Effect of thermal treatment on adhesion strength of Cu/Ni-Cr/polyimide flexible copper clad laminate fabricated by roll-to-roll process

In this study, the effect of a Ni-Cr seed layer on the adhesion strength of flexible copper clad laminate (FCCL) was evaluated after thermal treatment. The changes in the chemical composition, morphology and adhesion property were characterized by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), electron probe micro analyzer (EPMA), X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM) and 90° peel test. The peel strength of the FCCLs was significantly affected by the thermal treatment and the FCCL with a higher peel strength had a higher thermal stability than that with a lower peel strength. The roughness of the fracture surface for the FCCLs decreased with increasing thermal treatment temperature and holding time. The thermal treatment of the FCCL increased the ratio of the C-N bonds and reduced that of the C-O and carbonyl (CO) bonds in the polyimide.     

Effect of Ni-Cr Layer on Adhesion Strength of Flexible Copper Clad Laminate

In this study, the effect of a Ni-Cr layer on the adhesion strength of flexible copper clad laminate (FCCL) was evaluated after thermal treatment. The changes in the chemical composition, morphology, and adhesion properties were characterized by scanning electron microscopy (SEM), x-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), and 90 deg peel test. The results showed that both the peel strength and thermal resistance of the FCCL increased with increasing Cr ratio. The thermal treatment of the FCCL increased the proportion of C-N bonds and reduced that of the C-O and carbonyl (C=O) bonds in the polyimide. The roughness of the fracture surface decreased with increasing thermal treatment temperature and holding time. The chemical function and roughness of the fracture surface were affected by the Ni-to-Cr ratio.     

Effects of nodule treatment of rolled copper on the mechanical properties of the flexible copper-clad laminate

Rolled copper foil of 18 μm thickness underwent nodule treatment via electro plating in a solution containing dissolved CuSO₄ and NiSO₄. The product formed on the surface of the copper foil varied from copper oxides to nickel compounds of the sphere type with increasing current density and plating time. The highest surface roughness and maximum peel strength of 680 gf/cm were obtained with the formation of nickel compounds at a current density of 1.5 A/dm² and plating time of 30 s. In addition, the fracture location varied according to the plating parameters and occurred at the interface between the polyimide film and adhesive layer at the condition of the maximum adhesion strength.     

一种挠性印制电路基板的研制

以脂肪族二胺、芳香杂环二胺和芳香四羧酸二酐或芳香四羧酸二酐、芳香族二胺为原料,N-甲基吡咯烷酮为溶剂,合成两种聚酰胺酸。逐层涂覆,制备了表面为热可塑聚酰亚胺的三层聚酰亚胺复合膜,与铜箔热压复合制备了双面覆铜挠性印制电路基板。热塑性聚酰亚胺胶的玻璃化转变温度为133℃,三层聚酰亚胺复合膜的结晶熔融温度为222℃。该挠性印制电路基材平均剥离强度为7.1 N/cm。     

Enhancement of adhesion strength of Cu layer with low dielectric constant SiC:H liners in Cu interconnects

One of the primary candidates for the liner/etch stop layer in damascene process is silicon nitride (Si₃N₄). However, silicon nitride has a high dielectric constant of 7.0. To reduce the effective dielectric constant in Copper (Cu) damascene structure, dielectric SiC:H (prepared by plasma enhanced chemical vapor deposition (PECVD) using trimethylsilane source) as the Cu diffusion barrier was studied. The dielectric constant of SiC:H used is 4.2. A systematic study was made on the properties of liner material and electro-chemically plated (ECP) Cu to enhance the adhesion strength in Cu/low-dielectric constant (k) multilevel interconnects. Though the effects of as Si₃N₄ the liner have been much studied in the past, less is known about the relation between adhesion strength of ECP Cu layer and physical vapor deposited (PVD) Cu seeds, with seed thickness below 1000 Å. The annealing of Cu seed layer was carried out at 200 °C in N₂ ambient for 30 min was carried out to study the impact on adhesion strength and the microstructure evolution on the adhesion between ECP Cu and its barrier layer. In the study, our claim that SiC:H barrier/etch stop layer is essential for replacing conventional Si₃N₄ layer in enhancing adhesion strength and interfacial bonding between Cu/dielectric interconnects.     

Effect of plasma treatments on interface chemistry and adhesion strength between porous SiO2 low-k film and SiC/SiN layers

In this study, the interface chemistry and adhesion strengths between porous SiO₂ low-dielectric-constant film and SiN capping layer as well as SiC etch stop layer have been investigated under different plasma treatments. Elements of Si, O, and N constructed an interlayer region with mixing Si-N and Si-O bonds at the interface between the porous SiO₂ film and SiN capping layer. After plasma treatments especially O₂ plasma, the oxygen content at the interface increased, and the binding energy obviously shifted to a higher level. Under nanoindentation and nanoscratch tests, interface delamination occurred, and the interface adhesion strength was accordingly measured. After plasma treatments especially the O₂ plasma, more Si-O bonds of high binding energy existed at the interface, and thus the interface adhesion strength was effectively improved. The adhesion energy of SiO₂/SiN and SiC/SiO₂ interfaces was enhanced to 4.7 and 10.5 J/m² measured by nanoindentation test, and to 1.3 and 2.0 J/m² by nanoscratch test, respectively.     

Finite element method investigation into nanoimprinting of aluminum/polyimide bi-layer substrates

Finite element method (FEM) simulations are performed to investigate the nanoimprinting of aluminum/polyimide bi-layer substrates at temperatures ranging from 25 to 200 °C. In constructing the FE analysis model, the mechanical properties of the aluminum and polyimide layers are obtained from thermo-mechanical micro-force tensile tests. The validity of the FE model is confirmed by comparing the results obtained for the formation height ratio in single-layer aluminum substrates with the experimental results. Thereafter, simulations are performed to investigate the effects of the aluminum-to-polyimide thickness ratio and the substrate temperature on the imprint pressure required to obtain a complete filling of the mold cavities. The simulation results show that under low temperature conditions (i.e. <100 °C), the imprint pressure reduces as the aluminum-to-polyimide thickness ratio decreases. In addition, for temperatures lower than 100 °C, the use of a polyimide layer reduces the imprinting force by around 38% compared to that required to imprint a single-layer aluminum substrate of an equivalent total thickness. However, for temperatures higher than 150 °C and a polyimide-to-substrate thickness ratio of more than 40%, the imprint force reversely enlarged due to the strain-hardening of the polyimide film at elevated temperatures. The simulation results obtained for the variation of the imprint pressure with the aluminum thickness ratio, the polyimide thickness ratio, and the substrate temperature are compiled in the form of a contour chart. The chart provides a convenient means of establishing suitable processing conditions for a variety of nanoimprinting applications.     

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.     

ITO-free flexible organic light-emitting diode using ZnS/Ag/MoO3 anode incorporating a quasi-perfect Ag thin film

The multi-layer electrode (ZnS/Ag/MoO₃) was optimized by investigating the formation of a continuous Ag thin film according to the base layer. The aggregation of the Ag atom was strictly limited on the ZnS layer, which showed the best thermal stability for Ag. The thermally evaporated 7-nm-thick Ag film with surface coverage of 99.6% was achieved on the ZnS layer. We fabricated the ZnS (25 nm)/Ag (7 nm)/MoO₃ (5 nm) (Z25A7M5) multi-layer electrode, optimized through the numerical calculation. The transmittance of 83% at λ = 550 nm and sheet resistance of 9.6 Ohm/sq were recorded from the Z25A7M5 electrode. These results were mainly attributed to the uniform film-like morphology of the Ag thin film. The flexible OLEDs, based on the Z25A7M5 anode also showed feasible I–V–L characteristics compared to those of ITO-based devices.     

Interfacial Adhesion Characteristics Between Electroless-Plated Ni and Polyimide Films Modified by Alkali Surface Pretreatment

The effects of KOH + ethylenediamine (EDA) and subsequent KMnO₄ + KOH treatments on the interfacial adhesion characteristics of an electroless-plated Ni/polyimide system were investigated for flexible printed circuit board applications. The interfacial adhesion energy, evaluated from 180° peel tests during the steady-state peeling process, showed a twofold decrease after subsequent KMnO₄ + KOH treatment of the pyromellitic dianhydianiline- oxydianiline polyimide surface. Atomic force microscopy and x-ray photoemission spectroscopy results clearly reveal that this decrease can be attributed to both mechanical interlocking and chemical bonding effects.     

Effects of the intermetallic compound microstructure on the tensile behavior of Sn3.0Ag0.5Cu/Cu solder joint under various strain rates

The effects of the intermetallic compound (IMC) microstructure and the strain rate on the tensile strength and failure mode of Pb-free solder joints are investigated. The samples of Sn3.0Ag0.5Cu/Cu solder joints are aged isothermally at 150 °C for 0, 72, 288 and 500 h, and the thickness of the IMC layer and the roughness of the solder/IMC interface are measured and used to characterize the microstructure evolution of the IMC layer. The tensile tests of the aged solder joints are conducted under the strain rates of 2 × 10⁻⁴, 2 × 10⁻² and 2 s⁻¹. The results indicate that both the thickness and roughness of the IMC layer have influence on the strength and failure mode of the solder joint. With the increase of the aging time, the thickness of the IMC layer increases and the roughness of the solder/IMC interface decreases, as a result, the tensile strength of the solder joint decreases and the dominant failure mode migrates from the ductile fracture in the bulk solder to the brittle fracture in the IMC layer. There is a positive correlation between the tensile strength of the solder joint and the stain rate applied during the test. With the increase of the strain rate, the failure mode migrates from the ductile fracture in the bulk solder to the brittle fracture in the IMC layer.     

Fabrication of low-loss thin film microstrip line on low-resistivity silicon for RF applications

A detail fabricating process and characterization of thin film microstrip line (TFML) on low K polyimide, used for interconnects in radio frequency integrated circuits (RFICs) technology, is reported in this study. By incorporating a spin-on dielectric polyimide and sputtering of aluminum, the TFML is fabricated on low-cost low-resistivity silicon (LRS) substrate (ρ?10 Ω cm). The TFML with a thickness of 20 μm polyimide dielectric layer presents attenuation losses of 0.385 dB/mm at 25 GHz and 0.438 dB/mm at 50 GHz. Effective dielectric constant and attenuation of TFML on polyimide are carefully investigated and discussed.     

Analyses of interface adhesion between porous SiO2 low-k film and SiC/SiN layers by nanoindentation and nanoscratch tests

In this study, the interface adhesion between porous SiO₂ low-dielectric-constant film and SiN capping layer as well as SiC etch stop layer has been investigated. The SiN capping layer was found mostly composed of Si to N bonds, and the porous SiO₂ film composed of Si to O bonds. Elements of Si, O, and N constructed an interlayer mixing region of about 20 nm at the interface between the porous SiO₂ film and SiN capping layer. Under nanoindentation and nanoscratch tests, interface delamination between the porous SiO₂ film and both SiN capping layer and SiC etch stop layer occurred around the indented regions, and the interface adhesion strengths were accordingly obtained. The interface adhesion energy between the porous SiO₂ film and SiN capping layer was measured as about 3.7 and 0.9 J/m² by nanoindentation and nanoscratch tests, respectively, and that between the porous SiO₂ film and SiC etch stop layer was about 8.3 and 1.2 J/m².     

A novel fabrication process of MEMS devices on polyimide flexible substrates

Micro-electro-mechanic-system (MEMS) devices on flexible substrate are important for non-planar and non-rigid surface applications. In this paper, a novel and cost-effective fabrication process for an 8 × 8 MEMS temperature sensor array with a lateral dimension of 2.5 mm × 5.5 mm on a polyimide flexible substrate is developed. A 40 μm thick polyimide substrate is formed on a rigid silicon wafer using as a mechanical carrier throughout the fabrication by four successive spin coating liquid polyimide. The arrayed temperature sensing elements made of 1200 Å sputtered platinum thin film on polyimide substrate show excellent linearity with a temperature coefficient of resistance of 0.0028/°C. The purposed sensor obtains a high sensitivity of 0.781 Ω/°C at 8 mA at constant drive current. Because of the low heat capacity and excellent thermal isolation, the temperature sensing element shows excellent high sensitivity and a fast thermal response. The finished devices are flexible enough to be folded and twisted achieving any desired shape and form. Employing spin-coated liquid polyimide substrate instead of solid polyimide sheet minimizes the thermal cycling as well as improves the production yield. This fabrication technique first introduces the spin-coated PDMS (Polydimethylsiloxane) interlayer between the silicon carrier and the polyimide substrate and makes the polyimide-based devices separate much easier and greatly simplifies the fabrication process with a high production yield. A non-successive two-stage cure procedure for the polyimide precursor is developed to meet low-temperature requirement of the PDMS interlayer. The fabrication procedure developed in this research is compatible with conventional MEMS technology through an optimized integration process. The novel flexible MEMS technology can benefit the development of other new flexible polyimide-based devices.     

环保型挠性覆铜板的研制

采用端羧基丁腈橡胶（CTBN）增韧改性含磷环氧树脂体系,配合使用添加型磷系阻燃剂SPB-100得到挠性覆铜板用胶液,以此制备的环保型挠性覆铜板不含卤素、锑和铅、汞、镉、六价铬等有害重金属,满足欧盟RoHS指令要求,板材剥离强度为1．25N／mm,阻燃性达到UL94 VTM-0级,且具备较好的尺寸稳定性、电性能和耐折性。     

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.     

Effect of plasma treatments on interface adhesion between SiOCH ultra-low-k film and SiCN etch stop layer

The effect of different plasma treatments on the interfacial bonding configurations and adhesion strengths between porous SiOCH ultra-low-dielectric-constant film and SiCN etch stop layer have been investigated in this study. From X-ray photoelectron spectroscopic analyses, interlayer regions of about 10 nm thick with complicated mixing bonds were found at SiOCH/SiCN interfaces. With plasma treatments, especially H₂/NH₃ two-step plasma, a carbon-depletion region of about 30 nm thick with more Si-O related bonds of high binding energy formed at the interface. Furthermore, the adhesion strengths of the SiOCH/SiCN interfaces were measured by nanoscratch and microscratch tests. For the untreated interface, the adhesion energy was obtained as about 0.22 and 0.44 J/m² by nanoscratch and microscratch tests, respectively. After plasma treatments, especially the H₂/NH₃ treatment, the interfacial adhesion energy was effectively improved to 0.41 and 0.89 J/m² because more Si-O bonds of high binding energy formed at the interfaces.     

Light management in PCPDTBT:PC70BM solar cells: A comparison of standard and inverted device structures

We compare standard and inverted bulk heterojunction solar cells composed of PCPDTBT:PC₇₀BM blends. Inverted devices comprising 100 nm thick active layers exhibited short circuit currents of 15 mA/cm², 10% larger than in corresponding standard devices. Modeling of the optical field distribution in the different device stacks proved that this enhancement originates from an increased absorption of incident light in the active layer. Internal quantum efficiencies (IQEs) were obtained from the direct comparison of experimentally derived and modeled currents for different layer thicknesses, yielding IQEs of ∼70% for a layer thickness of 100 nm. Simulations predict a significant increase of the light harvesting efficiency upon increasing the layer thickness to 270 nm. However, a continuous deterioration of the photovoltaic properties with layer thickness was measured for both device architectures, attributed to incomplete charge extraction. On the other hand, our optical modeling suggests that inverted devices based on PCPDTBT should be able to deliver high power conversion efficiencies (PCEs) of more than 7% provided that recombination losses can be reduced.     

Oxidation of Lead Frame Copper Alloys with Different Compositions and Its Effect on Oxide Film Adhesion

Oxidation of four typical lead frame copper alloys was investigated. The oxidation rate and adhesion strength of oxide films to copper alloy substrates were studied by measuring the thickness and carrying out peel tests. The results show that, although copper alloys C5191 and C7025 have thinner oxide films, a lower adhesion strength and a higher proportion of CuO were obtained than in the other copper alloys EFTEC64T and C194. The adhesion strength is mainly influenced by the structure of the oxide film of the copper alloys, especially the CuO/Cu₂O ratio in the film. The highest adhesion strength is obtained for the copper oxide film with a basic structure of CuO/Cu₂O/Cu and a CuO/Cu₂O ratio of about 0.1. The segregation of additional elements in the copper alloy plays an important role in the oxide film structure.     

Sputtering of Ni/Ti/SiC ohmic contacts

The presented work describes the behaviour of contact structures of Ni/Ti type on 6H-SiC n-type prepared by the sputtering technology. Simultaneous deposition of Ni and Ti is better. Plasma cleaning improves adhesion of metals; however, contact resistivity is worse. The Ni(50)/Ti(th)-type metallization has the best electrical parameters at the titanium layer thickness of 100 nm. The XPS analysis shows that the annealing reactions consume about 75 nm or 120 nm of SiC in the case of the Ni + Ti or the Ni/Ti metallization, respectively.