Research On Surface-roughness Regulation And Transmission Loss For Conductive Pattern Of Printed Circuit

As the widespread application of the fifth-generation mobile networks,the electronics industry has put forward higher demand for high-speed printed circuit boards.This makes the signal integrity problem become a prominent issue to deal with for the signal transmission at high speed.This paper focuses on the influence,including the brown oxidation technology selection and the brown oxidation process parameters set,on the conductor surface roughness and transmission loss.Then,we find the optimal brown oxidation technology and corresponding process parameters setting.At the same time,a prediction model for hyper-very-low-profile copper foil was also established to quantify the increase of transmission loss with roughness change.Besides,this model can benefit for the cost reduction of verification on brown oxidation technology selection and parameter optimization.The detailed work and result are as follows.We compared the influence of three different kinds of browning oxidation technology called B(low etching with organic silane treatment),C(low etching adhesion promoter)and D(traditional brown oxidation),on copper foil surface roughness,transmission loss,and reliability.The results showed that the brown oxidation treatment significantly raised the surface area ratio of the copper foil surface above 0.25,while the effect on the roughness depth was less obvious.Meanwhile,the transmission loss results of the test module were D>B>C,which confirmed that the transmission loss would increase as the roughness increased.All three brown oxidation treatments could satisfy the requirement of the lowest peel strength 0.175 N/mm.Besides,all test modules from three brown oxidation treatments could meet the thermal reliability requirements.On the basis of the simplified model established through the Maxwell equation for the transmission loss prediction,we considered both influence of the relatively finegrained roughness-structures and the signal-current distribution between the shiny and matte sides of the transmission line on transmission loss to establish a more complete model.As verified by the test modules,this model was more accurate than the current model and the difference between prediction and measured result was 1.8%.In this paper,all the brown oxidation parameters and roughness results were collected for the multiple linear regression.Then the regression result was used to figure out the parameters having significant effects on roughness,according to the P value.Besides,the response surface optimization experiment design was carried out for the significant process parameters chosen before.So,a fitting regression model,using the significant process parameters,for roughness was obtained.Furthermore,the contour map of roughness,which was obtained according to the regression model,was used to obtain a more optimized process parameter set: the line speed was 3.69 m/min as the line speed given by supplier,the temperature for browning oxidation was set in 33.5°C-35.5°C,and the alkaline washing temperature was controlled between 53.3°C-55.3°C.Under the premise of ensuring the bonding force,the roughness was minimized: the surface area ratio increased to 0.26,and the root-mean-square value of roughness depth increased to 0.218 ?m.In addition,the roughness model proposed in this paper was used to verify the optimized process parameters for transmission loss optimization.The results showed that for the application of low-rough browning process,the process parameter optimization for the test boards could help reduce the transmission loss about 0.4%.