Electrochemical Behavior and Analysis of Organic Additives in Modern Lead Free Wafer Level Packaging Plating Baths
Authors: Pavlov Michael , Lin Danni , Shalyt Eugene , Tsimberg Isaak 
Published: February 2020

Replacement of tin-lead solder bumps by a suitable lead-free material for flip chip attachment has become an urgent necessity due to the impending ban on the use of lead in electronics. Alloys containing Sn and Ag as well as pure Sn are the most common for the replacement of Sn-Pb. The mechanical strength, wetting, and fatigue resistance of these alloys and pure Sn is comparable or surpass that of Sn-Pb”. Electroplating with lead-free alloys is the most desirable technique due to its low cost and usefulness in building small dimension bumps. However, the co-deposition of elements is complicated by the large difference in the electrode potentials of each element. Besides metal ions, these plating baths include organic additives, chelating agents, and acids. For appropriate plating bath performance, these components must be kept within specific concentration ranges. This is achieved through the use of dedicated chemical analyzers and dosers [1]. Most of these systems use multiple analytical methods that typically include electrochemical techniques. The introduction of new electroplating processes requires the development of new analytical methods.

Before a new analytical electrochemical method is developed, the interactions between bath components should be investigated and understood. For this purpose, we utilized an electrochemical cell with three electrodes connected to a potentiostat/galvanostat. We studied the responses of organic components under varying electrochemical and hydrodynamic conditions as well as at different concentrations of bath components. Fig. 1 shows the electrochemical responses of organic additives used in commercial lead-free plating baths [2]. All tests were performed with the working and counter platinum electrodes and a low maintenance Ag/AgCl double junction reference electrode.

Optimized electrochemical analysis parameters enable the determination of a wide range of concentrations of organic plating additives without interference from other bath components.

Analysis of organic additives can be performed with relatively simple fluidics that include a single electrochemical cell with accurate temperature control. Typical analysis steps include fast electrode conditioning in support electrolyte, several injections of plating solution to determine changes in plating rate, and then subsequent calculation of the concentrations.

This presentation will provide more information related to the electrochemical behavior of organic additives and inorganic components. Results of Electrochemical Impedance Spectroscopy investigations will also be presented. Results of electrochemical analyses will be correlated to data obtained with an HPLC analytical technique. The presentation will be concluded with a discussion of analytical results for each organic additive at different concentration levels.

References:

Pavlov, D. Lin, E. Shalyt, I. Tsimberg, “Electrochemical Analysis of Semiconductor Plating Baths”, MAM Conference, Milano, Italy, March 18-21, 2018

Foyet, M. Clauss, W. Zang-Beglinger, J. Woertink, Y. Qin, J. Prange, P. Lopez, , “Electroplating baths of silver and tin alloys”, US Patent, US9512529B2

Figure 1