Effect of aging on fatigue crack growth at sn-pb/cu interfaces

The effect of isothermal aging on fatigue crack growth behavior at the Sn-Pb solder/Cu interface was examined, with emphasis on the role of interfacial microstructure. Flexural peel interface-crack specimens were made from the joints of eutectic Sn-Pb solder and Cu and were further aged at 443 K for 7 and 30 days. Kinetics of fatigue crack growth along the solder/Cu interfaces were measured from flexural peel specimens as a function of strain energy release rate. Aging was found to induce not only microstructural changes in the solder and at the interface, but also degradation in fatigue crack growth resistance of the interface from the fatigue threshold to the fast fracture. The fatigue threshold decreased from 25 to 20 J/m² after aging for 7 days and to 10 J/m² following aging for 30 days. The degradation in the fatigue crack growth resistance is related to the formation of a Pbrich layer at the interface.     

Effect of Aging Temperature on the Microstructure and Shear Strength of SAC0307-0.1Ni Lead-Free Solders in Copper Joints

This paper presents an investigation of the effects of aging temperature on the microstructure and shear strength of SAC0307-0.1Ni/Cu solder joints. Single-overlap shear solder joints were aged for 1 h at 80, 130, and 180°C. The microstructure of the interface between the solder and the Cu substrate contained phase of the intermetallic compounds (IMCs) (Cu,Ni)6Sn5 formed along the interface. The shape of scallop-like (Cu,Ni)6Sn5 IMCs changed to the long dendrite and grew larger at the interface of solder joints after increased aging temperature. In addition, a phase of particle-like Ag3Sn IMCs was formed in the solder matrix. The growth of the interfacial IMC layer in the solder joints increased with increasing the aging temperature. The thickness of this layer was controlled by diffusion mechanism. The shear strength of the as-reflowed solder joints was greater than that of the aged solder joints, and the shear strength of all the aged solder joints decreased with increasing the aging temperatures. Therefore, the aging temperature mainly affected the thickness of the interfacial layer of IMCs and the shear strength of the solder joints.     

Layer growth in Au-Pb/In solder joints

The solid state reaction between a Pb-In solder alloy and thin film Au has been investigated at ten aging temperatures ranging from 70 to 170°C. Also, bulk Au-solder samples were aged at 150°C for metallographic analysis. No significant difference was found between the aging behavior of thin and bulk Au specimens. A thin single phase layer of Au₉In₄ was found adjacent to Au while a thick two-phase layer of AuIn₂ and Pb was found between Au₉In₄ and solder. The Pb phase was shown to have considerable mobility and able to ripen at room temperature. Peculiar planar interface instabilities and voids in the Au-Au₉In₄ interface were found. Although the total layer thicknessvs aging time data could be closely fitted with a power law relationship, it was shown that a linear relationship also fits well and is consistent with accepted metallurgical concepts. An activation energy of 0.61 eV was found by regression analysis of the intermetallic growth kinetics.     

Layer growth in Au-Pb/In solder joints

The solid state reaction between a Pb-In solder alloy and thin film Au has been investigated at ten aging temperatures ranging from 70 to 170°C. Also, bulk Au-solder samples were aged at 150°C for metallographic analysis. No significant difference was found between the aging behavior of thin and bulk Au specimens. A thin single phase layer of Au₉In₄ was found adjacent to Au while a thick two-phase layer of AuIn₂ and Pb was found between Au₉In₄ and solder. The Pb phase was shown to have considerable mobility and able to ripen at room temperature. Peculiar planar interface instabilities and voids in the Au-Au₉In₄ interface were found. Although the total layer thicknessvs aging time data could be closely fitted with a power law relationship, it was shown that a linear relationship also fits well and is consistent with accepted metallurgical concepts. An activation energy of 0.61 eV was found by regression analysis of the intermetallic growth kinetics.     

热镀锌TRIP钢还原铁/基板界面表征

预氧化还原工艺是改善热镀锌先进高强钢(AHSS)可镀性的有效手段之一。当它用于生产热镀锌先进高强钢时,有时也会出现镀层附着性不良的问题。为了明确还原铁/基板界面对热镀锌高强钢镀层附着性的影响,以预氧化还原工艺生产的、镀层附着性不同的热镀锌TRIP钢为研究对象,采用GDOES、SEM、FIB、TEM等手段研究了还原铁/基板界面位置的微观特征。结果表明,镀层附着性不良表现为150～300 nm厚的还原铁层与镀层一起从基板表面脱落,失效发生在还原铁/基板界面,而非镀层/还原铁界面,与常见的镀层/基板界面Fe₂Al₅抑制层缺失引起的镀层附着性不良明显不同。镀层附着性不同的试样在还原铁/基板界面位置均存在硅、锰元素富集,但硅、锰富集程度有差异,镀层附着性不良试样的界面硅、锰富集更高。还原铁/基板界面氧化物形态显著影响了还原铁/基板界面的结合力,当还原铁与基板之间形成连续的氧化膜时,界面结合力较差,易发生界面分离;当还原铁/基板界面形成细小的、不连续的氧化物颗粒时,界面结合力较好。在对热镀锌先进高强钢实施预氧化还原工艺时,为了获得良好的还原铁/基板界面结...     

银铜侧向复合材料界面结合机理分析

本文采用“包覆锭坯+扩散烧结+冷轧复合”联合工艺制备了银铜侧向复合带材,利用金相显微镜（OM）、扫描电镜（SEM）和能谱仪（EDS）观察分析银铜复合界面结构和元素分布,并分析其银铜复合界面的结合机理。结果表明,银铜复合界面形成过程为：1）银铜接触界面处凹凸不平的表面在轧制力的作用下相互咬合,形成机械结合界面;2）接触面在轧制力的作用下,银铜表面氧化膜破裂,新鲜表面质点间在轧制变形热的作用下产生原子结合;3）在扩散烧结过程中,银铜界面处的原子在高温作用下被激活,银铜原子相互扩散,在界面处发生银铜共晶反应形成液相金属层,随着烧结时间的延长,其共晶反应液相层厚度逐渐增加,随后冷凝结晶,使银铜实现侧向冶金结合。4）在后续中间退火过程中,共晶层与两侧的铜、银基体相互扩散,铜、银原子向更深的方向逐渐扩散,在靠近共晶层铜侧和银侧逐步形成固溶体层,使银与铜的结合强度进一步提高。银铜侧向复合界面结合机理包含机械咬合结合、接触共晶反应自钎焊结合和原子扩散结合3种,复合界面结合强度较好,剪切强度达220 MPa。     

Effect of Operation Parameters on Diffusion Bonded AA5083, AA6082 and AA7075 Aluminum Alloys

Rolled plates of 5 mm thick AA5083, AA6082 and AA7075 aluminum alloys Joints were fabricated by diffusion bonding at different temperatures. The microstructure evolution of AA5083, AA6082 and AA7075 aluminium alloys were characterized by transmission electron microscopy. Metallurgical investigations and mechanical tests were also performed to correlate the microstructural investigations with the mechanical properties of the produced diffusion bonded joints. It was observed that the bonding and shear strength increased with the increase in bonding temperature due to the diffusion of micro-constituents in the interface. Higher temperature enhanced the uniform distribution of secondary phase particles, which further improved the reduction in pores/defects in the bonded joints.     

Thermal stability of electroless-nickel/solder interface: Part B. Interfacial fatigue resistance

The relationship between fatigue resistance and interfacial microstructure was studied along the interface between the Sn-Pb eutectic alloy and an electroless Ni-P coating. The fatigue resistance of the solder interface was measured from the flexural peel fracture mechanics specimens in the asreflowed, mild-aged, and overaged conditions. While the mild aging had only a marginal effect on the fatigue resistance of the interface, overaging was found to significantly degrade the interfacial resistance to fatigue-crack growth, resulting in a lower fatigue threshold and a much earlier onset of the fast fracture. The effects of the overaging were shown to result from the transformation of the interfacial microstructure, which weakened the crack-sliding resistance in the near-threshold regime and embrittled the interface in the high crack-growth rate regime.     

Mechanical strength of thermally aged Sn-3.5Ag/Ni-P solder joints

This work presents an investigation on the influence of the solder/under bump metallization (UBM) interfacial reaction to the tensile strength and fracture behavior of Sn-3.5Ag/Ni-P solder joints under different thermal aging conditions. The tensile strength of Sn-3.5Ag/Ni-P solder joints decreases with aging temperature and duration. Four types of failure modes have been identified. The failure modes shift from the bulk solder failure mode in the as-soldered condition toward the interfacial failure modes. Kirkendall voids do not appear to affect the tensile strength of the joint. The volume change of Ni-P phase transformation during the thermal aging process generates high tensile stress inside the Ni-P layer; this stress causes mudflat cracks on the remaining Ni-P coating and also leads to its delamination from the underlying Ni substrate. In general, interfacial reaction and the subsequent growth of Ni₃Sn₄ intermetallic compound (IMC) layer during solid-state reaction are the main reasons for the decrease of tensile strength of the solder joints. The current study finds there is an empirical linear relation between the solder joint strength and the Ni₃Sn₄ intermetallic compound (IMC) thickness. Therefore, the IMC thickness may be used as an indication of the joint strength.     

Structure of gap junction intercellular channels

The water durability at adhesion interfaces was investigated by measurement of the peeled area of thin resin films bonded with 4-META resin on metal surfaces after imposing thermal stress using liquid nitrogen. Thermal stress at the adhesion interface was calculated by a computer-aided finite element method. On 18-8 stainless-steel specimens which bond strongly with 4-META resin, total interface failure occurs on specimens with resin thicker than 0.55 mm in dry condition. A resin layer of 0.25 mm was chosen to study degradation of the adhesion interface by water. The shearing stress was calculated as 16 MPa for a 0.25 mm thick resin layer. On mild-steel adherent interface with 4-META resin which degrades rapidly by water molecule, the relationship between water immersion time and degradation at the adhesion interface was discussed together with the amount of water penetrated at the interface. The method proposed in the present study is effective as a quick evaluation method for water durability at the adhesion interface.     

Intermetallic growth and mechanical behavior of low and high melting temperature solder alloys

The presence of an intermetallic is often an indication of good wetting in a solder joint. However, excessive intermetallic growth and the brittleness of the intermetallic layer may be detrimental to joint reliability. This study examined the growth and mechanical behavior of interfacial intermetallics between copper and six solder alloys commonly used in electronics assembly. The solder alloys tested were 60Sn-40Pb, 63Sn-37Pb, 95Sn-5Sb, 96.5Sn-3.5Ag, 50Pb-50In, 50Sn-50In, and 40In-40Sn-20Pb. The 50Sn-50In and 40In-40Sn-20Pb exhibited faster solid state growth of the intermetallic layer at 100 °C as compared to the near-eutectic Sn-Pb control solder. The 50In-50Pb had a slower growth rate, relative to 63Sn-37Pb, at the aging temperature of 170 °C due to slower reaction rate kinetics of indium with copper. The 96.5Sn-3.5Ag and 95Sn-5Sb had similar intermetallic growth rates at 170 °C and 205 °C, and the aging was comparable to that of the 63Sn-37Pb alloy. The 95Sn-5Sb solder/copper intermetallic had a faster growth rate of the Cu₃Sn layer than was observed in the Sn-Ag or Sn-Pb alloys. Modified fracture toughness and low load indentation tests were used to characterize the mechanical behavior of the intermetallics. The intermetallics were harder than both the base metal and the solder alloy. The fracture behavior of the joints in tension was dependent upon the strength of the solder alloy. Solders with low strengths failed in the solder by plastic deformation. The failure of solders with higher strengths was dependent upon intermetallic thickness. When the intermetallic was thin, fracture occurred in the solder or at the solder/ intermetallic interface. As the interfacial intermetallic thickened, the fracture path moved into the intermetallic layer.     

The growth of Cu-Sn intermetallics at a pretinned copper-solder interface

This article reports a comparative study of the formation and growth of intermetallic phases at the interface of Cu wetted with a thick solder joint or a thin, pretinned solder layer. The η phase (Cu₆Sn₅) forms when Cu is wet with eutectic solder at temperatures below 400 °C. The intermetallic layer is essentially unaffected by aging at 70 °C for as long as 13 weeks. On aging a eutectic joint at 170 °C, the η-phase intermetallic layer thickens and ε phase (Cu₃Sn) nucleates at the Cu/intermetallic interface and grows to a thickness comparable to that of the η phase, while a Pb-rich boundary layer forms in the solder. The aging behavior of a thin, pretinned eutectic layer is qualitatively different. At 170 °C, the Sn in the eutectic is rapidly consumed to form η-phase intermetallic, which converts to ε phase. The residual Pb withdraws into isolated islands, and the solderability of the surface deteriorates. When the pretinned layer is Pb-rich (95Pb-5Sn), the Sn in the layer is also rapidly converted into η phase, in the form of dendrites penetrating from the intermetallic at the Cu interface and discrete precipitates in the bulk. How ever, the development of the intermetallic largely ceases when the Sn is consumed; ε phase does not form, and the residual Pb remains as an essentially continuous layer, preserving the solderability of the sample. These observations are interpreted in light of the Cu-Sn and Pb-Sn phase diagrams, the temperature of initial wetting, and the relative diffusivities of Cu and Sn in the solder and intermetallic phases. A.J. SUNWOO, Formerly with the Lawrence Berkeley Laboratory, Berkeley, CA,     

微量Ga元素对低银系无铅钎料抗氧化性能的影响

电子封装波峰焊从有铅到无铅的转换过程中,由于无铅钎料中锡含量比传统Sn37Pb钎料高,导致波峰焊过程中氧化渣的产生量很大。其不仅造成生产中的浪费,还会影响焊接质量。控制钎料氧化渣的产生量是当前无铅波峰焊技术必须要解决的一个重要问题。研究了目前常用的Sn-0.3Ag-0.7Cu无铅钎料在模拟波峰炉中的抗氧化情况。主要研究了微量Ga元素的加入对该钎料抗氧化性的影响。通过钎料的润湿实验和氧化锡渣的产出量的比较可以发现微量Ga元素的加入可以提高钎料的抗氧化性能,Ga元素的最佳含量是0.02%(质量分数),Sn-0.3Ag-0.7Cu-0.020Ga的抗氧化有效温度范围是320℃以下,有效时间控制在120 min以下。利用俄歇能谱AES分析表明,微量元素Ga在焊料表面富集,O原子浓度的降低。热力学分析表明:Ga元素会在合金中优先氧化,阻碍钎料的进一步氧化;动力学分析表明:在保护膜内高价Ga离子使表面层离子排列空位增加并使电导率降低,是产生抗氧化性的原因。     

25AgCuZnCd钎料脆性的研究

２５ＡｇＣｕＺｎＣｄ钎料在加工成形时常出现脆性。为此,本文对Ａｇ２５Ｃｄ２０Ｃｕ５５－ｘＺｎｘ钎料显微组织、微区化学成分、相及其结构、强度、塑性和熔化特性进行了较详细的研究。研究发现钎料的脆性与合金中的组织和相结构有密切联系,并指出,当ｗ（Ｚｎ＋Ｃｄ）≤４５％、合金中出现塑性相时,能同时满足钎料的钎焊性和加工成形性的要求。     

石墨炉原子吸收光谱法测定锡铅焊料中铝

以硝酸(1+2)-盐酸(1+1)溶解样品,采用盐酸沉淀大部分铅及银,在16 g/L柠檬酸、0.12 mol/L盐酸介质中,取澄清液直接采用石墨炉原子吸收光谱法测定锡铅焊料中铝。结果表明:在选定的酸度介质中,不需要挥锡,锡也不会水解;大部分铅及银以氯化物形态沉淀于底部,无需用盐酸处理的脱脂棉-纸浆过滤分离银及铅沉淀,直接取澄清液进行测定即可;样品溶液保持清亮时间长,样品中锡及共存元素不干扰测定。方法线性范围为3.00～100.00 μg/L,检出限为4.04 μg/L。将方法应用于锡铅焊料标准物质中铝的测定,结果与认定值或GB/T 10574.13—2003采用的电感耦合等离子体原子发射光谱法(ICP-AES)一致,相对标准偏差为6.2%～8.9%。     

Isothermal fatigue of low tin lead based solder

Low tin lead based solder fails by intergranular and/or transgranular modes depending upon experimental conditions. At low frequency and in tests with hold times separation of grains is the main mode of fracture. In the 5 to 100 °C temperature range at high frequency (> 10⁻² Hz) and at high total strain range (0.75 pct) the failure mode is mixed transgranular-intergranular; at a low total strain range (0.3 pct) the mode of failure is intergranular. Change in failure mode leads to a bend in the Coffin-Manson plot. Tensile hold time and combined tensile and compressive hold times are found to reduce dramatically the fatigue cycles to failure of this solder. A simple mathematical relation between the fatigue life of the solder and ramp time, tensile, and compressive hold times is developed.     

Interfacial Reactions,Microstructure, and Strength of Sn-8Zn-3Bi and Sn-9Zn-Al Solder on Cu and Au/Ni (P) Pads

The Sn-8Zn-3Bi and Sn-9Zn-Al Pb-free solders were used to mount passive components onto printed circuit boards (PCBs) with electroless Ni immersed Au (ENIG) finishing layers using a reflow soldering process. The component mounted boards were aged at 150 °C for 200 to 1100 hours. The interfacial reactions and microstructure of the interfaces between the solders and the pads were observed using scanning electron microscopy and energy-dispersive spectrometry (EDS). Both solder joints on the two pads had similar interfacial microstructures; i.e., a very thin γ ₂-AuZn₃ layer was formed at the interface of the solder and Ni-P layer. The γ ₂-AuZn₃ layer transformed to an ε-AuZn₈ intermetallic compounds (IMC) with a consistent thickness during aging. Zinc atoms redeposited onto the IMC layer increased with increasing aging time. After aging at 150 °C for various times, the shear strengths of the ENIG and organic solderability preservative (OSP) joints were evaluated. The shear strength of the Sn-8Zn-3Bi solder joint was better than that of the Sn-9Zn-Al solder joint. All of the solder joints deteriorated after aging; however, the degradations of the OSP solder joints were more evident than those of the ENIG solder joints.     

Environmental and hold time effects on fatigue of low-tin lead-based solder

The effect of environment on the strain-controlled fatigue resistance of a high-lead-low-tin solder was determined by comparing results in vacuum to those in air (wet and dry) and CO₂ (wet and dry). At low strain amplitude, air and CO₂ were shown to reduce the cycles to failure defined on the basis of the decrease in maximum cycle stress. The effect increases as the strain amplitude is reduced. Water vapor had little effect. Previously, the Coffin-Manson (C-M) relation was shown to fail for tests in air. The amount of failure is less in vacuum. The main fatigue failure mode is grain-boundary (GB) cracking, and this is accelerated by air or CO₂. Auger spectroscopy showed that there is tin buildup near the surface during fatigue in air or CO₂. The more rapid GB fracture was attributed to tin oxide (or tin oxide-lead oxide solid solution) buildup in the GB, where diffusion is more rapid. Formerly Research Assistant, Northwestern University     

Effect of thermal spray on the microstructure and adhesive strength of high-velocity oxy-fuel-sprayed Ni-Cr coatings on 9Cr-1Mo steel

Coatings of 80Ni-20Cr and 50Ni-50Cr on a 9Cr-1Mo steel substrate were produced by high-velocity oxy-fuel (HVOF) spraying to protect the steel against steam oxidation in ultrasupercritical (USC) boilers. The oxidation studies on the coated specimens showed good protection against the scale growth on the steel substrate. Both the 80Ni-20Cr and 50Ni-50Cr coatings formed a thin protective oxide film on the coating surface. The 80Ni-20Cr coating showed Fe diffusion from the substrate to the coating and nickel diffusion from the coating to the substrate during the oxidation process. In the case of 50Ni-50Cr coatings, the diffusion process was reduced, but a continuous layer of chromium carbide was observed at the coating/substrate interface during the oxidation. The adhesive/cohesive strength of these coatings was evaluated on aged specimens at 750 °C by using a simple tensile test. The results of the as-coated 80Ni-20Cr specimens showed an adhesive-strength value of 68 MPa. On extended aging, the strength of the coating increased beyond the detection limit of the resin. The nickel diffusion from the coating to the substrate and the iron diffusion from the substrate to the coating caused the increased adhesive strength. In the case of 50Ni-50Cr, the as-coated specimens showed an average adhesive strength of 76 MPa and showed a decreasing trend on the aged specimens. The formation of chromium carbide at the interface caused inferior values in the adhesive/cohesive strength of the 50Ni-50Cr coatings. The chromium carbide formed on the coating/substrate interface was identified as M₂₃C₆-type carbide.     

62Sn36Pb2Ag组装焊点长期贮存界面化合物生长动力学及寿命预测

Sn基合金焊接接头是电子产品不可或缺的关键部位,是实现电子元器件功能化的基础,电子整机失效往往由于焊点的损伤所导致,焊点的寿命预测对电子产品的可靠性研究具有重要意义.金属间化合物（IMC）厚度是衡量焊点质量的重要参数,以IMC层厚度为关键性能退化参数,以62Sn36Pb2Ag组装的小型方块平面封装（QFP）器件焊点为研究对象,采用扫描电子显微镜对在94、120和150°C三种温度贮存不同时间后的焊点微观形貌进行表征,测量了IMC层的厚度,基于阿伦尼乌斯方程建立了双侧界面金属间化合物生长动力学模型.并以其作为关键性能退化函数,通过对初始IMC厚度进行正态分布拟合获得失效密度函数,进而获得可靠度函数对焊点的长期贮存失效寿命进行了预测.研究结果有望对长期贮存焊点的寿命预测方式提供新的思路,为62Sn36Pb2Ag钎料的可靠应用提供试验和数据支撑.