ABSTRACT

The use of printed circuit board is unavoidable within the electrical and electronic industries. Various types and models exist, all made from synthetic substrates. The environmental impact of discards of printed circuit boards as well as the need to go green globally poses challenges to the printed circuit board manufacturing industry. In the attendant search for wider utility value for agro-waste based particle boards, this work presents the research of utilizing agro-waste based particle boards as virgin substrates for the production of printed circuit board wafers. The agro-waste materials were pre-treated, ground and pressed into boards using a Novalac resin (Melamine- formaldehyde). After cutting to sample sizes, the samples were cleaned and electroless deposition was carried out on the boards using non-precious metal catalyst ( as against the conventional precious metal catalyst-Palladium). Material strength characterization of the boards was carried out to determine the durability of samples when in use. Scanning electron microscopy of the samples showed good deposition and acceptable roughened topography which compared well with that of a commercial grade sample. A simple conductivity test was done with an ammeter to prove the transfer of electrical current at the surface of the substrates. This phase of work concludes that there can be deposition on natural waste materials and that going ‘green’ in the area of circuitry is achievable. Optimization of process conditions will create another niche for the use of conversion products from agro waste discards while giving the products a value-added status.

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CHAPTER ONE

INTRODUCTION

1.0       GENERAL INTRODUCTION

Printed circuit boards are boards used in the connection of lead lines of various electronic parts/components. Such important circuitry parts like resistors, capacitors, transistors are housed and connected using metal-clad non-conducting substrates and the whole network is known as a printed circuit board(1). These boards are made in three basic structural classes, (i) with a shield or earth plate; (ii) with a multilayer structure; and (iii) as a thin film, single layer. They are pathways made of copper or some other conducting material that is etched or laminated onto a rigid or flexible surface. The "printed" means that the material is deposited onto the substrate and the discrete wires are not used.

The search for printed circuit boards dates back to the 19th century when telegraph, telephone and radio inventions were being recognized as practical devices for everyday use and they all required wiring connections(2). For example, the increasingly complex radio circuits needed an alternative wiring technology which ought to be simpler than the existing tedious and error prone wiring technology. As a result, in 1903, Albert Hanson

(3)   filed a printed wire patent which was to solve the problem of multi-wire connection dilemma. His patent clearly described the concept of double-sided through–hole circuitry. This first circuit pattern touched on so many concepts that are seen to be of modern origin.

Printed circuit board is synonymous to printed wiring board which is undoubtedly the most common type of printed circuit. It is a copper-clad dielectric material with conductors etched on the external or internal layers. It is subdivided into single-sided, double-sided, and multilayer boards.

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It performs structural, functional and aesthetic duties in any electronic device, while ensuring safety and convenience in the handling of point-to-point lead line linkages. There are five primary types of this board, depending on the desired utility in the electronic circuitry. These five types are:

1.                 Motherboard: This is the board that forms the principal circuit board in the circuitry and it houses the basic components of the system.

2.                 Expansion board. This is a printed circuit board that plugs into an expansion slot present alongside the mother board. This board compliments the utility of the

mother board.

3.           Daughter board. This is a board that attaches to an expansion board as a supplementary utility board

4.                 Network Interface Card (NIC). This is a type of expansion board that is mostly found in personal computers (PC). It enables the PC to be connected to a local area network. It is a connector circuit board.

5.                 Adaptor. This is a type of expansion board that controls the graphics monitor because it houses the controller chip.

The top side of a printed circuit board is referred to as ‘component side and the bottom side the ‘solder side’. The components are located on one side of the board and the conductor pattern on the opposite side necessitating the making of hole (through hole) in the PCB for the component legs to penetrate the board. Consequently the legs are soldered to the PCB on the opposite side of where the components are mounted. There are oftentimes the need for complex PCB designs as a result of product utility and this prompted the designing and manufacture of PCB boards of various ‘face’ categories(4). These categories are:

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1.                 Single Sided: These are boards that have only the conductor pattern on one side and the components mounted on the other side. This type of board has serious limitation with respect to the routing of the wire in the conductor pattern because the wires cannot cross and have to be routed around each other. This category of board design is only used in very primitive circuits (5).

2.                 Double –sided: These are boards with a conductor pattern on both sides of the board. They have electrical connection between two conductor patterns, this electrical bridges are called ‘vias’ which are holes in the PCB that are filled with metal and touches the conductor pattern on both sides. This type of PCB design is suited for complex circuits.

3.                 Multi-layer boards: There are boards with one or more conductor patterns inside them. The multilayer is achieved by laminating several double – sided boards together with insulating layer in between. The number of layers is known from the number of separate conductor patterns and is usually even and includes the two outer layers. The most common ones are the 4 and 8 layers, though some with as many as 100 layers are obtainable(6). The ‘vias’, which connects the conductor patterns, becomes a hindrance when only a few of the conductors are needed in service. Therefore, ‘buried’ and ‘blind’ vias types are used in multi-layer boards. This is feasible because the ‘buried’ and ‘blind’ vias are produced in such a way that they only penetrate as many layers as are necessary. The blind vias connects one or more of the inner layers with one of the surface layers without penetrating the whole board, while ‘buried’ vias only connects

the inner layers.

In multi-layer PCBs, whole layers are almost always dedicated to ground and power and are classified as signal, power or ground planes (7). In situations where it is necessary to

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have the different components on a PCB connected to different supply voltages, there is usually more than one of both power and ground planes.

Printed circuit board (PCB) substrates are materials that are polymeric, which perform the function of structural platforms/bases for the mounting of electronic units in the electronic industry (8). Literarily, from the definition of the two component make-up of the phrase, "PCB substrates", are materials of large number of structural units that are joined by the synergy of linkages, which forms a stratum on which is mounted electronic units that collectively make-up a system's circuit. These supports are non-conductors/dielectrics that are dimensionally, thermally and chemically stable when in use. The choice properties of such materials are:

a.                  high dielectric strength

b.                 low dielectric constant,

c.                  good flexural strength

d.                 low thermal coefficient of expansion

e.                  high resistance to humidity and

f.                   possession of high degree of fire retardancy

The use of polymers (plastics) as substrate in plating process can be traced back to the plating of celluloid pen parts in 1905, where electroless silver solution was applied to the surface of the celluloid material after a stannous chloride sensitization of the surface of the plastic(9). Some of the advantages of using polymers in place of metals in plating processes are:

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a.                  Plastics give extended shelf life because only the surface of a plated plastic is prone to corrosion whereas all parts of a metal corrode with an eventual failure in service (10).

b.                 The plastics require no other production finishing steps such as buffing, before plating, whereas metals require such steps and this increases the overall cost of production.

c.                  When plastics are plated on, they acquire improved tensile strength, elasticity and flexural strength, with a reduced total coefficient of thermal expansion. The plastic material also has an enhanced abrasion and weathering resistance.

Some examples of platable plastics are:

i.                   acrylonitrite butadiene – styrene (ABS)

ii.                 poly (phenylene ether)

iii.              nylon

iv.              polysulfone

v.                 polypropylene

vi.              polycarbonates