Investigation Of Copper Electrodeposition In Through Hole With Thin-dielectric Layer For Printed-circuit Interconnection

The miniaturization,thin and high-performance of electronic products drives printed circuit board to develop in the direction of thinner,high density and high reliability,which will give rise to the dielectric layer of printed circuit board be more thinner.Through-hole is a way of printed circuit board interconnection.Its electroplating quality will directly affect the reliability of printed circuit board and the performance of electronic components on the board.When the dielectric layer is thinner than 100?m,the original electroplating solution for through-hole electroplating with thick-dielectric layer will no longer be suitable for that with thin-dielectric layer.Therefore,it is very necessary to study the copper electrodeposition of through-hole with thin-dielectric layer.This paper focuses on the research on additives to develop formulas to solve the problem of low throwing power in the process of non-uniform deposition and realize the superfilling of through-hole in printed circuit board with thin-dielectric layer.(1)Additives play irreplaceable roles in copper deposition process.The presence of additives in plating solutions can result in a better throwing power since additives effectively improve the current distribution.In this paper,the adsorption characteristics,molecular orbital characteristics and electrochemical properties of 3-N,N-Dimethylaminodithiocarbamoyl-1-propanesulfonic acid(DPS),Bis-(3-sulfopropyl)-disulfide(SPS)and mercaptopropane sulfonic acid(MPS)were studied by means of molecular dynamics simulation,quantum chemical calculation and electrochemical method.The results of molecular dynamics simulation showed that the adsorption of DPS,SPS or MPS on Cu(111)surface was chemical adsorption under the model with aqueous solution.And the electronic properties and orbital information of DPS,SPS and MPS determined by quantum chemical calculations based on DFT,suggested that the possiblly preferential adsorption sites on the Cu(111)surface of DPS,SPS and MPS might be the sulfur atoms in C=S,C-S-S-C and-SH structures,respectively.It was found that DPS could act as suppressor as well as accelerator depending on its concentration while the continuous acceleration SPS performed with the increased concentration in the electrochemical analyses.This concentration-dependent behaviour of DPS was speculated as the consequence of its asymmetric dissociation during copper eletrodeposition.The produced MPS might act as the actual anti-suppressor species leading to the accelerating behavior of DPS.And the accumulation of the nitrogen-containing by-producrs from the dissociation of DPS might be referred to reason for the suppressing effect at the high concentration rather than the dimmers formation of DPS.The relevance of this surface reaction for the Cu electrodeposition process used DPS was discussed in detail.(2)The development of copper electroplating technology gives new requirements to additives.With multiple characteristics of the additive will become a development trend.In this paper,the synthesis of a new accelerator with characteristics of brightener and leveling agent was carried out with DMTD,1,3-propanesulfonic acid lactone and sulfur as the basic raw materials.Both the electrochemical performance of the synthesized accelerator was analyzed.(3)In combination with the characteristics of SPS and DPS,the non-uniform deposition of through-hole with thin-dielectric layer was studied in this paper.Cu electrodeposition under three-component additive system was studied with the comparisons of the one under two-component additive system.The results showed that the throwing power(TP?200%)of the two-component additive was better than that of the three-component additive(TP ? 100%).Moreover,the influential factors in the non-uniform deposition under two component additive systems of through-hole with thin-dielectric layer were analyzed.(4)Conventional through hole(TH)process plugged with conductive epoxy material already could not satisfy the requirements of high density interconnection(HDI)manufacturing.Through-hole fill(THF)technology was designed to improve reliability,electrical conductivity and thermal conductivity,to increase productivity and to reduce process costs.In this paper,a target leveling agent was selected after a screening of a series of candidates leveling agents and invested in the TH filling process,achieving a good filling performance of through-hole with thin-dielectric layer eventually.Meanwhile,the influential factors of through hole filling were examined.The effects of the concentration of sulfuric acid,chloride ion,leveler and suppresser,and the solution flow rate were discussed,respectively.Among them,the flow rate was found the critical factor.Higher flow rate directly led to more significant decrease in the filling performance.For further understanding of the Cu TH filling proceeds,the hole filling condition at different electroplating duration were also demonstrated.It was found that under the condition of high concentration of accelerator,the THF filling process was butterfly filling.While under the condition of low concentration of accelerator,The THF filling process will no longer be butterfly filling,where the process came into copper electrodeposition along the airflow direction resulting from asymmetric electrodeposition on both sides of the hole.