A Study of Low Temperature and Low Stress Electroless Copper Plating Bath

• Published in: International journal of electrochemical science Vol. 8; no. 4; pp. 5191 - 5202
• Main Authors: Li, Li-Sha, Li, Xi-Rong, Zhao, Wen-Xia, Ma, Qian, Lu, Xu-Bin, Wang, Zeng-Lin
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01.04.2013
• Subjects: additives; adhesion strength; deposition rate; electroless copper film; low stress; low stress; electroless copper film; adhesion strength; additives; deposition rate
• ISSN: 1452-3981; 1452-3981
• DOI: 10.1016/S1452-3981(23)14673-6

To meet the requirement of PCB copper interconnection, a low temperature and low stress electroless copper plating bath containing Cu(II)-Rochell salt as complex was investigated. The effects of additives, such as 2,6-diaminopyridine as accelerator, 2,2'-dipyridyl as stabilizer, NiSO4·6H2O as stress-relief agent and sodium dodecyl sulfate as surfactant, on the deposition rate, deposited copper microstructure and surface morphology were investigated by deposition rate measurement and surface SEM observation. Though the deposition rate of electroless copper solution was accelerated by 2,6-diaminopyridine addition and was inhibited by 2,2'-dipyridyl addition, it reached 3.45 μm·h-1 at 33 °C with the composite addition of the four additives, and the deposited copper film also became smooth and uniform. The effects of additives on the polarization behaviors of the electroless copper plating bath were investigated by the linear sweep voltammetry method and mixed potential theory. The internal stresses of copper films were measured by XRD analysis method using the (220) and (311) peaks. The internal stresses of deposited copper film on the (220) and (311) crystal planes were decreased from -164.49 and -122.34 MPa to -16.50 and -31.00 MPa with an addition of 15.0 mg·L-1 NiSO4·6H2O, and the adhesion strength between the substrate and electroless copper film was also increased from 0.84 to 1.12 kN·m-1. Finally, a low temperature and low stress electroless copper plating bath was obtained.