Study On The Technologies Improving The Surge Current Capacity Of Tantalum Chip Capacitors

As one of the general components,chip tantalum capacitor has the advantages of small size,light weight and good filtering effect.It has been widely used in military electronics.However,when used in low impedance and high frequency circuits,the MnO2 cathode chip tantalum capacitors often often experience surge current failure at the moment of switching on and off.According to statistics,more than 80%of the failure cases of chip tantalum capacitors are caused by surge current.Therefore,improving the capacity of chip solid tantalum capacitors to withstand surge current can effectively reduce the impact of chip tantalum capacitors’ failure due to surge current on the application of the whole machine and improve the application reliability of the products.At present,foreign companies have studied the failure mechanism of surge current,and put forward four main failure mechanisms.There is no corresponding theory on the failure mechanism of surge current in China,mainly referring to and drawing lessons from foreign theories.In order to meet the domestic demand for substitution of components and improve the reliability of domestic chip solid electrolyte tantalum capacitors,relevant research is urgently needed.In this paper,the key technological process of chip tantalum capacitor is analyzed,including anode design,pressing,sintering,forming,coating and screening.Then four kinds of failure mechanism of surge current are studied and summarized.The theory of flashover breakdown is that the dielectric oxide film is defective,and the flashover breakdown failure is caused by current concentration.The theory of voltage oscillation is that the voltage withstand of the product is insufficient and the high voltage breakdown of the starting machine fails.The theory of local thermal breakdown is that the cathode layer is uneven,the local electric field is strong,and the current density is high,resulting in high temperature thermal breakdown failure.The theory of mechanical stress failure is that the strength of tantalum core is low,and the internal mechanical stress damage caused by the thermal stress expansion of the welding fails.Then,starting from the failure mechanism of surge current,combined with the structure and process flow of chip tantalum capacitor,the influence of each key process flow on the surge current resistance of chip tantalum capacitor is analyzed in detail.Based on the above research,the relationship between each process and different failure mechanism is obtained,and the influencing factors of each process are put forward clearly.For example,anode design is related to the theory of voltage oscillation and flasmodic breakdown failure.The main influencing factors include tantalum powder selection,tantalum core size and weight design,and design of forming voltage.Thepressing process is related to the theory of voltage oscillation,local thermal breakdown and mechanical stress failure.The main influencing factors are powder weight deviation,pressing density,uniform distribution of tantalum powder pressing and the integrity of tantalum core.Finally,combined with the failure mechanism and process influencing factors,the anode design optimization,key process optimization and optimization of screening method for chip solid electrolyte tantalum capacitors are carried out in order to improve the ability of chip tantalum capacitors to withstand surge currents.The research results include choosing flake powder tantalum powder as much as possible,adding organic acid to binder,adopting passivation process in sintering process,adding inert gas in heat treatment,etc.According to the results of the process optimization study,a large number of products were invested for process test verification,which proved the effectiveness of the optimal process optimization research.The research results of this paper have practical guiding significance for improving the surge current capacity of chip tantalum capacitors.