| Printed circuit board lining surface treatment must be conducted to meet the requirements of the adhesion strength of the laminate, however, with the rapid development of communication technology, the demand for the rapid transmission,storage, processing of mass data is higher and higher. PCB tends to high density and high frequency that the line becomes finer, and the traditional etching surface treatment technology has received a big serious challenge. Therefore, in this paper, a kind of non-etching adhesion promoter, namely smooth surface modification technology, is proposed, which is aimed at minimize the roughness of the copper surface, improve the adhesion strength of the copper and resin, and reduce the high frequency signal transmission loss.In this paper, starting with the combination mechanism of metal and resin to explore the isoelectric point of metal oxide, we proposed a kind of smooth modification technology, which selected metallic tin as deposited metal and organic silane coupling agent as auxiliary adhesion promoter. Its each technological process was elaborated in detail, which affects the final bonding force. After calculation with analysis of variance, we found that the immersion tin of the five steps has a highly significant influence on bonding strength.With some characterization methods such as scanning electron microscope,X-Ray thickness tester, 3D microscope, peel strength tester, we explored the impact of the formula component and the working conditions of immersion tin on the result of this reaction and the final binding force by using the single factor experiment. Then the optimal immersion tin formula was confirmed: SnCl2 15-25g/L, thiourea 50-80 g/L,hydrochloric acid 70-90 g/L, sodium hypophosphite 20 g/L, citric acid 15 g/L, lactic acid 10mL/L, OP-10 emulgator 2g/L, pH=1.0, 65?-75?/120s, stirring speed 100rpm.Analyzing the tin layer though X-ray diffraction, we found the preferential crystal plane in this experiment was Sn (200) and Sn (101). By means of electrochemical analysis method, we explored the working mechanism of thiourea in this reaction and found that thiourea was combined with copper through adsorption, complexation,desorption to provide impetus. The equivalent circuit at the concentration of 0.5mol/L thiourea by simulating the oxidation reaction in this reaction was R((RW)Q).The smooth modification technology applied to the process of the multilayer printed circuit board which made by the traditional alkaline etching method was also investigated in this paper, with the smooth modification technology instead of electroplating tin lead. It simplified the process of annealing tin lead and subsequent surface treatment, and satisfied the requirements of the "lead free". Observing the product which was made into microsection by metallographic microscope, we found that the combination of tin and copper layer is well bonded.Comparing the high frequency signal transmission of smooth surface modification technology with traditional brown oxide after agilent network analyzer testing, it found that the smooth modification technology can effectively reduce the high frequency signal loss, indeed 0.1075 dB/inch lower than brown oxide at 20 GHz. Observing the surface roughness with 3D microscopy, it showed that parameter Rc was 0.4?m lower than brown oxide in average value. Meanwhile the binding force of smooth surface modification technology can transcend brown oxide by an average value of 11.3%. The printed circuit board which applied with smooth modification technology can through a variety of reliability testing, such as heat resistance, impact resistance and corrosion resistance. |
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