TABLE OF CONTENTS Happy T. Holden
Westwood Associates, Loveland, Colorado
The use of more complex components with very high I/O counts has pushed board fabricators to reexamine techniques for creating smaller vias, and many new or redeveloped processes have appeared on the market. These processes include revised methods of creating holes, such as laser drilling, micropunching, and mass etching; new methods for additively creating dielectric with via holes using photosensitive dielectric materials; and new methods for metallizing the vias, such as conductive adhesives and solid-post vias. All of these methods share some common traits. They all allow the designer to significantly increase routing density through the use of vias in SMT pads, to reduce the size and weight of product, and to improve the electrical performance of the system. These types of boards are generically called high-density interconnects (HDIs). An HDI board typically will have, as an average, over 120 to 130 electrical connections per square inch (20 connections per square centimeter) on both sides of the board. The IPC defines any via, blind, buried or through, of 150 m (0.006 in) or less in size, as a microvia. HDI boards require microvias.
This generation of printed boards is characterized by microblind, buried, and through vias made by techniques other than mechanical drilling. In order to turn blind vias into buried vias, these process techniques are repeated and...
