TWISTED WIRE INTERCONNECTS: AN ALTERNATIVE TO MULTI-LAYER BOARD CONSTRUCTION FOR HIGH COMPONENT DENSITY PRINTED CIRCUIT BOARD ASSEMBLIES
Authors: Tom Borkes, Steve Garcia, and Randy Boudreaux Company: Medallion Technology Date Published: 10/11/2007
Abstract: This paper analyzes twisted wire interconnects (TWI) as a high density interconnect tool for electronic circuit board applications. A comparison is done between traditional multi-layer circuit board construction and circuit boards constructed using TWI. High layer count board designs with components on both sides, requiring blind and buried via interlayer connecting, are replaced with a series of simple double-sided boards that are jointed using twisted wire interconnects – the TWI effectively replacing the traditional plated-through via holes used in multi-layer designs. The paper demonstrates that a geometric increase in component density is achieved as TWI construction replaces higher layer count laminates. When an n-layer board is designed (i.e., n/2 plies laminated together) only two surface -- the top and the bottom of the laminate -- are available for component attachment regardless of layer count. Replacing this traditional design with a TWI assembly produces n surfaces for component attachment. The paper examines the physical, mechanical and electrical design aspects of TWI, as well as the processes used for TWI assembly. A comparative simplified modal analysis was done between a traditional multi-layer board and an equivalent TWI assembly. The TWI natural frequency was about seven times higher than the multi-layer board. In practice, this results in lower solder joint strains and corresponding stresses. Performing a resonance dwell and subjecting assemblies to two Mil–Std-810F random vibration environments – general integrity and jet aircraft, provided additional evidence of TWI mechanical robustness.
Key words: High density interconnects, lead-free, solderless interconnects, multi-layer printed circuit boards