Study On Etching Behavior And Electroless Plating Technology Of LTCC Substrate

In recent years,Low Temperature Co-fired Ceramic?LTCC?technology,which have the properties of excellent high frequency and wide pass band characteristics,has become the preferred package method of electronic component integration.In order to reduce the cost of LTCC components,the use of silver conductors instead of gold conductors is an inevitable development trend.However,silver is difficult to meet the high reliability requirements in military electronic devices due to the presence of surface oxidation and electrical migration phenomenon.The electroless nickel/gold plating process allows surface protection of silver conductors,can use silver replacing the gold conductors in the context of reliability assurance.But most of the commercial LTCC materials can not resist the corrosion in electroless nickel/gold plating process.Therefore,focusing on typical LTCC substrate material acid etching behavior research,this paper designed and prepared the LTCC substrate material and co-fired silver conductor paste which have good acid corrosion resistance.The feasibility of electroless plated substrate samples was initially verified.The acid etching behavior of different LTCC substrate materials were studied by using the methods of SEM,EDS,XRD and ICP to characterize the changes of mass,micro structure and phase composition before and after corrosion.The results showed that wollastonite and barium feldspar which were the main crystal phase in some common glass-ceramic LTCC substrates,reacted with acid and resulted in different degree of substrate corrosion.The substrate materials made of borosilicate glass and alumina which hardly reacting with acid had excellent corrosion resistance,of which the weight loss after soaking 30h in nitric acid solution with a concentration of 1N at80?was less than 10mg.cm^-2.A substrate with excellent acid corrosion resistance was prepared by using B2O3-Al2O3-Si O2 glass and Al2O3 as the main component.The densification behavior and comprehensive properties of the substrate were characterized by DSC,DIL and dielectric spectrum tester.The results showed that the non-crystallization B₂O₃-Al₂O₃-Si O₂ glass with softening point of 625.3?had good wettability to alumina,which can improve the density and mechanical properties of the composite.The composite with alumina content of 45%showed well both electric and corrosion resistance properties,of which the density was 2.51 g.cm^-3,the dielectric constant was5.27,the dielectric loss was 0.0027?at 1MHz?,the thermal expansion coefficient was5.79 ppm/?,and the flexural strength was 142.5MPa.After soaking 30h in nitric acid solution with a concentration of 1N at 80?,the surface weightlessness was 2.78mg.cm^-2.A silver paste was prepared by spherical silver,borosilicate glass and organic solution,of which the viscosity was within 90?130Pa.s,the fineness was less than15?m.An LTCC substrate sample was prepared by using the silver paste as surface wiring conductor.The conductor was dense and smooth,while the square resistance was less than 5m?/sq.The electroless nickel/gold surface treatment was performed on the sample.The result showed that the co-fired substrate samples can be plated by commercial plating bath,while nickel/gold layers after plating were dense and smooth,the thickness of nickel coating was 2?4?m,the thickness of gold layer was about0.1?m.The plating process did not cause the conductor and the substrate corrosion.The gold wire bonding test was used to evaluate the coating adhesion,the results showed that the tensile strength was about 7.5?8.5g.The results of water droplet experiment showed that electroless plating treatment could effectively prevent the electric migration of silver conductor and greatly improve the reliability of the sample.