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The purpose of the study was to explore heat-accumulative and thermal-conductive characteristics of copper-graphene composite film (Cu-G film) while applying it to a human-skin analogue.

In the preliminary experiment, the authors evaluated the thermal conductive characteristics of the Cu-G film in three covered conditions (no film, copper film, and Cu-G film conditions). For the first factorial experiment, the heat-accumulative properties over heated pig skin were compared at air temperatures of 10, 25 and 35°C. For the second factorial experiment, 105 trials were conducted on pig skin by combining air temperatures, trapped air volumes, and numbers of film layers.

The results from the preliminary experiment showed that the Cu-G film distributed the surface heat to the outside of the Cu-G film, which resulted in even distribution of heat inside and outside the Cu-G film, whereas the copper film accumulated heat inside the copper film. The human-skin analogue of pig skin, however, showed the opposite tendency from that of the plastic. The pig-skin temperatures beneath the Cu-G film were higher than those beneath the copper film, and those differences were remarkable at the air temperature of 10°C. The accumulative heat was affected by the trapped air volume, fit to the skin, and number of Cu-G film layers.

In conclusion, the Cu-G film more effectively accumulated heat on the human-skin analogue than copper film, and those effects were more marked in cold environments than in mild or hot environments.

Manufacturers of multilayer copper thick‐film circuitry face the challenge of firing parts in an inert nitrogen atmosphere to prevent the copper from oxidising. Nitrogen, while protecting the copper from oxidation, offers no efficient mechanism for removing the carbon‐based vehicles used in the copper thick‐film paste. Because of this, carbon residues or soot often deposit on the parts during the firing process. In an attempt to improve the nitrogen furnace atmosphere's ability to remove the vehicles, several gases or gas blends were added to a nitrogen‐based furnace atmosphere. Thick‐film copper conductors and dielectric test pieces were then processed using the various gas blends. The physical properties of adhesion, aged adhesion, solderability, and conductivity of the copper conductor test pieces were studied along with the dielectric properties of dissipation factor, insulation resistance, and dielectric constant. Some of the gases tested included H2, H2O, CO, CO2, and a variety of other gas combinations. Test results demonstrated the atmosphere's ability to effect changes in the physical properties of the parts being processed. A proprietary gas blend was developed which proved effective in removing carbon residues while maintaining the desirable physical properties of the thick films. This work demonstrates the ability of certain gas additives to improve the performance of conventional nitrogen atmospheres when firing copper thick‐film circuitry. With the proper selection of the gas additive, atmosphere flows can be reduced, carbon residues eliminated, and the physical properties of the copper conductors and dielectrics maintained or improved.

The emergence of new interconnection technologies involving double‐sided surface mounted components has put stronger restrictions on the method of preserving the solderable finish on printed circuit (PC) boards. The popular Sn/Pb coatings have come under strong scrutiny due to environmental hazards of lead and also because they do not provide flat, planar surfaces for SM assembly. Organic solderability preservative coatings (OSP) are emerging as strong contenders for replacing Sn/Pb surface finishes. Benzotriazole based organic coatings have been successfully used in the past by several electronics manufacturers. However, assembly technologies involving multiple thermal operations have necessitated a fundamental understanding of the thermal stabilities and the mechanism of corrosion protection provided by the OSPs. This paper reports the results of an investigation of the thermal stabilities of two organic corrosion protection coatings. Although both are organic azole based, they operate in two distinct regimes: one forming thin films (∼100 Å) and the other forming thick films (∼5000 Å). The mechanism of surface protection has been studied using direct surface analytical techniques such as X‐ray photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES), scanning transmission electron microscopy (SEM/TEM) and Fourier transform infrared spectroscopy (FT‐IR). The solderability of the copper was measured by wetting balance techniques and correlated to the amount of copper oxidation. The results indicate that, although the thin films provide excellent protection for storage and handling operations, they decompose under heat, thereby causing oxidation of the copper. The thick films appear to withstand multiple thermal cycling. However, the underlying copper substrate can still be oxidised by oxygen diffusion through pores or cracks, or the film may undergo chemical changes that render the copper unsolderable.

An evaluation of the feasibility of copper ball‐wedge bonding on Au, Cu thick film and aluminium metallisations was carried out. This evaluation is not merely a check for feasibility, but will also give more insight into the problems concerning copper ball‐wedge bonding. This article does not pretend to represent profound research on copper ball bonding, but will give qualitative insight. Copper ball bonding, without using cover gas, is possible, but the bond quality decreases. Extrusion and penetration of the ball bond in the substrates are caused by the hardness of the copper. This can only be avoided when the hardness of the substrate is matched to the hardness of the copper ball/wire. Bonding mechanisms are similar for bonding on thick film to those for bonding on metallisations. Matching hardness of the substrate to the ball/wire seems to be a necessity for proper ball‐wedge bonding.

This paper outlines methods and results of wetting, leaching and adhesion analyses on copper thick film conductors over alumina and multilayer glasses after different processing conditions. The intention is to provide a better background for evaluating and optimising materials and processing conditions in copper thick films and working out quick, reliable and quantitative methods for better characterisation of copper conductors in production. For these reasons the following methods were used: (a) wetting and leaching analyses with a scanning wetting balance, working in nitrogen, (b) pull tests with solder contacts on copper thick film conductors after soldering, ageing and thermal cycling, and (c) some additional surface analyses (REM, EDX, Auger) for a better understanding of copper pastes and their material interactions, when processed under different conditions. The results are summarised under three general aspects: surface structure and wetting of copper thick films, wetting and leaching of various copper thick films after different processing conditions, and finally the influence of different wetting properties of such surfaces on the solder adhesion strength after soldering, ageing and thermal cycling. The results give good insight into the various interactions of copper thick films with their substrate materials and confirm the ability of the described wetting and leaching analyses for these purposes.

For TAB tapes and flex circuitry, laminates with adhesives (3‐layer laminates) are commonly used. The drawbacks of adhesives are well known. Adhesiveless flexible copper‐polyimide laminates (2‐layer laminates) could avoid such disadvantages. Two‐layer thin film laminates may be produced using sputtering technology. Good adhesion strength between the copper and the polyimide film may be achieved by means of special plasma treatment. The advantages and disadvantages of 2‐layer flexible thin film laminates are discussed in this paper, along with their different production methods. The adhesion strength of 2‐layer laminates in comparison with 3‐layer laminates will be pointed out. Future uses of 2‐layer flexible thin film laminates will be considered, along with their benefits.

A major drawback of current copper thick‐film technology is the inefficient removal of the organic binder associated with the dielectric material in the low‐oxygen inert gas (N2) atmosphere of the furnace. In processing large area and/or multilayer substrates, the incomplete binder removal causes deleterious effects which have been well documented. Therefore, it is necessary to remove hydrocarbons and residual carbon from the films in the burn‐out section of the furnace before the films begin developing their characteristic microstructures. However, the atmosphere currently employed is not capable of removing all the carbon and hydrogen in the form of gaseous oxides. In literature, in addition to furnace modifications, several atmosphere modifications and manipulations have been proposed to achieve optimum properties for the fired films. With few exceptions, the scientific basis for such atmosphere modifications and manipulations has been left either unaddressed or obscure. With this background, this paper examines the feasibility of using a reactive gas mixture in the furnace to achieve efficient organic binder removal. Phase stability diagrams are presented to illustrate the stability of (i) carbon, (ii) thick film copper ingredients, (iii) active phases of resistors, and (iv) components of glassy and crystalline phases of dielectrics in selected reactive atmospheres. The stability of certain furnace belt constituents is also addressed. Mass balance calculations are shown to demonstrate the extent of carbon removal and copper oxidation in typical nitrogen atmospheres. Based on the interpretation of thermodynamic data and reaction mechanisms involved, a specific H2‐H2O mixture with nitrogen as the carrier gas is recommended. The approach presented here constitutes a general analytical scheme to understand materials‐atmosphere interactions occurring across a temperature range. Several issues in furnace design are also discussed from the standpoint of gas‐solid reaction kinetics. These deal with the design of gas‐flow systems that facilitate removal of organic binders.

Knowledge of critical materials and process parameters necessary to fabricate quality copper thick film multilayer and hybrid circuits is being amassed and distributed throughout the industry via technical reports and presentations. Generally the information being provided in a single report deals with specific segments of the industry or only one or two specific nitrogen fireable materials. In order for hybrid manufacturers to commit themselves to the technology they need to know that sufficient flexibility exists to permit design of complex circuits and accommodate circuit design changes without imposing changes in basic process guidelines and controls. The OEM's concern, which is valid, has been that the investment required for capital equipment and establishing new processes must be fully supported by and provide reasonable return from the technology being initiated. This paper introduces new information on wire bonding in copper thick film circuits and some improvements in nitrogen fireable resistor characteristics and processing. Materials are available to produce a broad range of circuits without varying basic process parameters, and adding wirebonding as an interconnect capability further expands the circuit complexity and density achievable with copper thick films.

This paper aims to focus on an assessment of the electrochemical corrosion performance of bulk NC copper in a variety of corrosion environments.

The electrochemical corrosion behavior of bulk nanocrystalline (NC) copper prepared by inert gas condensation and in situ warm compress technique was studied by using potentiodynamic polarization and electrochemical impedance spectroscopy tests in de-aerated 0.1 M NaOH solution.

NC copper exhibited a typical active-passive-transpassive behavior with the formation of duplex passive films, which was qualitatively similar to coarse-grain (CG) copper. Although a compact passive film formed on NC copper surface, the corrosion resistance of NC copper was lower in comparison with CG copper. The increase in corrosion rate for NC copper was mainly attributed to the high activity of surface atoms and intergranular atoms. These atoms led to an enhancement of passive ability and an increase of dissolution rate of passive film in oxygen-deficiency solution. For NC copper, the corrosion resistance decreased as grain size increased in NC range.

The difference in corrosion resistance between bulk NC copper and its CG counterpart is dependent upon the corrosion solution. In a previous work, the potentiodynamic polarization tests revealed that NC copper bulks (grain size 48, 68, 92 nm) had identical corrosion resistance to CG copper bulk in naturally aerated 0.1 M NaOH solution. The results might be related to the dissolved oxygen in the medium.

It is proposed that reliable multilevel thick‐film conductor interconnect, having high track conductivity, can be fabricated with conventional air‐firing thick‐film materials, by combining the high conductivity of a pure silver conductor with the solderability of a palladium‐silver conductor. Thick‐film conductor interconnect fabricated in this manner was shown to meet comfortably the stringent requirements of a 20 year service life. A development in the standard technology used to obtain high conductivity interconnect, nitrogen‐firing copper thick‐film materials was also evaluated. It was found that new lower porosity dielectrics may allow copper thick‐film conductor interconnect to be as reliable as the air‐firing alternatives. The activation energy for the process of silver migration through a thick‐film dielectric in a humid environment was found to be in the region of 0.6 eV. The accelerating influence of humidity was also measured.