Circuit World
30/4 [2004] 10
Emerald Group Publishing Limited
[ISSN 0305-6120]

I am delighted to welcome you to this themed edition of Circuit World. Much has been written and spoken about the changing market for printed circuit boards and it would have been easy to miss the exciting developments to the basic building block for printed circuit boards the substrates. The longevity and resilience of printed circuit board substrates is a testament to the committed researchers around the world who have continued to develop products meeting the increasing performance demands of the end-user whilst maintaining the essential attribute of processability. If we were to compare the basic properties of a modern day FR4 with that defined by NEMA L1-1 in 1965 there would be little similarity in performance. In addition to the basic chemistry and raw material improvements the laminate industry has made great gains in reducing product variability in order to deliver known and consistent performance to their customers.

The evolution of printed circuit board substrates has necessitated a changed view of how performance is classified. Traditionally, substrates have been classified according to the physical properties of their basic chemistry. By way of example, we are used to classifying substrates according to their glass transition temperature T _g. Accordingly we refer to standard or high T _g substrates. It is no surprise therefore that many have assumed that the T _g value has a direct relationship to the thermal endurance of the substrate...