| The wire bonding technology is widely used in electronic packaging, occupiedmore than3/4market share of the total output of IC chip package. Au-Al bondingsystem was widely used in wire bonding, along with growth of gold aluminidecompounds, leading to the degradation of electrical properties of device, reduction ofbonding strength, and welding failure. In order to prevent the formation of Al-Auintermetallic compounds, Al/Cu bonding pad is used to change the bonding systemfrom Au-Al to Al-Al contact. In this way, wire bonding reliability can be improved,and the cost of package can be reduced. On the basis of technical study towards thelayered Al/Cu composite material, the structure and electrical properties wasresearched, the intermetallic compounds formation regularity in Al/Cu composite wasdiscussed combined with vacuum annealing process. The Al/Cu bonding pad with asize of1mm×1mm was fabricated by stamping, and the stamping process wassimulated by Deform-3D.Electron beam evaporation deposition method was elected to fabricate Al/Cucomposite material, the Al/Cu composite material with conductive properties close tothe theoretical value can be obtained by controlling the deposition rate and thesubstrate temperature, we can prepare dense Al film with uniform particle size whenthe deposition rate is0.4nm/s, and the resistivity of Al/Cu composite material is low,interface bonding strength is more than12.24MPa. When the substrate temperature ishigh, due to the formation of Cu9Al4and CuAl2caused by mutual diffusion betweenatoms occurs at the interface of Al/Cu, the resistivity of the composite materialgreatly increased. To avoid the formation of intermetallic compounds in Al/Custructure, a layer of300nm thickness Ti film was deposited as diffusion barrierbetween Al and Cu layers, samples without Ti layer heated at200℃have formedCu9Al4and CuAl2, samples with Ti diffusion barrier layer only formed a smallamount of compounds until400℃annealling, indicated that the addition of Titransition layer can effectively inhibit the formation of intermetallic compounds,without influence in the resistivity and interfacial bonding properties of the compositematerial of Al/Cu.Using Deform-3D software, the stamping process of Al/Cu bonding pad wassimulated, and Al/Cu bonding pad with a size of1mm×1mm was fabricated, itconfirmed stamping of Al/Cu bonding pad is feasible, the most stress and strainhappened in the edge region. When the blanking gap is0.013mm, the amount ofdeformation of the pad is small, this can be used as reference standard in the actualstamping process. |
