David Noel Light

Process considerations in the fabrication of fluoropolymer printed circuit boards

Fluoropolymer-based dielectric materials provide desirable electrical and mechanical properties when used as insulator materials for printed wiring boards (PWBs). However, along with the significant performance and reliability advantages of these insulator materials for microwave and high speed digital applications, there are also significant processing challenges. This paper reviews the significant electrical and mechanical properties of fluoropolymer-based packaging materials, and discusses the unique processing challenges encountered in the fabrication of PTFE printed circuit boards and modules. Key features of the TSM Microelectronics High Performance Carrier fabrication process will be described as they relate to those challenges. >

A Wide Area Vertical Expansion (WAVE/sup TM/) packaging process development

During the later 1990s, Tessera introduced a semiconductor packaging technology called WAVE (Wide Area Vertical Expansion) package to address the growing need for high pin count, high speed, high thermal dissipation, and high environmental reliability in advanced electronic packaging. The WAVE technology is an extension of Tesseras compliant packaging technologies that places a low modulus encapsulant between the silicon die and the package substrate to solve their CTE mismatch problem. The WAVE technology allows for compliant vertical interconnection links to be formed between the ICs and the substrate, with no need for a bond window. These interconnections are made simultaneously, in contrast to single point wire or lead bonding. The compliant interconnections and low modulus encapsulant enable the stress on BGA solder balls to be minimized. The WAVE package utilizes advanced materials and design to provide a unique combination of high electrical and thermal performance, high environmental reliability, and cost effective IC interconnection methodology. This paper presents one of the latest WAVE technology developments at Tessera.

Process considerations in the fabrication of Teflon printed circuit boards

Teflon-based dielectric materials provide desirable electrical and mechanical properties when used as insulator materials for printed wiring boards (PWBs). However, along with the significant performance and reliability advantages of these insulator materials for microwave and high speed digital applications, there are also significant processing challenges. This paper reviews the significant electrical and mechanical properties of Teflon-based packaging materials, and discusses the unique processing challenges encountered in the fabrication of Teflon printed circuit boards and modules. Key features of the IBM Microelectronics High Performance Carrier fabrication process are described as they relate to those challenges.<<ETX>>

Aluminum thick-metal-backed circuits: conductive adhesive technology

Thick-metal-backed printed wiring boards are commonly used in high frequency wireless circuit applications requiring significant thermal dissipation, such as power amplifiers. The thick metal backer (TMB) typically functions as a ground plane, heat sink, and in some cases, part of a shielded housing. Electrical interconnections between RF/microwave printed wiring boards (PWBs) and TMBs have traditionally been accomplished using sweat soldering, plated through holes, or mechanical interconnections. More recently, conductive adhesive technology has been investigated to mechanically and electrically interconnect the PWB to the thick metal ground plane, due to perceived advantages in cost and performance. However, providing mechanically and electrically stable interfaces between conductive adhesives and large area metal surfaces has proven to be a significant challenge, particularly in the case of aluminum-backed circuits. Aluminum, while a cost effective material for these applications, is prone to hydrolytic processes induced by moisture and accelerated by temperature, active ionic species, galvanic effects, and other environmental factors. These processes can compromise both the electrical and mechanical stability of the bond, and thus the performance and reliability of the packaging structure. This paper describes work performed at IBM Microelectronics to understand the interfacial resistance between conductive adhesives and typical metal bonding surfaces for TMB printed circuits, and will discuss how reliable and functional adhesive interconnections were achieved for commercial designs using appropriate adherend pretreatment, mechanical design, and adhesive material.

THE EFFECT OF PH ON THE ELECTROCATALYTIC PROPERTIES OF ADSORBED METAL IONS

The electrocatalytic behavior of adsorbed lead atoms on mercury towards O2 reduction in neutral electrolyte at ambient temparature is examined. The results shows that O2 reduction on these modified surfaces proceeds through the series mechanism and that the enhancement is mainly due to hydrogen peroxide elimination through reduction and/or heterogeneous chemical decomposition. Measurements performed as a function of pH in the range pH = 4 to pH = 10 indicate that the hydrogen peroxide decomposition reaction slows down as the pH increases. Using cyclic voltammetry and rotating ring-disk techniques, it is demonstrated that for the PbHg system the catalytic species is lead oxide or lead hydroxide.