Testing Controlled Impedance Boards

Abstract

This paper presents the results of research into the process of testing controlled impedance circuit boards. It aims to provide a general introduction to the subject of controlled impedance circuit board production for manufacturers wishing to make this type of board in the future and offers constructive suggestions for those who may want to improve on their current process. Consequently, in addition to describing test issues there are references to some of the other main subject areas that require attention when the production of high quality controlled impedance circuit boards is to be considered, namely design, materials and fabrication. The content of this paper is based on production trials that were conducted by MEPD Met‐Etch (Selkirk) Ltd at their manufacturing facilities in Scotland as part of a UK Ministry of Defence research contract. The results of this research were included in a report for the UK Defence Research Agency (Electronics Division) and subsequently were also detailed in an individual ‘Guidelines for Designers’ document. This document has since been separately submitted to ECL 19 with a view towards incorporation into the CECC 23000 Approval System. In order to verify the test results, separate comparison measurements were also conducted by other circuit board manufacturers using a range of suitable test instrumentation. There is a growing requirement in the printed circuit board industry for a simple means of testing controlled impedance boards. This paper promotes the use of computer‐controlled test instrumentation so that accurate and repeatable measurements can be made by production staff in a manufacturing environment. If this is achieved, it should be possible to close the quality loop on controlled impedance circuit board production using normal statistical process control techniques.