Here’s what we learned about additive PCB manufacturing from the USAF
When we think about the United States Air Force, our mind takes us to the skies, where the aircraft swirls the air and blasts the jets to leave us looking in wonder. How did humanity ever get to create such amazing machines?
But there is so much more to be seen and admired inside the United States Air Force, most of it happening in the ground.
Two months ago, BotFactory concluded an SBIR Phase II grant in collaboration with the USAF EMXG-402. The grant's purpose was to further develop our additive PCB manufacturing technology to help them solve the immense challenge of maintaining the fleet, keeping it ready whenever needed.
Let’s talk about REARM
With the impressive capabilities of the USAF fleet, you may think it is all a parade of bleeding-edge and high-tech. You would not be wrong for the newest aircraft, but one must not forget many of these aircrafts have been flying for more than sixty years. The McDonnell Douglas F-4 Phantom has been flying since 1958!!
So yes, many venerable aircrafts are still flying with the USAF, and have plenty of stories to share, but to keep collecting them for us, someone has to maintain and repair them. After all, not everyone ages as well as Merryl Streep.
REARM, or the “Reverse Engineering, Avionics Redesign and Manufacturing” center, has been charged with maintaining the electronics for a large part of the aging fleet. This includes the C-130, B-52 bombers, F-15 fighter planes, and the HH-60 helicopters, to name a few.
Because many of these aircraft use components that are no longer in production and are very likely out of warranty, the REARM group has to find creative ways to either repair old PCBs, adapt new components onto old PCBs, or create completely new PCBs that behave exactly as the old ones, but with new components.
The mission at hand is not easy. In many cases, the original designs are not available because of the way the contracts were executed or because the technology was kept a trade secret by the manufacturing company. Engineers at REARM go the distance and then some to understand the inner workings of the PCBs and devise ways to make them work again.
Current Manufacturing Process
To carry out its mission REARM has developed an impressive manufacturing capability. The engineering labs are spread over 10k sq. ft, It can take up to 26 steps to manufacture and test the PCBs that will go into repairing and upgrading the aging aircraft fleet.
Although REARM has the talent and the equipment required to carry out this commitment, the manufacturing process is slower than desired. Each board design must be processed through the 26 steps, without skipping the necessary steps. These include tuning the acid baths, the pressure at the drill press, and the plating times. The process, which can take more than 48 hours, becomes stable after the tuning, and then hundreds of boards can be reliably produced at high speed.
Unfortunately, the tuning and process for a single board is the same as the one required for producing hundreds of boards. The process, which is optimized for building hundreds of units of the same PCB design, is the main bottleneck for manufacturing the single board that is required for the airplane waiting on the tarmac.
And while some may think that the best way to manufacture a single board is to use a milling machine or a small prototyping machine, we need to remember that these boards can be really complex and will need to be compliant with the military standard in order to operate safely in all aircrafts. This is not your typical prototype.
Enters Additive PCB Manufacturing
BotFactory’s technology is a great fit to meet the requirements of the 402-EMXG when it comes to PCB fabrication. By additively manufacturing PCBs, on a desktop printer, the engineers can rapidly iterate on designs and test them in quick cycles. Furthermore, by allowing the fabrication of complex multi-layer PCBs, the unit can manufacture the replacement boards in a matter of hours and under a simplified process.
It could be said that additive manufacturing of electronics is a perfect match for the 402-EMXG group because it's an ideal solution for high-mix/low-volume production, which is the type of work the REARM group does most of the time
During the execution of this SBIR Phase II grant, in which BotFactory collaborated with the USAF 402-EMXG / REARM group, a series of parameters were measured to determine the usability of Additively Manufactured Electronics (AMEs) in the USAF daily operations.
The first requirement was related to the quality of the features on the board. To define the desired quality level, we used the IPC 600 class 2 Standard as a reference. The results showed that the Additive Manufacturing process has no issues printing well-defined trace, vias, and thru-holes. Furthermore, some of the tolerances allowed by The Standard were unnecessary and easily complied with by the new manufacturing process. The grant didn’t extend into further analyzing compliance with the IPC 600 Class 3 Standard, but the initial results showed promising results.
A second and very important test was to validate the durability of the printed PCBs and their behavior when used in thru-hole applications. A Tensile Strength test was put in place to objectively compare the AM PCB against the traditional PCB. The same was done with the Flexural Strength.
The finding of the tests showed that the current AM PCBs have lower tensile and flexural strength than FR4 or FR1.
The lower strength of the AME boards make them prone to breakage or damage during handling or installation. This immediately limits the application of AME boards in the daily operations of the unit. Furthermore, and particularly affecting the use of thru-holes, the low tensile strength would reduce the lifespan of any circuit board that uses connectors, switches or any other component that requires thru-holes to provide mechanical strength to a component.
The Next Steps
In this grant, BotFactory showcased an implementation of its Superviced PCB manufacturing system, composed of a probe head and an AI that optimizes the conductivity of the prints, layer by layer. The system is functional, and provides an incredible increase in the production yield of the printed PCBs.
Our next target is to increase the strength of the printed boards to further comply with the requirements of the United States Air Force.