Digital Circuit Boards: Mach 1 GHz

6.1 Introduction

Early circuit boards were made of bakelite, where components were soldered on to mounting pins and vacuum tubes were plugged into sockets. Insulated wires were used to interconnect sockets, pins, and components. Building a board was labor intensive. Component leads were cut and bent to provide strain relief, interconnecting leads had to be stripped and tinned, and all the parts had to be assembled and soldered by hand.

A great step forward was made when copper/epoxy laminates were introduced. Traces replaced insulated leads. Components were mounted in holes that were plated and tinned. If shielding was needed, then critical circuits were surrounded by metal boxes. The logic was slow enough that circuit traces were routed point-to-point, and there were few cross talk or overshoot problems. Wire-wrap technology was introduced when the number of interconnections could not be handled by traces on two layers. Progress in IC design then increased clock rates, which meant that rise and fall times were shorter. Attempts to operate at higher clock rates were often met with failure, as there were just too many problems in signal integrity. It was soon recognized that wire-wrap technology was a blind alley, and it was necessary to go to multilayer boards with added ground planes to provide circuit performance. The trend to smaller trace widths and multilevel boards soon followed. We often take for granted the amazing technology that we now enjoy. It makes our computers, servers, ...