Eiichi Hosomi

Electrical design optimization and characterization in Cell Broadband Engine package

Cell Broadband Engine is a microprocessor that has very high processing performance and very high speed I/O to communicate with other devices such as system LSI and memory chips. Design optimization with statistical analysis was carried out. DOE matrix was made with dimension of signal traces and dielectric constant of the insulator in the package substrate. After major factors were detected, random sampling was done to make sure that the distribution of characteristic impedance of signal traces is within the specification. Passive characterization was carried out with test vehicle. Insertion loss and characteristic impedance is dependent on both temperature and water absorption. These environmental factors need to be taken into account when the design rule is determined. After design rule is fixed, circuit simulation for whole signal channel was carried out with considering impedance tolerance in both the package and the printed circuit board. DOE matrix was made and analyzed to determine the major factors on mid-frequency and low-frequency noise in power distribution. Inductance of package substrate and decoupling capacitor are the major effect on the mid-frequency noise, and capacitance of on-module and on-PCB affect low frequency noise. The effect of on-chip parameters was also evaluated. Several types of capacitors were characterized to measure their parasitic parameters

A new bonding mechanism of 50 /spl mu/m pitch TAB-ILB with 0.25 /spl mu/m Sn plated Cu lead

A 50 /spl mu/m pitch TAB has been developed by applying newly developed TAB tape and inner lead bonding technology. A new electrodeposited Cu foil which has a high tensile strength and 18 /spl mu/m thickness was adopted as the lead material. Sn plating on the inner leads has been thinned to 0.25 /spl mu/m from the conventional 0.6 /spl mu/m to avoid excess alloy formation. The inner leads were gang-bonded to the Au bumps. The cross sections of the bonded region were observed by SEM and EPMA for the specimens before and after high temperature storage (HTS), The Au-Sn fillets formed by the bonding supported the inner leads at the initial state. Ternary Au-Cu-Sn alloy was also formed at the interface between the inner lead and the bump. After HTS, cracks formed between the fillet and the inner lead, and the fillets could not contribute to supporting the inner lead. The ternary Au-Cu-Sn alloy which was formed at the bottom of the inner lead in ILB processes transformed to binary Cu-Au alloys after HTS. Sn was driven away from the lead-bump interface. The binary Cu-Au alloys kept the bonding strength after HTS. A destructive lead pull test was performed before and after HTS. The failure mode was a lead fracture in all cases.