Estimated reading time: 5 minutes

Flex Talk: Squink—Integrating Fabrication and Assembly in one Package

When walking through trade show expos, I tend to be drawn into product demonstrations on the show floor. Recently, at the IPC APEX EXPO, I stopped in front of a piece of desktop printing equipment that was demonstrating with a flexible circuit. What really caught my eye was that the equipment could not only print the trace pattern, but it could also do pick and place assembly. I did not know that those two capabilities were being combined into one unit and in fact, to the best of BotFactory’s knowledge, the BotFactory Squink is the only machine on the market today that integrates circuit fabrication and assembly into a single package. In addition, Squink is a relatively small device that can easily fit on a workbench in any office, factory, research lab or school. I had the opportunity to sit with JF Brandon of BotFactory to learn more about this equipment and technology. 

How does this technology work?

Squink has three tool heads that can be swapped out by the user. One head is used for printing both insulating and conductive inks, using a heat-bed and a UV lamp to cure each ink and create conductive traces and insulated layers. The dispensing head extrudes conductive epoxies or solder paste through a syringe, placing tiny dots of material onto the pads. BotFactory provides a two-part epoxy that works best with the Squink printed circuits—solder paste is not ideal. The pick-and-place head uses a vacuum pump to pick up components via a suction tip. A motor rotates the parts according to the fabrication files. An upward-facing camera is utilized to image the undersides of the parts to correctly identify, orient, and place them with high precision. The power of embedded computing and artificial intelligence is used to achieve this. 

What type of substrates can be used?

This machine can print on FR-4 and Kapton® (flexible polyimide), two materials that are widely used in the industry. It can also print on any non-porous yet smooth surface that can withstand 110 degrees C, which is how hot the heat-bed gets to cure the conductive ink. Materials that are given to warping or contortion under heating and cooling are not ideal for printing. Even when a material is perhaps too porous or not smooth enough, a few passes of insulating ink can make it printable. 

What are the size constraints?

5” x 5” is the maximum size for single-layer boards, or for assembling third-party boards. The maximum size for multilayer boards is 3.35” x 5”. 

What do we need know about nano-silver ink vs. copper?

The proprietary conductive ink used consists of silver nanoparticles. The heat-bed is used to sinter the particles after inkjet printing them, vaporizing the carrier fluid and leaving behind pure silver traces. The traces printed with this technology exhibit a typical resistance about one order of magnitude larger than copper, which makes them a good choice for digital applications but not so much for high-power or super-high-frequency (SHF) applications. 

How does reliability compare to circuits done with the subtractive etch process?

Additively manufactured traces are more fragile than subtractively manufactured traces, as the former is less dense and merely sintered by heat and not laminated and formed like the latter process. However, printed traces can be protected from scratches by printing insulating ink on top of them. There are a couple of challenges in this nascent technology: soldering and resistance. Regarding soldering, it has proven difficult to solder directly to printed traces without affecting their conductivity, but excellent results can be achieved by simply utilizing conductive epoxy. When analyzing resistance, it’s been found that, due to the inherent nature of inkjet printing, there are small variances in the thickness and width along the traces which may create noise at extremely high frequencies, or slight differences in the effective conduction of electrons. 

How are the plated through-holes achieved?

Neither plated through-holes nor connections between any two layers are built and connected as the board is printed. There is no need for drilling and plating; no etchants or cleaning are necessary, reducing the environmental impact and any needed hazardous waste management. If a user needs plated through-holes to connect double-sided boards or through-hole components, a PCB rivet press can be used. After printing a circular pad in silver ink, the user can drill through it using a drill press and place a copper rivet to create a compress-contact between the rivet and the pad. 

Does this work with the standard Gerber packages?

The Squink works with standard Gerber files, with drill files for the insulating layers, and a ‘centroid-and-rotation’ file for assembly (which is typically one of three files: .tsv, .csv., or .pos). In addition, it is possible to import image files like .jpg or .png for printing traces or dispensing. The minimum printable width for traces and spaces .010”. The pick-and-place system can place components as small as 0603s. 

The Story Behind the Product

In addition to being interested in the technology itself, I found the story behind the equipment intriguing as well. BotFactory was founded by Nicolas Vansnick, Carlos Ospina and Michael Knox in 2013. Carlos and Nico were grad students at NYU, where Mike was an EE professor. The genesis of the idea began when Nico and Carlos were in an electronic design class, and the final project was to create an EEG headset. Nearly half of the class failed because it took too long for each group to have their PCB design fabricated by outside vendors in time—iterations took more than a week, sometimes two, to be made. 

The idea was born: If turnaround time was a problem that was typical for any project, the solution could revolutionize how electronics could be prototyped and fabricated. Working with their professor, Mike Knox, they founded BotFactory to take all of the fabrication processes and ‘miniaturize them’ for the first time. Up until then, most had been trying to miniaturize electronics and chips, but not the processes that are employed to create PCBs. Universities are the largest market for this technology but interest is growing from all industries. With a low cost of entry and the ability to quickly prototype ideas, I imagine we will be seeing more of this technology. 

Tara Dunn is the president of Omni PCB, a manufacturer’s rep firm specializing in the printed circuit board industry. To read past columns or to contact Dunn, click here.