3-D Printing Fast-Tracks Circuit Prototyping

　　Circuit prototyping traditionally requires tedious layouts using CAD tools, transfer of those plans to a printed-circuit board maker, precise placement of components on the pc board using pick-and-place robots, and then a wave soldering step to establish electrical contact between the components and the board. Prototyping engineers wait weeks before they can test the circuit board, find its flaws, and repeat the process until they get it right.

　　The Charles Stark Draper Laboratory Inc. (Cambridge, Mass.) has reported on an approach for 3-D printing of circuits that it says can slash the wait time from weeks to days. The components are glued down to a substrate with no traces and then are interconnected in real time with conductive ink in the 3-D printer.

　　To prove the concept, Brian Smith, principal member of the technical staff at Draper, and Peter Lewis, member of the Draper technical staff, used a 3-D printer from Optomec Inc. and inks suitable for aerosol jet printing (AJP) of electronic circuits. NovaCentrix’s HPS-030AE1 silver flake ink and NeXolve’s Corin XLS polyimide ink were used as the AJP conductor and dielectric, respectively.

　　“We are making all sorts of 3-D electronic devices, both to interconnect conventional microprocessors, by flipping them over, gluing them down, and printing silver interconnection lines that go right up the side of the chip in 3-D to its pads,” Smith told EE Times in an interview. “Plus, we are 3-D printing microfluidic devices by printing their silver sensor electrodes as well as the epoxy to precisely seal up their channels in just the right places.”

　　Lewis said the lab is “also using printable dielectrics, carbon nanotubes, and other exotic biomaterials to print everything from spiral 3-D antennas, which take up a fraction of the space of traditional circuit-board antennas, to implantable biosystems where metals are not tolerated.”

　　Draper does not build products; rather, it is an R&D shop that performs proof-of-concept prototyping work for both military and civilian applications, and then hands over the design plans to its customers for optimization and manufacturing. The 3-D printer has been a godsend for Draper’s team — for whom a working prototype is the “finished product” — since it cuts prototyping time by orders of magnitude.

　　“There are many 3-D-printer manufacturers working on ways to make it a mass-production tool, too, but that’s not a part of our work at Draper,” said Smith. Draper’s next step is to solve the electromigration problem that plagues 3-D printing of conductors. Silver, in particular, is subject to electromigration, which can cause open circuits to form. By working with its AJP ink vendors, Draper’s tech staff hopes to come up with better formulations that provide long-term-reliability solutions for 3-D-printed conductors.

　　Lewis, Smith, and coauthor Robert White detail Draper’s work in the article “Lessons Learned in the Implementation of Aerosol Jet Printing for Fabricating Multilayer Circuit Boards.”