Barcelona scientists bond chips to circuit boards with ink containing silver nanoparticles
March 16, 2017
Source: ASM International
A team of researchers at the University of Barcelona has reportedly demonstrated a new bonding technique for surface mounted devices in which an inkjet printer with ink that incorporates silver nanoparticles bonds the devices. The technique, described in the Journal of Applied Physics, was developed in response to the industrial necessity for a fast, reliable, and simple manufacturing process.
Nanoparticles of silver for inkjet ink were selected because of their industrial availability. Silver is easily reproduced as nanoparticles into a stable ink that can easily be sintered. Though silver is not cheap, the amount was so small that costs were kept low.
The challenge for the research team was to "do everything with the same equipment." According to Javier Arrese, a member of the research team, the goal was to improve or confirm the performance of standard manufacturing processes by using inkjet printing technology for the circuitry and for bonding the chips.
"We developed several electronics circuits with inkjet printing, and many times we had to insert an SMD chip to reach the objectives," Prof. Arrese said. "Our approach was to use the same machine for bonding that was used for the printed circuit."
The biggest challenge was obtaining high electrical contact values for all the SMD size families. To do this, the team proposed using silver ink, printed by inkjet as assembling/soldering solution. The silver ink droplets were deposited close to the overlapping area between the SMD device pads and the printed bottom conductive paths, with the ink flowing through the interface by capillarity. This phenomenon works much like a sponge: The small voids of the sponge's structure absorb liquid, allowing a fluid to be drawn up from a surface into the sponge. In this case, the thin interface acts as the small voids in the sponge.
By taking advantage of surface energies existing at the nanoscale, silver nanoparticle (AgNP) ink ensures high electrical conductivity after thermal processing at very low temperatures, and thus a high electrical conductive interconnection can be achieved. Using this proposed method, an intelligent flexible hybrid circuit was demonstrated on paper, where different SMDs were assembled by AgNP ink, demonstrating the method's reliability and feasibility.
"There were many surprises in our research. One of them was how well bonded the SMD chips were to previous inkjet printed circuits using our new method as compared with the current standard technology," Prof. Arrese said.
Industries and Applications | Electronics
Industries and Applications | Nanotechnology
Materials Processing and Treatment | Soldering
Metals and Alloys | Precious Metals