Showing papers by "Ming Li published in 2013"

A facile process for preparing superhydrophobic nickel films with stearic acid

Abstract: Nickel surface with nanocone array structure was fabricated by electrodeposition. By controlling electrodeposition condition, various nickel films with different cone sizes were also fabricated. Wettability results revealed that with the increase of cone height, water contact angles increased from 148°to 154°while sliding contact angles dramatically decreased from 90° (sticky condition) to nearly 0°. Three-phase contact model and a simple calculation were given to demonstrate the relations between sliding angles and surface structures.

Behaviors of Chloride Ions in Methanesulfonic Acid Bath for Copper Electrodeposition of Through-Silicon-Via

Abstract: Due to the demand for a high throughput of through-silicon-vias (TSV) manufacture, fast via filling technique is required. Cu electrodeposition in methanesulfonic acid bath (MSA) is considered as one of the potential approaches to achieve the short time plating of TSV with larger diameter and deeper depth than the damascene via. In this paper, the effect of chloride ion in MSA plating bath on via filling for TSV was investigated by electron paramagnetic resonance and electrochemical techniques with a rotating disk electrode. Furthermore, wafer-segment plating using the real TSV structure is also examined. The results indicated that the chloride ions may form a "chloride bridge" to catalyze the reduction of Cu, and eliminate the inhibiting effect of PEG in MSA bath. Moreover, the Cl− accelerates the Cu deposition at the bottom of via where the electrochemical process is diffusion controlled, and inhibits the deposition at the top of via where that is non-diffusion controlled. These behaviors of chloride ion are very helpful to the TSV via filling.

Influence of Cr alloying on the oxidation resistance of Sn–8Zn–3Bi solders

Abstract: Influence of Cr alloying on the oxidation behavior of Sn–8Zn–3Bi–xCr (SZBxCr) (x = 0, 0.1, 0.3, 0.5) solders under 250 °C has been investigated. It was found that the poor oxidation resistance of the solders is attributed to the oxidation of Zn–rich phase and other Zn atoms which diffused to the β-Sn matrix grain boundaries which form ZnO. With Cr addition, two types of Sn–Zn–Cr phases, along the grain boundaries of β-Sn matrix and across the Zn-rich phase, were detected in Cr-bearing solder alloys, which prevent the oxygen from diffusing into the bulk of the solder, and the SZB0.3Cr alloy had the best oxidation resistance.

Enhanced Ni3Sn4 nucleation and suppression of metastable NiSn3 in the solid state interfacial reactions between Sn and cone-structured Ni

Abstract: Interfacial reactions of Ni micro cones with Sn at solid state temperatures from 373 K to 473 K were studied and compared with Sn/flat Ni diffusion couples. Due to its morphological characteristics, cone-structured Ni enhanced the nucleation of Ni3Sn4, resulting in thicker Ni3Sn4, which is also smaller in grain size and different in texture. At lower annealing temperatures (<423 K), cone-Ni also strongly suppresses the nucleation of metastable NiSn3. The stripe-like micromorphology and special texture of Ni cones are believed to be the reasons for enhanced Ni3Sn4 nucleation.

Formation and growth of interfacial intermetallic layers of Sn-8Zn-3Bi-0.3Cr on Cu, Ni and Ni-W substrates

Abstract: In this paper, the formation and growth of intermetallic compounds (IMCs) of Sn-8Zn-3Bi-0.3Cr solder on Cu, Ni and Ni-W substrates have been investigated. For the Cu substrate, only Cu5Zn8 intermetallic compound was observed. For the Ni substrate, a Ni5Zn21 film formed at the interface due to the fast reaction between Ni and Zn. For the Ni-W substrate, a thin Ni5Zn21 film appeared between the solder and Ni-W layer, whose thickness decreases with the increase of W content. An amorphous bright layer was also found to form below the Ni5Zn21 layer as aging time extended, which is caused by the diffusion of Zn into Ni-W layer.

Thermal reliability of Ag-8Au-3Pd alloy wire bonds

Abstract: Ag-8Au-3Pd alloy wire has great potential of low-cost candidate for traditional gold wire interconnects. This study aims to light the behavior of degradation that took place in Ag-8Au-3Pd alloy wire bond interface. Two layers of intermetallic compound (IMC) at the Ag-8Au-3Pd/Al bond interface were observed by transmission electron microscopy (TEM). The specimens were annealed at 175°C in a closed oven for 24, 72, 168, 336 and 500 h in atmosphere respectively to reveal the evolution of IMC at interface. The high-temperature storage (HTS) test of Ag-8Au-3Pd/Al Ag-95Pd-5/Al and Ag-98Pd-2/Al interface was conducted for contrast. Interface evolution tracking by back scattered electron (BSE) imaging showed that after 336 h, the bonding interface began to fail. JEDEC standard of HTS test was successfully passed. Ag-8Au-3Pd wire showed great promise as an economical substitute for gold wire.

Interfacial reaction of Sn–2.0Ag–2.5Zn solder on Cu and Ni–W substrates

Abstract: The interfacial reactions of Sn–2.0Ag–2.5Zn solder on Cu and Ni–W substrates after soldering and subsequent aging have been investigated in this study. Ni–W alloy layers with tungsten content of 3.0 and 10.0 at.% were electrodeposited on copper substrate. The interfacial micrographs of solder joints prepared at 250 °C for 15 s and aged at 150 °C for 24, 96 and 216 h are shown. Double-layer IMC composed of Cu5Zn8 and Ag3Sn was observed at the interface of Sn–2Ag–2.5Zn and Cu couple, which was compact and acted as a barrier layer to confine the further growth of Cu–Sn IMC. On Ni–W barrier layer, a thin Ni3Sn4 film appeared between the solder and Ni–W layer, whose thickness decreases with the increase of W content. During the aging process, a thin layer of the Ni–W substrate transforms into an amorphous bright layer, and the thickness of amorphous layer increased as aging time extended. Referring to the elemental line-distribution and the thickness of different layers at the interface, the formation of the bright layer is caused by the fast diffusion of Sn into Ni–W layer.

Simulation of TSV copper electrodeposition process with additives

Abstract: The kinetics which explained the Copper Super-filling by electrodepostition was investigated since the copper deposition became the standard technique for TSV. A simple numerical model is built to explain the copper deposition process. Consider with the effect of the accelerator, a linear equation is built to explain the relationship between the exchange current density and the coverage of accelerator as well as the relationship of the potential and the coverage of accelerator. The parameter of the equation is investigated in the article. The results show that the linear equation indicates process of copper electrodeposition sufficiently with properly parameters.

Pure Bottom-up filling process for efficient TSV metallization

Abstract: TSV (Through Silicon Via) is an enabling technology for 3D WLP (Wafer Level Packaging) and 3D integration. TSV is a very hot topic for semiconductor industry today. One of the key processes for TSV is the electroplating process. The quality and rate of electroplating are two critical parameters for TSV filling, which can be significantly improved by Bottom-Up filling with much thinner overburden. Also, bottom up plating is a critical process to thin overburden. In this study, the copper plating of TSVs with the diameter and the depth in the ranges of 2.5-30 μm and 50-300 μm, respectively, was investigated. A nearly 100% bottom up plating recipe was developed in order to achieve void-free and seamless filling. The performance of this plating recipe was evaluated by vertical and top-down cross-sections images of filled TSVs using optical microscopy and X-ray inspection. The influence of the suppressor and cupric ion concentrations on Bottom-Up filling were investigated. Pure Bottom-Up filling can be achieved with a strong enough suppressor and high copper concentration. The strength of suppressor determines the required amount of copper concentration. The influence of diffusion time to different via diameter were also discussed. The copper concentration can be up to 120g/L in Methylsufonic Acid (MSA). The void-free and seamless copper deposition results with via diameter from 2.5μm-25μm or aspect ratio up to 20 can be achieved.

Effect of different pretreatments on through silicon via copper filling

Abstract: Pretreatments have a great effect on the through silicon via (TSV) copper electroplating filling process In this study, we compared the wetting effect by observing cross-sectional images of samples pretreated with ultrasound and vacuuming method And the electrochemical test was used to verify the effect of acid plating solution on the oxidation of the Cu seed layer Without any pretreatment, vias showed a poor wettability that large voids existed at the bottom The TSV pretreated by ultrasound and vacuuming method both were coated well with copper deposition layer, which showed a good wettability However, when the Cu seed layer of the TSV was not well sputtered, ultrasound vibration may cause the exfoliation of the Cu seed layer resulting in the formation of void at the bottom of the vias Diluted additives as prewetting solution made no much difference on filling effect The acidic plating solution could dissolve the oxide layer at a high speed and react with the Cu seed layer as well

A numerical model for bottom-up copper electrodeposition of TSV with additives

Abstract: The kinetics which explained the copper Superfilling by electrodeposition was investigated since the copper electrodeposition became the standard technique for TSV. In order to interpret the bottom-up Superfilling process conveniently and exactly, a numerical model focused on the mass which can make the copper deposition in the via is built. This model only considered the effect of accelerator and cupric which directly affect the electrodeposition velocity in the via. The effect of two species in the numerical model is represented to two reaction constants kr and kA. Both of two constants are the compound parameters including desorption, adsorption and reaction of deposition mass. Experimental electrodeposition of variable dimension via is used to verify the accuracy of a numerical model. The results show that the model can demonstrate the electrodeposition process of via which is 50μm in diameter.

A simulation of IGBT module under power cycling test condition

Abstract: The performance of IGBT (Insulated Gate Bipolar Transistor) power module under power cycling test is investigated based on a FEA (Finite Element Analysis) method. Critical point of solder fatigue has been discovered through analysis. Thermal cycling test has also been simulated as a comparison. The impact of power module parameters, such as power dissipation of chip, cycle period, solder layer thickness and heat spreader has been studied through DOS (Design of Simulation). The disciplinary conclusion can be a reference for package design.

Electro-migration of silver alloy wire with its application on bonding

Abstract: In recent years, silver alloy wire has been widely used in semiconductor industry. In contrast to conventional gold wire, silver alloy wire has better electrical property, thermal conductivity and lower cost while tends to migrate more easily under high temperature and current density. In this paper, electro-migration (EM) of silver alloy wire after wire bonding has been studied. Under accelerated test, cracks forms not only on silver alloy wire surface but also in silver alloy wire while gold wire remain the same. Silver ion not only migrates on the wire surface also inside the wire. Temperature and current density both accelerate the EM. The conclusion could be a reference for further gold reduction of Au/Ag alloy wire in semiconductor bonding.

Analysis of accelerator consumption in TSV copper electroplating

Abstract: Accelerator consumption was analyzed by electrochemical method. As the presence of SPS and PEG in the acidic cupric sulfate solution with chloride ions, the cathodic polarization curves become have peaks and valleys. The peak and valley have a strong association with the additive concentration and are associated with the electroplating process. The effect of electroplating time on the cathodic polarization curves is similar to the effect of SPS concentration. The linear relation between parameter Q with the concentration of SPS is Q = 0.007624 + 0.150992CSPS. The parameter Q is useful for the analysis of SPS consumption in TSV copper electroplating. The real deposition in TSV verifies that SPS consumption in the process of plating can be obtained by analyzing cathodic polarization curves.

Numerical simulations based thermal reliability of power device packages

Abstract: Discrete high power packages: TO-220FP, TO-247, TO-3P are investigated for their thermal-mechanical behaviors. Junction-to-ambient thermal resistance measurements and Computational Fluid Dynamics (CFD) simulations are utilized to judge the thermal performance of these packages with the same material properties. The finite element method (FEM) simulations of temperature cycling is also applied to analyze the internal stress and strain, impact of different die size and thickness have been compared, which provides references for further studies and power packages optimization.

Effect of leveler on microstructure and stress of electroplated copper for TSV application

Abstract: Through silicon via (TSV) with many advantages comparing with traditional technology is playing an important role in three-dimensional large-scale integration. In this paper, we have studied Effect of leveler on microstructure and stress of electroplated copper for TSV application. We demonstrate residual stress, SEM, TEM and electrochemistry results which have strong connection with leveler in via copper electroplating solution.

Substrate with Ni/Au microcones surface for wire bonding

Abstract: Ni/Au microcones were fabricated and thermosonic bonded with Au wire. The thickness of Au film was only 0.05μm. The substrate with Ni/Au microcones showed good Au wire bondability with the average pull strength 4.85 gf and ball shear strength 54.33 gf. Microscopi observation showed that Ni/Au microcones were inserted into Au wire, thus physical interlock between the substrate and Au wire was formed. High temperature storage showed a perfect reliability.

Synthesis of copper nanowires on the substrates in aqueous solution

Abstract: Copper nanowire is a promising material in the electronic packaging industry. However, at present, most of the preparation methods of Cu nanowires growing on substrates are highly dependent on templates or need relatively high temperature. In this study, Cu nanowires growing on substrates are synthesized by both pulse current electrodeposition and electroless plating, which is both template-free and conducted under mild conditions. The final morphology and structure of the products have been studied by X-ray diffraction method, scanning electron microscope and transmission electron microscope respectively. The Cu nanowires have smooth surfaces, with length between 10-30μm and diameter between 60-70nm. Moreover, the Cu nanowires have single-crystal structure of face-centered-cubic copper growing along the [100] direction.

Growth of Cu-Sn intermetallic compounds during isothermal aging processing in electroplated Cu/Sn/Cu system

Abstract: Microstructure evolutions of as-reflowed and aged electroplated Cu/Sn/Cu sandwich structure with 20 or 40μm Sn layer have been investigated. Cu3Sn was observed at lower side of Cu/Sn/Cu structure with 40μm Sn layer after isothermal aging treatment for 24 hours, as for that structure with 20μm Sn layer, Cu3Sn appeared after aging for 48 hours. Regardless of Sn volume, the thickness of the blanket Cu6Sn5 and total intermetallic compounds (Cu6Sn5+Cu3Sn) increased linearly with the increasing aging time. After long-time aging processing, the layers of blanket Cu6Sn5 and Cu3Sn in the the Cu/Sn/Cu structure with 20μm Sn layer are both thicker. Volume of Sn layer has significant effect on the growth of Cu-Sn IMCs in the electroplated Cu/Sn/Cu system.

Study of diffusion mechanism in low-temperature bonding method based on surface Cu microcones

Abstract: Study of diffusion mechanism in low-temperature bonding method based on Cu microcones is reported. A Sn layer was electrodeposited on the Cu microcones and the electrodeposited Cu substrate then annealing at bonding temperature 463 K. IMC grains of Sn/Cu-microcones diffusion samples grew slow with smaller size. The special morphology of Cu microcones was beneficial for the growth of intermetallic layer in short annealing time and the advantage disappeared with longer annealing time, which ensured the good performance of this bonding method.

Research on 0.6 mil Ag-8Au-3Pd alloy wire bonding process

Abstract: Ag-8Au-3Pd alloy wire has shown its advantages as a kind of interconnect material in semiconductor packaging. In thermosonic wire bonding, a uniformed and stable Free-Air-Ball (FAB) created by electronic flame-off (EFO) is crucial to a reliable 1st bond. In this study, the relationship between Free-Air-Ball (FAB) size and EFO parameters (EFO current, EFO time) of 0.6 mil Ag-8Au-3Pd alloy wire has been investigated. According to the FAB formation curve of 0.6 mil Ag-8Au-3Pd alloy wire, a suitable EFO parameter was settled down, then a design of experiment (DOE) was set up to investigate the optimum parameter window. As expected, the experiment results illustrate that 0.6 mil Ag-8Au-3Pd alloy wire is workable as the interconnect material with less cost.