Predicting the Punchability of Laminates

In laminate specifications, attention is rarely paid to punching requirements. Although printed circuit manufacturers often assess the punchability of laminates in situ by trial and error, there is an increasing need for the laminate manufacturer to have access to laboratory punching tests in order to conform with quality control requirements and keep abreast of current demands on laminate properties. Several national specifications refer to existing punching tests of varying efficacity, a selection of which are discussed. The success of in‐house punching tests is analysed. The EXCELL tool has proved its value in the assessment of blanking and laddering, and two versions of a specially designed piercing tool have been devised to contend with large quantities of small holes. Laboratory investigations have been carried out into the measurement of the forces required for punching, with a variety of laminates, temperatures and punch/die clearances. Penetration/withdrawal force ratios have also been studied in detail. It now remains to research into the area of hole blocking during piercing.