Study Of IMC Growth And Control At Interface Of Micro Copper Pillar Bumps For High Density Package

With the fast miniaturization trend of modern electronic products,the demands for higher integration in chip electronic package increased rapidly.Flip-chip and 3D chip-stacking packaging using bump connection becomes one of the best candidates of high-density package in the industry.As a novel connection technology,copper pillar bump combines excellent electrical and thermal performance for ultra-fine pitch connection.However,as the package size decreasing,thermal and electrical as well as mechanical loading on a single copper pillar bump increases dramatically.Study on the growth of intercalation compounds?IMC?in copper pillar bump interface is more and more important.How to effectively inhibit the growth of the interfacial IMC so as to improve the reliability of copper pillar bump in 3D packaging has draw much attention.In this paper,we research two kinds of Cu/Sn copper pillar bump with the diameter of 15?m and 25?m.The growth rule of IMC at the interface after aging treatment under different conditions was studied.The reduced graphene oxide films were used to control the rapid growth of IMC at interfaces after bonding.The main contents and conclusions are as follows:?1?We studied the stability and reliability of 15?m copper pillar bumps by heat aging method.The similarities and differences of the growth rules and mechanism of IMC at the interface were analyzed.The same points include:interface IMCs were Cu₆Sn₅ and Cu₃Sn;Cu₆Sn₅ were observed before Cu₃Sn;IMC thickness increased as the aging time increased gradually;the growth rate of IMC accelerated with the increase of aging temperature;the Kirkendall voids were formed along with the formation of Cu₃Sn;IMC grew down along the outer edge of copper pillar when the diffusion reached a certain extent.The differences include:Compared to 25?m bumps,15?m bumps'Cu₃Sn and Kirkendall voids were more difficult to grow;the growth of IMC at the outer edge of the copper pillar occurs later;the IMC diffusion rate at the interface was lower;the resulting Kirkendall voids'size was also smaller.?2?The process of IMC growing at the bump interface is not simply a process in one or two kinds IMC increase,but rather the complex result of the interaction among the two kinds of IMCs,Cu and Sn.Under certain conditions,the formation of Cu₃Sn consumes a large amount of generated Cu₆Sn₅previously,slowing down the growth of Cu₆Sn₅.The total amount of IMC tends to be stable or even reduced.?3?Using a method of reducing the oxidized graphene suspension at a circulating current,a relatively uniform thin layer of graphene can be obtained on the surface of the copper microcones.The corresponding sample can be bonded with 25?m copper pillar bumps with high stability under the bonding temperature of 120?,bonding time of 10 min and bond pressure of 14.63MPa.In this condition,the metal atoms can both diffuse during the bonding process to form an effective bond,and stop the diffusion during the aging process due to the presence of the graphene barrier,so that the rapid growth of the bonding interface IMC can be prevented successfully.