Dimensional and Electrical Characteristics of Printed Boards Made with Multipurpose Test Pattern, B-25.

摘要

Printed boards fabricated at six suppliers with Multi-Purpose Test Pattern, B-25are compared. Fabrication included both panel and pattern plating. Characteristics of bare as well as coated boards were measured. Average deviations of conductor widths from design widths ranged from -10to -38microns on phototools and -74to +33microns on boards. The deviations depended manly on fabrication period and source. Copper thicknesses obtained from resistance measurements,which ranged from 36to 84microns,were within 5% of those obtaid from beta backscatter and cross section measurements. The influence of close spacing of adjacent,current-carrying conductors was illustrated with this test pattern. Breakdown voltages between conductors at separations of 0.08to 0.76mm,were roughtly 70% of those for the Paschen curve for air in a quasi-uniform electric field. Mean breakdown voltage V/sub BD/in kV for conductor separation S in mm is expressed by the relationship, V/sub BD/ = 2.7 S exp 0exp 60 ,regardless of board source. For coated boards,breakdown voltages were significantly higher,but also showed more scatter. Measured data indicate that in most normal board environments,the minimum conductor clearances recommended for circuit design are too conservative and should be changed. (ERA citation 04:037414)