Study On Aluminum Alloy Surface Modification And Influence On The Performance Of Electroplated Copper

Aluminum alloy has excellent electrical conductivity,thermal conductivity,and other comprehensive properties.It has a wide range of uses in printed circuit boards(PCBs),such as serving as a metal substrate for PCBs.At present,the electroplating of copper on aluminum alloys often uses a secondary zinc dipping process.The process is complicated,the amount of acid and alkali is large,it will cause serious pollution to the environment,and zinc will be dissolved in the plating solution,which will interfere or shorten the life of the plating solution.Therefore,it is of great significance to develop a pretreatment process for electroplated copper on aluminum alloys.In this paper,the surface modification method is used to perform electroless nickel plating on the aluminum substrate,and then electroplating copper.Before the copper plating,the surface of the aluminum substrate is protected by a dense nickel layer.The problems of aluminum corrosion and poisoning of the plating solution will not occur during copper plating,which can improve the binding force between the plating layer and the aluminum substrate,and a copper-plated layer having a uniform thickness and a good appearance was obtained.The main research work of this thesis is described as follows.First,the electroless nickel plating modification on the surface of aluminum alloy often requires special activation methods,such as adjusting the commonly used ionic Pd activation solution to make it suitable for the activity of aluminum and avoid excessive corrosion and activation.Secondly,in this paper,during the discussion of the activation of ionic Pd,it was unexpectedly found that both ionic Ag and ionic Cu have the ability to activate aluminum alloys.Therefore,three researches on the activation-induced electroless nickel plating process and testing the properties of the nickel layer were carried out.Thirdly,in order to realize the simultaneous metallization of the aluminum layer and the resin layer,the ionic palladium activation method is optimized.Finally,performance tests were performed on the electroplated copper layer on the surface of the modified aluminum alloy in terms of cohesion,appearance,and uniformity.Experiments show that the electroless nickel plating layer activated by Pd,Ag and Cu shows a typical spherical cell structure.Compared with the electroless nickel plating layer obtained by zinc leaching activation,the coating structure is more dense,the number of spherical cells is larger,and there are no obvious cracks and holes between the coating and the substrate.In addition,the three kinds of activated electroless nickel plating adhesion and Tafel polarization curve tests show that the adhesion between the plating and the substrate is good,and the corrosion resistance of the electroless nickel plating is ranked from high to low as: Cu activation > Pd activation> Ag activation 1> Ag activation 2> Zn activation> Al substrate.When the open-circuit potential-time curve was used to study the initiation process of electroless nickel plating,it was found that all three types of activated electroless nickel plating had undergone dissolution,activation,mixing control,and electroless nickel plating in the early stages.The initiation time of electroless nickel plating decreases with the activation time of palladium,and the optimal activation time is 30 s;the initiation time of electroless nickel plating caused by Ag activation is generally fast first and then slow,and sometimes shows behaviors that are not affected by the activation time.When Cu is activated,as the displacement copper thickness increases,the initiation time of electroless nickel plating decreases.Compared with zinc activation,all three activations can trigger the electroless plating process faster.The study of the mechanism of Cu activation on aluminum shows that after Cu activation,aluminum can successfully initiate the electroless nickel plating process,which is related to the presence of corrosive microbatteries.That is,when aluminum is activated by copper and the copper layer is not completely coated with aluminum,in the electroless nickel plating solution,copper and aluminum form a corrosive microbattery,and copper serves as the cathode and aluminum serves as the anode.Aluminum is oxidized to release electrons,and the nickel ions in the plating solution are deposited on the copper surface.The deposited nickel has the function of catalyzing the oxidation of sodium hypophosphite,and autocatalysis makes the electroless nickel plating continue.In addition,when the aluminum surface is partially covered,the more copper particles are,the more micro-cells are formed,and the more electrons are released from the aluminum,which leads to the accelerated electroless nickel plating process and the reaction to be violent.Regarding the simultaneous metallization of the aluminum layer and the resin layer in the holes of the aluminum substrate,this article uses silanization technology to perform silanization modification treatment on aluminum and resin,and then analyzes the performance of the electroless nickel plating layers deposited on them.The results show that the resin layer and aluminum layer in the aluminum substrate hole have been successfully metallized simultaneously,and The adhesion between the plating layer and the hole wall is good,and the corrosion resistance of the electroless nickel plating layer is ranked from high to low as silanization modification? Pd activation> Zn activation> Al substrate.Finally,when analyzing the properties of the electroplated copper coating obtained after the modification of the aluminum alloy,it was found that the time of electroless nickel plating has an effect on the corrosion resistance and adhesion of the copper coating;when investigating the bonding force between the copper coating and the substrate,Pd,Ag and Cu activation have better bonding strength than zinc immersion activation;the corrosion resistance of the electroplated copper plating is ranked from high to low as Pd activation ? Cu activation > Ag activation > Zn Activation> Al matrix directly electroplated copper.In addition,the silanization modification successfully solved the problem of copper electroplating on the resin,and the copper plating layer had a good bonding force with the hole wall.