Adhesives Technology for Electronic Applications

Materials, Processing, Reliability

James J. Licari, Dale W. Swanson

• Publisher: William Andrew
• Year: 2011
• eBook ISBN: 9781437778908
• Edition: 2
• Topic: Technology & Engineering
• Subtopic: Electrical Engineering & Telecommunications
• Index: Technology & Engineering

Adhesives are widely used in the manufacture and assembly of electronic circuits and products. Generally, electronics design engineers and manufacturing engineers are not well versed in adhesives, while adhesion chemists have a limited knowledge of electronics. This book bridges these knowledge gaps and is useful to both groups.The book includes chapters covering types of adhesive, the chemistry on which they are based, and their properties, applications, processes, specifications, and reliability. Coverage of toxicity, environmental impacts and the regulatory framework make this book particularly important for engineers and managers alike.The third edition has been updated throughout and includes new sections on nanomaterials, environmental impacts and new environmentally friendly 'green' adhesives. Information about regulations and compliance has been brought fully up-to-date.As well as providing full coverage of standard adhesive types, Licari explores the most recent developments in fields such as: - Tamper-proof adhesives for electronic security devices - Bio-compatible adhesives for implantable medical devices - Electrically conductive adhesives to replace toxic tin-lead solders in printed circuit assembly – as required by regulatory regimes, e.g. the EU's Restriction of Hazardous Substances Directive or RoHS (compliance is required for all products placed on the European market) - Nano-fillers in adhesives, used to increase the thermal conductivity of current adhesives for cooling electronic devices. - A complete guide for the electronics industry to adhesive types, their properties and applications – this book is an essential reference for a wide range of specialists including electrical engineers, adhesion chemists and other engineering professionals - Provides specifications of adhesives for particular uses and outlines the processes for application and curing – coverage that is of particular benefit to design engineers, who are charged with creating the interface between the adhesive material and the microelectronic device - Discusses the respective advantages and limitations of different adhesives for a varying applications, thereby addressing reliability issues before they occur and offering useful information to both design engineers and Quality Assurance personnel

1. Introduction

Chapter Outline

1.1. Adhesive types and classifications2

1.1.1. Classification by form2

1.1.2. Classification by polymer or chemical type3

1.1.3. Classification by formulation5

1.1.4. Classification by curing method5

1.1.4.1. Heat-cured adhesives5

1.1.4.2. Ultraviolet (UV)/visible-light-cured adhesives5

1.1.4.3. Microwave curing6

1.1.4.4. Moisture curing6

1.1.5. Classification by function6

1.1.5.1. Mechanical attachment6

1.1.5.2. Electrical connection6

1.1.5.3. Thermal dissipation8

1.1.5.4. Stress dissipation8

1.1.6. Classification by intended use8

1.1.6.1. Die attachment8

1.1.6.2. Substrate attachment9

1.1.6.3. Lid attachment9

1.1.6.4. Surface mounting10

1.1.6.5. Underfill for flip-chip-attached devices10

1.1.6.6. Underfill for ball-grid-array (BGA) packages11

1.1.6.7. Solder replacements11

1.1.6.8. Particle getters11

1.2. Summary of packaging technologies12

1.2.1. Single-chip packaging12

1.2.1.1. Dual-in-line package (DIP)13

1.2.1.2. Quad-flat packs (QFPs)13

1.2.1.3. Area-array devices and packages14

1.2.1.4. Chip-scale packages (CSPs)15

1.2.1.5. Lead-on-chip (LOC)18

1.2.1.6. Chip stacks18

1.2.2. Surface-mount technology19

1.2.3. Multichip packaging19

1.2.3.1. Hybrid microcircuits20

1.2.3.2. Multichip modules21

1.2.3.3. High-density interconnect (HDI) overlay process22

1.2.3.4. Chip-on-board23

1.2.3.5. Flexible circuits23

1.2.3.6. Chip-on-flex (COF)24

1.3. History of adhesives in electronic applications24

1.4. Comparison of polymer adhesives with metallurgical and vitreous attachment materials29

1.5. Specifications29

1.6. Market and market trends30

References32

This chapter provides a description of the various electronic packaging and assembly approaches where adhesives are used. Various single chip and multichip packaging designs are described and augmented with 21 figures and three tables. Applications include PWAs (Printed Wiring Assemblies), thin- and thick-film hybrid microcircuits and MCMs (Multichip Modules). Polymer adhesives are classified as to types and compared with metallurgical and vitreous attachment materials. Electrically conductive, insulative , and thermally conductive adhesives are also discussed.

The chapter provides a basis for understanding terminology covered in subsequent chapters. A brief history and timeline of the use of adhesives in electronics is given and a section is provided on market and market trends for the continued use of adhesives in current electronics as well as for emerging electronic applications such as Light Emitting Diodes (LEDs), Organic Light Emitting Diodes (OLEDs), and nanotechnology

Adhesives are used extensively and are vital in the assembly and packaging of electronic devices, especially in the current proliferation and mass production of electronic hardware. Adhesives are used in assembling semiconductor die, both in single-chip packages and in multichip assemblies. Both bare-chip devices and prepackaged components are attached and electrically connected with adhesives to produce electronic circuits such as printed-wiring assemblies (PWAs), thin- and thick-film hybrid microcircuits, and multichip modules. Adhesives, as pastes or as solid films, are also used in fabricating high-density multilayer interconnect substrates, flexible circuits, flat-panel displays, and a host of other emerging applications including optoelectronics; high-speed, high-frequency circuits; sensors; and smart cards. Due to their low cost, ease of rework, and low-processing temperatures, polymer adhesives have replaced many traditional interconnect materials such as solder, eutectic alloys, and wire, especially for most commercial and consumer electronics. However, because of the large number of adhesives available and the variety of polymer types, forms, and formulations, a basic understanding of adhesives and their properties is necessary in their selection and application to assure performance and to avoid subsequent reliability problems. The prime objective of this book is to provide this basic understanding and define guidelines for selecting and qualifying adhesives based on the product and the conditions the adhesive is expected to meet.

1.1. Adhesive types and classifications

Adhesives used in assembling electronic circuits may be classified based on their physical form, polymer type, molecular structure, formulation, curing method, function, or intended application.

1.1.1. Classification by form

In terms of their physical forms, adhesives may be liquids, solids, or pastes. Liquids may be used where excessive flow or spreading is not a problem. In most electronics applications, however, adhesive flow needs to be contained and controlled during cure especially when used in the assembly of microcircuits. Pastes are generally highly filled with mineral fillers and thixotropic compounds such as fine silica powder to produce semi-solid properties having non-Newtonian flow behavior. They are easily dispensed by forcing them through a needle or by pressing them (squeegeeing) through a screen or stencil. Paste or liquid adhesives, in turn, may be one-part or two-part adhesives.

A one-part adhesive may contain a polymer resin system that cures directly on exposure to moisture, oxygen, UV light, or elevated temperature. Two-part adhesives consist of a separate resin portion, referred to as Part A and a hardener or catalyst portion, Part B, either of which may contain fillers and other formulation ingredients. The two parts are packaged and stored in separate containers. When ready for use, the parts are weighed, mixed, deaerated, dispensed, and cured. Some two-part systems can be formulated as one part by admixing the resin portion with a hardener or catalyst that is unreactive under normal conditions (latent) but decomposes at some elevated temperature to release a reactive curing agent as, for example, the dicy (dicyandiamide) curing of epoxy resins.

Two-part adhesives may also be converted to one-part systems by quickly mixing weighed amounts of Parts A and B, deaerating, freezing, packaging and then storing at temperatures of −40 °C or lower. These one-part systems, known in the trade as frozen adhesives, may be purchased from several suppliers in tubes or syringes of various sizes and amounts. Frozen adhesives, generally epoxies, are highly desira...

Table of contents

• Cover image
• Table of Contents
• Dedication
• Front Matter
• Copyright
• Preface
• Acknowledgments
• Disclaimer
• 1. Introduction
• 2. Functions and theory of adhesives
• Chapter 3. Chemistry, Formulation, and Properties of Adhesives
• Chapter 4. Adhesive Bonding Processes
• Chapter 5. Applications
• Chapter 6. Reliability
• Chapter 7. Test and Inspection Methods
• Appendix
• Index