Characterization and Electrochemical Mechanism for Bromide-Containing Conductive Anodic Filament (CAF) Failure

被引:7
作者
Caputo, Antonio [1 ]
Turbini, Laura J. [2 ]
Perovic, Doug D. [1 ]
机构
[1] Univ Toronto, Toronto, ON, Canada
[2] Res Mot, Waterloo, ON, Canada
关键词
Printed wiring board; solder flux; conductive anodic filament; POLARIZATION BEHAVIOR; POURBAIX DIAGRAMS; COPPER CORROSION; EXPOSURE TIME; LITHIUM; DISSOLUTION;
D O I
10.1007/s11664-011-1694-x
中图分类号
TM [电工技术]; TN [电子技术、通信技术];
学科分类号
0808 ; 0809 ;
摘要
Conductive anodic filament (CAF) is a failure mode in printed wiring boards (PWBs) that occurs under temperature-humidity-bias (T-H-B) conditions. The filament, which is copper containing, grows subsurface from the anode to the cathode along the epoxy-glass fiber interface. In this study, hole-to-hole test coupons were processed using two thermal excursions for a high-bromide-containing (similar to 15 wt.%) hot air soldering leveling (HASL) fluid. The coupons were then exposed to accelerated temperature, humidity, and bias conditions of 85 degrees C, 85% relative humidity (RH), and 200 V bias, respectively, for 28 days. The aged coupons were then cross-sectioned, and scanning electron microscopy (SEM) and energy-dispersive spectroscopy (EDS) revealed that, in addition to bromide CAF, a copper-bromide-containing compound was present in the polymer matrix. The bromide-containing CAF was characterized using transmission electron microscopy (TEM) to be Cu(2)(OH)(3)Br. In addition, the copper-containing compound formed in the polymer matrix was characterized using x-ray photoelectron spectroscopy (XPS) to be CuBr. An electrochemical mechanism for the formation of bromide-containing CAF has been proposed based on the XPS data. It has been shown using Fourier-transform infrared (FTIR) spectroscopy that the polyol constituent from the flux diffuses into the board during soldering. Ion chromatography was used to show that bromide ions from the flux also diffuse into the board material during soldering.
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页码:1884 / 1894
页数:11
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