Study On New Brown Oxidation Of Copper/Resin Resistance To Stripping In Printed Circuit Board Industry

With the development of electronic products in the direction of light,thin,short,small and multi-function,higher requirements are put forward for the densification and refinement of printed circuit boards（PCB）.In the process of multi-laminar manufacturing,the improvement of the binding force between interlayers is the key to improve the quality of the laminates.Brown oxidation process is used as an inner bonding technique for multilayer laminates and has the characteristics of short process,easy to control and safe and high efficiency.Brown solution is mainly composed of sulfuric acid,hydrogen peroxide and special additives.In the process of brown oxidation,the oxidizing agent oxidizes Cu into Cu₂O,and the heterocyclic organic compound containing N,O and S forms a layer of organic metal film on the surface of the rough and uneven surface.In the process of laminating process,the organic copper oxide film layer and resin solidify crosslinking reaction,thus improving the bonding force between interfaces.In this paper,three kinds of economic and environmental corrosion inhibitors,including methionine,adenine and histidine,were researched.The anti-corrosive effect for copper in 1 M H₂SO₄ has been systematically studied via electrochemical tests,quantum chemical calculation and molecular dynamics simulation method.Meanwhile,the mechanism of sustained release was briefly analyzed.Finally,the three kinds of corrosion inhibitors are applied to brown oxidation on the basis of theoretical research.The research contents and conclusions are as follows:（1）Theoretical researchPotentiodynamic polarization tests show that three kinds of corrosion inhibitors are considered as a mixed-type inhibitors and cathodic action are more marked by preventing the reduction of H⁺in the electrode surface,and inhibiting the dissolution of anode copper in the charge transfer process.Electrochemical impedance spectra indicated that corrosion inhibitors suppress the surface reaction of the active site by simply form a protective film on the metal copper surface,thus reducing the corrosion reaction rate.The results of quantum chemistry calculation manifest that the HOMO and LUMO of methionine molecules are concentrated in heteroatoms（S,O）;The HOMO and LUMO of adenine molecules are more evenly distributed in the imidazole ring and pyrimidine ring,and the parallelly adsorbed on the copper surface.The HOMO of the histidine molecule is mainly distributed in the imidazole ring,while the LUMO is mainly distributed in the heteroatoms（O,N）.It is suggested that the three kinds of compounds are adsorbed on the surface of metal copper,which provides the theoretical basis for the later application of brown study.（2）Applied research（1）Study on the optimization of brown oxidation bath.According to the appearance of brown copper foil（even tan）,microerosion depth（1.4-1.8μm）and peel strength comprehensive effect standard,the bath composition andprocess conditions of brown oxidation for copper foil were optimized using simplex optimization.The experimental data showed that the peeling strength is up to 0.72 kg/cm when the newly brown oxidation process and optimized conditions were applied.In terms of thermal performance,there is no delamination and blister on the test specimens after tin immersion at a high temperature for 6 times,lead-free reflow soldering for 6 times and thermal shock cycle for 100 times.（2）Physical and chemical tests.The SEM shows that it is microscopically uniform with a honeycombed and porous structure from a lamellar structure that is not smooth and has no apparent bite after brown oxidation process.Under the magnification of5000,it can be observed that there is a certain gap between the particles in the test samples,which is closely packed together,and there is no obvious difference between the different processes.The XRD tests indicate that the crystal surface of Cu（111）plays a major role in laminating process and the stratification occurs at the interface between organic copper oxidation film and copper substrate.Meanwhile,the result of XPS ensured that a higher proportion of carbon–oxygen covalent bonds attributed to increase of the binding force owing to the formation of chemical bonds,such as Cu–N–O and Cu–O–C.So,we can conclude that the constituents of the organic metallic film formed on the copper surface plays a crucial role on the binding force and delamination may occur at the film/resin interface.