Study On Electroplating Interconnection Of Printed Circuit Induced By Conductive Film

The rapid development of electronic information technology is inseparable from the highly integrated and multi-functional electronic products.Printed circuit board,a carrier of the electronic components,rapidly development in the direction of the higher density of interconnection.Therefore,it is very important to realize the interconnection between layers of printed circuit board.It is the precondition of interlayer interconnection and high reliability of printed circuit board to obtain metallization hole with complete coating,high throwing power and good reliability.In this thesis,the research is carried out from three aspects:1)direct electroplating of copper on conductive film,2)optimization of copper plating additives;3)construction and realization of metallization hole with keyhole structure.The effects of concentration of copper sulfate,concentration of sulfuric acid and current density on plating deposition rate were studied by single factor experiment in the process of direct electroplating on conductive film.The results show that the current density can be raised to increase the deposition rate,and the copper growth can be controlled by adjusting the concentration of copper sulfate and sulfuric acid.Through orthogonal experiment design,the comprehensive influence of copper sulfate concentration,sulfuric acid concentration and current density on direct electroplating of conductive film were analyzed,and the optimal electroplating parameter combination was obtained.The optimized condition requires the concentration of copper sulfate with70g/L,the concentration of sulfuric acid with 180g/L,and the current density of 2.2A/dm~2.The deposition rate was 48.66mg/min,and the copper on the plate grew well.The peel strength obtained was approximately 210N/m.The reliability of direct electroplating copper with through-hole conductive film at different thickness to diameter ratios was studied from the aspects of coating morphology,plating capacity,backlight test and thermal stress test.The results show that the direct electroplating of copper on conductive film can form smooth copper coating.With the increase of aspect ratio,the throwing power of the conductive film in the through-hole decreases,the copper in the center of the hole becomes thinner,and the reliability of the through-hole interconnection drops.In order to obtain higher throwing power through electroplating hole,three kinds of electroplating additives were selected,and the optimized electroplating parameters were obtained through orthogonal optimization test design.The optimal ratio of electroplating copper additives was obtained:accelerator concentration was 2mg/L,inhibitor concentration was 600mg/L,leveler concentration was 8mg/L,and current density was2A/dm~2.Under this parameter,the throwing power of the through-hole with the aspect ratio of 6:1 was 92.6%,and the surface copper layer was smooth and bright,and the copper coating inside the through-hole was uniform and without defects.The research on throwing power of copper plating with different aspect ratio shows that throwing power of copper plating with the same aspect ratio decreases with the increase of current density.With the same electroplating current density,the throwing power decreases with the increase of the aspect ratio.For the through-hole with higher aspect ratio,the improvement of current density reduces the throwing power.A kind of copper lock hole structure for metallized hole is designed and made.It innovatively uses etching to remove the base copper adjacent to the orifice on the surface of the copper-coated substrate,and then forms a circle of copper-free covering area around the hole of the printed circuit board.In this way,the conductive film can be coated in the pore area and the orifice area,the deposition area of the conductive film on the substrate can be increased,and the metallized hole with a keyhole structure can be formed in the direct electroplating process.At the same time,the subsequent deposition of copper can be interlinked with the base material,thus improving the binding force between the subsequent electroplating copper and the base material.Meanwhile,it avoids the need for preplating on the plate and in the hole before copper plating in the traditional process,so that the thickness of copper layer on the inner wall of the hole is the same as the thickness of copper layer on the surface of the copper substrate.Therefore,the existing phenomenon that the copper on the metallized pore surface is thicker than the copper layer at the orifice is avoided,thus preventing the copper layer at the orifice from fracture.So the reliability of the metallized hole is improved.In addition,there is no need for pre-plating on the plate and in the hole before copper plating,which effectively ensures the uniform thickness of copper on the plate when electroplating.