Lead Frame Alloy Research Articles

HOT-300 – A Multidisciplinary Technology Approach Targeting Microelectronic Systems at 300 °C Operating Temperature

Abstract Several applications in the fields of industrial sensors and power electronics are creating a demand for high operating temperature of 300 °C or even higher. Due to the increased temperature range new potential defect risks and material interactions have to be considered. As a consequence, innovation in semiconductor, devices and packaging technologies has to be accompanied by dedicated research of the reliability properties. Therefore various investigations on realizing high temperature capable electronic systems have shown that a multidisciplinary approach is necessary to achieve highly reliable solutions. In the course of the multi-institute Fraunhofer internal research program HOT-300 several aspects of microelectronic systems running up to 300 °C have been investigated like SOI-CMOS technology and circuits, silicon capacitor devices, a capacitive micromachined ultrasonic transducer (CMUT), ceramic substrates and different packaging and assembly techniques. A ceramic molded package has been developed. Die attach on different leadframe alloys were investigated using silver sintering and transient liquid phase bonding (TLPB). Copper and gold wire bonding was studied and used to connect the chips with the package terminals. Investigations in flip chip technology were performed using Au/Sn and Cu/Sn solder bumps for transient liquid phase bonding. High operating temperatures result in new temperature driven mechanisms of degradation and material interactions. It is quite possible that the thermomechanical reliability is a limiting factor for the technology to be developed. Therefore investigations on material diagnostics, reliability testing and modeling have been included in the project, complementing the technology developments.

Effect of Thermomechanical Processing on the Microstructure and Properties of a Cu-Fe-P Alloy

A Cu-0.7Fe-0.15P (wt.%) alloy was designed, and its comprehensive properties, especially electrical conductivity and temper-softening resistance of the designed alloy, were higher than those of traditional Cu-Fe-P alloys. The microstructure of this alloy was investigated with optical microscopy, scanning electron microscopy, and transmission electron microscopy. The particle of secondary phase was confirmed to be Fe2P with x-ray spectroscopy and digital diffractogram. By virtue of precipitation hardening and work hardening, the tensile strength and electrical conductivity of Cu-0.7Fe-0.15P alloy were 498 MPa and 62% IACS, respectively. The electrical conductivity of this alloy can be up to 92% IACS due to the complete precipitation of Fe2P. After repeating the cold rolling and aging process for three times, the tensile strength, elongation, and conductivity of this alloy were 467 MPa, 22%, and 78% IACS, respectively. Due to the low driving force of recrystallization and the pinning effect of fine dispersed Fe2P, the alloy with low deformation rate showed excellent softening resistance. The designed alloy can be used as a high-strength, high-electrical-conductivity lead-frame alloy.

Effects of Copper Plating Thickness of Ni/Fe Alloy Leadframe on Thermo-Mechanical and Die Cracking Behaviors of Small Outline Transistor (SOT) Packages

Small outline transistor (SOT) packages, because of their low cost and low profile, are widely used in consumer electronics. Ni/Fe alloy (A42) is the most widely used leadframe material of SOT packages because of its good formability and coefficient of thermal expansion (CTE) match with silicon die. The very small size of SOT packages allow a higher package density on a board, but the small size and close proximity of SOT packages make thermal management difficult. The low thermal conductivity of A42, which is less than one tenth of that of copper, makes the thermal conduction even more difficult. Thus, the method of copper plating on A42 leadframe is used to enhance the thermal conductivity of SOT packages while keeping their low cost and good CTE match between leadframe and silicon die. In this paper, the junction temperature Tj, the junction-to-ambient thermal resistance θj-a and the junction-to-solder joint thermal resistance θj-sp are used to evaluate the heat dissipating ability of the package. The finite element method is applied to study the influence of copper plating thickness on the thermal performance of a SOT package. A thermal resistance circuit model and the corresponding thermal resistance expression on function of the copper plating thickness are then proposed to quantify the influence of copper plating thickness. The proposed expression, which follows a hyperbolic form, can well predict thermal resistance of the model. Finally, die cracking issue of the SOT packages with copper leadframe is examined and the residual stress on silicon die after die bonding process is studied. By comparing the cracking pattern and the stress state, shear fracture is proposed to be the crack initiation mechanism. Results also show that copper plating on A42 leadframe has little influence on the distribution of the thermal residual stress in the die. The stress level for the SOT package with copper plated A42 leadframe is much lower than that with copper leadframe, which makes the die cracking risk much lower.

Oxidation of the copper alloy with pure copper plating

The oxidation failure of a copper alloy lead frame with/without a copper plating layer was investigated. The oxidation rate and adhesion strength of oxide films on copper alloy substrates were studied by measuring the thickness and by carrying out peel tests. The adhesion strength of the oxide film was mainly influenced by the composition but not the thickness of the oxide film. The highest adhesion strength was obtained when the oxide film was composed mainly of Cu2O. When the thickness of the copper preplated layer was over 0.165 μm, the Cu atoms of the preplated copper were available for oxidation. Thus the oxidation process was within the copper preplated layer, and the main product of the oxidation was Cu2O. It was found that the large column grain of the oxide film on the copper alloy with a copper plated layer, favored the diffusion of copper or oxygen atoms that led to the formation of Cu2O, and lead to higher adhesion strength. This indicated that the oxidation resistance of a copper alloy lead frame can be effectively improved by electroplating copper.

Simulation Analysis of Springback for Lead Frame Copper Alloy

The bending performance of lead frame materials is a very important in improving the quality of lead frame alloys and meeting the needs of high performance integrated circuit. The sringback amount of curvature variation of CuFeP , CuCrZrMg , CuNiSi and CuCrSnZn alloy are researched by numerical simulation. Bending model is built by 3D modeling software, and the necessary post-processing is carried out. The bending springback amount △K of the four kinds of copper alloy materials are calculated out. The results show that the sringback amount of curvature variation of four copper alloys at the same condition from large to small in turn is CuCrZrMg, CuNiSi, CuFeP, CuCrSnZn. Smaller the minimum relatively bending radius of copper alloy used in lead frame, less the springback amount and better the forming performance.

Effect of Rare Earth Y Addition on the Properties and Precipitation Morphology of Aged Cu-Cr-Ti Lead Frame Alloy

The influence of rare earth Y addition and ageing treatment on the properties and precipitation morphology of Cu-Cr-Ti alloy was investigated. The results show that 0.1wt%Y addition increases the hardness, and decreases the electrical conductivity slightly. However, both the hardness and electrical conductivity decrease with an excessive Y addition. After ageing at 550°C for 2h, Cu-0.3Cr-0.2Ti-0.1Y alloy has a good combination of the hardness and electrical conductivity, which has the hardness of 134HV and the electrical conductivity of 73.9%IACS. After ageing treatment, most Cr rich phases precipitate in the form of sphere shape while a small amount of Cr rich phases exist in the form of acicular, and Y rich phases precipitate in the form of flake along the grain boundary.

Phase transformation in Cu–Cr–Zr–Mg alloy

After solid solution treatment, the effects of aging processes on the microstructure and electrical conductivity of Cu–Cr–Zr–Mg lead frame alloy were investigated in order to determine the phase transformation and the time–temperature-transformation (TTT) behavior. The results show that aged at 470 °C the fine precipitation of an ordered CrCu 2(Zr,Mg) phase is found in copper matrix as well as fine Cr and Cu 4Zr, aged at 550 °C the phase CrCu 2(Zr,Mg) is decomposed into Cu 4Zr and Cr phase, aged at 600 °C the precipitates is bcc Cr only. The phase transformation kinetics equation was deduced from the Avrami empirical formula based on the linear relationship between the electrical conductivity and the volume fraction of the phase transformation.

Effect of Fe particle on the surface peeling in Cu−Fe−P lead frame

Under the surface peeling of Cu−Fe−P lead frame alloy larger Fe particles were observed by energy dispersive spectroscopy. By using the large strain two-dimension plane strain model and elastic-plastic finite element method, the cause for peeling damage of Cu−Fe−P lead frame alloy was investigated. The results show that when the content of Fe particles is more than 30% at local Fe-rich area the intense stress concentration in the Fe particle would make the Fe particle broken up. The high equivalent stress mutation and the mismatch of equivalent strain 10% at the two sides of interface make it easy to develop to crack and peeling damage on finish rolling. The larger Fe particles in the Cu−Fe−P alloy should be avoided.

Aging process optimization for a copper alloy considering hardness and electrical conductivity

A multi-objective optimization methodology for the aging process parameters is proposed which simultaneously considers the mechanical performance and the electrical conductivity. An optimal model of the aging processes for Cu–Cr–Zr–Mg is constructed using artificial neural networks and genetic algorithms. A supervised artificial neural network (ANN) to model the non-linear relationship between parameters of aging treatment and hardness and conductivity properties is considered for a Cu–Cr–Zr–Mg lead frame alloy. Based on the successfully trained ANN model, a genetic algorithm is adopted as the optimization scheme to optimize the input parameters. The result indicates that an artificial neural network combined with a genetic algorithm is effective for the multi-objective optimization of the aging process parameters.

Intermetallic compounds evolution between lead-free solder and cu-based lead frame alloys during isothermal aging

This paper investigated the intermetallic compounds (IMCs) formation between SnAgCu solder and four Cu-based lead frame alloys during reflow soldering and isothermal aging. Scanning Electron Microscope (SEM) and Energy Dispersive X-ray (EDX) were used to study the cross-sectional microstructure and stoichiometric information. Optical Microscope (OM) was used to measure the mean thickness of IMCs. It was found that Ni and Sn trace element have important influences on the interfacial reactions. After soldering, for the case of Sn-Ag-Cu solder on Cu-Sn-Cr-Zn, Cu-Sn-P and Cu-Fe-P-Zn-Pb, an island type Cu6Sn5 and a thin Cu3Sn layer were formed at the interface. However, for the case on Cu-Ni-Si-Mg alloy, no Cu3Sn was detected and only a layer of ternary (Cu,Ni)6Sn5 was confirmed and some Cu6Sn5 particles was observed to disperse in the bulk solder. The top morphology of IMCs was also characterized after the solder was selectively etched away. The IMCs on the Cu-Ni-Si-Mg showed long rod-like shape, whilst the IMCs on the other three alloys appeared round. After different duration of aging at 150°C, all the IMCs grew thicker and the grain size became larger. The rod-like IMCs on Cu-Ni-Si-Mg gradually transformed into round shape and it was relatively smaller compared to that on the other three alloys. Moreover, the growth rate of IMCs on Cu-Ni-Si-Mg is the fastest among the four alloys.

Optimization of aging treatment in lead frame copper alloy by intelligent technique

An intelligent technique of artificial neural networks combined with genetic algorithms is developed for the analysis and optimization of the correlation between heat treatment parameters and properties in Cu–Cr–Sn–Zn lead frame alloy. A supervised artificial neural network (ANN) to model the nonlinear relationship between parameters of aging treatment with respect to hardness and conductivity properties was proposed for the alloy. The ANN sub-model improved by the Levenberg–Marquardt training algorithm has good generalization performance. Genetic algorithms (GAs) are used to optimize the input parameters of aging temperature and time. The verifying experiment has shown that the theoretical optimization agrees with the experimental evidence.

Optimization of thermomechanical processes in Cu-Cr-Zr lead frame alloy using neural networks and genetic algorithms

The thermomechanical treatment process is effective in enhancing the properties of the lead frame copper alloy. In this study, an optimal pattern of the thermomechanical processes for Cu−Cr−Zr was investegated using an intelligent control technique consisting of neural networks and genetic algorithms. The input parameters of the artificial neural network (ANN) are the reduction ratio of cold rolling, aging temperature and aging time. The outputs of the ANN model are the two most important properties of hardness and conductivity. Based on the successfully trained ANN model, genetic algorithms (GA) are used to optimize the input parameters of the model and select perfect combinations of thermomechanical processing parameters and properties. The good generalization performance and optimized results of the integrated model are achieved.

Sn whiskers: material, design, processing, and post-plate reflow effects and development of an overall phenomenological theory

Replacement of Pb/Sn terminations on electronic devices with pure Sn has proven to be much more difficult than expected. The main problem is Sn whisker formation. Sn whiskers are typically single-crystal, mechanically strong, metallic filaments that can nucleate and grow over time in such a way as to lead to device failure in the field. In this study, we present the results of Sn whisker formation and growth studies for plated matte-Sn on Cu Pb frames. We include data on the effects of Sn-thickness, post-plate annealing, and simulated board attach reflow. Also included are data on two different bath base chemistries, methane sulfonic acid (MSA) and mixed acid, three different plating bath suppliers, and three different lead-frame plating suppliers. The effects of trim and form as well as lead-frame alloy type were also investigated. Whisker testing was completed by storing devices for at least 1 year at room ambient, 60/spl deg/C/93%RH, and 60/spl deg/C/<10%RH. Additional tests were done by subjecting devices to temperature cycling between -55/spl deg/C and +85/spl deg/C. Finally, condensing environmental testing and bias/temperature/humidity tests were completed. The results indicate that the propensity for whisker formation and growth decreases with increasing Sn thickness, and with a post-plate heat treatment. The data imply that the improvement is one of increasing the incubation time, not one of complete elimination of the potential for whiskers. Analysis of the data also indicates the interpretation of Sn whisker formation and growth data taken from a small set of experimental conditions and or small number of devices or leads may lead to incorrect conclusions when compared to a larger data set. When taken in totality, no exact systematic dependency on the propensity for whisker formation was found between dependent variables of trim and formed and nontrim and formed lead frames or for stamped versus etched lead frames. With the exception of 60/spl deg/C/93%RH exposure, no systematic interaction with process conditions and/or process/stress conditions were found. For stressing at 60/spl deg/C/93%RH, there was a clear indication that the trim and form devices were significantly more susceptible to whisker formation than nontrim and formed devices. The propensity for whisker growth was found to be similar at room ambient and 60/spl deg/C/<10%RH. The propensity for whisker formation is lowest for the room temperature and 60/spl deg/C/<10%RH storage, followed by temperature cycling, followed by noncondensing 60/spl deg/C/93%RH storage. A condensing 60/spl deg/C/93%RH environment was found to result in an accelerated corrosion assisted whisker growth mechanism producing locally dense clusters of whiskers or "flowers". No effects of electrical bias on the propensity for whisker growth were observed, and it is concluded that electrical bias itself does not appear to be a promary driving mechanism for Sn whisker growth. Finally, the application of a post-plate solder reflow is found to significantly impact the propensity for whisker growth. In particular, the incubation time for whisker growth in 60/spl deg/C/93%RH was found to be of order 10-15 weeks for all devices subjected to a simulated board-attach reflow process at peak temperatures greater than 232/spl deg/C. Whereas for devices not subjected to a simulated reflow, the incubation time was 26 weeks for 7-/spl mu/m-thick films and 61 weeks for 15-/spl mu/m-thick films. We have observed whisker growth on all samples independent of lead-frame alloy type, plating chemistry, and plating supplier. Finally, we have found that a Ni-underplate, if implemented correctly, eliminated whisker growth for at least 52 weeks at 60/spl deg/C/93%RH independent of simulated reflow process. We present a model that reveals the improvements afforded by the post-plate anneal is one of extending the incubation time not one of complete elimination of whiskers. Finally, we propose a model tha

Research on aging precipitation in a Cu–Cr–Zr–Mg alloy

The effects of aging processes on the properties and microstructure of Cu–0.3Cr–0.15Zr–0.05Mg lead frame alloy were investigated. Aging precipitation phase was dealt with by transmission electronic microscope (TEM). After solid solution was treated at 920 °C and aged at 470 °C for 4 h, the fine precipitation of an ordered compound CrCu 2(Zr, Mg) is found in copper matrix as well as fine Cr and Cu 4Zr. Along the grain boundary, there are larger chromium. The hardness and electrical conductivity can reach 109 HV and 80% IACS, respectively. Sixty percent cold-rolled deformation prior to aging at 470 °C enhances the hardness of the alloy. The coherent precipitates Cr in copper matrix and the dislocations pinned by the fine precipitates are responsible for maximum strengthening of the alloy. So the hardness 165 HV and electrical conductivity 79.2% IACS are available.

Microstructure, adhesion strength and failure path at a polymer/roughened metal interface

Metals and polymers are extensively used in microelectronics packaging where they are joined together. Since both the yield and reliability of packages are strongly affected by the interfacial adhesion between polymers and metals, extensive studies have been performed in order to improve the resistance to debonding of many resulting interfaces. In the present work, the interfacial fracture energy of representative polymer/metal interfaces commonly encountered in micoroelectronics packaging was characterized. A copper-based alloy leadframe was used as the metal and an epoxy molding compound (EMC) was used as the polymer. The leadframe surfaces were roughened by chemical oxidation in a hot alkaline solution and molded with the EMC. In general, roughening of metal surfaces enhances their adhesion to polymers by mechanical interlocking, yet often produces a cohesive failure in the polymer. Sandwiched double-cantilever beam (SDCB) specimens were employed to measure the adhesion strength in terms of interfacial fracture energy. After the adhesion test, the microstructures of metal surfaces before molding with the EMC were correlated to the adhesion strength, and the fracture surfaces were analyzed using various techniques to determine the failure path.

Growth Kinetics of Cu–Sn Intermetallic Compounds at Interface of 80Sn–20Pb Electrodeposits and Cu Based Leadframe Alloy, and Its Influence on the Fracture Resistance to 90°-Bending

Electrodeposits of 80Sn–20Pb were formed on a Cu-based leadframe alloy from organic sulfonate solutions under different plating conditions, and were then aged at 100 to 180°C to examine the effects of the microstructure of electrodeposits on the growth kinetics of the Cu–Sn intermetallic layer formed at the electrodeposit/substrate interface, and the resultant influence on the fracture resistance of the electrodeposits under bending. The Cu–Sn intermetallic compound layers [ε (Cu3Sn) + η (Cu6Sn5)] increase linearly in thickness with the square root of aging time. However, the growth rate of the intermetallic compounds layer exhibits significant differences depending on the deposition condition; it is fastest in an extremely fine elecrodeposit formed using pulse current in a bath without any grain refiner, but is slowest in that formed using dc current in a bath with grain refiner, in spite of an equivalent grain size in both electrodeposits. This is due primarily to the inhibiting effects of the grain refiner remaining at grain boundaries of the electrodeposit on the diffusion of Sn across the intermetallic compounds/electrodeposit interface. The occurrence frequency and the degree of opening of surface cracks, formed when the aged samples are subjected to the 90°-bending test, are found to be associated with the growth rate of the intermetallic compound layer and the ductility of the electrodeposit. For samples aged under the same conditions, the sample electrodeposited from the solution containing grain refiner shows the highest resistance to surface cracking during the 90°-bending test due to the lower growth rate of its intermetallic layer and the higher ductility of the electrodeposit compared with those of other samples.

Effect of thermomechanical treatments on microstructure and properties of Cu-base leadframe alloy

The effect of thermomechanical treatments (TMT) on the microstructuresand properties of Cu-1.5Ni-0.3Si-0.03P-0.05Mg leadframe alloy wasinvestigated. The Cu-base leadframe alloy was received as hot rolledplates with 8 mm thickness. The hot rolled plates were solutiontreated at 700°C or 800°C for 1 hour, and coldrolled with 40–85% reduction, then followed by aging treatment at450°C. The leadframe alloy solution treated at 800°Cshowed larger grain size of 15 μm comparing with the grain size of10 μm in leadframe alloy solution treated at 700°C. Theleadframe alloy with smaller grain size of 10 μm showed highertensile strength and lower electrical resistivity than that withlarger grain size of 15 μm. The dislocation density increased withincreasing reduction ratio of cold rolling from 40% to 85% andresulted in finer Ni2Si precipitates. Tensile strength increasedand electrical resistivity decreased with increasing reduction ratioof cold rolling due to the formation of finer Ni2Si precipitates.Two types of thermomechanical treatments were performed to enhance theproperties of leadframe alloy. One type of thermomechanical treatmentis to refine the grain size through the overaging, cold rollingfollowed by recrystallization. The recrystallization process improvedthe tensile strength to 540 MPa and elongation to 15% by reducing thegrain size to 5 μm. The other type of thermomechanical treatmentis to refine the precipitate size by two-step aging process. Thetwo-step aging process increased the tensile strength to 640 MPa andreduced the electrical resistivity to1.475 × 10−8 Ωm by reducing the size of Ni2Si precipitates to 4 nm.

OLIN C151

Abstract Olin C151 is an age-hardenable dispersion strengthened zirconium-copper lead frame alloy. This datasheet provides information on composition, physical properties, hardness, elasticity, and tensile properties. It also includes information on corrosion resistance as well as heat treating, machining, joining, and surface treatment. Filing Code: CU-632. Producer or source: Olin Brass.

Linear Fracture Mechanics Analysis of Interfacial Delamination in LSI Packages under Temperature Cyclic Loading. 2nd Report, The Effects of Material Properties and Package Geometry Factors.

Further fracture mechanics analyses to understand comprehensively the effects of material properties and package geometries on two configurations of delaminations along the interfaces at a) die-bonding layer and b) the bottom surface of the die pad in LSI plastic packages subjected to temperature cyclic loading were performed. Specifically, the effects on these delaminations of such package constituent material properties as 1) coefficients of thermal expansion and 2) Young's moduli of the encapsulant resin and die-bonding material were examined. Package geometry factors such as thickness and width, including chip size were also considered. The analyses were conducted on the basis of three models of delaminated packages, in which large stress intensity factors at the tips of growing delaminations were induced in our previous work. The impact of these parameters on the delaminations were determined and several design guides of Cu alloy and Fe-42% Ni alloy leadframe packages were pointed out.

Linear Fracture Mechanics Analysis of Interfacial Delamination in LSI Packages under Temperature Cyclic Loading.

A study is made for interfacial delaminations between dissimilar materials in LSI plastic packages caused by temperature cyclic loading. Combining a thermoelastic finite element method for nonlinear contact problems and linear fracture mechanics approach, stress intensity factors at the tips of growing delaminations are obtained for the packages with Cu alloy or 42 alloy (Fe-42%Ni) leadframe. The tendency of delamination growth are compared for the two configurations of delamination ; one along the interfaces between the top surface of the die pad and die-bonding layer and the other along those between the bottom surface of the die-pad and encapsulant resin. It is concluded that the former case is more likely to occur for the package with Cu alloy leadframe while for packages with 42 alloy leadframe, the latter case is more likely to occur.