THE SMALLER THE BETTER - SIMULTANEOUS ELECTROLYTIC SOLDER DEPOSITION ON BOTH SIDES OF A FINE-PITCH PACKAGE SUBSTRATE

摘要

For the electronics packaging industry the continuing reduction of the bond pad size and pitch poses a major technological challenge. Specifically, when applied to such small geometries the use of solder paste is becoming increasingly difficult, primarily resulting from limitations of stencil design and inherent paste properties. This technical paper summarizes the findings and conclusions from a comprehensive evaluation of high-speed electrolytic solder deposition into solder resist openings (SRO) on fine-pitch, organic package substrates. The paper compares deposit quality for ultra fine-pitch SRO on the C4 side of the package substrate, as well as for larger SRO (up to 550μm) as typically seen on the BGA side. Also included is an assessment of the technical challenges related to the simultaneous electrolytic solder filling of SROs on both C4 and BGA sides. Additional information obtained using this Pb-free approach includes results and discussion of the alloy composition following solder ball attach and reflow. The electrolytic solder deposition process is examined as an alternative to the more conventional paste/stencil methods to produce solder-on-pad (SOP) technology. The process is well suited to meet the demands of current and future finefeature technology, while offering the added benefit of eliminating the need for a separate process to create a solderable surface finish.