Hardware development on the fast lane

Technology News | January 5, 2017

By Julien Happich

Materials & processes Boards & Embedded Cards

Each cycle of designing and testing requires prototype circuit boards, however, the delays traditionally begin compounding because the only source of these boards in low volumes are the same large factories that have been optimized for high volume production.

Every designer has at one point been faced with the high minimum order quantities, set up costs, labor costs, shipping costs, and most infuriatingly, the lead times that can span several weeks – and that is for every iteration!

A unique additive approach

Recently, additive processes for fabricating circuit boards have drawn much attention in the field of rapid prototyping. Since material is added and not removed, there is minimal waste. Additionally, the equipment can be small enough to fit on a benchtop, eliminating the need for a full factory for prototyping and the travel time to the customer.

Fig. 1: Voltera V-One PCB prototyping tool.

As pioneers in this industry, Voltera recognized the advantages that this additive approach can provide during early hardware development and created the award winning Voltera V-One ( see figure 1). The V-One is a multifunctional desktop tool that allows hardware developers to prototype PCBs in as little as an hour.

A user can use the V-One to:

Create circuitry on the standard FR-4 substrate and other materials by dispensing a fully-solderable conductive ink
Dispense solder paste onto boards created by the V-One as well as traditionally fabricated boards
Reflow solder components directly on the heated built-in platform

How it works

All of this is done through software that is as intuitive and visually appealing as an app on a mobile phone. The interface guides you through every step from uploading your Gerber files (from Altium, CadSoft EAGLE, PADs, OrCAD, KiCad, etc.) to dispensing paste and reflowing the board once the circuit has been printed and thermally cured.

This is possible because the V-One is currently offered with three detachable tools that magnetically snap onto the gantry system with a satisfying click. These include a dispensing head for the conductive ink, a dispensing head for the solder paste, and a touch probe for generating a topographical map of the printing surface with 20µm precision.

First, this touch probe will zero itself in the XYZ directions before making contact with a series of points on the board to store the distance between the substrate and the nozzle tip. This is critical for accurate printing and consistent resolution. The machine can currently print down to 8 mil traces and can even dispense features as small 0402 passives.

Printing with silver nanoparticles

Fig. 2: V-One printing a circuit with conductive ink.

Once the height map is created, a highly specialized silver nanoparticle ink is dispensed from a precision-machined 200µm nozzle ( see figure 2). Print time varies by size and complexity. Finally, the V-One’s integrated 550W heater thermally cures the ink during a 20 minute bake cycle. During this process, solvents are evaporated and the nanoparticles fuse into tight silver matrix that is fully conductive and solderable (see figure 3).

Fig. 3: Microscopic view of silver nanoparticle
printed pad before (left) and after soldering (right).

Finishing with solder paste dispensing and reflow

With traditional prototypes, one would normally begin the tedious task of hand soldering components or stenciling solder paste onto the pads. While both are still doable with these new printed boards, most users opt for the automatic paste dispensing and reflow.

Iterating stencils is as costly and time prohibitive as board iteration and it wastes significant amounts of paste through the screen printing process. Outsourcing all this assembly often has more exorbitant costs and procedures.

Fig. 4: V-One dispensing solder paste on pre-fabricated PCB.

If applying paste onto a traditionally fabricated board (as in figure 4), the touch probe and two user-selected pads or fiducials are used for board alignment. This technique also allows for dispensing onto boards with pre-existing features such as recessed areas.

Printing the popular Arduino Leonardo

To get further insight into the workflow and design considerations when prototyping PCBs with the tool, an Arduino Leonardo will be used as a demonstration. After clamping a blank FR-4 substrate to the V-One platform, the accompanying software guides you through the workflow by providing detailed instructions on the left panel of the screen, and complementary videos of each step on the right side.

A few design considerations

Fig. 5: V-One printed ground plane (top)
and complementary hatch plane (bottom)

Several steps must be taken to ensure a smooth and crisp print

the pin-to-pin distance and trace width was set to 8 mil and 10 mil respectively which is compatible with all the original components of the Arduino Leonardo
all ground planes were converted to a hatch pattern.The density of the hatch presents a trade-off between resistance versus ink consumption and print time.For this application the density was set to 16 mil. Figure 5 shows a comparison between a ground plane and its complementary hatch pattern
the isolation was set to 16 mil indicating how much space to leave between the hatch and non-connected features
the via diameters were designed no smaller than 0.6 mm keeping in mind the bits used to drill them were too fragile at smaller diameter
through holes were used for USB ports, tactile switches, and larger components that were expected to undergo shear stress
In this scenario, the Gerber files were generated through EAGLE from the layout files provided by Arduino

Creating two sided boards

The Leonardo has traces routed on both sides of the board. The V-One is capable of aligning features on both sides by using the touch sensor to identify holes and vias just as it would for a traditionally manufactured board.

After the first side of the board has been mapped, printed on, and thermally cured, the substrate can be removed for the holes and vias to be drilled (figure 6). Currently, it is suggested that this is done on a small drill press or Dremel press. Conveniently, any holes are printed as a donut allowing the drill bits to self-center for easier alignment.

Fig. 6: Vias drilling through top side
of V-One printed Arduino Leonardo

Vias can then be filled with ink to create an electrical connection between both sides of the board, while through holes can be left empty. The board then gets remounted to the platform with the bottom side up. The touch probe locates key features of the board and is then swapped with the conductive ink dispenser to complete printing of the bottom side (see figure 7).

Fig. 7: Bottom side of V-One printed Arduino Leonardo

After the final cure, solder paste was dispensed onto the pads using the solder paste dispenser, components were manually placed onto the board, and the substrate went through a reflow profile, provided by the integrated V-One heated bed, to create the electrical and mechanical connections. Any through hole components were then hand soldered with the lead-free solder that ships with the printer.

Review of the demonstration

Ultimately, it took 2 hours to create this board using a completely additive manufacturing approach. The V-One was left unattended the majority of this time as it dispensed material and completed baking cycles. Apart from a few minor design considerations, small calibration steps, and drilling the vias, it was a fairly hands-off procedure.

The board was then used in a project that an engineering student from the University of Waterloo was working on in their spare time. Future iterations of this board will likely change the layout of components to meet the necessary form factor and integrate the sensors and actuators required specifically for that project.

It is worth mentioning that before the through hole components were added, it was noticed that one of the ICs was rotated 180 degrees. The heated bed on the V-One was turned on once again to de-solder the components, rotate the chip in question, and then re-solder the board.

Multi-material prototyping

A refreshing additive approach to PCB manufacturing allows for experimental prototyping that was not possible before. Prototyping is not limited to circuitry on conventional, rigid FR-4, but is versatile to an abundance of materials such as Polyimide and PET, glass and silicon, bio-compatible thin films, consequently allowing for accelerated research efforts in fields of flexible electronics, radio frequency applications, and medical diagnostics devices, respectfully.

Figures 8 a-c show a variety of circuitry applications that were printed on Kapton, Glass and PET, respectively, thus demonstrating the ability of electronic prototyping on multiple materials. We look forward to watching as the technology matures. Such an approach allows for potentially boundless prototyping and can conceivably be a true catalyst for innovation.