Interactions between solder and metallization during long-term aging of advanced microelectronic packages
Journal
Journal of Electronic Materials
Journal Volume
30
Journal Issue
4
Pages
379-385
Date Issued
2001
Author(s)
Abstract
The reactions between the eutectic PbSn solder and the Au/Ni/Cu tri-layer metallization in advanced microelectronic packages were studied. In this investigation, reflowed packages were subjected to aging at 160°C for times as long as 4000 h. Immediately after the reflow, all the Au had left the Au/Ni/Cu metallization, forming many (AU1-xNix)Sn4 particles distributed throughout the whole solder joint. In addition, there was a thin layer of Ni3Sn4 (1.4 μm) at the interface. After 500 h of aging, most of the (Au1-xNix)Sn4 particles regrouped at the interface as a continuous (Au0.45Ni0.55)Sn4 layer over the Ni3Sn4 layer. After 2500 h of aging, nearly all the Ni layer had been consumed. A 15 μm layer of (Au0.45Ni0.55)Sn4 and a 20 μm Ni3Sn4 were found over the remaining Ni. At 3000 h, the Cu had started to react with both Ni3Sn4 and (Au1-xNix)Sn4, forming a layer of(Cu1-p-qAupNiq)6Sn5, a layer of (Cu1-r-sAurNis)6Sn5, and a layer of Cu3Sn over the Cu layer. A small amount of Cu (2.7-5.7 at.%) was found to dissolve in this Ni3Sn4, forming a ternary compound (Ni1-yCuy)3Sn4. It was revealed that Au diffused up-hill during the reaction. After aging for 4000 h, all the (Au1-xNix)Sn4 had disappeared and Au atoms had diffused into the (Cu1-p-qAupNiq)6Sn5 and (Cu1-r-sAurNis)6Sn5 phases. The practical implications for the above findings were pointed out in this paper.
Publisher
Minerals, Metals and Materials Society
Type
journal article