Intel and Carnegie
Mellon University
have developed tuned magnetic nanoparticles that mix with environmentally
friendly solders which can be heated with radio frequency signals, thereby
substituting a green room temperature process for the environmentally
unfriendly high-temperature solder reflow process used today.
CMU received Intel funding for a project "using
magnetic nanoparticles in the radio frequency heating, melting and reflow of
solder for microelectronics circuits," said Michael McHenry, the CMU
professor of materials science and engineering who collaborated on the project
with Intel Senior Packaging Materials Engineer Raja Swaminathan. The research
group—which included doctoral candidates AshFague Habib and Kelsey Miller and
undergraduate student Matt Ondeck—presented its results at this week's
Magnetism and Magnetics Materials Conference (Jan. 18-22, 2010, Washington,
D.C.).
Integrated circuits—from Intel microprocessors to Micron
memory chips—are connected together on a printed circuit board with solder made
molten all at once, allowing it to reflow over the entire connected circuit. As
it cools, the solder solidifies into a single massive interconnection that
holds all the integrated circuits in perfect electrical contact with each other
for the lifetime of the device.
Unfortunately, soldering circuit boards is one of the most
environmentally unfriendly processes in electronic device manufacturing, and
one that has gotten worse instead of better in recent years, due to the high
melting temperature of environmentally friendly solders.
Lead-free solder mandates forced manufacturers to switch to
lead-free formulations, most of which had to be reflowed at higher temperatures
than lead solders. As a result, chip warpage has gotten worse in recent years,
resulting in lower yields during manufacturing and higher failure rates in the
field. CMU and Intel's new RF soldering technique, on the other hand, does not
significantly heat a chip's entire package, but only locally heats its metal
leads—resulting in almost no warpage, thereby improving both manufacturing
yields and the prospect of fewer in-field failures.
Today, the conventional method of solder reflowing requires
pulling populated circuit boards off the assembly line and baking them with
either hot-air convection or an infrared oven. CMU's green process, on the
other hand, removes the need for the baking step by mixing magnetic nanoparticles
into the soldering paste, and just passing boards through an RF coil to melt
the solder. This cuts the energy required to reflow solder in an oven and turns
the baking step into just another room-temperature assembly line process.
Intel cautioned, however, that several engineering
refinements need to be made before the new RF soldering method can be used
commercially.
But if it ends up working as advertised, others will have to
also resort to RF soldering procedures to remain competitive, since it not only
speeds up the manufacturing process by moving soldering onto the line, but it
also improves the integrity of the electrical interconnection itself.
Funding for this project was also supplied by the National
Science Foundation.
