Search results

A new aramid base material for use in laminates to be applied to advanced surface mount technology was developed. A new fibre based on PPDETA (Poly‐p‐phenylene/3,4'‐diphenylether terephthalamide) was found to have negative thermal and hygroscopic expansion coefficients, low ionic impurities and high affinity to epoxy and polyimide resins. The fibre was processed into fabrics and papers to be used as a base material for printed circuit boards for advanced surface mount technology. Impregnation with a new epoxy resin with high purity and high temperature resistance implemented the development of a new laminate with minimal electromigration and high dimensional stability. Thus, a new laminate was developed to be used for LCCC, PGA, COB, TAB, Flip‐Chips and other advanced surface mount technologies. Reliability of the laminate to electromigration between surface conductors, between plated‐through barrels, and between opposed conductors was found to be one of the highest available today. These types of behaviour were related to the high purity and high temperature resistance of both the reinforcement material and the resin. The short life of through‐hole plating in thermal shock was improved by the application of a new plating technology. Application to multilayer boards and laminates with a low dielectric constant is also being investigated.

Low Shrinking: Epoxies react with their hardeners by direct addition, without the evolution of volatile by‐products and with very little chemical rearrangement. Unlike phenolics and polyesters, the epoxies exhibit very low shrinkage during cure. Abstract—A new punchable high performance epoxy/glass printed circuit laminate has been developed. It is designed to replace more costly and troublesome composite type laminates commonly used in high volume electronic assemblies using two‐sided boards with plated‐through holes. The excellent punching and plating characteristics, coupled with electrical properties equal to those of FR‐4, should make this laminate attractive to all those involved in high quality electronics. This paper was originally presented at the First Printed Circuit World Convention held at the Cafe Royal, London in June 1978.

The purpose of this paper is to show production process developments and innovations that resolve many of the issues faced with certain process steps for printed circuit board (PCB) manufacturing following “green” practices.

Several key PCB manufacturing processes have been developed or studied with respect to new environmental legislations and practises.

The introduction of new legislations designed to protect the environment require changes to laminate materials, solders, and PCB manufacturing techniques. The effect of new laminate materials on the desmearing and metallising processes have been assessed and recommendations given. The effect of increased thermal stress on plated copper has been assessed. Developments in adhesion enhancement for black oxide alternatives have been made and are presented with their suitability for the newer green laminate materials. The development of a new laminate manufacturing technique to reduce environmental impact is introduced. The capabilities of different surface finishes in relation to new lead‐free soldering techniques is investigated and presented.

This is a short paper covering several major PCB processing steps and covers experiences and development results.

The paper details how “green” PCB manufacturing affects some key processes, developments to improve results and environmentally friendlier innovations in laminate manufacturing techniques.

The purpose of this paper is to investigate the buckling strength of simply supported plates with mechanical extension-twisting coupling. Bounds of the compression buckling strength are presented for a special sub-class of extension-twisting coupled laminate that is free from the thermal distortions that generally arise in this class of coupled laminate as a result of the high temperature curing process. These special laminates are generally referred to as hygro-thermally curvature-stable (HTCS).

This paper gives an overview of the methodology for developing laminates with extension-twisting coupling properties, which are derived from a parent laminate with HTCS properties. A closed form buckling solution is applicable for this special class of coupled laminate, which facilitates an assessment of compression buckling strength performance for the entire laminate design space.

Extension-twisting coupled laminates have potential applications in the design of aero-elastic compliant rotor blades, where the speed of the rotating blade, and the resulting centrifugal force, can be used to control blade twist. Extension-twisting coupling reduces the compression buckling performance of the blade, which represents an important static design constraint. However, the performance has been shown to be higher than competing designs with extension-shearing coupling in many cases.

Bounds of the buckling curves have been presented for the entire HTCS laminate design space, possessing extension-twisting and shearing-bending coupling, in which the laminates contain standard ply angle orientations and up to 21 plies. These laminates can be manufactured without the undesirable thermal warping distortions that generally affect this class of coupled laminate, and in particular, those containing angle plies only; previously thought to be the only form of laminate design from which this particular type of mechanical coupling can be derived.

Fokker Aircraft, with nearly forty years' experience in bonded metal and composite materials manufacture, is about to move into the flight test phase with components produced in a new and innovative structural laminate combining the physical attributes of the two techniques.

A novel rapid prototyping technology incorporating a curved layer building style was developed. The new process, based on laminated object manufacturing (LOM), was designed for efficient fabrication of curved layer structures made from ceramics and fiber reinforced composites. A new LOM machine was created, referred to as curved layer LOM. This new machine uses ceramic tapes and fiber prepregs as feedstocks and fabricates curved structures on a curved‐layer by curved‐layer basis. The output of the process is a three‐dimensional “green” ceramic that is capable of being processed to a seamless, fully dense ceramic using traditional techniques. A detailed description is made of the necessary software and hardware for this new process. Also reviewed is the development of ceramic preforms and accompanying process technology for net shape ceramic fabrication. Monolithic ceramic (SiC) and ceramic matrix composite (SiC/SiC) articles were fabricated using both the flat layer and curved layer LOM processes. For making curved layer objects, the curved process afforded the advantages of eliminated stair step effect, increased build speed, reduced waste, reduced need for decubing, and maintenance of continuous fibers in the direction of curvature.

To meet the ever increasing quality standard set by the manufacturers of multilayer printed circuit boards, IMASA, in association with Enthone Inc. USA, has further developed the Enplate MLB permanganate etch back system to improve the hole quality of a multilayer printed circuit board. To enable manufacturers to utilise this improvement using existing equipment, Short Line Chemistry was developed.

Earl Moon of Viking Interconnect Systems addressed those present at the 21 May meeting on the subject of ‘Characterisation of Military SMT/MLB Requirements as a Function of the Total Package Concept’.

In recent years, with the development trends towards lighter, shorter and smaller high performance and high reliability electronic products, printed circuit boards have ceaselessly been growing in terms of higher density and layer count. At present, conventional FR‐4 laminate, which is reinforced by glass fabric, has become the universal purpose base material because of its excellent adhesion, good electrical insulation and mechanical properties. However, with its relatively low glass transition temperature (T_g) of approximately 135°C, large coefficient of thermal expansion in the z‐axis direction, poor thermal resistance and propensity for resin smear while drilling, normal FR‐4 is severely limited in high performance applications, especially for multilayer board fabrication, and is used only for multilayer boards with layer counts below ten. Furthermore, conventional FR‐4 is usually cured using dicyandiamide, which could potentially cause insulation deterioration of the printed circuit boards and vulnerability in terms of delamination under high temperature treatment. These effects could degrade the reliability of PCBs and therefore, base material suppliers have focused on improving the T_g and thermal resistance to broaden the operating window of conventional FR‐4.