Effect of Pd thickness on wettability and interfacial reaction of Sn-1.0Ag-Ce solders on ENEPIG surface finish

The wetting balance test was used to study the wettability of Sn-1.0Ag-Ce (Ce content = 0, 0.1, 0.3, and 0.5 wt%) solder alloys on electroless nickel/electroless palladium/immersion gold (ENEPIG) surface finishes with Pd thicknesses of 0, 0.05, 0.1, and 0.15 μm. Scanning electron microscopy was used to evaluate the interfacial reaction between the molten solders and surface finish materials during the wetting test. The Ni₃Sn₄ intermetallic compound (IMC) plays an important role in promoting wetting properties. The Pd layer retards formation of the Ni₃Sn₄ IMC and changes its morphology, thereby affecting the wettability of the surface finish/solder systems. ENEPIG surface finishes seem to be suitable for use with cerium-containing solders.     

Joining of sialon ceramics by Sn-5 at % Ti based ternary active solders

The effect of a third element, such as silver, copper, indium, nickel or aluminium, on the joining of sialon ceramics with tin-5 at % titanium based ternary active solders was investigated. The content of the third element in the Sn-based solders was varied from 5–40% for Cu, from 5–10% for Ag and Al from 5–20% for In and from 1–5% for Ni. The joining was carried out in vacuum at 1100 K for 20 min. The four point bend testing of a butt joint of a ceramic/ceramic structure with dimensions 40 mm long, 3 mm wide and 4 mm high was used to study the bond strength between the ceramic and the Sn-based solders. The results show that the bond strength of the Sn-based solder with the sialon ceramic varied from 54–103 MPa. Small additions of Cu or Ag (about 5–10%), In (about 5–10%), or Ni (about 1–3%) to the solder is beneficial, but too much Ni (more than 5%) or In (more than 10%) is detrimental. On the other hand, Al in the active solder considerably decreased the bond strength of the solders with the ceramic. Suggestions are made for the selection of the third element in order to improve the bond strength of the soft solders with the ceramic. These include a high surface energy, improving the wetting of the solder on the ceramic and strengthening of the solder. This revised version was published online in November 2006 with corrections to the Cover Date.     

Microstructure and kinetic analysis of the properties and behavior of nickel (Ni) nano-particle doped tin–zinc–bismuth (Sn–8Zn–3Bi) solders on immersion silver (Ag)-plated copper (Cu) substrates

In order to identify the effect on the properties and behavior of tin–zinc–bismuth (Sn-8 wt% Zn-3 wt% Bi or Sn-13.6 at.% Zn-1.6 at.% Bi) based solders produced by adding nickel (Ni) nano-particles, the interfacial microstructure between plain and composite solders with newly developed immersion silver (Ag) plated copper (Cu) substrates has been investigated as a function of reaction time, at various temperatures. For plain Sn–8Zn–3Bi solder joints, a scallop-shaped Cu–Zn–Ag intermetallic compound layer was found to adhere to the surface of the immersion Ag-plated Cu substrate. However, after addition of Ni nano-particles into the Sn–8Zn–3Bi solder, Cu–Zn–Ag (at the bottom) and (Cu, Ni)–Zn (at the top) intermetallic compound layers were observed at the interfaces. In addition, these intermetallic compound layer thicknesses increased substantially with increases in the temperature and reaction time. In the solder ball region, needle-shaped α-Zn rich phase and spherically-shaped Bi-particles appeared to be homogeneously distributed throughout a beta-tin (β-Sn) matrix. However, after the addition of Ni nano-particles, needle-shaped α-Zn rich phase appeared that exhibited a fine microstructure, due to the heterogeneous nucleation of the Ni nano-particles. The calculated activation energy for the Cu–Zn–Ag intermetallic compound layer for the plain Sn–8Zn–3Bi solder/immersion Ag-plated Cu system was 29.95 kJ/mol—while the activation energy for the total [Cu–Zn–Ag + (Cu, Ni)–Zn] intermetallic compound layers formed in the Sn–8Zn–3Bi–0.5Ni (Sn-13.6 at.% Zn-1.6 at.% Bi ~1 at.% Ni) composite solder/immersion Ag-plated Cu system was 27.95 kJ/mol. Addition of Ni nano-particles reduces the activation energy which enhanced the reaction rate as we know that lower the activation energy indicates faster the reaction rate.     

Effect of TiO<Subscript>2</Subscript> nanoparticles on the microstructure and bonding strengths of Sn0.7Cu composite solder BGA packages with immersion Sn surface finish

This study investigated the effects of TiO₂ nanoparticles on the interfacial microstructures and bonding strength of Sn0.7Cu (SC) composite solder joints in ball grid array packages with immersion Sn surface finishes. The addition of TiO₂ nanoparticles to SC solders resulted in significant changes in the interfacial microstructure. The nanoparticle addition suppressed the growth of the Cu₆Sn₅ IMC layer, significantly improving shear strength and reliability of solder joints after multiple reflows. The fracture surfaces of the SC solder exhibited a semi-brittle fracture mode with a relatively smooth surface, while those of the SC composite solder showed typical ductile failures with very refined dimpled surfaces.     

Effect of addition of TiO2 nanoparticles on the microstructure,microhardness and interfacial reactions of Sn3.5AgXCu solder

In this work, TiO₂ nanoparticles were successfully incorporated into Sn3.5Ag and Sn3.5Ag0.7Cu solder, to synthesize novel lead-free composite solders. Effects of the TiO₂ nanoparticle addition on the microstructure, melting property, microhardness, and the interfacial reactions between Sn3.5AgXCu and Cu have been investigated. Experimental results revealed that the addition of 0.5 wt.% TiO₂ nanoparticles in Sn3.5AgXCu composite solders resulted in a finely dispersed submicro Ag₃Sn phase. This apparently provides classical dispersion strengthening and thereby enhances the shear strength of composite solder joints. After soldering, the interfacial overall intermetallic compounds (IMC) layer of the Sn3.5AgXCu lead-free solder joint was observed to have grown more significantly than that of the Sn3.5AgXCu composite solder joints, indicating that the Sn3.5AgXCu composite solder joints had a lower diffusion coefficient. This signified that the presence of TiO₂ nanoparticles was effective in retarding the growth of the overall IMC layer.     

Sn3.0Ag0.5Cu3.0Bi钎料对化学镀镍SiCp/6063Al复合材料真空钎焊接头组织和性能的影响

采用Sn3.0Ag0.5Cu3.0Bi软钎料对镀镍后的两种不同体积比SiC_p/6063Al复合材料进行真空钎焊。通过SEM、剪切试验等方法分析了化学镀镍后SiC_p/6063Al复合材料真空钎焊接头的显微组织以及保温时间对接头性能的影响。结果表明:两种不同体积比SiC_p/6063Al复合材料真空钎焊后的焊缝组织致密,钎料对镀镍复合材料的润湿性良好;在270℃、保温35min的钎焊工艺下,钎焊接头的剪切强度最大值为38.3 MPa;钎料中的Sn、Cu元素能够与复合材料表面的Ni层发生化学反应,实现钎料与母材的冶金结合;镀镍后SiC_p/6063Al复合材料真空钎焊接头断裂形式为韧性断裂为主的混合断裂,断裂主要发生在钎料内部,部分发生在镀镍层与钎料的结合处。     

Direct robust bonding between Sn-based solder and Si substrate

The robust bonding between silicon and low melting point solders composed of Sn–Ag solder with addition of Ce and Nd rare earth (RE) element is obtained. The content of the RE element is 2, 5 wt.%, respectively. The RE elements are stored as island compounds in the solder matrix and their addition has little effect on the melting point of the Sn–Ag solder. When soldering at 250 °C, the intermetallic compounds (IMC) layer is discontinuous and the bonding strength is lower. While soldering at 300 °C, the IMC layer become continuous and stronger bonding strength is obtained. The addition of 5 wt.% RE can result in higher bonding strength than that of 2 wt.% RE. In the present research work, we find that in order to get strong bonding between the Si substrate and the composite solders, suitable pressure should be employed to overcome the oxide skin of the liquid solders formed during soldering. The interfacial structure and fracture analysis of the solder joints are investigated to reveal the bonding nature. Complex IMC are found in the residual IMC layer after shear test. Therefore it is clear that RE elements diffuse to the interface and react with thin SiO₂ layer that exists on the Si surface to form IMC during soldering.     

Corrosion failure analysis of printed circuit boards exposed to H2S-containing humid environments

The corrosion failure of a printed circuit board (PCB) with electroless nickel/immersion gold (ENIG) surface finish in a hydrogen sulfide-containing humid environment was analyzed in this work. To establish a comprehensive mechanism for the damage, the exposed surfaces were characterized by visual inspection, scanning electron microscopy/energy-dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy. It was realized that merely copper traces under the edge of soldermasks (on electrical junctions) suffer a galvanic-type corrosion reaction with hydrogen sulfide and moisture adsorbed, forming dominantly copper sulfides and a small amount of copper sulfate and oxide. The creep of the corrosion products on the surfaces of ENIG-plated layers, tin-based solders and adjacent soldermasked areas was also found to be responsible for creating short circuits on the outer layers of the miniaturized PCB.     

SnAgCuBi无铅钎料对不同体积比SiCP/6063Al复合材料真空软钎焊接头组织和性能的影响

在不同保温时间下,分别采用 Sn-3.0Ag-0.5Cu 和 Sn-3.0Ag-0.5Cu-3.0Bi 无铅软钎料,对表面镀镍的两种不同体积分数的 SiCP/6063Al 复合材料进行真空软钎焊。通过剪切强度测试、显微组织分析、能谱分析等手段研究了钎焊接头的组织和性能。结果表明：Bi 元素的加入改善了 Sn-3.0Ag-0.5Cu 钎料的铺展润湿性,降低了熔点,提高了焊缝的抗剪强度;在270℃保温35 min 时,Sn-3.0Ag-0.5Cu-3.0Bi 钎料钎焊接头抗剪强度达到最高值38.23 MPa;钎焊过程中只是两侧镀镍层间的焊接,钎料并未透过镍层与母材发生扩散反应。     

等温时效对新型Sn-Ag基复合钎料显微组织和力学性能的影响

研究了等温时效对Sn-3.5Ag共晶钎料及其复合钎料的力学性能和显微组织变化的影响。为了弥补传统复合钎料制备和服役中强化颗粒容易粗化的问题, 制备了不同种类最佳配比的具有纳米结构的有机无机笼型硅氧烷齐聚物(POSS)颗粒增强的Sn-Ag基复合钎料。对钎焊接头在不同温度（125、150、175℃）下进行时效,通过SEM和EDAX分析了钎料与基板间金属间化合物层(IMC)的生长情况。结果表明, 经过不同温度时效,复合钎料钎焊接头界面处金属间化合物的生长速率比Sn3.5Ag共晶钎料慢, 复合钎料的IMC生长的激活能分别为80、97和77kJ/mol,均高于Sn3.5Ag共晶钎料。经过150℃时效1000h后,复合钎料钎焊接头的剪切强度分别下降了22%、13%和18%,下降幅度相当或明显小于Sn-3.5Ag钎料钎焊接头。      

Effects of nano-Al2O3 particles on microstructure and mechanical properties of Sn3.5Ag0.5Cu composite solder ball grid array joints on Sn/Cu pads

A Sn3.5Ag0.5Cu (SAC)–XAl₂O₃ nano-composite solder was prepared by adding 100 nm Al₂O₃ to SAC (wt.%) solder. The interfacial microstructures and mechanical properties of SAC–XAl₂O₃ nano-composite solder balls on immersion Sn surface finished BGA joints after multiple reflows was investigated. As a whole, adding Al₂O₃ nanoparticles to SAC solders significantly changed in the interfacial microstructure, and both scallop-type and prism-type modes were observed in the plain SAC solder and SAC–XAl₂O₃ nano-composite solder after reflowing, respectively. The nanoparticles suppressed the growth of the Cu₆Sn₅ layer, significantly improving the shear strength. The fracture surfaces of the plain SAC solder showed a semi-brittle fracture mode, but those of the SAC–XAl₂O₃ nano-composite solder exhibited typical ductile failures.     

应力对Ag颗粒增强SnCu基复合钎料蠕变性能的影响

使用搭接面积为1mm2的单搭接钎焊接头,研究了恒定温度下应力对Ag颗粒增强SnCu基复合钎料钎焊接头蠕变寿命的影响,结果表明:Ag颗粒增强SnCu基复合钎料的蠕变抗力优于99.3Sn0.7Cu基体钎料;随着应力的增大,复合钎料及其基体钎料钎焊接头的蠕变寿命均呈下降趋势,且应力对复合钎料钎焊接头蠕变寿命的影响比基体钎料明显.     

Mechanical behavior of NiTi shape memory alloy fiber reinforced Sn matrix “smart” composites

The detrimental effects of Pb on the environment and human health have provided the driving force for replacement of Pb–Sn solders with Pb-free alternatives. Sn-rich Pb-free solder alloys with silver and copper alloying additions have higher strength but lower elongation-to-failure than Pb–Sn solders. Thus, these alloys are more susceptible to failure under mechanical shock, drop, and thermal fatigue conditions. In this article, mechanical tensile testing of NiTi–Sn3.5Ag single fiber composites demonstrates superelastic behavior of the composite with 85% strain recovery. Fatigue experiments show an evolution in damage over cycles, and an S–N curve shows sharp transition between a nearly vertical low-cycle fatigue behavior and the high-cycle fatigue regime. The solder composite exhibits constant fatigue strength over the superelastic range of the NiTi fiber.     

Effects of Ag particles content on properties of Sn0.7Cu solder

To improve properties of Sn0.7Cu solder, method of particles reinforced was employed. Effects of Ag particle contents (1, 3, 5, 7.5, and 10 vol.%) on spreadability, microstructure, shear strength and creep rupture life of Sn0.7Cu solders have been studied. The experimental results indicate that intermetallic compound (IMC) grows, Shear strength is increased and grains are fined with the increasing of Ag particles. When content of Ag particles is more than 5 vol.%, growth rate of IMC is increased significantly. When the content of Ag is 5 vol.%, the composite solder presents best spreadability and excellent creep rupture property which have maximum spreading area, minimum wetting angle and longest creep rupture life (about 22 times as long as that of Sn0.7Cu solder).     

Effects of indium addition on properties and wettability of Sn–0.7Cu–0.2Ni lead-free solders

This paper reports the investigation on indium addition into Sn–0.7Cu–0.2Ni lead-free solder to improve its various performances. The effects of indium addition on melting temperature, coefficient of thermal expansion (CTE), wettability, corrosion resistance and hardness of the solder alloys were studied. The results showed that when the addition of indium was ⩽0.3 wt.%, the change in melting temperature of Sn–0.7Cu–0.2Ni–xIn solders was negligible, but the melting range of the solder alloy increased. The CTE and spreading area of Sn–0.7Cu–0.2Ni–xIn solders on copper both increased with the addition of indium. An optimal CTE was 17.5 × 10⁻⁶/°C by adding 0.3 wt.% indium. At this concentration, the spreading area of solder on copper was about 15.6% larger than that of Sn–0.7Cu–0.2Ni indium-free solder. The corrosion resistance also increased with the addition of indium increasing, and the corrosion rate of Sn–0.7Cu–0.2Ni–0.3In solder was reduced by 32.8% compared with Sn–0.7Cu–0.2Ni alloy after 14 days in 5% hydrochloric acid solution at room temperature. However, a decrease of 11.7% in hardness of the solder was found when 0.3 wt.% indium was added.     

Crystalline rice husk silica reinforced AA7075 aluminium chips by cold compaction method

Aluminium matrix composite is highly demanded in various industries due to its low density and good mechanical properties as most commonly studied for metal matrix composite. The properties of the composite be improved with the addition of reinforcement significantly such as silicon carbide, aluminium oxide, and boron carbide that can be mixed easily to metal matrix composite. The study of crystalline rice husk silica reinforced AA7075 aluminium chips on mechanical properties were investigated. The rice husk ash was burned at 1200 °C and it was characterized in the crystalline phase by conducting x-ray diffraction test. The mechanical properties of aluminium matrix composite were obtained by microhardness and compression tests. Results of mechanical properties for the addition of rice husk silica up to 7.5 wt.% composition of crystalline rice husk silica showed increase value of microhardness and compression strength which are the highest value of 75.94 HV 0.1 and 443 MPa, respectively compared to another aluminium matrix composite. Hence, based on investigation to crystalline rice husk silica reinforced aluminium, it has good potential to improve the mechanical properties of aluminium matrix composite which were dependent to the composition of crystalline rice husk silica reinforcement in aluminium matrix composite.     

纳米结构强化的新型Sn-Ag基无铅复合钎料

通过外加法向Sn-3.5Ag钎料中加入质量分数为1%,2%和3%的纳米级多面齐聚倍半硅氧烷(polyhedral oligomeric silsesquioxanes,POSS)颗粒制备无铅复合钎料.系统研究POSS颗粒的显微组织,钎料的熔化特性、润湿性能和力学性能.结果表明:POSS颗粒的加入并没有改变Sn-Ag基复合钎料熔化温度.复合钎料的铺展面积均有所增加,润湿角有所下降,表现了良好的润湿性.POSS颗粒的加入显著提高钎料钎焊接头的剪切强度.     

Investigation of rare earth-doped BiAg high-temperature solders

In the present work, the microstructure and properties of the rare earth Ce-doped BiAg solders with various Ag content are investigated. The results indicate that the maximum of the shear strength appears in the BiAg solder joints containing 5 and 7.5 wt.% Ag. At the same time, a similar trend appears in the hardness test of the BiAg bulk solders. Moreover, the results show that the microstructure and properties of the solders can be modified due to the unique properties of rare earth element. Small amounts of rare earth addition may enhance the wettability of SiAg solder on Cu substrate, and result in the increase of the shear strength of the solder joints. However, the rare earth addition may not give obvious influence on the melting temperature and the electrical conductivity. Thus, it is expected that the BiAg solder containing small amounts of rare earth element may possess a better potential as a replacement for high-Pb solders.     

Shear performance of microscale ball grid array structure Sn–3.0Ag–0.5Cu solder joints with different surface finish combinations under electro-thermo-mechanical coupled loads

The shear performance and fracture behavior of microscale ball grid array structure Sn–3.0Ag–0.5Cu solder joints with different substrate surface finishes (Cu with organic solderability preservatives and electroless Ni/immersion Au) combinations under electro-thermo-mechanical (ETM) coupled loads with increasing current density (from 1.0?×?10³ to 6.0?×?10³ A/cm²) were systematically investigated by experimental characterization, theoretical analysis, and finite element simulation. The results reveal that the shear strength varies slightly with different surface finish combinations, initially increasing and then decreasing as the current density is increased. Moreover, the increase in current density shifts the fracture location from the solder matrix to the interface between solder and intermetallic compound (IMC) layer, resulting in a ductile-to-brittle transition. The interfacial fracture is triggered by electric current crowding at the groove of the IMC layer and driven by the mismatch strain at the solder/IMC layer interface.

     

The effect of cooling rate during multiple reflow soldering on intermetallic layer of Sn‐4.0 Ag‐0.5Cu/ENImAg

The effect of intermetallic compound layer between Sn‐4.0 Ag‐0.5Cu solder bump and electroless nickel/immersion silver (ENImAg) surface finish under different cooling rate during multiple reflow condition was investigated. The results show that the interfacial (Cu, Ni)₆Sn₅ intermetallic compound were formed at the early stage after the first reflow process. After multiple reflow processes, both (Cu, Ni)₆Sn₅ and (Ni, Cu)₃Sn₄ appeared as needle‐shaped at interface due to the amount of copper concentration into a solder balls. The spalling intermetallic compound of (Cu, Ni)₆Sn₅ was spotted in the solder which was caused by the formation of needle‐shaped from the gaps of (Cu, Ni)₆Sn_5. The intermetallic compound thickness and grain sizes became thicker and coarser with increasing reflow time, respectively. The results also perceived that the cooling rate condition can influence the growth of intermetallic compound formation. Faster cooling rate produced thinner intermetallic layer as well as smaller grain sizes compared to slow cooling rate. Hence, the cooling rate is a necessary parameter in the solder reflow process because it has an impact on the microstructure of morphology and intermetallic growth.