried out in high vacuum to promote deoxidation. Interfacial reactivity, joint microstructure and type of failure occurring during cooling are examined by optical and scanning electron microscopy.     

Microstructure of alumina ceramic/Ag–Cu–Ti brazing alloy/Kovar alloy joint

Abstract

The microstructure of the alumina ceramic/Kovar alloy joint brazed with Ag–35·2Cu–1·8Ti (wt-%) was studied. The effects of brazing temperature on the microstructure were also discussed. It was found that the microstructure of the joint brazed at 1173 K for 5 min was TiO + TiNi₃ + TiFe/eutectic Ag–Cu/TiFe₂ + TiNi₃/TiFe₂ + Cu (s.s) +Ag (s.s). When the brazing temperature was >1193 K, there was no TiO formed on the alumina ceramic/brazing alloy interface.     

Al-Ti异种合金真空钎焊的研究

在结合界面上生成层状的脆而硬的金属化合物（TiAl3,TiAl和Ti3Al)是Al-Ti异种合金焊接所存在的主要问题,本工作基一协内外研究成果和相关资料,利用正蛟设计在理,以Al-11.5Si近共晶合金为基,通过添加元素Sn和Ga形成9种钎料,并利用各新钎料对Al合金和Ti合金进行了真空钎焊,勇于强度试验和铺展性试验,对该9种钎料进行评定,试验结果表明,含10％Sn,0.20%GAa的Al-11.5Si铝基钎料铺展性和抗剪强度等方面都具有较好的性能,使Al-Ti异种合金构件达到较好的机械性能。     

电触头感应钎焊工艺研究

对Ag-CdO触头与Cu触桥的感应钎焊工艺进行了系统的研究。分析了钎焊温度、保温时间、钎焊间隙对钎着率、组织形态和力学性能的影响规律，并确定了钎着率和组织形态均为良好的最佳工艺规范。通过分析表明：钎料中锌元素烧损是钎缝生成共晶体组织的本质所在；触头的针焊强度不仅与钎着率有关，而且还受钎缝组织形态的影响，即当钎着率在75％以上时，触头钎焊强度随钎缝中共晶体组织的增加而降低。因而应从钎着率和组织形态两方面综合考核触头的针焊质量。     

Microstructural evolution of brazing 422 stainless steel using the BNi-3 braze alloy

The 422 stainless steel (422SS) is one of the typical martensitic stainless steels with both excellent creep strength and corrosion resistance up to 650°C. Its application includes steam turbine blades, high temperatures bolting ... etc. Repair welding of 422SS is one of the most common methods to fix the turbine blade. However, repair brazing of surface shallow cracks, e.g., less than 1 mm in depth, is an alternative way to fix such blades. The microstructural evolution of brazing 422SS with BNi-3 braze alloy using both infrared and furnace brazing was performed in the study. Based on the experimental results, BNi-3 cannot effectively wet 422SS substrate below 1025°C. As the brazing temperature increases above 1050°C, comprehensive wetting can be obtained in 1200 sec. For the infrared brazed specimen with a short brazing time, the cooling path starts from the formation of a BNi₃ phase in the molten braze, subsequently forms a Ni-rich phase, and finally a eutectic phase is solidified from the residual eutectic liquid. The microstructure of the furnace-brazed specimen is similar to that of infrared brazed specimen, but the interfacial reaction zone is significantly increased in furnace brazing. There are Kirkendall voids in the braze close to the interface between BNi-3 and 422SS, and the size of Kirkendall porosity is increased with increment of the brazing time and/or temperature. The homogenization treatment of the brazed joint at 900°C results in growth of both the interfacial reaction zone and porosity.     

Microstructure and bond strength of Ni-Cr steel/Si3 N4 joint brazed with Ag-Cu-Zr alloy

Abstract

The interfacial microstructure and bond strength were examined for a Ni-Cr steel/Si3 N4 joint brazed using an Ag-Cu eutectic alloy containing 5 wt-%Zr. The reaction of Si₃N₄ with the brazing alloy formed a very thin ZrN layer with a cubic structure (a = 4.577 Å) at the interface. No Zr silicide (Zr₅Si₃) was present at the interface even though its formation is thermodynamically possible. The reaction product did not contain any of the dilute ceramic phases or intermetallics which are commonly seen in other active metal brazing systems. This strongly implies that the elements of the Ni-Cr steel and Ag or Cu in the brazing alloy, did not participate in the interfacial reaction. The shear strength of the joint was strongly dependent on the thickness of the reaction layer and the morphology of CuZr₂ precipitates in the brazement. A joint with a reaction layer thickness of 0.5 μm, which was formed by brazing at 950°C for 30 min, showed the highest fracture shear strength (～ 202 MPa).     

有机胶体黏附力作用下的钎焊工艺

利用有机胶体的黏附作用力改善待连接表面的界面张力,可为实现异种材料间的钎焊连接提供有利条件。以环氧树脂为黏性胶体,TiH_2粉为活性元素源,AgCu共晶合金箔为钎料,将TiH2与环氧树脂混合后涂敷在SiO_2f/SiO_2复合材料表面,并在此表面进行钎料润湿实验。结果表明:胶体黏附力对钎料的润湿铺展具有促进作用。将此工艺用于钎焊连接,可实现SiO_2f/SiO_2复合材料、Cf/SiC复合材料以及Al_2O_3陶瓷与Invar合金的冶金致密连接。     

Joining of C/C composite to TC4 using SiC particle-reinforced brazing alloy

Silicon carbide particles were used as reinforcement in the Ag-26.7Cu-4.6Ti (wt.%) brazing alloy for joining C/C composite to TC4 (Ti-6Al-4V, wt.%). The mechanical properties of the brazed joints were measured by shear strength testing. The effects of the volume percentage of SiC particles on the microstructures of the brazed joints were investigated. It is shown that the maximum shear strength of the joints is 29 MPa using 15 vol.% SiC in the brazing alloy which is greater than that with Ag-26.7Cu-4.6Ti brazing alloy alone (22 MPa). Ti is reacted with SiC particles, forming Ti–Si–C compound in the particle-reinforced brazing alloy. Due to this, more SiC particles in the brazing alloy, the thickness of TiC/TiCu reaction layer near C/C composite decreases. Moreover, SiC particles added to the brazing alloy can reduce the CTE of the brazing alloy which results in lower residual stress in the C/C composite-to-metal joint. Both of the above reasons lead to the increasing of the shear strength of the brazed joints. But excessive SiC particles added to the brazing alloy lead to pores which results in poor strength of the brazed joint.     

The microstructure and mechanical properties of fluxless gas tungsten arc welding–brazing joints made between titanium and aluminum alloys

Butt joining of a titanium alloy to an aluminum alloy by gas tungsten arc welding–brazing using an Al-Si eutectic filler wire without flux is investigated. The butt joints have dual characteristics, being a welding on the aluminum side and a brazing on the titanium side. The thickness of the reaction layer varies with position in the titanium alloy interfacial area of the joint, ranging from 2 to 5 μm. At the upper part of interfacial area, the reaction layer includes only the rod-like TiAl₃ phase with 10 at.% dissolved Si. At the bottom of interfacial area, the reaction layer consists of the needle-like τ1 phases (Ti₇Al₅Si₁₂) and the block-like TiAl₃ phase. Hardness of the reaction layer near the welded seam/Ti alloy interface was as much as 400–500 HV. The highest tensile joint strength observed was 158 MPa. Tensile joint failure was by cracks initiating from the reaction layer at the bottom of the joint propagating into the welded seam at the upper part of the joint.     

Evaluation of transient liquid phase bonding between nickel-based superalloys

Induction brazing of Inconel 718 to Inconel X-750 using Ni-7Cr-3Fe-3.2B-4.5Si (wt.-%) foil as brazing filler metal was investigated in this paper. Brazing was conducted at the temperature range 1373–1473 K for 0–300 s in a flow argon environment. Both interfacial microstructures and mechanical properties of brazed joints were investigated to evaluate joint quality. The optical and scanning electron microscopic results indicate that good wetting existed between the brazing alloy and both Inconel 718 and Inconel X-750. Microstructures at joint interfaces of all samples show distinct multilayered structures that were mainly formed by isothermal solidification and following solid-state interdiffusion during joining. The diffusion of boron and silicon from brazing filler metal into base metal at the brazing temperature is the main controlling factor pertaining to the microstructural evolution of the joint interface. The element area distribution of Cr, Fe, Si, Ni and Ti was examined by energy dispersive X-ray analysis. It was found that silicon and chromium remain in the center of brazed region and form brittle eutectic phases; boron distribution is uniform across joint area as it readily diffuses from brazing filler metal into base metal. The influence of heating cycle on the microstructures of base material and holding time on the mechanical properties of brazed joint were also investigated.