Encapsulation Technologies for Electronic Applications

Haleh Ardebili,Jiawei Zhang,Michael G. Pecht, James J. Licari

• Publisher: William Andrew
• Year: 2018
• ISBN:
  9780128119792
• Edition: 2
• Topic: Technology & Engineering
• Subtopic: Materials Science
• Index: Technology & Engineering

Encapsulation Technologies for Electronic Applications, Second Edition, offers an updated, comprehensive discussion of encapsulants in electronic applications, with a primary emphasis on the encapsulation of microelectronic devices and connectors and transformers. It includes sections on 2-D and 3-D packaging and encapsulation, encapsulation materials, including environmentally friendly 'green' encapsulants, and the properties and characterization of encapsulants. Furthermore, this book provides an extensive discussion on the defects and failures related to encapsulation, how to analyze such defects and failures, and how to apply quality assurance and qualification processes for encapsulated packages.

In addition, users will find information on the trends and challenges of encapsulation and microelectronic packages, including the application of nanotechnology.

Increasing functionality of semiconductor devices and higher end used expectations in the last 5 to 10 years has driven development in packaging and interconnected technologies. The demands for higher miniaturization, higher integration of functions, higher clock rates and data, and higher reliability influence almost all materials used for advanced electronics packaging, hence this book provides a timely release on the topic.

• Provides guidance on the selection and use of encapsulants in the electronics industry, with a particular focus on microelectronics
• Includes coverage of environmentally friendly 'green encapsulants'
• Presents coverage of faults and defects, and how to analyze and avoid them

1

Introduction

Chapter Outline

• 1.1 Introduction
• 1.2 Historical overview
• 1.3 Electronic packaging
• 1.4 Encapsulated microelectronic packages
  • 1.4.1 2D packages
  • 1.4.2 3D packages
• 1.5 Hermetic packages
  • 1.5.1 Metal packages
  • 1.5.2 Ceramic packages
• 1.6 Encapsulants
  • 1.6.1 Plastic molding compounds
  • 1.6.2 Other plastic encapsulation methods
• 1.7 Plastic versus hermetic packages
  • 1.7.1 Size and weight
  • 1.7.2 Performance
  • 1.7.3 Cost
  • 1.7.4 Hermeticity
  • 1.7.5 Reliability
  • 1.7.6 Availability
• 1.8 Summary
• References
• Further Reading

1.1 Introduction

Electronics are used in a wide range of applications including computing, communications, biomedical, automotive, military, and aerospace. An electronic package is defined as an electronic structure that protects an electronic or electrical element, and the package must be environmentally friendly. From the silicon chip to the printed wiring board level, technologies all belong to the electronic packaging hierarchy. An IC package protects, powers, and cools the microelectronic device and provides mechanical connection. The trends of higher speed, small package size with higher I/O, and low cost with multiple application range push higher requirements that the electronic devices be packaged for protection from their intended environment, as well as to provide handing, assembly, and electrical and thermal considerations.

Electronic packaging may involve either hermetic (ceramic or metallic) packaging or nonhermetic (plastic) encapsulation. Currently, > 99% of microelectronic devices are plastic encapsulated. Improvements in encapsulant materials and cost incentives have stretched the application boundaries for plastic electronic packages. Many electronic applications that traditionally used hermetic packages, such as military, are now using commercial off-the-shelf (COTS) plastic packages. Plastic encapsulation has the advantages of low cost, availability, and manufacturability.

Much of the focus is aimed at the research and development of new and improved encapsulants. With recent trends in environmental awareness, new environmentally friendly or “green” encapsulant materials (i.e., without brominated additives) have emerged. Plastic packages are also being considered for use in extreme high- and low-temperature electronics. 3D packaging and wafer-level packaging require unique encapsulation techniques. Encapsulants also play a role in emerging technologies. Modified existing or newly developed encapsulant materials are being developed for microelectromechanical systems (MEMS), bio-MEMS, bioelectronics, nanoelectronics, solar modules, and organic light-emitting diodes. Nanocomposite encapsulants with improved material properties are also being explored.

This chapter provides a historical overview of encapsulation. Electronic packaging including package levels, encapsulated microelectronic devices, hermetic packages, and encapsulation methods and materials is discussed. Some new technology on microelectronic packages such as 2D, 3D, integrated fan-out wafer-level packaging (InFO-WLP), and wafer-level system in packaging will be presented. Finally, hermetic and plastic packages are compared.

1.2 Historical overview

Electronic devices have been packaged in a variety ways. Among the first package types was a preformed package made of Kovar (an alloy of nickel, cobalt, manganese, and iron). Kovar, a trade name of Westinghouse Electric and Manufacturing Company, was invented by Howard Scott in 1936 [1] and has the advantage of a coefficient of thermal expansion (CTE) similar to that of glass. It is a suitable choice for sealing to glass because of lower CTE mismatch stresses.

One of the early transistor packages is shown in Fig. 1.1 [2]. In this package, the emitter, collector, and base connector leads were inserted through a glass bushing positioned in a Kovar ring or cylindrical housing. The bushing was made of a suitable electrical insulating and moisture-impervious (hermetic) glass material. The transistor device was then bonded to the base lead and interconnected to the emitter and collector leads using wires. The Kovar disc covers were later hermetically sealed by welding. Ceramic packages, similar in construction to the Kovar casing, appeared later as less expensive alternatives.

Fig. 1.1 Kovar transistor package: (A) top view; (B) side view [2].

The first plastic-encapsulated packages appeared on the market in the early 1950s. By the early 1960s, plastic encapsulation emerged as an inexpensive, simple alternative to both ceramic and metal encasings, and during the 1970s, virtually all high-volume integrated circuits (ICs) were encapsulated in plastic. By 1993, plastic-encapsulated microelectronics accounted for over 97% of the worldwide microcircuit production.

Most early microelectronic devices were compression-molded, where the molding compound is heated and compressed inside the mold. Potting soon emerged as a suitable alternative. Potting involved positioning the electrical circuit in a container and pouring the liquid encapsulant into the cavity. Fig. 1.2 shows a typical transistor encapsulated using the “can and header” method [3]. The transistor chip was soldered to a carrier, which was then attached to the header assembly. The header assembly consisted of three parallel conductive lead posts sealed into a button-like header made of premolded plastic encapsulant mater...