faculty of mechanical and manufacturing engineering …in faculty of engineering technology utem,...

Faculty of Mechanical and Manufacturing Engineering

Technology

INVESTIGATION OF COVERLAY ADHESION BY ACRYLIC-BASED

ADHESIVE ON COPPER-POLYIMIDE LAMINATE FOR FLEXIBLE

PRINTED CIRCUIT

Aida Nazifa Binti Abdul Aziz

Bachelor of Manufacturing Engineering Technology (Process and Technology) with

Honours

2018

INVESTIGATION OF COVERLAY ADHESION BY ACRYLIC-BASED

ADHESIVE ON COPPER-POLYIMIDE LAMINATE FOR FLEXIBLE

PRINTED CIRCUIT

AIDA NAZIFA BINTI ABDUL AZIZ

A thesis submitted

in fulfilment of the requirement for the degree of Bachelor of Manufacturing

Engineering Technology (Process and Technology) with Honours

Faculty of Mechanical and Manufacturing Engineering Technology

UNIVERSITI TEKNIKAL MALAYSIA MELAKA

2018

DECLARATION

I declared that this thesis entitled “Investigation of Coverlay Adhesion by Acrylic-Based

Adhesive on Copper-Polyimide Laminate for Flexible Printed Circuit” is the results of my

own research except as cited in references. The thesis has not been accepted for any degree

and is not concurrently submitted in candidature of any other degree.

Signature : ………………………………………….

Name : Aida Nazifa Binti Abdul Aziz

Date : …………………………………………

APPROVAL

I hereby declare that I have read this thesis and in my opinion this thesis is sufficient in terms

of scope and quality for the award of Bachelor of Manufacturing Engineering Technology

(Process & Technology) with Honours.

Signature : ………………………………………….

Supervisor Name : Hairul Effendy Bin Ab Maulod

Date : …………………………………………

DEDICATION

To my beloved family, lecturers and friends.

i

ABSTRACT

This study is to investigate the coverlay adhesion by using acrylic-based adhesive on copper-polyimide laminate for Flexible Printed Circuit (FPC). Nowadays, the functionality of electronic devices continues to increase at higher rate. FPC is one of the higher requests in various industries. In FPC, lamination process is required to join the coverlay with copper clad laminate (CCL) using acrylic-based adhesive under heat, pressure and interval time. This process is to improve the bonding strength between the materials after curing. One issue that may occur after curing process is delamination of FPC. Thus, the overall thickness of FPC and the correlation of pressure and temperature distribution of lamination press machine towards delamination issue on coverlay adhesion by acrylic-based adhesive on copper polyimide laminate is investigate in this study. Testing and analysis included cross-section test and thermogravimetric analysis (TGA) to characterize the adhesive bonding correlated with acrylic-based adhesive with copper polyimide after curing process in FPC. From the analysis of the layer thickness, the highest and lowest thickness of adhesive is determined using 3D Laser Microscope where the highest thickness is on middle book while the lowest thickness is on top book of FPC. There are no delaminations occurred but the result of the adhesive thickness obtained showing the tendency of delamination to occur. The TGA curve analyzes the weight loss of each material in the FPC where the FPC starts to degrade at temperature 400oC. From the analysis of TGA, the more weight loss in the thermal analysis shows the less bonding strength of adhesive.

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ABSTRAK

Kajian ini adalah untuk mengkaji lapisan penutup pelekat menggunakan pelekat berasaskan akrilik pada lamina copper polyimide dalam litar bercetak fleksibel. Pada masa kini, fungsi komponen elektronik terus meningkat pada kadar yang tinggi. Litar bercetak fleksibel mempunyai permintaan yang tinggi dalam pelbagai industri. Dalam litar bercetak fleksibel, proses laminasi digunakan untuk mengabungkan lapisan penutup dengan copper clad laminate (CCL) menggunakan pelekat berasaskan akrilik di bawah haba, tekanan dan jangka masa. Proses ini adalah untuk meningkatkan tahap kekuatan ikatan antara bahan selepas proses pengawetan. Salah satu isu yang mungkin berlaku selepas proses pengawetan adalah delaminasi. Oleh itu, keseluruhan tebal dalam setiap lapisan litar bercetak fleksibel dan hubungkait tekanan dan pembahagian suhu dalam mesin laminasi terhadap isu delaminasi pada lapisan penutup pelekat oleh pelekat berasaskan akrilik pada copper clad laminate akan dikaji. Uji kaji dan analisis termasuk kajian keratan rentas dan analisa thermogravimetric yang akan dijalankan untuk menggambarkan ciri-ciri kekuatan pelekat yang dikaitkan dengan pelekat berasaskan akrilik dengan copper polyimide selepas proses pengawetan dalam litar bercetak fleksibel. Daripada analisa ketebalan lapisan litar, ketebalan pelekat yang paling tinggi dan yang paling rendah telah ditentukan di mana tebal yang paling tinggi terletak pada bahagian tengah buku dan tebal yang paling rendah terletak pada bahagian atas buku. Tiada isu delaminasi berlaku tetapi selepas mengkaji setiap lapisan, isu delaminasi mungkin berlaku. Analisis thermogravimetric telah mengurangkan berat daripada setiap bahan dalam litar bercetak fleksibel di mana degradasi bermula pada suhu 400oC. Daripada analisa TGA, lagi banyak berat berkurang, lagi sikit kekuatan ikatan antara pelekat tersebut.

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ACKNOWLEDGEMENT

First and foremost, Alhamdulillah all praises to the Almighty Allah S.W.T for His blessing

which have given all the strength in fulfilling and completely this final year project (FYP). All

the praise and blessing be upon Prophet Muhammad S.A.W. I would like to express my

sincere acknowledgement to those who had been involved in helping me to complete my final

year project. It could not have been written and produced without the help of many people.

I express my gratitude to my supervisor Mr. Hairul Effendy bin Ab Maulod for his constant

guidance, support, insightful comments and encouragement during my period of study. Special

thanks to my co-supervisor Dr. Lau Kok Tee and not to forget to my industry supervisor Miss

Nurhazirah Binti Rosli for their guidance and suggestions that provide me necessary insight

into the research problem. I would also like to extend my deepest appreciation to all the staff

in Faculty of Engineering Technology UTeM, Faculty of Manufacturing Engineering UTeM,

and Faculty of Mechanical Engineering UTeM. Not to forget to MFS Technology that allows

me to complete my entire project in the industry.

Last but not least, a special thanks to my mother, my father, siblings and all my peers for

giving me moral support, views and tips which were useful. Finally, to everyone who has

directly or indirectly contributed to this project, only Almighty Allah S.W.T can repay your

kindness and may Allah S.W.T bless you all. Amin.

iv

TABLE OF CONTENT

PAGE DECLARATION APPROVAL DEDICATION ABSTRACT i ABSTRAK ii ACKNOWLEDGEMENT iii TABLE OF CONTENT iv LIST OF TABLES vi

LIST OF FIGURES vii LIST OF APPENDICES ix LIST OF ABBREVIATION, SYMBOLS AND NOMENCLATURE x CHAPTER 1. INTRODUCTION 1

1.1 Background of Study 1 1.2 Problem Statement 3 1.3 Objectives 4 1.4 Scope 5 1.5 Organization of Research Study 5

2. LITERATURE REVIEW 7

2.1 Assembly of Flexible Printed Circuit (FPC) 7 2.1.1 Flexible Circuit Materials 9 2.1.2 Type of Board 10 2.1.3 Adhesive 14

2.1.3.1 Acrylic-Based Adhesive 16 2.1.3.2 Epoxy-Based Adhesive 17

2.1.4 Copper Clad Laminate (CCL) 18 2.1.4.1 Polyimide 21 2.1.4.2 Polyester 22

2.1.5 Copper Electroplating 23 2.1.5.1 Factor Effecting Copper Plating 24

2.2 Stack-up of Materials 25 2.3 Lamination Process 27

2.3.1 Curing Process 28

v

2.4 Defects in FCB 30 2.5 Thermal Analysis 34

2.5.1 Thermogravimetric Analysis 35 2.5.1.1 Filler Content in Polymers 36 2.5.1.2 Compositional Analysis of Multi-component Polymers 37

3. METHODOLOGY 39

3.1 Methodology 40 3.1.1 Flow Chart of Methodology 40

3.2 Gantt Chart 42 3.3 Material Preparation 43

3.3.1 Coverlay 43 3.3.2 Copper Clad Laminate 44

3.4 Assembly of Flexible Printed Circuit (FPC) 45 3.5 Lamination Press Process 46

3.5.1 Parameter in Lamination Process 48 3.6 Analysis Testing 48

3.6.1 Cross-section Test 48 3.6.2 Thermogravimetric Analysis 52

4. RESULT AND DSCUSSION 55

4.0 Introduction 55 4.1 Analysis of cross-section test 55

4.1.1 Figures of Region 1, 2, 3, 4 and 5 56 4.1.2 Comparison of Highest and Lowest Adhesive Thickness 62

4.2 Degree of degradation of adhesive using TGA 64

5. CONCLUSION AND RECOMMENDATIONS 69

5.1 Conclusion 69 5.2 Limitation and Future Work 70

REFERENCES 71

APPENDICES 74

vi

LIST OF TABLES

TABLE TITLE PAGE

2.1 Comparison of polyester and polyimide films 20

2.2 Comparison of Different Adhesive Lamination Processes 28

2.3 Summarize sketch map of defects in the FPC 30 3.1 Gantt Chart 42

3.2 Parameter in the Lamination Process 48

3.3 Procedure of Cross-section Method 50

3.4 Procedure of thermogravimetric analysis 52

vii

LIST OF FIGURES

FIGURE TITLE PAGE

2.1 Constructional part of FPC (schematic view) (Khandpur, 2005) 8

2.2 Continuous process of manufacturing flexible printed circuit board (Khandpur,

2005). 9

2.3 Single-Layer Flex Circuit 11

2.4 Double-Sided Flex Circuit 13

2.5 Multi-layer Flex 14

2.6 How materials are placed relative to one another in a lamination (Fjelstad, 2011)26

2.7 Curing process of epoxy 29

2.8 Short circuit across FCB 31

2.9 Example of failed circuit with delamination (Krzmarzick, Dzarnoski, & Xing,

2013) 32

2.10 Example of acceptable circuit without delamination (Krzmarzick, Dzarnoski, &

Xing, 2013) 33

2.11 Delamination of FPC 34

2.12 TGA results generated on a glass filled epoxy resin 37

2.13 TGA results obtained on ABS 38

viii

3.1 Flow chart of Methodology 41

3.2 Coverlay Material and Construction 43

3.3 Flexible copper clad laminate 44

3.4 Simplified flow diagram for flexible circuit assembly. 45

3. 5 Process of lamination and sample position 47

3.6 Front view of FPC in 1 book 49

3.7 Top view of FPC in 1 book 49

3.8 Mould of FPC cross-section sample 51

3.9 3D Laser Microscope 51

3.10 Thermogravimetric Analysis Machine 54 4.1 Thickness of layer of region 1 56

4.2 Thickness of layer of region 2 57



4.5 Thickness of adhesive in region 5 60

4. 6 Average thickness of adhesive 61

4.7 Lowest adhesive thickness in top book (tray), layer 5, region 1 62

4.8 Highest adhesive thickness in middle book (tray), layer 5, region 2 63

4.9 TGA curve for highest thickness 65

4.10 TGA curve for lowest thickness 67

ix

LIST OF APPENDICES

APPENDIX TITLE PAGE

A1 Adhesive thickness layer of top in layer 1 for region 1, 2, 3, 4 and 5 74



A4 Adhesive thickness layer of middle in layer 1 for region 1, 2, 3, 4 and 5 77



A7 Adhesive thickness layer of bottom in layer 1 for region 1, 2, 3, 4 and 5 80



x

LIST OF ABBREVIATION, SYMBOLS AND

NOMENCLATURE

μ - Microns

oz - Fluid Ounce

mil - Milliliter

mV - Millivolts

oC - Degree Celsius

mm - Millimeter

min - Minute

m - Mass

- Density

SiO2 - Silicon Dioxide

ANSI - American National Standard Institute

AOI - Automated Optical Inspection

CCL - Copper Clad Laminate

CFRP - Carbon fiber reinforced plastic

CO2 - Carbon dioxide

ECM - Electrochemical migration

EVA - Ethylene-vinyl acetate

FEP - Fluorinated ethylene propylene

FPC - Flexible Printed Circuit

xi

FPCB - Flexible Printed Circuit Board

IEC - International Electro-technical Commission

IPC - Institute for Interconnecting Packaging Electronic Circuits

NEMA - National Electrical Manufacturers Association

MIL - Military Standard

PCB - Printed Circuit Board

PI - Polyimide

PTH - Plate Through Hole

PET - Polyethylene terephthalate

PEN - Polyethylene naphthalate

PTFE - Polytetrafluoro ethylene

PBA - Printed Board Assembly

SMD - Surface Mount Device

SMT - Surface Mount Technology

TGA - Thermogravimetric Analysis

V - Volume

1

CHAPTER 1

INTRODUCTION

This chapter will explain the overview of the study and the purpose of this study. The

chapter includes the background of the study, problem statement, objectives that is expected to

be achieved and the scope of the study that is going to be conducted.

1.1 Background of Study

Nowadays, flexible printed circuit (FPC) has many requests in industry due to their

thin, lightweight and flexible properties. They are evolves and high-growth technology in

electrical interconnectivity and improved performance by making electronic devices more

compact, lighter and thinner for applications spanning automobiles, cellular phones, smart

watches and portable laptops (Kim, S. Lee, Yu, & Han, 2017). FPC is a perfect solution for

the electronic packaging need. A flexible printed circuit board (FPCB) is a polymer-based

substrate with metal interconnects for the wiring of integrated circuits. The raw materials of

FPCBs include a flexible copper clad laminate (FCCL) and epoxy or acrylic coverlay, in

which the copper foil and epoxy or acrylic resin were both bonded with the polyimide (PI)

film. The bonding methods of copper foil in FCCLs are both physical and chemical.

Generally, the bond of the FCCL and coverlay is by adhesive using lamination press process.

Lamination is a method of manufacturing that widely used in industry where the

joining or stacking of the two or more layers of material together permanently. Lamination are

also used in wide range of applications such as for the manufacture of technical laminates for

2

the solar energy and insulation panel sectors as well as in the food and non-food packaging

industries. This technique is to ensure the strength, stability, appearance and properties of the

materials are improved by using two or more materials stacked in multiple layers in flexible

circuit board. In general terms, a laminate is permanently assembled by heat, pressure or

adhesive.

Technological advancement in the field of lamination has led to different ways in

which sheet can be laminated. Hot-roll lamination, extrusion lamination, flame lamination and

adhesive lamination are a few example of processing approaches. In this study, a detailed

discussion on the fundamentals of lamination is provided. Thermal lamination is the approach

of bonding two substrates with an adhesive. The adhesive, which is in the form of polyolefin

such as EVA (ethylene-vinyl acetate) is first applied to and cooled and dried on one of the

substrates. The substrates are pressed together in the nip of the two rollers under constant heat,

providing an adequate amount of force to establish the intimate contact required for the bond.

Extrusion lamination is another approach to bonding two substrates. The hot extruded film is

trapped between two substrates and cooled to bond two substrates. Wet bond lamination uses

solvent-based adhesives, which are only to be used with substrates with high permeability to

water or other solvents. Wet bond is not generally successful with plastic films, even when

laminating them to paper. Dry bond lamination is considered as a process of choice when

laminating two materials using either an aqueous or solvent-based adhesive. In a solvent-less

lamination, two substrates are bonded together by curing without the presence of a solvent.

The adhesive layer formed by curing systems does not release solvents, but small traces of

carbon dioxide (CO2) have been found (Ashter, 2014).

3

For this study, lamination process is used to combine the coverlay and the copper clad

laminate (CCL) with adhesives using hot press laminate machine. The conductor of the

finished flexible circuit is protected and enhances the flexibility by the coverlay. CCL in

flexible printed circuit consist of two type of thermoset that is polyimide and polyester. The

adhesives used in lamination are acrylic-based adhesive and epoxy-based adhesive. Typically,

a laminate is done by bonding together a base material, an adhesive and a metal foil. The stack

is then exposed under heat and pressure in a hot press laminate machine to create a

permanently bonded metal polymer laminate.

1.2 Problem Statement

A flexible printed circuit (FPC) is widely used in industry in area of electrical

interconnectivity. The production of FPC is very high due to many requests of the customers.

Many process in FPC that has been developed to improve the quality and properties of the

board. In FPC, one of the processes used to manufacture the board is lamination process. The

layer of the laminates consists of copper clad laminate (CCL) and coverlay with adhesive are

bond together under heat and pressure with interval time. The coverlays are etched to form the

required pattern of conducting traces, and the adhesive of the layers fills the spaces where the

copper was removed. When an adhesive is used to fill the gap between the undersides of a

component, it will result the other issues of delamination. The bonds of „„underfill” adhesives

act to reinforce the connection with the FPC. Delamination is one of the main failure modes

that occurred in FPC. During the soldering process, delamination may occur particularly with

lead-free solders which require higher reflow temperatures than leaded solders. Bending of

steel plate during installation, service and repair can also can cause FPC delamination.

4

Therefore, it is very important to understand the delamination process in FPC (Akbari,

Nourani, & Spelt, 2018).

One enabler for shrinking electronics has been the flexible circuit board that allows the

circuit board to fit in a wide variety of shapes. Flexible circuit boards have the capability to be

very thin and can have unpackaged components directly attached using surface mount

assembly and flip chip on flex technologies. Unfortunately, with this flexibility come other

reliability issues. One issue is the tendency of flexible circuit panels absorbing the chemical

solvents that are used during the surface mount device (SMD) assembly cleaning process,

specifically the process of vapor degreasing. These solvents can remain trapped in the circuit

layers and cause blistering and delamination of the circuit boards during subsequent assembly

steps (Krzmarzick, Dzarnoski, & Xing, 2013). In FPC, polymer coverlay is applied on the

copper-polyimide laminate using acrylic-based adhesive, followed by elevated time,

temperature and pressure during process.

1.3 Objectives

The objective of the project is to:-

i. To characterize the thickness of acrylic adhesive of lamination Flexible Printed Circuit

(FPC) from different areal and layer positions.

ii. To assess thermal degradation behavior of the laminated Flexible Printed Circuit (FPC)

by TGA-DTG analysis.

5

1.4 Scope

The study on this topic can be benefit for certain circumstances. This project is

“Investigation of coverlay adhesion by acrylic-based adhesive on copper-polyimide laminate

for Flexible Printed Circuit” through lamination process and test the effect after curing. The

scopes of this study are focusing more on curing of coverlay adhesive by acrylic-based

adhesive on copper polyimide laminate correlation with temperature and pressure profiles.

Next, the study also looks on the relationship of delamination with the evenness distribution of

temperature and pressure at specific interval time. The findings will be further supported by

the analysis of Thermogravimetric analysis (TGA) and cross section test using 3D laser

microscope.

1.5 Organization of Research Study

This project is divided into five chapters that describe the analytical and experimental

research performed. This dissertation shows the defect occurred after the lamination press

process in flexible printed circuit. The cause regarding the delamination with copper clad

laminate has been studied, in search of improvements on their physical and mechanical

properties. The organization of this research study is as follows. This dissertation has been

organized into five chapters. The first chapter is introduction to the study that brief about

objectives, problem statement, significant of study and the project overview.

Chapter two begins on the literature background of this study. It discusses on the

history of flexible circuit board, types of material used in flexible circuit board and it

processes. The important element that included in this chapter is about the lamination process

of coverlay with copper clad laminates (CCL) and the defect occurred after curing process

which is delamination of the FPC.

6

Chapter three provides details explanations on the methodology used for overall

research work, raw materials, procedure property analysis that had been done. In this chapter

four, instead of investigation of coverlay adhesion by acrylic-based adhesive on copper-

polyimide laminate, also want to understand the factors that contribute delamination after

curing process in FPC and discuss about the analysis result after done the analysis testing for

the FPC. The last chapter (chapter 5) concludes the overall results obtained from this research.

In this chapter, it explains either the objectives of this study are achieved or not. The

recommendation for future project also has been included in this Chapter 5.

7

CHAPTER 2

LITERATURE REVIEW

In this chapter, it will explain about the previous research that has been writing from

the numerous of the journalist and researcher which come from the internet, journals, article

and books about the topic that is related to this final year project study. This chapter also

explains about the overview of the acrylic-based adhesive on copper-polyimide laminate for

flexible printed circuit. The success of a design and material testing also depends on the

creativity of designers and the use of appropriate technology to meet the needs of effective and

functional. The design and study is ongoing process that involved creative problem solving is

known as a literature.

In the production this project, all theory and information of material substance used,

production and testing in relation this project has been described to achieve objective of the

project those implemented.

2.1 Assembly of Flexible Printed Circuit (FPC)

Flexible printed circuit (FPC) board interconnect rigid boards, displays, connectors and

various other components in a three-dimensional package. They can be bent-folded or shaped

to interconnect multiple planes or conform to specific package sizes. Flex circuits also have

the ability to connect moving components, a prime requirement in disk drives, printer heads

and other continually moving electronic assemblies.

8

FPC assembly is very like the rigid printed circuit board (PCB) assembly yet the thin

substrate of FPC makes it more vulnerable to various types of defects that range from minute

twist on the board to the spacing between soldering. Thus, it drags the production yield down.

Figure 2.1 shows the constructional part of flexible printed circuits which consist of cover

layer, copper foil, adhesive and polyimide.

Figure 2.1: Constructional part of FPC (schematic view) (Khandpur, 2005)

Comparing to PCB, cleaning flexible material need more caution and it involve

different procedure of cleaning even both type of printed board required same number of

cleaning cycles. Cleaning of FPC involves an environmentally safe process which include an

alkaline bath, a through rinse, a micro etch and a final rinse. Usually, damage to the thin clad

materials often occurs with racking of the panels, agitating the panels in the tank, breaking the

surface tension in the cleaning tanks, removing racks from the tanks. Research found that the

FPC can be less expensive of mass production compared to rigid PCB. This is due to the

manufacturing process of flexible printed circuit boards that enable to be produce on a

continuous basis which is start from laminate roll and directly produces the finished boards

(Khandpur, 2005).

Figure 2.2 shows the continuous process of manufacturing flexible printed circuit

board. This continuous process enable all manufacturing steps can be done in-line by

machines that placed sequentially.

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