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20 The PCB Magazine • June 2015 electroless copper solution without stress reduc- ing additives. Next, the S2 circuit, which con- tained the MVs, was evaluated. After 1000 cycles there were no defects present at any parameters evaluated. A cross section is shown in Figure 9. No additional evaluation was necessary. Due to the IST coupon design and test parameters used in this study, the S2 circuit has already experi- ence up to 1000 cycles during testing of the S1 circuit. Therefore, the S2 circuits have experi- enced up to 2000 cycles of heating and cooling. Conclusion Select additives can be added to an electro- less copper solution, which decrease the stress of an electroless copper deposit. The reduced stress allows for a blister free copper deposit on smooth, difficult to metallize substrates such as PI. These additives showed no adverse effects on the interconnect reliability of the resulting copper deposit when exposed to thermal stress as evaluated by solder shock and IST. PCB References 1. C. F. Coombs, Printed Circuits Handbook, 6 th Edition, McGraw Hill, NY, 2008. 2. Z. Wang, A. Furuya, K. Yasuda, H. Ikeda, T. Baba, M. Hagiwara, S. Toki, S. Shingubara, H. Kubota and T. Ohmi, J. Adhes. Sci. Technol., 16 (2002) 1027. 3. D. Bhusari, H. Hayden, R. Tanikella, S. Allen, and P. Kohl, J. Electrochemical Soc., 152 (2005) F162. 4. J. Jones, J. Polymer. Sci., 22 (1969) 773. 5. J. C. R. Shipley, L.H. Shipley, M. Gulla, O.B. Dukewych, Electroless Copper Plating, United States Patent 3615733 (1971). 6. F. W. Schneble, R.J. Zeblisky, J. F. McCor- mack, J. D. Williamson, United States Patent 3310430 (1967). 7. R. Brüning, B. Muir, E. McCalla, É. Lempereur, F. Brüning and J. Etzkorn, Thin Sol- id Films, 519 (2011) 4377. Figure 9: cross-section of an IST coupon MV after 1000 cycles. Jason carver is an r&D chemist II at OM Group Electronic chemicals. alvin Kucera is a former senior product specialist, r&D at OM Group Electronic chemicals. A HIGH-RELIABILITY, STRESS-FREE COPPER DEPOSIT FOR FPC, POLYIMIDE AND RIGID-FLEx continues FeAtuRe