Study On Process And Additives Of Periodic Pulse Reverse Electroplating Copper In PCB Through-hole Interconntction

Printed circuit board（PCB）is known as the"mother of electronic products",which is the medium to realize the interconnection and relay transmission between electronic components.Copper is widely used for electrical interconnection on PCB layers and through-holes due to its excellent conductivity and thermal conductivity.Copper electroplating is one of the key technologies for metallization of interconnect holes in PCB layers.The development of 5G era puts forward higher requirements for high-speed communication and large-capacity transmission of data.PCB design tends to be miniaturized,functional,highly integrated and highly reliable.The aspect ratio of the through-hole increases,the current density distribution in the through-hole is uneven,which makes it difficult for the traditional direct current electroplating to uniformly electrodeposit the through-hole.In order to improve the uniformity of through-holes between layers of PCB,the influence of process parameters of periodic pulse reverse electroplating on the quality and uniformity of coating was investigated,and the optimal process parameters were optimized.The behavior changes of single additive and combined additives under the action of anode pulse were investigated by means of electrochemical measurements and molecular dynamics.The periodic pulse reverse electroplating process with high thickness to diameter ratio and high through-hole throwing power（TP）interconnection was developed.The influence of process parameters of periodic pulse reverse on the quality of copper coating was studied by single factor experiment,and the appropriate range of each parameter was determined:forward pulse peak current density 1～2A·dm^-2,forward pulse time 10～30 ms,forward pulse duty ratio 0.8～1.0,number of forward pulse peaks 1,reverse pulse peak current density 3i_f,p～4i_f,p,reverse pulse time 1～2 ms,reverse pulse duty ratio 0.8～1.0,number of reverse pulse peaks1.Through the range analysis and matrix analysis of orthogonal experiments,the comprehensive optimization of multiple evaluation indicators was carried out.The optimization results were as follows:forward peak pulse current A·dm^-2,forward pulse time 30 ms,forward pulse duty ratio 1.0,reverse pulse peak current density to forward pulse peak current density ratio 3,reverse pulse time 1.5 ms,and reverse pulse duty ratio 1.0.Compared with DC electroplating,the comprehensive quality of copper coating has been significantly improved by using the optimized process parameters in low copper and high acid system,high acid and low copper system,pyrophosphate system,citrate tartrate system and HEDP system.A PCB through-hole copper interconnection model is constructed.The influence of different period pulse reverse electroplating parameters on the uniformity of through-hole copper interconnection is systematically analyzed by finite element analysis method.The process parameters are optimized,and the secondary optimization is carried out with through-hole copper electroplating experiment.The numerical simulation results show that the reverse pulse width has the greatest impact on TP,reducing the forward peak current density and increase the forward and reverse pulse time ratio improve the TP of the through-hole.The TP of the through-hole with the aspect ratio of 10:1 simulated by the optimal periodic pulse reverse process is 256.2%,while the TP of the through-hole with the DC electroplating is only 38.7%.The process parameters of the secondary optimized through-hole electroplating experiments are basically consistent with the process parameters optimized by numerical simulation.The forward peak current density is 1 A·dm^-2,the forward and reverse pulse width ratio is 30,the forward duty ratio is 1.0,the forward and reverse peak current density ratio is 4,the reverse pulse width is 1 ms,and the reverse duty ratio is 1.0.TP of through-hole using DC electroplating and optimizing periodic pulse reverse process are 71.9%and 90.2%respectively.The effects of five accelerators SPS,MPS,UPS,ZPS and SH110 and two inhibitors PEG and EO-PO with different polymerization degrees on copper deposition potential and their behavior changes after anode pulse were investigated by molecular dynamics simulation and electrochemical test methods.The anodic pulse weakens the adsorption of accelerator on Cu（111）surface;Turn the inhibitor upside down and change its inhibition ability.Moreover,SH110desorbs the thiazoline ring intermediate prior to MPS-Cu（I）after anode pulse,and MPS-Cu（I）can occupy the active site of the thiazoline ring intermediate,thus improving the deposition rate.Due to the large molecular weight of PEG and EO-PO,their diffusion is affected by convection.After the end of the anode pulse,the inhibitor molecular inversion process causes the weak convection to produce a lag peak,which reduces the inhibition effect of the weak convection,temporarily promotes the deposition rate of the weak convection,and improves the coating thickness in the through-hole.The periodic pulse reverse electroplating can make the inhibitor molecules uniformly arranged,eliminate copper nodules,broaden the concentration window of the inhibitor,and show its application prospect in the multicomponent additive system.A composite additive system was developed and applied to the deposition of copper through hole with high thick-diameter ratio by periodic pulse reverse.The addition of SH110 promoted the deposition of copper in SPS-PEG-JGB-SH110system.Due to the slow diffusion of thiazoline intermediate in weak convection,more MPS-Cu（I）occupied the active site in weak convection after anode pulse,which reduced the cathodic polarization.The through-holes with thickness to diameter ratio of 10:1 were electroplated.The average plating capacity of through-holes obtained by DC and periodic pulse reverse electroplating was 94.3%and 124.3%,respectively.The ZPS-EO-PO-JGB system retains the hysteresis peak at the weak convection after the anode pulse,and the EO-PO is convection dependent,effectively inhibiting the copper deposition in the strong convection area.The through-hole with thickness to diameter ratio of 10:1 was plated under two current conditions,and the average plating capacity of the through-hole was89.6%and 124.6%,respectively.