Reliable Interconnection With Electroplated Cu Pillars And SnAg Solder Caps
Authors: Yi Qin, Jui-Ching Lin, Julia Woertink, Jonathan Prange, Pedro Lopez Montesinos, Inho Lee, Yil- Hak Lee, Masaaki Imanari, Erik Reddington, Mark Lefebvre, Jianwei Dong, Wataru Tachikawa, Jeffrey Calvert Company: Dow Electronic Materials, Advanced Packaging Technologies Date Published: 11/5/2013
IWLPC (Wafer-Level Packaging)
Abstract: Lead-free solder capped Cu pillar keeps gaining momentum in next generation flip chip electronic interconnection. One of the critical steps in a flip chip bonding process requires a high temperature solder reflow to turn as-plated solder caps into spherical solder balls. During this step, a layer of intermetallic compounds (IMCs) is formed. This IMC layer is desirable for forming a metallurgical bonding, but it also keeps growing over multiple reflow processes and also over the service life of the end device. Understanding and controlling the IMC layer growth is critical, as failures of the interconnection are prone to happen around this IMC layer, due to its brittle property and CTE (coefficient of thermal expansion) mismatch to adjacent materials. As such, temperature cycling at high and low temperatures models the environments that solder joints encounter during services. It provides an accelerated route to testing the potential evolutions of IMCs, along with multiple reflow tests. Both methods were applied in the current study, to samples prepared with the current commercial products and next generations of SnAg and Cu electroplating chemistry from DOW. It was found that the two phases in the interfacial IMC layers (Cu6Sn5 (?-phase) and Cu3Sn (e-phase)) evolved significantly over different test conditions. Void-free performance was achieved in both multiple reflowed (10 times) and temperature cycled (250 times) interfaces. This indicates a reliable interconnection between the electroplated Cu pillar and SnAg solder caps.
SnAg, Cu pillar, flip-chip, intermetallic compounds, reliability