Bismaleimide Triazine Substrate Research Articles

Characterization of Ag-Pd Nanocomposite Paste for Electrochemical Migration Resistance

Direct printing such as inkjet, gravure, and screen printing is an attractive approach for achieving low-cost circuitry in the printed circuit board industry. One of the challenges for direct printing technology, however, is the poor resistance to electrochemical migration (ECM), especially for silver (Ag) which has been widely used in printed electronics. We demonstrate improved resistance to Ag electrochemical migration by adding palladium (Pd) nanoparticles to the Ag nanopaste. Conductive comb-type patterns were fabricated on a bismaleimide-triazine substrate via screen printing. Their ECM characteristics were assessed by water drop test with deionized water. These results showed that the ECM time required for dendritic growth from cathode to anode to cause short-circuit failure was affected by the Pd content and applied voltages: the ECM time of Ag-15wt.% Pd nanopaste was nearly threefold that of Ag nanopaste, and the ECM time decreased by 94.22%, on average, while the applied voltage increased from 3 V to 9 V.

Silicon-on-Organic Integration of a 2.4–GHz VCO Using High-Q Copper Inductors and Solder-Bumped Flip Chip Technology

High-Q copper inductors were fabricated on low-cost and low-loss bismaleimide triazine (BT) and glass substrate using electroplating process. A differential LC voltage-controlled oscillator (VCO) circuit was designed using these high-Q inductors at 2.4 GHz. Flip chip and multichip module (MCM) technologies were applied to assemble the active chips on BT and glass substrate. The inductors exhibited Q-factor as high as 25 at 2.4 GHz. VCOs with copper inductors on BT and glass substrate had phase noise of -108 dBc/Hz at 600 kHz offset for a 2.4-GHz carrier, which is 6-dB improvement compared with the one with on-chip Al inductors. There was almost no substrate loss for inductors on BT and glass substrates. The effect of fabrication defects and solder joint resistance were also investigated. This technique can be extended to other building blocks, thus realizing integration of the whole RF system.

Electromigration Behavior in Sn-37Pb and Sn-3.0Ag-0.5Cu Flip-Chip Solder Joints under High Current Density

The electromigration of conventional Sn-37Pb and Pb-free Sn-3.0Ag-0.5Cu (in wt.%) solder bumps was investigated with a high current density of 2.5 × 104 A/cm2 at 423 K using flip-chip specimens comprised of an upper Si chip and a lower bismaleimide triazine (BT) substrate. Electromigration failure of the Sn-37Pb and Sn-3.0Ag-0.5Cu solder bumps occurred with complete consumption of electroless Ni immersion Au (ENIG) underbump metallization (UBM) and void formation at the cathode side of the solder bump. Finite element analysis and computational simulations indicated high current crowding of electrons in the patterned Cu on the Si chip side, whereas the solder bumps and Cu line of the BT substrate had a relatively low density of flowing electrons. These findings were confirmed by the experimental results. The electromigration reliability of the Sn-3.0Ag-0.5Cu solder joint was superior to that of Sn-37Pb.