Lead-Free and Other Process Effects on Conductive Anodic Filamentation Resistance of Glass-Reinforced Epoxy Laminates
Conductive anodic filamentation is a subsurface failure mode in woven glass-reinforced laminate (FR4) materials, where a copper salt filament allows bridging between via walls and other copper conductors. In this study, FR4 laminates, in the form of high-via-density multilayer test circuits, are exposed to different manufacturing conditions and assessed for resistance to conductive anodic filamentation (CAF). CAF performance was assessed using high temperature and humidity conditions to promote failures, with a voltage applied across adjacent via. By the application of a range of voltages and via geometries, a performance map for laminates can be obtained to compare materials for performance. The changes due to exposure of laminate to tin–lead and lead-free temperatures are then examined using the technique.
KeywordsFeed Speed Copper Salt Weft Direction Test Voltage Copper Plane
The work was part of a project in the Materials Processing Metrology Programme of the UK Department of Trade and Industry. NPL gratefully acknowledges the work of the industrial partners: Alcatel Submarine Networks, TRW Automotive Group, Graphic Plc, Prestwick Circuits, Invotec, Isola and Polyclad.
- 1.Lando D, Mitchell JP, Welsher TL (1979) Conductive anodic filaments in reinforced polymeric dielectrics. Formation and prevention. In: Proceedings of the 17th annual reliability physics symposium, pp 51–63Google Scholar
- 2.Rudra B (1994) Electrochemical migration in multichip modules. In: Surface mount international conference and exposition. Edina, MN, USA. Proceedings of the technical program, NY, USA, Surface Mount Int, IPC: 50–6Google Scholar
- 3.Bi-Chu WU, Pecht M, Jennings D (1994) Conductive filament formation in printed wiring boards. In: Thirteenth IEE/CHMT international electronics manufacturing technology symposium. Edina, MN, USA, pp 74–79Google Scholar
- 4.Tsujioka N, Pecht M, Jennings D (1990) Generative mechanisms and preventive methods for micro-defects in PCB. In: Proceedings of the printed circuit world convention, Aylesbury, UK, Hazell Books B2/3–12Google Scholar
- 5.Mitchell JP, Welsher TL (1981) Conductive anodic filament growth in printed circuit materials. In: Proceedings of the printed circuit world convention II, Wurtt, Germany, Eugen G. Leuze Verlag, vol. 1 of 2 vol., pp 80–93Google Scholar
- 6.Ready WJ, Stock SR, Freeman GB, Dollar LL, Turbini LJ (1995) Microstructure of conductive anodic filaments formed during accelerated testing of printed wiring boards. Circuit World 21(4):5–9Google Scholar
- 7.Brewin A, Zou L, Hunt CP (2004) Susceptibility of glass reinforced epoxy circuit laminates to conductive anodic filamentation. NPL Report MATC(A)155Google Scholar
- 8.Wickham M, Zou L, Hunt C (2002) An assessment of the suitability of current pcb laminates to withstand lead-free reflow profiles. NPL Report MATC(A)91Google Scholar