Study On Key Techniques For Fabrication High Thickness Fine Lines Of HDI Board

Printed circuit board(PCB)is the pivotal carrier of electronic components for electric signal interconnection.It is the key unit for variety of electronic products to achieve their function,and is widely applied in variety of electronic equipments.In recent years,high-density interconnection(HDI)printed circuit board was proposed to meet the requirement of miniaturization and high-speed of electronic products,and the HDI has made development rapidly.Unfortunately,there are still challenges in PCB industry,and one of them is how to solve the key techniques for fabrication high density and high thickness conductive lines of HDI with highly quality.To solve this problem,the key techniques for fabrication fine line with high thickness of HDI board were studied in this thesis.First of all,the prediction model of fine line thickness in semi-additive process was studied,and the limitation of semi-additive process for fabrication high thickness fine line of HDI was discussed.Secondly,the feasibility and key techniques for fabrication high thickness fine lines of HDI with modified full-additive method(MFAM)were studied in detail.The main contents and conclusions were given as follows: 1.Semi-additive process(1)Study on prediction model of fine line thickness in semi-additive process.In this paper,H2SO4-H2O2 etching solution was applied for experiments,the effect of line density on etching degress of copper line and base copper was studied,and the experimental data revealed that: 1)the relationship between the etching thickness of copper line and base copper is in accordance with the nonlinear model while the line density(line width/line space)of HDI is in the tested range;2)the relationship between the etching thickness of copper line and base copper is related to the line density.The denser the line,the larger the difference in etching rate between copper line and base copper;3)the relationship between the etching thickness of base copper(x)and etching thickness of copper line(y)is y =-0.0239x2 + 1.2593 x,while the line density(line width/line space)is in the range of 50μm/50μm to 125μm/125μm.(2)Application of the prediction model.1)A trial product of HDI with line density(line width/line space)of 50μm/50μm and thickness of 30μm was successfully produced,and the difference between the actual line thickness(29.4μm)and the design value(30μm)is very small(meet quality requirements);2)The prediction model supposed that the maxium line thickness is always less than the increment thickness of copper lines by electroplating in semi-additive process.Forthermore,the denser the fine line,the smaller the maximum line thickness is.In addition,a maximum line thickness of 30μm was possible to be fabricated in semi-additive process when the fine line density(line width/line space)is 50μm/50μm,if more than 30μm,the quality of copper lines will drop abruptly.2.Modified full-additive method for fabrication high thickness line of HDI(1)Optimization copper electroplating bath for palting on aluminum substrate.A commercial bath for electroplating copper on copper substrate was chosen and optimized with simplex optimization method.The coefficient of variation(COV)of coating thickness is decreased from 3.82% ~ 7.28% to 2.71% ~ 4.39% when the optimized copper electroplating bath was applied,which implied that the uniformity and stability of electroplating on aluminum substrate were improved after electroplating bath was optimized.(2)Study on the transfer of copper lines.The experimental data showed that the peeling strength is up to 9.245 N/cm when the newly brown oxidation process and optimized conditions were applied.The peeling strength of 9.245 N/cm is 45.5% higher than average peeling strength of 6.355 N/cm from traditional brown oxidation process.Most importantly,copper lines which were electroplated on aluminum substrate were transferred perfectly to insulating substrate.3.Application of modified full-additive methodThe findings mentioned above were applied for fabrication high thickness lines of HDI with a line dengsity(line width / line space)of 50μm/50μm.It was showed that: 1)the quality of copper lines fabricated by modified full-additive method is much better than those fabricated by semi-additive method and subtractive method when the thickness of lines is the same(30μm).It is means that,modified full-additive method is more suitable for fabrication of high thickness lines of HDI board;2)the thickness of the dry film affects resolution of copper lines of HDI board.The cross-section of copper lines obtained from thinner dry film is more regular than that from thicker dry film when the copper lines are same in density and thickness.On the contrary,the thickness of copper lines from thicker dry film is higher than that from thinner dry film;3)in the case of line density(line width/line space)of 50μm/50μm,a high quality HDI with line thickness up to 45μm can be prepared through modified full-additive method with 38μm dry film.