Interfacial voiding in solder joints formed with Sn-Ag-Cu solder alloys and electroplated Cu was examined as a function of the plating solution chemistry and parameters. Galvanostatic Cu plating of *10 lm thick Cu films was performed in a commercially available plating solution, and in model generic plating solutions. Analysis of the current voltage behavior along with Secondary Ion Mass Spectrometry studies of organic impurity content of two plated and a wrought copper samples, yielded a conclusion that for certain chemistry solutions (e.g., H 2 SO 4 + CuSO 4 + Cl -+ PEG) and current density ranges above 2.5 mA cm -2 , organic impurities were incorporated into the growing Cu. Solder joints were produced with a variety of electroplated Cu samples. These joints were, then, annealed at a temperature of 175°C for 1 week, cross sectioned and examined. In general, it was observed that interfacial voiding in laboratory electroplated Cu layers was qualitatively similar to the unexplained voiding observed in some industrially plated Cu products. More specifically, it was found that the propensity for voiding could be correlated with specific electroplating parameters that in turn were associated with significant incorporation of organic impurities in the Cu deposit.

The sporadic voiding phenomenon in Cu 3 Sn intermetallic compound (IMC) formed during thermal aging, sometimes referred to as "Kirkendall voiding", has been found to lead to degradation of solder joint reliability in board level shock testing. It was suggested that the voiding phenomenon resulted from the incorporation of specific impurities in the copper during electroplating. In this study, Cu samples were electroplated from a generic suppressor-brightener additive system using a rotation disk electrode (RDE) apparatus. Overpotential during plating, surface morphology and the propensity for voiding of plated samples were investigated. Galvanostatic (constant current density) plating was conducted at 10 mA/cm 2 sequentially up to 18 hours. The solution exhibited dependences of overpoential and voiding propensity on bath aging, due to the breakdown of the organic additives. Cu samples were also plated in the current density range of 0.8-40 mA/cm 2 . In the 10-20 mA/cm 2 , current density range, a fine-grain, smooth, deposit surface was observed, accompanied by an especially low voiding level of samples plated in that range.

Between 65 and 175 K, nitroxyl radicals with spirocyclohexyl groups at the 2-and 6-positions of the piperidine ring exhibit spin echo dephasing rates that are slower than for nitroxyl radicals with 2,5-gem-dimethyl or 2,6-gem-dimethyl substituents that are currently used as spin labels, and are slow enough to permit DEER measurements at temperatures up to about 125 K for spin labels with analogous ring structures.Pulsed double electron-electron resonance (DEER or PELDOR) spectroscopy is increasingly being used to measure electron-electron interspin distances in biomolecules and polymers. [1][2][3][4] This method is particularly powerful for systems such as membrane proteins that are difficult to crystallize and that are too large for solution NMR studies. Analysis of DEER data permits determination of both the mean distance and the width of the distance distribution. Faster spin echo dephasing rates restrict the measurements to shorter interspin distances and limit the accuracy to which the width of the distribution can be determined. 1In addition to molecules with native paramagnetic centers, distance measurements are made possible for other biomolecules by introduction of cysteines via site-directed mutagenesis and subsequent attachment of thiol-specific nitroxyl spin labels. 5 Polymers also can be spin labeled. All the currently available labels have gem-dimethyl groups adjacent to the nitroxyl N-O moiety, as in MTSSL. Rotation of these methyl groups at rates comparable to the anisotropy in the electron-proton hyperfine coupling to the methyl protons enhances the spin echo dephasing rates at temperatures above about 60 K, 6-8 so the optimum temperature for DEER measurements with these labels is 50 to 60 K. 1 It would be significantly less expensive if the experiments could be performed at higher temperatures with liquid nitrogen. However, for the methyl-containing spin labels, DEER experiments at higher temperatures have substantially poorer signal-to-noise and are limited to shorter distances because of the faster spin echo dephasing rates. 1 † Electronic supplementary information (ESI) available: Preparation of samples, EPR spectroscopy, determination of tumbling correlation times, modeling of the temperature dependence of 1/T 1 , and orientation dependence of relaxation rates.

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The electrochemical behavior of levelers was studied and compared for two commercial Cu plating chemistries in an effort to correlate the electrochemical behaviors with their impacts on bottom-up filling, impurity incorporation, and grain structures. While a strong complexing between leveler and accelerator resulted in a leveler-sensitive bottom-up filling rate and low impurity level in the deposit, a traditional non-interacting leveler showed little impact on the filling performance and yielded a high impurity incorporation. An oscillatory behavior was reported for the strongly-interacting leveler chemistry during galvanostatic plating, this oscillation manifested itself in both the potential and impurity incorporation. High impurity incorporation is known to inhibit the Cu grain growth; a laminated structure with alternating layers of big and fine Cu grains was obtained by annealing the Cu films plated with the oscillatory behavior.