Formation of metal–polymer interfaces by metal evaporation: influence of deposition parameters and defects

Metal–polymer interfaces with different but well defined morphologies were prepared by evaporating noble metals (Au, Ag, Cu) onto chemically different polymers, i.e. bisphenol-trimethyl cyclohexane polycarbonate (TMC-PC), pyromellitic dianhydride-oxydianiline (PMDA-ODA) polyimide (PI), polystyrene (PS) and the low-k dielectric Teflon AF 1601. The interfaces were characterised using transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM). The combination of these techniques allowed one to determine morphological parameters such as concentration and distribution of metal clusters at the surface and in the near-surface region. In addition, radiotracer measurements yielded exact metal condensation coefficients C and was used to determine the extent of diffusion of metal atoms into the polymers. First experiments on the macroscopic adhesion of Cu on TMC-PC showed that the initially low peel strength can be increased substantially by subsequent annealing above the polymer glass transition temperature, T_g.     

Ultrasonic evaluation of the silicon/copper interfaces in IC packaging

The silicon die and copper lead-frame in integrated circuit (IC) packaging are bonded using a die attach adhesive, and the quality of the adhesive interface is a critical issue in the reliability testing of IC packaging and during the manufacturing process. Common defects such as cracks and delamination can be detected using the C-mode ultrasonic microscopic method with sufficient confidence. However, a weak interface due to weak adhesion and poor cohesion has often gone undetected and may become a potential defect at a later stage. There is a desire to study the interface quality quantitatively, so that any potentially defective area can be evaluated and identified early. This paper describes work in evaluating the quality of the interfaces that typically exist in IC packages by using longitudinal ultrasonic wave propagation with contact transducers. An interface spring model is used to predict the ultrasonic reflection coefficient relationship with varying interfacial spring constants. Experimental results of normal incidence reflection coefficients are obtained from the two-layered specimen bonded with die attach adhesive under varying conditioning process that simulates the degrading of the interface. Good qualitative agreement between the measurement and the prediction is obtained, and shows that the reflection coefficient depends strongly on the interface quality. The study demonstrates that the quantification of the interface quality is possible, using the reflection coefficient as a criterion.     

封装用铜框架表面化学组成和粘接强度

电子封装用铜框架表面采用不同温度处理,与电子封装用环氧材料复合制备用于拉伸测试的Tap pull样品。XPS分析表明,一般铜框架表面成分包括一价的氧化亚铜和二价的氢氧化铜等。175℃热处理120 min可使表面的二价氧化铜质量分数达到73%,氧化铜和表面约20%的氢氧化铜一起显著提高界面的粘接性能。     

Modification of electronic and chemical structure at metal/cdte interfaces by pulsed laser annealing

We have measured the effects of metallization and thermal processing on the chemical interaction, band bending, and deep level formation at Au and In/CdTe interfaces using soft x-ray photoemission, photoluminescence, cathodoluminescence, and surface photovoltage spectroscopies. Metallization and laser processing induce major increases in the intensity of several deep photoluminescence transitions. Core level shifts and cathodoluminescence spectra show Fermi level movements characteristic of both a classical work function model and chemically-induced defect pinning. Both interfaces displayed staged Fermi level movements with the evolving metal-semiconductor interaction. Intermediate and final Fermi energies for both systems correlated with the energies of the processing-enhanced photoluminescence transitions, suggesting that the states associated with these transitions are determining the Fermi level.     

The electronic structure of Ni-phthalocyanine/metal interfaces studied by X-ray and ultraviolet photoelectron spectroscopy

Nickel phthalocyanine (NiPc) thin films were grown stepwise on polycrystalline gold and silver substrates and the formed interfaces were characterized by X-ray and ultraviolet photoelectron spectroscopies (XPS, UPS). The variation of the XPS core level binding energy with NiPc film thickness yields information about band bending and interface dipoles. The valence band structure of the NiPc thin films was determined by UPS and exhibits four main features at binding energies 1.50 eV, 3.80 eV, 6.60 eV and 8.85 eV, respectively. The NiPc highest occupied molecular orbital (HOMO) cut-off was measured at ∼1.00 eV from the analyzer Fermi level and from the measured work function change of the growing NiPc film a final work function value for NiPc was estimated at 3.90 ± 0.10 eV. The main C1s peak of the NiPc film (∼5.0 nm) consists of two components at 284.8 eV (C–C bonds), 286.2 eV (C–N bonds) reflecting photoemission from multiple carbon sites within the molecule and a satellite at 287.9 eV, whereas the Ni2p and N1s peaks appear at ∼855.9 eV and ∼399.3 eV, respectively and are due to Ni–N bonds. The energy level diagrams of the NiPc/Au and NiPc/Ag interfaces were determined from a combination of the XPS and UPS results, yielding a hole injection barrier of 0.90 ± 0.10 eV for both substrates.     

Characterization of adhesion property between fused silica and thermoplastic polymer film in thermal nanoimprint lithography using a novel pull-off test

A novel pull-off test that mimics the actual thermal NIL process was conducted to investigate the adhesion properties between a flat fused silica and thermoplastic polymer film used in thermal NIL process. The pull-off force was measured under various NIL conditions—such as use of various polymer materials, imprint pressures, and separation velocities—and the surfaces of the mold and polymer film were observed after the test. The anti-sticking layer (ASL) derived from (1H,1H,2H,2H-perfluorooctyl)trichlorosilane (F₁₃-OTS) was coated on the fused silica and its effects on the adhesion characteristics was also examined. In cases of the mold without ASL, the pull-off force varied significantly according to the process conditions and damage on the polymer film was observed in most of the tests. In cases of the mold coated with the ASL, on the other hands, the pull-off force was maintained at a lower level in the range of the imprint pressure from 2 to 10 MPa or separation velocity from 1 to 25 μm/s, and there was no damage to the polymer film due to adhesion.     

Effect of Ar<Superscript>+</Superscript> Radiofrequency Plasma Treatment Conditions on the Interfacial Adhesion Energy Between Atomic-Layer-Deposited Al<Subscript>2</Subscript>O<Subscript>3</Subscript> and Cu Thin Films in Embedded Capacitors

The effects of Ar⁺ radiofrequency (RF) plasma pretreatment conditions on the interfacial adhesion energy of a Cu/Cr/Al₂O₃ system were investigated for thin-film capacitors in embedded printed circuit board applications. The interfacial adhesion energy was evaluated from 90 deg peel tests by calculating the plastic deformation energy of peeled metal films from the energy balance relationship during the steady-state peeling process. The interfacial adhesion energy was fivefold higher after RF plasma pretreatment of the surface of 50-nm-thick Al₂O₃ prepared by atomic layer deposition. Atomic force microscopy, Auger electron spectroscopy, and x-ray photoemission spectroscopy results clearly reveal that this increase can be attributed to both mechanical interlocking and chemical bonding effects.     

Micromechanical modeling of stress evolution induced during cure in a particle-filled electronic packaging polymer

Particle-filled polymers are widely used in electronic industries. From microscale view, cure-induced residual stress can be generated not only by the external constraints but also by the constraint effect among the particles. In this paper, a three-dimensional micromechanical finite element method (FEM) model has been setup for a silica particle filled epoxy. In the micromechanical model, the epoxy matrix is modeled with a previously developed cure-dependent viscoelastic constitutive model, whereas the silica particles are modeled as elastic with high stiffness. Cure shrinkage is applied to the matrix as an initial strain for each time increment. The cure-dependent viscoelastic properties were obtained from shear and tension-compression dynamical mechanical analysis measurements. Cure shrinkage and reaction kinetics were characterized with online density measurement and differential scanning calorimeter measurements, respectively. In order to simulate a partly constrained object, the micromechanical model is coupled with a macromodel FEM analysis. The displacements from the macromodel are used as boundary conditions for the micromodel. The effect of external constraints on the generation of the micro stresses is studied by using the boundary conditions related to different external constrained states.     

Materials for high-density electronic packaging and interconnections in the higher packaging levels

This paper concentrates on the materials requirements anticipated for future packaging strategies of electronic components beyond the 1st level package. This includes Wafer Scale Integration (Level 0), hybrid assembly of bare chips in multichip modules (Level 1.5), printed wiring board (PWB) assembly, including surface mount (Level 2), and higher levels (connectors, mother boards, and cables). Furthermore, high-performance digital VLSI logic packaging only is addressed, to the exclusion of memory, analog, and power circuitry (except power supplies).     

Degradation of interfacial adhesion strength within photovoltaic mini‐modules during damp‐heat exposure

The degradation of adhesion strength between the back sheet and encapsulant due to moisture penetration has been investigated for commercial crystalline silicon photovoltaic mini‐modules. The damp‐heat tests originating from the International Electrotechnical Commission qualification test were carried out at five different temperature and relative humidity (RH) conditions (95 °C/85% RH, 85 °C/85% RH, 65 °C/85% RH, 85 °C/65% RH and 85 °C/45% RH). The adhesion strength was measured by 90° peel tests, carried out at specified time intervals during degradation. Several visible defects were observed, including delamination, moisture ingress and bubble formation. The adhesion strength showed a stretched exponential decay with time, and significant influence of test conditions was demonstrated. A humidity dose model was proposed by assuming micro‐climates seen by the modules, that is, surface relative humidity of the back sheet as the driving factor for an Arrhenius‐based model using temperature as accelerating factor. The correlation between adhesion strength degradation and humidity dose was investigated through linear and exponential models. Results showed that the conventional linear model failed to represent the relationship while the exponential model fitted to this correlation with extracted activation energy (E_a) of around 63 kJ/mol. This provides a model for the estimation of adhesion strength decay in dependence of the humidity conditions. © 2014 The Authors. Progress in Photovoltaics: Research and Applications published by John Wiley & Sons, Ltd.     

聚苯胺金属纳米复合材料在电子元件中的应用

综述了聚苯胺与金属纳米所组成的复合材料在各种电子元件,如燃料电池、二次电池、超电容器、传感器和信息存储器件等方面的应用进展。针对该应用领域所存在的问题,提出了可能的解决方法和建议,最后指明了聚苯胺金属纳米复合物在电子元件应用中的发展方向。     

Determination of the electroaffinity and potential barrier heights at polymer/ metal interfaces of poly(4,7-benzothiophene vinylene) (PBTV)

In this paper we determine the LUMO level position of poly(4,7-benzothiophene vinylene) (PBTV), a heterocyclic poly(phenylene vinylene) (PPV) analogue, using tunnelling current measurements. We compare the energy level positions with those measured for PPV and determine their shifts. The experimental results are compared with theoretical predictions and good agreement is observed. © 1998 John Wiley & Sons, Ltd.     

The frequency-dependent electrical characteristics of interfaces in the Sn/p-Si metal semiconductor structures

The purpose of this paper is to investigate frequency-dependent electrical characteristics of the interface states in Sn/p-Si metal semiconductor (MS) Schottky structures. To yield quantitative information about their frequency (f) and voltage (V) dependent characteristics, Sn/p-Si MS structures have been studied by using capacitance (C) and conductance (G/ω) measurements over a wide range of frequencies (50 kHz-1 MHz). The increase in capacitance at lower frequencies is seen as a signature of interface states, and the densities of which are evaluated to be of the order of ≅10¹⁰ cm⁻² eV⁻¹. The presence of the interfaces states (N_SS) is also evidenced as a peak in the capacitance-frequency characteristics that increases in magnitude with decreasing frequencies. Furthermore, the voltage and frequency dependence of series resistance (R_S) were calculated from the C-V and G/ω-V measurements and plotted as functions of voltage and frequency. The effect of R_S on C and G/ω is found noticeable at high frequencies. The C-V-f and G/ω-V-f characteristics of studied structures show fairly large frequency dispersion especially at low frequencies due to N_SS in equilibrium with the semiconductor. The experimental values of interface state densities and series resistance from C-V-f and G/ω-V-f measurements were obtained in the ranges of 3.46 × 10¹⁰−1.26 × 10⁹ cm⁻² eV⁻¹ and 71.1-57.3 Ω, respectively. Experimental results show that both the R_S and N_SS values should be taken into account in determining frequency-dependent electrical characteristics.     

影响不流动半固化片粘结因素的探析

不流动PP的流动性很低,与常规FR-4有很大的区别,如采用常规的压合条件,PCB板件经常出现不流动PP粘合不良问题。结合实验验证,详细分析了影响不流动半固化片粘合的因素,为有效提高不流动半固化片粘结强度提供了若干建议。     

Effects of dimple and metal coating on interfacial adhesion in plastic packages

This paper reports on the effects of dimple and metallic coating of the Cu-alloy lead frame on interfacial adhesion with an epoxy-molding compound. Round dimples of varying number are introduced on one side of the lead frame by chemical etching. The plating materials studied include bare-Cu alloy and microetched Cu, Ag, Ni, Pd/Ni, and Au/Ni coatings. The surface characteristics, such as wettability, surface roughness, and element compositions, were evaluated based on several characterization tools, which, in turn, are correlated with adhesion performance. The dimples enhanced the interfacial-bond strengths through improved mechanical interlocking of the molding compound, depending on the type of coating. The improvement was much more significant for the coatings with inherently weak interfacial adhesion (e.g., microetched Cu and Ni coating) than those with inherently strong adhesion characteristics (e.g., Au and Pd coatings). The wettability of the metal surface represented by the surface energy or interfacial energy played a dominant role in the resulting interfacial adhesion. Elemental analysis of the fracture surface indicates that the silicon content had roughly a linear relationship with the interfacial-bond strengths for different coatings. The surface roughness was insensitive to the interfacial-adhesion performance. The silicon content measured from the lead-frame fracture surface was shown to directly correlate to the interfacial-bond strength. Higher silicon content was a reflection of larger surface-area coverage by the molding compound associated with cohesive failure.     

SEM insitu study on high cyclic fatigue of SnPb-solder joint in the electronic packaging

The high cycle fatigue (HCF) cracking behaviors in the SnPb solder joints were investigated experimentally via in situ observations with scanning electron microscope (SEM). The results indicate that the HCF cracks incubate at the toe of the solder joints and propagate mainly along an angle from 20° to 45° tilted to the applied stress axis differing greatly from the propagation behaviors reported previously for low cycle fatigue (LCF). The HCF crack growth rate is evaluated by the term of based on the experimentally measured parameters, i.e. the maximum applied stress σ_s-max and the surface crack propagation length ?. The finite element analysis (FEA) is carried out and shows that the stress relationship between the components of the chip-substrate-solder can be evaluated quantitatively when the applied loading acts on the substrate. Therefore, for most SnPb solder alloys, the failure threshold value for SnPb-solder joint can also be estimated by this work.     

The metal/organic monolayer interface in molecular electronic devices

The metal/molecules/metal is the basic device used to measure the electronic properties of organic molecules envisioned as the key components in molecular-scale devices (molecular diode, molecular wire, molecular memory, etc.). This review paper describes the main techniques used to fabricate a metal/molecules/metal device (or more generally electrode/molecules/electrode junctions, with electrodes made of metal or semiconductor). We discuss several problems encountered for the metallization of organic monolayers. The organic/electrode interface plays a strong role in the electronic properties of these molecular devices. We review some results on the relationships between the nature of the electrode/molecule interface (physisorbed or chemisorbed, evaporated metal electrode, mechanical contact, etc.) and the electronic transport properties of these molecular-scale devices. We also discuss the effects of symmetric versus asymmetric coupling of the two ends of the molecules with the electrodes.     

电子封装无铅化现状

近年来铅污染广泛地受到了人们的重视。2003年2月13日欧盟颁布WEEE/RoHS法案,在世界范围内引发了一场电子封装的无铅化革命。综述了电子封装技术的现状以及我国如何面对无铅化的问题。     

Study on the Effects of Copper Oxide Growth on the Peel Strength of Copper/Polyimide

In this study, various copper oxides [CuO, Cu₂O, and Cu₂O + polybenzimidazole (PBI)] were studied as alternative adhesion layers. Specimens were aged under harsh conditions (300°C, 5% O₂ or humid condition), and then peel tests were conducted to investigate the reliability of Cu oxides/polyimide (PI). The peel strength of the bare Cu, CuO, and Cu₂O specimens dropped substantially, close to nil, due to void formation after 2 h of aging at 300°C. The degree of void formation near the Cu₂O/Cu interface showed a clear inverse relationship with the peel strength, suggesting that the formation of voids beneath the Cu₂O layer was directly responsible for the peel strength degradation. Void growth was controlled by Cu₂O layer growth, while voids originated from the difference between the diffusion rate of Cu atoms through the Cu₂O layer and Cu layers. Humidity tests did not lower the peel strength significantly in any of the specimens, none of which showed voids that were detrimental to the peel strength, in contrast to the results of the aging treatments at 300°C.     

Ionization and diffusion of metal atoms under electric field at metal/insulator interfaces; First-principles study

The ionization and diffusion of metal atoms at metal/SiO₂ interfaces under an electric field are studied by first-principles calculation. It is shown that the ionization of metal atoms occurs when the hybridization of metal-atom electronic states with metal-induced gap states (MIGS) is broken. Moreover, we show that an electric field markedly decreases the penetration barrier of metal atoms from a metal electrode into SiO₂ and enhances the diffusion of metal atoms.