Time for a second 3D printer in the lab
Article By : Damian Bonicatto and Phoenix Bonicatto
The low-cost resin printer has been refined to the point of being a must-have in a lab.
I would guess at this time most electronics R&D labs have an 3D filament (FFF/FDM) printer for the engineers to use. These printers have become very handy for things like creating 3D models of a PCB assembly to check it for fit into an enclosure. You may be printing out the enclosure so you can create a full working prototype. If needed, you could also create custom knobs, handles, insulating washers, etc. But along with your product parts, FFF printers are also useful for creating various tools and fixtures for the lab such as:
Every once in a while, the printer can allow you to solve an engineering problem.
Recently I needed to improve reception for an ultrasonic receiver, so I quickly modified an existing small parabolic dish designed to hold the receiver. This improved the ultrasonic signal reception by 9 dB. As useful as the FFF printer is, it would be nice to have a little better printing resolution to build a few things that the FFF printer has a hard time producing.
In the last few years, the low-cost resin printer has been refined to the point of being a must-have in a lab. It can print all the items above but with a resolution that is roughly 10x better than an FFF printer. That may not be a big deal for a scope probe holder or for a cable organizer, but there are a few things that need the improved resolution. Let’s take look closer look at resin printers and a couple of the useful things it can print.
LCD-based resin printers (sometimes referred to as a masked stereolithography apparatus, or MSLA) have recently evolved and improved in the lower-priced space. Now for less than $400, you can get a printer capable of creating models with a Z (vertical) resolution of 10 µm and an XY resolution down to 25 µm (for reference, printer paper is about 100 µm thick). This very fine detail size opens up the possibility for creating new parts that can assist in electronic product development and prototyping. Not only are new and better printers being introduced, but a steady stream of new resins is constantly arriving. These are not just new colors, but resins with various mechanical properties such as improved strength, more flexibility, translucent, clear, static dissipating, etc.
Now let’s look at a couple of examples where these printers would be useful. One area to be explored is the creation of small bed-of-nails test fixtures. A bed-of-nails test fixture can be used for board testing, programming onboard devices, board monitoring during debug, or simply holding a PCB securely while on a lab bench. A bed-of-nails test fixture consists of a block of non-conductive material with an indentation in the shape of the PCB to be inserted. Within the indentation, there are typically spring-loaded probes, known as pogo pins, inserted into snug fitting holes in the block. The holes, and therefore the probes, are accurately aligned so as to create an electrical contact to the bottom of the PCB at a specific place on the copper. (There can also be a bed-of-nails test fixture on the top, creating similar contact on the top of the PCB.) These pins are also electrically connected at the bottom of the block, to some electronic equipment and to power in order to send signals and monitor signals, voltages, and currents on the PCB. To assist in PCB alignment within the test fixture, there are typically two stainless steel pins inserted into the fixture that align with holes in the PCB.
3D modeling software could be used to model the indented block including all the holes for pins, any holes for a latch mechanism to hold the board down, as well as the legs and a cable entrance hole. Some modeling software, Autodesk’s Fusion 360 for example, can pull in a PCB design so the required holes for pogo and alignment pins can be easily located and created in the block. The newer inexpensive LCD-based resin printers are capable of creating a clean 100 µm hole in the assembly and with some fine tuning of the slicer, a 50 µm hole should be feasible. With these clean and accurate holes, no drilling should be required. Note that FFF printers could also be used, but due to its lower resolution, the minimum practical hole is around 2 mm. This may work for less dense PCBs.
Our friends at Autodesk have created a video for us demonstrating how to design a bed-of-nails using Fusion 360:
Another area that resin printers can excel is in the creation of optical light pipes. Many applications of light pipes require a custom design to deliver the LED light to a front panel. This may mean various bends or multiple pipes as one part for displaying assorted indicators. Creating light pipes has been attempted using FFF printers and clear filament with less-than-optimal results. This resulted in either poor light transmission or significant post processing involving cutting and polishing. But with resin printers, creating custom light pipes becomes very doable. Any configuration of light pipe can be easily created in 3D modeling software and by following a few best practices (such using internal reflections in the design when bending). The light pipe can also be configured with guide pins, snap fit tabs, or even threads. Resin for the light pipes is available in clear of translucent colors.
Figure 1 shows some simple light pipes that we’ve designed using Fusion 360 and printed using a Creality Halot One Plus resin printer. These light pipes were designed for directing light from a 5 mm through-hole LED. (Downloads for the files for these light pipes are available here.) I am currently experimenting with flexible resin printed light pipes that would be easier to assemble into an enclosure. If successful, I will post them on the same thingiverse page.
Figure 1 Simple light pipes 3D printed using a Creality Halot One Plus resin printer.
Note in Figure 1, there are two light pipes that are still attached to supports that are typically required to achieve a successful print. This is a good time to note that resin printing requires post processing, where FFF generally does not, except for removing supports. And as noted above, post processing involves a cleaning operation, removing supports, and then curing. None of these steps are difficult nor take very long but can be a bit messy.
Designing and printing the light pipes in Figure 1 only took a few hours, so your next project won’t need to wait for weeks, or longer, for prototypes to test your light pipes for fit, form and function.
A couple of caveats for resin printers: the build size tends to be smaller than FFF printers. Also, as stated above, the resin can be messy and may need good ventilation. Uncured UV resin should not come into contact with skin or eyes. UV curing typically requires a UV curing station, although outdoor exposure to sunlight will cure the part.
As you can see, two printers are better than one, and I believe in the near future all labs will have both FFF and resin printers. Then next will come the metal printers and hopefully, someday, someone will figure out how to build a printer that that makes a multilayer PCB from scratch.
This article was originally published on EDN.
Damian Bonicatto is a consulting engineer with decades of experience in embedded hardware, firmware and system design. He holds 30 patents.
Phoenix Bonicatto is a freelance writer.
