Search results

Different techniques applied for the fabrication of thick‐film fine lines have been analysed. The basics, achievements, advantages and disadvantages of improved screen printing, screen printing with metal masks, the direct writing method, offset printing and photoformed or photoetched thick‐film are presented. In addition, current trends in front metallisation of silicon solar cells are described. Based on a critical review, the use of thick‐film fine lines for this purpose is discussed.

This paper is intended to be of interest to those involved in electronic applications of the screen printing process, including PCBs, membrane switches, thick film printing and instrument control panels. In recent years there have been a number of advances in screen printing technology which have significantly increased the capabilities and versatility of the process. Developments have included improvements in performance of screen printing machinery, mesh fabrics, stretching equipment, screen frame design, exposure devices, stencil systems and ink rheology and printability. In spite of these advances, there are many applications in PCB production where screen printing is under‐utilised, despite its cost effectiveness for volume board production when compared with dry film resists. This paper outlines some of the developments which have produced the modern screen stencils, and describes the rôle of mesh and stencil in determining the properties of the final printed result.

The purpose of the paper is to show up the current possibilities by combination of classic thick-film technology with advanced processing. Thick-film hybrid ceramic substrates have been a base for highly reliable devices for space, aerospace, medical and industrial applications since many years. The combination of classic thick-film printing with advanced technologies for fine line structuring provides substrates best suited for packaging solutions with challenging requirements, such as temperature stability and extended product lifetime. Combined with state of the art assembly technologies, thick-film substrates are used in highly demanding industries.

In recent years, several technologies for fine line structuring have been introduced, e.g. fine line printing, photo imaging, etching, laser structuring for local chip fan-out or fine line structuring on single layers. For further miniaturization of thick-film multilayers circuits, after solving the fine line resolution, the reduction of electrical connection of conductive layers through printed insulation/dielectric layer (via) diameters to connect the layers should be addressed.

The focus of this paper is to show the results of combining fine line structuring with laser microvias and to compare laser drilling in thick-films with different established via forming technologies.

The reduction of via size to 60 µm – smaller than 50% compared to using state-of-the-art printing technologies enables a solution for significant relaxation of current design possibilities.

In this research work thick‐film manufacturing technology on stainless steel baseplates was developed. Adequate adhesion of dielectric IP211 to the steel substrate was achieved only by sand blast roughening. Standard PdAg thick‐film conductors were not solderable to IP211. The solution was to have a separate multilayer dielectric under conductors to be soldered. The reliability of soft soldering and gold wire bonding of thick‐film metallisation on stainless steel and other baseplate materials was evaluated. The technology developed was applied to manufacturing an intelligent signal node. Present expertise enables the manufacture of thick‐film hybrids on stainless steel baseplates. Development of an industrial production line would, however, involve considerable effort.

Thick printing Cu and Ag conductors have been developed specifically for use in power applications where excellent printing, thermal, electrical, wire bonding and soldering properties are prerequisite. Efficient thermal management can require fired films on alumina in excess of 150μm and often printed in large areas. In some designs the thickness of mounting pads alone for bare silicon dies may need to be built up locally. This approach enables a single substrate to comprise both thinner printed, dense circuitry for signal control and thick device mounting pads for efficient thermal management. The flexibility of thickness control, through hole connections and the ability to incorporate printed resistors using standard thick film processing can offer solutions which complement the other substrate technologies in many applications. This paper describes the advancements made in optimizing the performance of thick printing copper and silver conductors designed for use in power applications and their role in this demanding technology. The features of the materials, process guidelines, and performance characteristics will be discussed.

Diffusion patterning is a dielectric patterning technology, which is used in the screen printed thick film technology for higher density multilayer circuits. This technology is suitable for producing lower cost multichip modules and requires a low additional investment in conventional thick film technology production lines. Comparisons of via resolution capability of diffusion patterning versus conventional thick film technology are described and discussed. Preliminary experimental results obtained with a test circuit showed that 200μm lines and 200μm vias could be achieved with acceptable yield and with minimal modification to standard production lines. The electronic circuit for the pressure sensor was designed and realised with the verified technology as a low‐cost ceramic multichip module. A few results of an investigation of some thick film materials, which comprise the “set” of pastes for diffusion patterning technology, are presented.

The aim of this paper is to investigate microwave Ku band absorbance, complex permittivity, and permeability of SrFe₁₂O₁₉ thick films by a simple and novel waveguide technique.

The glass frit free or fritless strontium hexaferrite thick films were formulated on alumina by screen printing technique from the powder synthesized by chemical co precipitation method for pH 11 adjusted during the reaction. The 13‐18 GHz frequency band microwave absorbance of the SrFe₁₂O₁₉ thick films by a simple waveguide method. The complex permittivity and permeability of strontium hexaferrite thick films was measured by voltage standing wave ratio technique.

SrFe₁₂O₁₉ thick films show high ∼80 percent absorbance in the whole 13‐18 GHz frequency band. The thickness dependant microwave properties of strontium hexaferrite thick films were observed. The real permittivity ε′ lies in between eight and 35 with the variation in thickness of the thick film SrFe₁₂O₁₉. The real microwave permeability μ′ of strontium hexaferrite thick films lies in the range 1.12‐6.41. The resonance type behavior was observed at frequency 14.3 GHz. The SrFe₁₂O₁₉ thick film of thickness 30 μm could be a wide band (∼5,000 MHz) absorber with absorbance ∼87 percent for the whole 13‐18 GHz frequency band.

The complex permeability of strontium hexaferrite thick films was measured by simple novel waveguide method. The high absorbance (∼87 percent) of thick film SrFe₁₂O₁₉ over a broad band ∼5,000 MHz will be useful in achieving RAM coatings required for 13‐18 GHz frequency band.

Thick‐film technology to implement passive elements, network and hybrid circuits has been widely used for four decades and its importance is still growing. While on one hand the technology has been improved to meet the requirements for more sophisticated circuits, on the other hand a better knowledge of its outstanding properties has promoted its application to a certain number of sometimes exotic devices, many of which are in the sensor and actuator area. This paper presents examples of a variety of applications to illustrate what thick film technology can offer outside the familiar area, and to stimulate the imagination of scientists towards possible new applications.

The Microelectronics Division of the Radio Measurement Engineering Research Institute of Lithuania has developed a unique photoimageable thick film chemistry and process technology which has been in use since the mid‐1980s. The main application of the technology was for complex thick film microwave integrated circuits at lower cost than equivalent thin film devices. The paper describes the photoimageable materials and processing used at the Institute and also gives examples of suitable application in the microwave, high density interconnect, sensor and component fields.

Military and commercial hybrids, using high speed integrated circuits with increased input/output density, require low cost, high reliability thick film circuits providing high density, multilayered interconnections with controllable electrical and mechanical characteristics. To meet these criteria it was necessary to adapt the silk screen printing process, including design, materials and reproduction processes, to cater for ‘thick film’, that is able to reproduce extremely fine lines without sacrificing the edge definition of the circuit layout. Printing screens were developed to deposit gold and silver pastes with line/space widths of 50 microns (0.002 in.) on bare ceramic and 100 microns (0.004 in.) on dielectric layers. Interconnection between layers was achieved with 150 micron (0.006 in.) dielectric via openings with corresponding via‐fill conductive connections (gold or silver). The development of the photo‐image onto the emulsion of the screen was deemed to be the most important single step in determining the final print definition of the circuit's design. The main body of this work was concentrated on this approach. The selection of the screens, emulsion system, UV exposure and development processes are also discussed. A capability circuit (CQC) was produced, consisting of five metal layers with line/spaces of 100 microns connected on each side of the ceramic by front to back lasered ‘through‐hole’ connections of 125 microns (0.005 in.) and layer interconnections through 150 micron (0.006 in.) dielectric vias. This capability circuit is classed as an Electronic Component of Assessed Quality by Capability Approval in accordance with BS 63200.