Abstract
CuantumFuse nano copper material has been used to assemble functional LED test boards and a small camera board with a 48 pad CMOS sensor quad-flat no-lead chip and a 10 in flexible electronics demo. Drop-in replacement of solder, by use of stencil printing and standard surface mount technology equipment, has been demonstrated. Applications in space and commercial systems are currently under consideration. The stable copper-nanoparticle paste has been examined and characterized by scanning electron microscopy and high-resolution transmission electron microscopy; this has shown that the joints are nanocrystalline but with substantial porosity. Assessment of reliability is expected to be complicated by this and by the effects of thermal and strain-enhanced coarsening of pores. Strength, creep, and fatigue properties were measured and results are discussed with reference to our understanding of solder reliability to assess the potential of this nano-copper based solder alternative.
Highlights
Soldering is ubiquitous in microelectronics assembly; it results in a practical balance between process capabilities and reliability, but process temperatures are too high for some applications and acceptable operating temperatures are too low for others
Microelectronics assembly usually relies on solder joints being ductile during temperature variation
The measured punch stresses cannot be converted into corresponding shear levels, indications are that fatigue failure may remain brittle up to substantially higher stresses than supported by current versions of the material
Summary
Soldering is ubiquitous in microelectronics assembly; it results in a practical balance between process capabilities and reliability, but process temperatures are too high for some applications and acceptable operating temperatures are too low for others. Even high-Pb solders are limited as far as the latter is concerned. For high-temperature applications, alternatives include new alloys yet to be systematically evaluated and approaches based on sintering of Ag or on fusing of Ag or Cu nanoparticles. An ideal alternative to solder would be compatible with the massive existing infrastructure, notably stencil printing and mass reflow, and meet or exceed the performance of commonly used solder alloys. It is clearly compatible with high operating temperatures and the electrical and thermal conductivity properties are extremely attractive. As for silver, sintering requires pressure, which is far from always practical
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