Home Project-material PRODUCTION OF COPPER-CLAD PRINTED CIRCUIT BARE BOARD SUBSTRATE FROM AGRICULTURAL AND PLASTIC WASTE MATERIALS.

PRODUCTION OF COPPER-CLAD PRINTED CIRCUIT BARE BOARD SUBSTRATE FROM AGRICULTURAL AND PLASTIC WASTE MATERIALS.

Dept: INDUSTRIAL CHEMISTRY File: Word(doc) Chapters: 1-5 Views: 1

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 determin
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 multilayer 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 nonconductors/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

vii. Phenolics

viii. Polycarbonate – ABS alloys

ix. Polyesters

x. Foamed polystyrene

xi. Phenolic-paper

xii. Epoxy-paper

xiii. Polyester-glass

xiv. Polyimide glass,

xv. Poly(vinyl chloride)

xvi. Poly(ethersulfone)

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xvii. Polyetherimide

xviii. Polyetherketone etc.

1.1 NATURAL POLYMERS (agro wastes)

These materials are wastes from the agricultural sector. Most of them have little or

limited utility values. They all have a common base raw material which is cellulose.

These materials are (a) corn cob, (b) saw dust and (c) rice husk.

1.1.1 CORN COB

A corncob is the central core of a maize (Zea mays ssp. mays L.) ear. The corn

plant’s ear is also considered a “cob” or “pole” but it is not fully a “pole” until the ear is

shucked, or removed from the plant material around the ear. Historically, corn cobs were

used in outhouses in lieu of toilet paper, source of furfural( an aromatic aldehyde used in

a wide variety of industrial processes), as fibre in ruminant fodder, smoking pipes. It

contains not less than 40% phosphorus as P205 (ash). The principal chemical constituents

of corn cobs are cellulose, pentosan and lignin. These are mainly from the wood blast and

cortical layers of the cob. Cellulose and lignin are usually good for board manufacture

while the pentosan content of 20.6 percent shows that the corn cobs could be used in the

manufacture of furfurals and other products(11).

The absence of acid and extractive content shows that the board properties may

not be affected because their presence affects board quality ( 12). It is therefore, assumed

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tentatively that corn cobs might be suitable raw material for particle board manufacture.

The various production steps involved are outlined using the flow chart.

1.1.2 RICE HUSK

Rice husk/hull is a “biogenic opal,” with approximately 20% opaline silica in

combination with a large amount of the phenylpropanoid structural polymer called lignin.

The silica which is amorphous is bound to water in a very intricate manner. This high

percentage of opaline silica within rice hulls is most unusual in comparison to other plant

materials(13 ). It is proposed(14 ) that during the combustion of rice hulls, the silica ash

may form a “cocoon” that prevents oxygen from reaching the carbon inside thereby

retarding burning. Another viewpoint(15 ) is that, since silica and carbon may be partially

bonded at the molecular level, silicon carbide is formed during high-temperature

combustion, and that the presence of this heat-resisting ceramic impedes the easy

combustion of the rice hull. Still other scientists project that at certain temperatures, the

molecular bond between the silica and carbon in the hull is actually strengthened, thereby

preventing the thorough and uniform burning of the hull. This flame-retarding and, at

ordinary temperatures, self extinguishing character as a result of the peculiar silicacellulose structure, impede uniform and thorough burning in a combustion process and

also ensures resistance to water penetration and fungal attack.

Attributes:

a) They are highly resistant to moisture penetration and fungal decomposition.

b) They do not transfer heat very well.

c) They do not smell or emit gases.

d) They are not corrosive with respect to aluminum, copper or steel where corrosion is

induced/propagated by either alkaline or acidic environmental conditions.

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In their raw and unprocessed state, rice hulls constitute a Class A or Class I insulation

material( 16). It is a by-product with very low protein and available carbohydrates, but

contains very high crude fiber, crude ash and silica. Of all cereal byproducts, the rice hull

has the lowest percentage of total digestible nutrients (less than10%) ( 17). Surprisingly,

rice hulls require no flame or smolder retardants. Nature has freely given to this

agricultural waste product all of the combustion properties needed to pass the Critical

Radiant Flux Test (ASTM C739/E970-89), the Smoldering Combustion Test

(ASTMC739, Section 14), and the Surface Burning Characteristics Test (ASTM E84).

Recent testing( 18) done by R&D Services indicates an average Critical Radiant Flux

(CRF) of 0.29W/cm2

, a smouldering combustion weight loss between 0.03% and 0.07%,

a Flame Spread

Index (FSI) of 10 and a Smoke Development Index (SDI) of 50.

1.1.2.2 Water Imbibition:

All organic materials will absorb or release moisture until they come into equilibrium

with the relative humidity of the surrounding air. The high concentration of opaline silica

on the outer surface of the rice hull impedes the atmospheric transfer of moisture into the

hull. Also, 2.1% to 6.0% of the rice hull consists of a bio polyester called cutin, which, in

combination with a wax produced by the rice plant, forms a highly impermeable barrier.

Nature employs several very effective strategies to protect the kernel of rice from the

water and high humidity generally associated with the cultivation and growth of this

plant. Consequently, studies done(19 ) on rice hulls at 25°C indicate that the equilibrium

moisture content of rice hulls at 50% relative humidity is at or below 10%, while at 90%

relative humidity, the equilibrium moisture content of rice hulls remains at or below 15%.

A Moisture Vapor Sorption Test (ASTM C739, Section12) conducted by R&D Services(

20) indicates a gain in weight of only 3.23%. This is well below the moisture content

needed to sustain the growth of fungi and mould.

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1.1.2.3 Industrial usesThese include:-

Mesoporous molecular sieves, which are applied as catalysts for various chemical

reactions, as a support for drug delivery system and as adsorbent in waste water

treatment, Pet food fibre, Building material, Pillow stuffing, Fertilizer, SiC production,

Fuel, Brewing to increase the lautering ability of a mash, Juice extraction to improve

extraction efficiency of apple pressing and as rice husk ash aggregates and fillers for

concrete and board production, economical substitute for micro silica / silica fumes,

absorbents for oils and chemicals, soil ameliorants, as a source of silicon, as insulation

powder in steel mills, as repellents in the form of “vinegar-tar”, as a release agent in the

ceramics industry, as an insulation material for homes and refrigerants

1.1.3 SAW DUST

Wood waste is wood that no longer has value at its current location, it may be a waste

product of a process, it may be from shipping/receiving, it may be from construction or

de-construction, etc. It is produced from manufacturing, forestry, construction, deconstruction sectors, municipalities and utilities. Sources include pallets/skids, crates,

wire reels, scrap wood, sawdust, shavings, milling residue, processed wood, cut offs,

trees, branches, brush, stumps and bark. Sawdust is composed of fine particles of wood. It

is produced from cutting with a saw, hence its name. It has a variety of practical uses,

including serving as mulch, fuel, manufacture of particle board. Until the advent of

refrigeration, it was often used in ice houses to keep ice frozen during the summer(21 ).

Historically, it has been treated as a by-product of manufacturing industries with inherent

hazard, especially in terms of its flammability( 22). It is also sometimes used to soak up

spills, allowing the spill to be easily swept clean. Perhaps the most interesting application

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of sawdust is in pykrete, a slow-melting, much stronger ice composed of sawdust and

frozen water.

The environmental impact of saw dust comes from the large amount of sawdust and

wood waste that is generated which is dumped without being fully utilized. Over a period

of time the wood waste is burnt or used for heating and when not removed from dump

area decomposes and emits methane, a greenhouse gas that is about 21 times more

harmful to the environment than carbon dioxide(23 ).

1.2 BACKGROUND OF STUDY:

This project stems from the fact that Nigeria today is matching towards a technological

independence of which the actualization of skill acquisition in the area of electronic

components, starting from the basic circuitry manufacture is one of it. Consequently the

production and acquisition of the skill of manufacturing this bare board will ensure the

non-dependence of our industries on imported bare boards which invariably cuts down

the overall production of electrical and electronic components/parts.

The utilization of waste cellulosic agro-materials will further make the cost of producing

the bare boards significantly cheaper while providing another means of converting the

wastes to utility items supporting the laudable ‘waste to wealth’ initiative of the country.

It will also create employment for the teaming youths.

The understanding and utilization of the cheap non precious metal catalyst reagents will

not only reduce the cost of manufacturing but also encourage the search for safer, cheaper

and more environmentally friendly alternatives to the palladium and/organic catalysts that

are presently in use, thereby keeping us abreast with the western technological approach

to this technology. The primary target of this study is to discover alternative raw

materials for the production of printed circuit board, different from the petrochemical

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based resources (synthetic polymers) considering the fact that our petrochemical industry

is not actively operational. The successful completion of the study will open a new

frontier in the actualization of the concept of ‘green’ electronics which will provide a

sustainability and efficient cycling status to this sector. It will also enhance the required

techno-socio-economic impact of utilizing renewable resources while bringing down the

cost of producing these board with attendant low cost electrical/electronic products. The

dependence on foreign expertise and/product importation will be reduced or completely

eradicated.

1.3 SCOPE OF STUDY:

This project boarders around the preparation of particle boards from agro wastes and the

determination of relevant properties that will ensure the possible utilization of the

material wafers for printed circuit board manufacturing. A preliminary electroless copper

deposition will be carried out to ascertain the feasibility of depositing copper on the

substrates. A further work at a higher level will perfect the plating process and upscale to

the industrial manufacturing stage and mass production.

1.4 IMPORTANCE OF WORK:

The aim of the electronic manufacturing industry has long been to achieve a reliable

circuit design with repeatable electrical characteristics, good mechanical properties and

acceptable aesthetics(24). Until the 1950s, electronic circuits and systems were

assembled by using individual wires to connect each of the components. The components

were then mounted on what were known as long strips and sockets.

In response to the desire by the consumer for repeatable performance, smaller sizes

and lower costs, it became very necessary for the development of assembly schemes that

would allow for greater manufacturing efficiency. The printed circuit board method

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proved very successful in providing the contact between components, laminates of an

insulating material are best suited for these work.

This study which is aimed at locally producing a non-conducting substrate for use

in the manufacture of printed circuit board, is very important to the scientific world

considering the areas of interest in the search for raw materials (synthetic (PVC) and

natural (sawdust, rice husk and corn cob)). The use of the agro-wastes, if successful will

open up a cheap source of raw material supply, apart from the fact that the overall cost of

producing those substrates will be reduced due to the elimination of chemical roughening

step of the sheets (etching). The overall time and energy for processing the board will be

minimized from the skipping of the etching step. On the other hand, the utility value of

those ‘ascribed’ wastes will be greatly enhanced and the negative environmental impact

will be totally eliminated. The study will also explore the possible recyclability of the

boards in any event where damage occurs to the circuit. There is also the possibility of

having an electronic item with close to hundred percent local content raw material input

which are also environmentally friendly and inexpensively sourced.

The study will also present us with the understanding of the possibility of cladding on

unprocessed (not like paper sheets) cellulosic material knowing that all three natural

materials chosen for this study (saw dust, rice husk and corn cob), are all cellulose based.

The degree of permanence achieved with the metal deposition will be verified by the

simple peel test.



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