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Previous studies have proven that, under optimised ultrasonic conditions, a range of materials used in electronic manufacturing can be sonochemically surface modified using benign solutions at low temperature. The purpose of this paper is to focus on a specific process, namely, the desmearing of through holes in printed circuit boards (PCB). The objective was to determine whether the introduction of low frequency ultrasound (20 kHz) to the “etch” stage of a standard “swell and etch” desmear system could enable reduced temperature processing and the use of less chemistry in the permanganate solution.

The study was divided into three main stages. In the first “screening” phase, the effect of ultrasound in the etch solution was studied by measuring the weight loss after desmear on a PCB laminate material (Isola 370HR). Factors such as etch temperature and concentration of permanganate (including permanganate‐free) were varied. In stage 2, confirmatory runs were carried out on the most promising conditions from the screening work and through holes in a four‐layer multi‐layer board (MLB) were assessed for smear removal using a scanning electron microscope (SEM). Finally, a four‐layer MLB was desmeared through the most promising ultrasonic process and then metallized at a PCB manufacturer. Thermal shock testing was subsequently carried out and sections from the board assessed for inter‐connection defects (ICDs).

The initial screening study indicated that, whenever ultrasound was used in the etch stage of the desmear process, significantly higher weight loss was achieved compared to a standard “silent” process. This effect was most pronounced when permanganate was removed from the etch solution and, in this situation, weight loss could be an order of magnitude higher than the silent equivalent. Further testing on through holes suggested that smear‐free inner‐layers could only be guaranteed if permanganate was present in the etch solution but that ultrasound again improved smear removal. Final testing under semi‐production conditions confirmed that, if ultrasound was employed in the etch part of the desmear process, then a reduction in processing temperature from 85°C to 60°C could be achieved and the permanganate concentration halved (65 to 33 g/L) whilst still achieving ICD‐free boards.

The paper indicates the feasibility of using ultrasound to reduce temperatures and chemical concentrations used in the permanganate etch solution, whilst still producing through holes with no ICDs.

With the ever increasing demands for high performance electronic devices there is a need for circuit board laminates that have enhanced properties when compared to conventional materials such as the widely used epoxide‐based FR4 laminates. Equipment manufacturers require boards with better mechanical stability and improved electrical characteristics. At the same time, new environmental legislation is set to drive electronics assembly temperatures much higher as manufacturers start to use lead‐free soldering processes. The legislation is also raising questions about the long‐term viability of brominated resins as the basis for imparting flame retardancy to laminates. Fortunately, laminate manufacturers have responded to these challenges by developing and introducing a wide range of new laminates that address these issues. This paper describes some of these challenges and gives an introduction to the new high performance laminates that are finding increasing use. It also highlights the need for chemical processes used in the manufacture of interconnects with laminates to be specifically optimised for the chosen substrate material.

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 develop an optimised sonochemical surface modification process which could be operated at low temperature and which uses non‐hazardous chemistry with short treatment times. A range of sonochemical parameters such as ultrasonic intensity/power and process temperature were investigated.

A 20 kHz ultrasonic probe was used as the ultrasonic source. Ultrasound was applied through deionised water (DI) to sonochemically surface modify a high Tg epoxy laminate material (Isola 370 HR). The efficiency of the sonochemical surface modification process was determined by weight loss, roughness, adhesion and scanning electron microscopy (SEM).

This study has confirmed that ultrasound has the ability to surface modify a high Tg epoxy substrate material (Isola 370 HR). Weight loss and roughness values were increased by using an optimised ultrasonic process compared to control samples which were processed under “silent” conditions. Adhesion testing showed an improvement in the adhesion level between the surface and the subsequently electroless plated copper.

Surface modification of high Tg materials generally utilizes wet chemical methods. These processes involve using hazardous chemicals, high temperatures, require high volumes of water for rinsing and need relatively long immersion times. This research has shown that by optimising ultrasonic parameters, surface modification can be brought about in deionised water (DI) at low temperature.

This paper aims to show critical processing issues observed for the newer restriction of the use of hazardous substances compliant laminate materials.

Several samples of the popular lead‐free and halogen‐free laminate materials were tested under laboratory conditions to ascertain their desmear characteristics in comparison to the standard FR4 and high T_g laminate materials available on the market. Literature searches and experiences in the field were used to give a supplier's point of view of the newer laminate materials.

The new directives forcing the exclusion of solder and restricting the use of halogens means that newer laminate materials have significantly different chemical and physical properties to laminates previously considered standard. These differences have a drastic effect on the desmearing process in general, making it more difficult to get high weight losses and, for almost all lead‐free materials, reducing the roughness that can be generated. This affects the copper/laminate bonding strength and so increases risks of blistering and hole wall pull away. Alternative approaches are required to improve this adhesion and one of these is to use a specifically designed low stress electroless copper with good adhesion properties.

Most of the work was performed under laboratory conditions and, although mainly substantiated in production lines, can only be used as a guide. Owing to the large amount of different laminate materials, applications and processing techniques it is difficult to predict the full effect for every PCB manufacturer. In‐house testing should be performed by individual PCB manufacturers on each laminate material considered suitable for their technical requirements.

The paper details the main areas to concentrate on when desmearing and metallising newer laminate materials and suggests alternative approaches to improve the processing of these materials.

During the past several years, technical requirements of the printed circuit board industry have increased greatly, due to the need for greater processing latitude, higher density devices and higher reliability in the finished parts. This need has resulted, in many cases, in the emergence and/or recognition of numerous problem areas which have created greater demands on the desmear and PTH processes, specifically. Problems such as hole‐wall pullaway, resin recession, blistering, gross voiding, and blow holes have grown in importance and severity as a result of today's needs. The development of a reliable and practical permanganate desmear process has proven to solve numerous of these technical problems. The characteristics, operation, and advantages of this three‐step permanganate process will be discussed in some detail, with particular emphasis on demonstrated improvement in PCB production results.

The paper briefly reviews the problems associated with resin smear in the manufacture of multilayer boards, the various types of material involved, and their influence on smear, and some of the techniques available for assessing the degree of smear. Following a short discussion on current methods of removing smear, the paper goes on to provide a critical comparison of traditional ‘wet’ chemical processes with the newer ‘dry’ plasma techniques. Key advantages of plasma desmearing are highlighted and the paper concludes with a more detailed description of the I V Products approach and current systems, together with results of recent development work.

This paper aims to describe the development of an approach that uses a flexible substrate to investigate the mechanism of conductive anodic filament (CAF) growth and effect of different material and manufacturing variables.

A new approach using a simulated test vehicle (STV) has been developed to study the CAF phenomena. The STV can be easily built under controlled conditions in the laboratory using different glass fibres and resin powder to investigate the effect of different variables separately on CAF. The advantage of the STV is that CAF can be formed in relatively short period in a controlled way, and CAF growth can be easily identified using a back-lighting under a microscope due to the thin flex material used as the test sample.

STV has been used to investigate a number of effects on CAF formation: different glass fibres, reflow process, acid contamination in drilled holes, desmear process and glass bundle size. The results demonstrate that for finished fibres acid contamination (plating solution) at the electrode was necessary for CAF formation. However, for unfinished glass fibres (loom state and heat cleaned) CAF can be formed without acid contamination. The reflow process significantly increases CAF formation. Running an aggressive desmear process and using large glass fibre bundle also increased CAF formation.

This new approach will be of benefit for printed circuit board (PCB) supplier to evaluate CAF performance on different resin systems and glass fibres to provide high CAF resistance quality PCBs. The test period (168 hours) would be much shorter than the traditional CAF testing (1,000 hours).

Today a large variety of printed circuit board (PCB) base materials exists on the market and new ones are added frequently. The base material suppliers, having good original equipment manufacturer (OEM) marketing, usually present the materials in an early development stage to the end customers. The customers, on the other hand, expect from their PCB suppliers that the materials are fully characterized and that qualification samples are available immediately. In many cases, the process recommendations given to the PCB manufacturers are very generic (“like FR4”), insufficient, or not practicable (“8 hours baking time”). However, optimized processing ensures the reliability of the finished PCBs, starting from general leadfree compatibility to CAF testing. This demonstrates the importance of thoroughly verified process parameters and of very specific process recommendations to minimize the number of costly and time‐consuming iterations, and to be able to meet the goal of submitting qualification samples and functional PCBs in minimum time. The purpose of this paper is to show the minimum required PCB processing recommendations, and why these have to be fixed by the material supplier before commercialization of a new base material.

The paper examines the base material suppliers' situation, customer expectations and reality and the PCB manufacturers' expectations.

The paper gives the reasons and consequences of early base material marketing.

The paper analyses today's PCB base materials market and shows the reasons and consequences of early base material marketing. Also, the minimum requirements by PCB fabricators concerning processing recommendations are given.