Copper Paste Research Articles

A Low Firing Temperature Copper Conductor for use on an Aluminum Metal Compatible Dielectric in LED Thermal Substrate Applications

One of the most important contributing factors in the long life of LEDs (Light Emitting Diode) is keeping them cool, i.e., lowering the junction temperature, which can get as high as 150 °C. One way to accomplish this when building a circuit containing many LED packages is to use a thermal substrate. The majority of High Power/High Brightness (HP/HB) LED thermal circuits manufactured today are based on Metal Core Printed Circuit Board (MCPCB) technology. The MCPCB system consists of a copper foil, polymer dielectric layer and either an aluminum or copper base layer that are laminated together. The process of making MCPCB is a subtractive process, where most of the copper foil is removed. The copper foil is etched to create a circuit layer, the polymer dielectric provides the insulation between the copper foil and the metal base, and the aluminum or copper base provides thermal dissipation. The thick film copper paste discussed in this document is processed using an additive process, like screening printing, where the copper conductor is deposited only in the chosen area. The copper thick film paste is screen printed to create a circuit design on top of a thick film dielectric (insulated area) layer which is also printed on a metal base layer. The selective deposition allows for less material usage, and potentially lower overall cost as well as improved thermal performance with inclusion of thermal vias. This paper discusses the results of a newly developed lead (Pb) and cadmium (Cd) free low firing temperature (580–600°C) copper thick film conductor paste on top of a low temperature firing dielectric paste. This study includes evaluations based on SEM photos, solderability, leach resistance, and initial and long term adhesions using SAC 305 solder and RMA flux. There are many different applications for HP/HB LED circuits, from general lighting to street lighting to automotive lighting and more. All of them have varying degrees of performance testing requirement. To try to cover as much of the reliability testing as possible we have included tests such as thermal aging (150°C), thermal cycling from −50 to+150°C, as well as 85°C/85% RH reliability testing under bias.

Phase Stability and Dielectric Properties of Low Temperature Fired BaTi<sub>4</sub>O<sub>9</sub> Microwave Material with Copper Electrodes in Reducing Atmosphere

In this study we report sintering behavior and microstructures of glass-added BaTi4O9 microwave dielectric ceramics with copper paste in reducing atmosphere. Experimental results show a buffer layer may form at the interface of Cu-electrode and BaTi4O9 microwave dielectric ceramics if the glass did not diffuse smoothly during sintering, and therefore materials exhibited different colors. X-ray results indicate that Cu reacted with Ba seriously to form complicated reaction products, and some BaTi4O9 transformed to barium titanate with various ration of Ba/Ti, which may degrade the dielectric properties of materials.

Characteristics of ZnO–B 2O 3–SiO 2–CaO glass frits prepared by spray pyrolysis as inorganic binder for Cu electrode

ZnO–B 2O 3–SiO 2–CaO glass frits were directly prepared by high temperature spray pyrolysis for use in Cu electrodes. The frits prepared at temperatures above 1400 °C were spherical, amorphous, of fine size and dense structure. The mean particle size and geometric standard deviation of the frits prepared at 1400 °C were 0.87 μm and 1.37, respectively. The temperatures of glass transition, crystallization and melting were 454, 534 and 800 °C, respectively. The glass layer fired at 800 °C had a dense structure due to the material's complete melting, despite some crystals being observed by SEM. A copper electrode formed from copper paste with glass frits had a dense structure when fired at 800 °C. The specific resistances of electrodes formed from copper paste with and without glass frits were 2.5 and 8.5 μΩ cm, respectively.

Influence of glass compositions on the microstructure and dielectric properties of low temperature fired BaTi 4O 9 microwave material with copper electrodes in reducing atmosphere

BaTi 4O 9 (BT4) dielectric ceramics, containing 10 wt% BaO–ZnO–B 2O 3–SiO 2 (BZBS) glass frit as sintering aid were co-fired with copper paste under reducing atmosphere at 950 °C and investigated on microstructures and dielectric properties. Experimental results show the microstructures and microwave dielectric properties of BT4–BZBS glass composite materials are strongly dependent on the Ba–Zn–B–Si ratio, especially for the content of SiO 2 addition, in BZBS glass. XRD and EDS results indicate that Cu reacts with BZBS glass-added BT4 ceramics seriously to form complicated reaction products such as BaCuO 2 phase, when the BZBS glass composition with lower content of SiO 2 (less than 20 wt%), and transformation of some BaTi 4O 9 into barium titanate with various ratios of Ba/Ti, which, fortunately, does not seriously degrade the dielectric properties.

Comparative study on the preparation of conductive copper pastes with copper nanoparticles prepared by electron beam irradiation and chemical reduction

Copper nanoparticles with narrow size distribution of 5–7 nm were synthesized by using electron beam irradiation. The copper nanoparticles were stable in ambient air for two months. TGA showed that the copper nanoparticles prepared by using electron beam irradiation have the higher wt% of pure copper metal compared with the one prepared by chemical reduction using hydrazine hydrate(N 2H 4· xH 2O). The conductive copper paste with copper nanoparticles prepared by electron beam irradiation showed higher conductivity than the paste with copper nanoparticles prepared by chemical reduction with N 2H 4 due to small size, less amount of surfactants on the surface and higher stability against the oxidation in ambient condition. The highest conductivity of copper paste was determined as 170 S cm −1 at 90 wt% of copper nanoparticles in the paste.

Copper tracks processing on alumina by laser cladding: Elaboration and characterization

A laser process allows achieving in air electrical tracks on alumina substrates with an electrical conductivity of 5.10 6 S m −1. Copper paste was first put on alumina substrates and it was heated following a narrow track (c.a. 400 μm wide). Copper melted and oxidized partially during treatment forming cuprite Cu 2O. A reaction occurs between Cu 2O and alumina substrates which provides, after cooling, a good bonding of the copper-based tracks onto the substrates. Conditions of laser exposure have to be sharply controlled: if insufficient, tracks do not adhere to the substrate, and if too long, alumina substrates are hollowed, cracked, with vaporizations of copper and ejections of alumina. However the feasibility of such a process is now established.

Adhesion Property of Copper Paste on Ceramic Radiator Fins

Ceramic radiator fins were produced by screen-printing copper paste on ceramic substrate, which could replace the traditional technique of direct bestrow copper and meet the requirements of surface mounted technology. This method could be used to manufacture high density, superior thin and micro-sized molectrons. The key processes were screen-printing copper paste, sintering and electroless plating of nickel. The adhesion of copper film onto the ceramic substrate was often reduced after the process of electroless plating of nickel, resulting in the low quality of manufacturing. In this study, we analyzed the ceramic radiator fins which were obtained by the screen-printing copper paste method and using scanning electron microscopy to examine the surface and the cross-sections of copper film and Cu/Ni film. The adhesive properties of copper film during electroless plating was studied. The corrosion resistance of copper film and sintering glass phase on alumina substrate (96%) was also studied in an electroplating bath. The study revealed that the glass phase of acidity of silicon, softening temperature, the interaction conjunction between glass phase and ceramics were important factors.

Preparation of fine copper powders and their application in BME-MLCC

The preparation of fine copper powders by chemical reduction method was investigated. The reaction of [Cu(NH 3) 4] 2+ complex with hydrazine hydrate gives spherical monodispersed fine copper powders. The spherical copper powder with a uniform size of 3.5 ± 0.5 μm was processed to obtain flake copper powder having a uniform size of 8–10 μm, excellent dispersibility and uniform shape. The spherical copper powder of 2.5 ± 0.3 μm in size, flake copper, glass frit and vehicle were mixed to prepare copper paste, which was fired in 910–920°C to obtain BME-MLCC (base metal multilayer ceramic capacitor) with a dense surface of end termination, high adhesion and qualified electrical behavior. Polarized light photo and SEM were employed to observe the copper end termination of BME-MLCC. The rough interface from the interfacial reaction between glass and chip gives high adhesion.

Characterization of copper pastes for end termination application of base metal electrode MLCCs

The steep rise in the cost of palladium metal in the last decade has necessitated significant research and development efforts for using the base metal nickel electrodes in the manufacture of multilayer ceramic capacitors (MLCCs). Copper termination paste is hence a natural choice for end termination application of MLCCs using nickel electrodes, manufactured employing the base metal electrode (BME) process. The inert nitrogen atmosphere processing of the BME MLCCs has posed many challenges in the selection of organics (vehicles, binders, and additives), copper powders, and glasses for copper termination paste development. The effect of various organics and glasses on the drying as well as fired properties of different copper termination pastes is discussed. The effect of drying temperature and drying time on the fired properties of the copper termination, and the selection criteria for right composition of glass for copper termination paste are discussed. The properties of low and high firing temperature copper termination pastes are also presented.

Bonding behavior of copper thick films containing lead-free glass frit on aluminum nitride substrates

The present work indicates through thermodynamic considerations that the calcium, barium-borosilicate glass, which was selected as the bonding agent in copper paste, is chemically compatible to aluminum nitride (AlN) substrate. Meanwhile it implicates the scarce of reactivity which results in poor adhesion strength between the copper thick film and the AlN substrate. However after pre-oxidized treatment on AlN substrate, the adhesion strength was improved significantly by about 1 kg/mm 2 (at 20 vol.% glass frit) than that of the untreated AlN substrate, due to the improved reactivity of the glass frit. The adhesion strength is also demonstrated being affected by frit content and firing temperature. The optimum value (1.85 kg/mm 2) was obtained when the copper paste (containing 20 vol.% glass frit) was printed on the pre-oxidized AlN substrate and subsequently fired at 850 °C.

Analytical Performance of a Glucose Biosensor Prepared by Immobilization of Glucose Oxidase and Different Metals into a Carbon Paste Electrode

Enzymatic metallized carbon paste electrodes prepared by incorporation of mixtures of different metals into the paste offer a substantial decrease in the overvoltage for hydrogen peroxide oxidation and reduction. Dramatic improvements in the sensitivity and selectivity for glucose determination were obtained after the addition of iridium into carbon paste electrodes (CPE) containing glucose oxidase and palladium, copper or ruthenium. In all cases a synergistic effect was observed with a large enhancement in sensitivity obtained specially in the case of palladium-composite materials. The improvement in selectivity was more evident in the case of copper and palladium carbon paste enzymatic electrodes containing iridium where even in the presence of large excess of ascorbic acid, uric acid and acetaminophen, no interference was observed. A linear relationship between current and glucose concentration was obtained up to 1.5×10−2 M (2.7 g/L) glucose in the case of Pd(2.65%)-Ir(8.00%)-GOx(7.00%)-CPE. The effect of metals and enzyme content on the analytical performance of the bioelectrodes is analyzed.

Bonding behavior of Cu/CuO thick film on a low-firing ceramic substrate

The adhesion strength between a low-firing substrate consisting of an alumina/glass composite and a copper thick film was affected by the addition of cupric oxide and glass frit to the copper paste in a new co-firing process. An interlayer, 3–4 μm in thickness, was produced in the metal-ceramic interface during the new co-firing process due to the diffusion of copper. At the same time, the adhesion strength was improved by controlling the cupric oxide content. The addition of about 3 wt.% glass frit (softening point = 670 °C, based on the calcium-barium borosilicate glass composition) to the metal paste resulted in highest adhesion strength of 3 kg/mm2 with a shift of the debonding site toward the ceramic substrate within the interlayer. The shift of the debonding site could be observed by comparing the ratios of Al2O3/Cu and Ca concentration at the test pad areas on the substrate after debonding. The shift of the debonding site is attributed to the migration of glass frit into the interfacial region. The migration of glass frit occurred easily when the softening point of the glass frit was compatible with the new co-firing process, regardless of how much frit was used.

高機能・高性能材料の動向 銅ペーストを用いたスルーホールプリント配線板技術

高機能・高性能材料の動向 銅ペーストを用いたスルーホールプリント配線板技術

ファイン化技術 セラミックス基板用感光性銅ペーストの開発

ファイン化技術 セラミックス基板用感光性銅ペーストの開発

有限要素法を用いた銅ペーストスルーホール目詰配線板の熱応力解析

有限要素法を用いた銅ペーストスルーホール目詰配線板の熱応力解析

特集：プリント配線板設計と電磁特性 ２． 「ノイズ対策法」 銅ペーストによるプリント配線板のＥＭＩ対策法

特集：プリント配線板設計と電磁特性 ２． 「ノイズ対策法」 銅ペーストによるプリント配線板のＥＭＩ対策法

Stress Measurement Using a Bilayer Metal-Ceramic Strip

AbstractResidual stresses that develop in metal/ceramic bonded systems due to thermal expansion mismatch have been calculated using finite element modelling and measured experimentally using a simple bilayer strip. Bending in the strip occurs during cooling due to the stress asymmetry. Residual stresses are calculated by measuring the deflection of the strip and the temperature at which the strip is flat. Various compositions of both copper and nickel pastes, with and without glass and other second phase additions were evaluated on glass-ceramic. The effects of further processes, e.g. thermal cycling, brazing and plating, are also reported in this work.

Influence of Shrinkage Mismatch between Copper and Ceramics on Dimensional Control of the Multilayer Ceramic Circuit Board

The shrinking behavior of Cu/ceramic circuit boards as it applies to controlling dimensional tolerances was studied. This report includes the shrinking behavior of ceramics and copper and of the Cu/ceramic interface. It also includes the relationship between the shrinkage of the Cu/ceramic circuit board during firing and the copper content of the laminated body (which is decided before firing). Results show that the mismatch in the onset of the components' sintering temperatures affects the microstructure of the Cu/ceramic interface. The total shrinkage mismatch causes compression stress in copper wiring. The firing shrinkage of the circuit board depends on its copper content and, as copper content increases, its shrinkage approaches that of copper paste.

銅ペーストを使用したＥＭＩ対策プリント配線板

銅ペーストを使用したＥＭＩ対策プリント配線板

New thick-film copper paste for ultra-fine-line circuits

Key technologies for processing of a thick-film copper conductor applicable to photolithographic techniques are described. A flexo printer was used to obtain a film of less than 2- mu m thickness on a substrate. Using photolithographic techniques, fine-line circuits with 40- mu m-wide copper conductor lines were realized using copper pastes doped with chalcogens. Dense thin films and good adhesion to the substrate were achieved by doping chalcogens from 0.01 to 0.05 wt.%. Characteristics of these conductor films satisfied the standard requirements for hybrid ICs.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>