Characterization of Copper Surfaces Used in Electronic Circuit Boards by Reflectance FT-IR
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289 Mat. Res. Soc. Symp. Proc. Vol. 591 © 2000 Materials Research Society
EXPERIMENTAL
Individual copper coupon specimens, measuring 1.27 cm by 2.54 cm (0.5" by 1"), were prepared using conventional dip coating procedures. To remove the native cuprous oxide on the copper surface the test coupons were treated with 1%HCl solution followed by a thorough distilled water rinse. The dip coat solution consisted of a 5mM solution of benzotriazole in water. A film thickness ranging between 3-5 microns was obtained by this method. The infrared reflection absorption spectra were recorded on a Perkin-Elmer Series 2000 Fourier transform spectrometer. The spectrometer was equipped with a Harrick variable angle reflectance accessory. The angle of incidence was set at 450 with a single reflection. Thus, the coating and Cu interface could easily be characterized. This is illustrated in Figure 1. Each spectrum was recorded by co-adding 256 interferometric scans at a resolution of 4 cmnl. Incident Beam (I)
Reflective Beam (R0 ) (Coating) Reflective (osp/cuBeam Interface)(Rint.)
OSP Coating (3-5 microns)
Figure 1: Illustration of Reflectance-Absorption Spectroscopy Contact Angle measurements were performed on a VCA 2000 Video Contact Angle
System, equipped with data reduction software. Data reported are the average for ten (10) separate droplets. Distilled water was used for all measurements. Test specimens were exposed to two (2) distinct environmental conditions. Half of the
specimens were placed in a conventional Blue-M oven subjected to a hot-dry environment of
80*C (176*F), using MIL-STD-883EF, Method 1004.7 (Temperature) as a guide. Although this temperature, is on average, extreme, it is not uncommon for certain electronic components attached to the PCB to experience these temperatures, such as thermal sinks and capacitors. Under the second exposure environment, panels were conditioned to an accelerated hot-wet environment of 40 0C (104-F) at 90% relative humidity (RH), using MIL-STD-202F, Method 103B (Humidity-Steady State). One thousand (1,000) hours of exposure at this condition roughly correlates to 2-3 years of service, depending upon the end-use environment. Coating spectral data was recorded at various time intervals. RESULTS The FT-IR results for the hot-dry environmental exposure are presented in Figure 2. We show the reflectance-absorption spectra in the initial state and two exposed states taken after 360 hours and 1030 hours. The spectra have been offset for clarity purposes. The major spectral change is the appearance of the 647 cm'l band, which can confidently be assigned to Cu-O
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stretching vibration. This is interpreted as direct evidence that copper oxide formation occurs in spite of the presence of the OSP protective coating. It is interesting that the data shows no evidence of degradation of the organic coating. The FT-IR spectra has no new features in the 1000-1200 cm"1 range which would indicate organic oxidation of the coating. Upon further analysis, some shifting in the baseline can be note
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