Research On Additives In Low Temperature And Low Stress Potassium Sodium Tartrate Copper Plating Syste

In order to meet the needs of the information age,the traditional printed circuit board（PCB）industry gradually developed towards the direction of high precision,lightweight,multi-function,multi-layer,high speed and good reliability.To meet the demand for increasingly narrow PCB line width,a modified semi-additive process had been used to produce PCB fine copper interconnects.Although the improved semi-addition method could design fine lines on printed circuit boards,using measures such as increasing the substrate surface roughness to enhance the bond strength between the substrate and the electroless copper plating film,it also caused significant phenomenon of signal attenuation and low signal-to-noise ratio in the process of high-frequency signal transmission.In order to achieve low attenuation of high-frequency signals and high signal-to-noise ratio,two stable electroless copper plating systems at low temperature and low stress was studied in this paper.Firstly,the surface of polyacrylonitrile-butadiene-styrene copolymer（ABS）substrate was micro-etched using MnO₂-H₂SO₄-H₂O micro-etching system.It was found that spherical micro-pores with reasonable depth,high density and uniform distribution were formed on the surface of ABS substrate when the micro-etching time was 20 min.And such micro-pore structure was beneficial to increase the roughness of ABS substrate surface and enhance the hydrophilicity of ABS substrate surface.So that,the bonding strength between ABS substrate surface and electroless copper plating layer was reached to 1.05 k N/m.Secondly,the effects of additives on the deposition rate and the appearance of the plated layer in the low-temperature potassium sodium tartrate chemical copper plating system were investigated in this paper.The composition of the basic electroless copper plating system was10 g/L copper sulfate pentahydrate,28.4 g/L sodium potassium tartrate,5 m L/L formaldehyde（37%）,operating temperature 35℃,and p H value was 12.5.Based on the basic plating system,it was found that the addition of the stabilizer 2,2’-bipyridine reduced the deposition rate of electroless copper plating while ensuring the stability of the electroless copper plating system.The single addition of L-malic acid and 2-mercaptobenzothiazole（2-MBT）could substantially increase the deposition rate of the electroless copper plating system and improve the surface microscopic morphology of the copper layer at the same time.Therefore,L-malic acid and 2-MBT were suitable as an accelerator for the low-temperature potassium sodium tartrate copper plating system.The result also indicated that the addition of surfactant cetyl trimethyl ammonium bromide（CTAB）could increase the deposition rate of electroless copper plating and improve the surface quality of electroless copper plating layer.While the addition of surfactant sodium dodecyl benzene sulfonate（SDBS）also could change the surface quality of electroless copper plating layer,which was a suitable surfactant for low temperature sodium potassium tartrate chemical copper plating system.The addition of stress-relieving agent NiSO₄·6H₂O could not only reduce the stress of electroless copper plating layer,but also improve the quality of copper plating layer.Finally,the effects of the compound addition of accelerator（L-malic acid,2-MBT）,stabilizer（2,2’-bipyridine）,surfactant（SDBS,CTAB）,and stress reliever（NiSO₄·6H₂O）on the deposition rate and copper layer surface morphology of electroless copper plating were investigated.It was found that the combination of 2.0 mg/L L-malic acid,1.0 mg/L2,2’-bipyridine,2 mg/L NiSO₄·6H₂O and 2.0 mg/L CTAB could form a good synergistic effect in the electroless copper plating system.Therefore,they were suitable additives in the low-temperature potassium sodium tartrate electroless copper plating system.It was also found that the combination of 0.25 mg/L 2-MBT,1.0 mg/L 2,2’-bipyridine,2 mg/L NiSO₄·6H₂O and 4.0 mg/L SDBS formed a good synergistic effect when they were added together to the electroless copper plating system,and they were suitable additives for low temperature potassium sodium tartrate electroless copper plating system.The cathodic and anodic polarization curves of the electroless copper plating system were analyzed by linear voltammetry.The result indicated that the compound additions of L-malic acid,2,2’-bipyridine,CTAB and NiSO₄·6H₂O increased values of the oxidation and reduction peak current densities,which was consistent with variation trend of the deposition rate change pattern.It was also found that the compound additions of 2-MBT,2,2’-bipyridine,SDBS and NiSO₄·6H₂O also increased values of the anodic oxidation and cathodic reduction currents densities,which indicated that the additives influenced the deposition rate of electroless copper plating by changing the current density.It was found that the addition of NiSO₄·6H₂O could reduce the stress of the electroless plating copper layer and improve the quality of the copper layer by the stress test on the electroless plating copper layer.And the stress was minimized when the additive concentration of NiSO₄·6H₂O was 2.0 mg/L.