Pb-free composition complies with many health and toxicology standards for electronics manufacturing. Maintains similar physical characteristics as previously used Pb-based solders
Track Code 2015-017
Two novel soldering techniques utilizing lead-free (Pb-free) nanosolder paste with physical characteristics comparable to those of Pb-based solders with a decreased melting temperature composed of tin and silver (Sn/Ag) and tin, silver and copper (SAC) alloys for microelectronic applications.
Halogen-free flux, microelectronics, flexible electronics, solder paste, surface mounting packaging, flux, ball grid array, copper, silver, tin, lead-free, nanosolder, solder
Jan 19, 2016 1:48 PM
Soldering techniques have been used in the manufacturing of electronic devices for many years and were historically composed of a tin and lead (Sn/Pb) alloy material. Specifically, solder paste, or a mixture of solder balls and solvent, is used for the bonding and assembly of electrical components commonly with a ball grid array (BGA) technique for surface mounting packaging. However, lead has been phased out from most electronics due to toxicology and health concerns.
New solder compositions have been developed to take the place of lead solders, including various compositions of tin, silver and copper, but these replacements have a much higher melting point than lead solders at approximately 220°C and above. High melting temperatures require the solder to be heated to a higher temperature during the reflow process, which requires greater energy consumption and places a large amount of thermal stress on the circuit board. An innovative solder paste for these applications is necessary for the expanding microelectronics industry that has a low melting temperature and can be utilized in nanoscale applications.
Researchers at UMass Lowell have developed two novel soldering techniques involving the preparation and usage of a lead-free nanosolder paste composed of a tin and silver (Sn/Ag) alloy. The Sn/Ag nanosolder paste is synthesized using a unique process containing individual particles that range in diameter from 15 to 40 nm and has melting temperature less than 220°C.
The first technique uses solely Sn/Ag nanosolder balls to replace the micron-sized solder balls previously used in industry, shown in Figure 1. These nanosolder balls are mixed with flux and can be applied directly to micro- and nano-electronic assembly.
The second technique involves using the synthesized Sn/Ag as well as tin, silver and copper (SAC) nanosolders as an additive to a microsolder paste of the same composition respectively, shown in Figure 2. The nano and microsolders are then mixed together with a flux to create a uniform paste and are then applied to joints in the microelectronic assembly process. The nanosolder additive of roughly the same respective composition gives the solder paste increased mechanical strength and decreases the melting temperature of the paste during the reflow process.
Pb-free composition complies with many health and toxicology standards for electronics manufacturing.
Maintains similar physical characteristics as previously used Pb-based solders.
Nanoscale solder can be used for smaller-sized applications.
Lower melting temperature leads to less thermal stress being placed on the devices as well as energy conservation in the assembly process.
Nanosolder additives of similar composition to the microsolder paste increases the mechanical strength of joints.
Bonding and assembly of micro- and nano-electronic devices.
Aerospace, defense and medical applications where properties of lead-based solders are necessary.
Development of flexible electronics.
Due to the toxicology and health concerns over lead in electronics manufacturing and the need for a smaller scale solder paste for the rapidly expanding micro- and nano-electronic industry, lead-free nanosolders are in high demand. According to a report from “Markets to Markets, July 2014”, the flexible electronic market is projected to reach $13.23 billion by 2020 at an estimated CAGR of 21.73%.