When it comes to PCB design for a particular market segment, often times the design methodologies readily transfer from one market segment to another with very few, if any, significant changes. Other times this is not the case and designing products for a particular market segment requires specific design practices, materials and testing procedures. This blog is the first in a series addressing design strategies for specific vertical market segments. The first segment I will be addressing will be military and aerospace application requirements. Mil-aero as a market area can be broken down into four specific product types:
- Ground Equipment
The one thing that these entire product types have in common is that they are all dominated by government contracts. But, beyond that they are so broad that trying to establish design commonality among them does not work. Therefore, I will be addressing these market segments as separate entities and the first entity that I will address is PCB design for navy implementations.
When we discuss developing PCB products for navy environments, we aren’t just looking at ships and boats—we’re also including airplanes relative to their use on aircraft carriers. The specific design issues for these product categories include:
- On a ship, cooling is rarely a problem because of the proximity to the ocean.
- PCBs are protected by fairly complex containers that often appear to have been over-designed and over-built.
- An aircraft carrier has on it every technology that can be named. But is separated from other categories by the salt environment.
- Similarly, on a large naval craft there is a vast spectrum of technology including:
- Huge computer centers
- Lots of different kinds of radios that range from multi gigahertz radar on one end to super computers on the other.
- Power consumption is usually not a concern.
- Price is often not a concern.
The Over Riding Concern–Corrosion
The key concern that drives every electronic design decision for a naval product implementation is corrosion. Salt air is the corrosive element in question and it is far worse than rust. When salt air and moisture are combined with two different metals, a galvanic cell is formed and the resulting corrosion is salt based. (Specifically, a galvanic cell is an electrochemical cell that derives electrical energy from spontaneous redox reactions taking place within the cell). For example, a battery is a galvanic cell. The battery generates current flow and that leads to the onset of corrosion. Proper insulation can prevent this from happening.
For PCBs used on ships or aircraft carriers, almost all the boards that go into a salt air environment have to be waterproofed. This is achieved through a conformal coating of the boards with a silicon-product. The coating is applied during the end of the assembly process after the PCB has gotten a green light from the testing operations. It should be noted that not every assembly house does conformal coating so a dedicated assembly operation must be found.
The Standards and Specifications Conundrum
All products developed for mil-aero usage—including those used in naval environments—have to be in compliance with a set of specifications and/or standards imposed by the government. This means that all of the product development operations from board design to fabrication and final assembly have to be certified to whichever standards are imposed as part of a specific contract. Now, there is an impetus for COTS (commercial off the shelf) materials and parts to be used whenever possible but they are still contract specific.
Further, the PCBs created for naval applications in the U.S. have to be designed, built, and assembled in the U.S.
This is to ensure that all portions of the product development process are contained within U.S. operations such that they cannot be copied or reversed engineered by non-U.S. entities.
The challenge is that most board fabricators in the U.S. don’t build the types of PCBs required for military and aerospace applications. While the boards are often built at a premium price because they are so specialized, their volume is never very high. In most instances, the boards have to be serialized, and the tracking of the manufacturing process has to go all the way back to the raw materials used to ensure that the final boards are compliant across all contract requirements. The cost of this documentation process is often two to three times the cost of the PCB itself.
On the material side of the spectrum, there are not many materials that are specifically banned for use in mil-aero products (despite some claims to the contrary). However, here too, the certification process involves jumping through all sorts of hoops in order to ensure that the chosen materials meet the specification requirements. This can be a lengthy, costly and time-consuming process. In addition, government contracts are populated with many different specifications and standards which have to be satisfied to ensure that the end products are built in accordance with those specifications.
This creates two challenges:
- In the past, it’s been possible to design in accordance with one specification, manufacture in accordance with another and assemble in accordance with yet another and be out of compliance with the design specification when the final board is presented after assembly. I was part of this phenomenon when I worked on an Air Force contract while employed at Martin Marietta. A senior quality engineer and I published an article in an industry trade publication regarding this “out of compliance” spec issue. We were asked if we could find more such conflicts. We did and we published our findings in additional articles.
- “Ownership” of standards and specifications has been a challenge for a number of years. None of the various military branches wanted to assume full ownership of the specifications. In fairness to them, they did not have the appropriate technical staff on hand to maintain the specifications. At one point in time, it was proposed that the industry group, the IPC Association Connecting Electronics industries, assume ownership of the mil-aero specifications. It maintains a broad spectrum of standards but it did not come to own the mil-aero standards and specifications. It should be noted, however, that certain mil-specs and standards do require adherence to certain IPC and other industry standards as part of their requirements.>
As a follow-on to the foregoing, certain long held mil-specs and standards have been replaced or “morphed” into other specifications. In May 2011, as part of the MilSpec Reform, the Defense Standardization Council (DSC) directed the following:
- Certain standards and specifications were canceled, inactivated or modified.
- Certain standards and specifications were replaced by performance specifications.
- Certain standards and specifications were replaced by commercial item descriptions.
- Certain standards and specifications were replaced by guidance handbooks.
- Certain standards and specifications were cancelled or combined with other military specifications and standards.
More about this topic can be found at www.dsp.dla.mil.
One of the challenges in maintaining compliance with any military specification or standard lies in trying to match up the requirements of those specifications with the parts and materials required by the particular performance and physical characteristics of a given project. Often times, the individuals involved in the initial negotiations of these contracts (both military and contractors) are not the same people who have to build and deliver the final products. This can create disconnects both large and small between the “as specified” contract requirements and the final “as built” products. These challenges flow down throughout the entire contract food chain as primary contractors attempt to flow down the same contract requirements to their various subcontractors—hence, why mil-aero contracts can be so expensive and so protracted.
Today, Tomorrow and Forever
One of the other major inherent challenges with mil-aero product implementations is that the contracting government entity wants to make the same product for many years to come. With today’s product evolution in place, it becomes impossible to comply with that kind of supply and demand. In most instances, the original parts won’t be available for the life of a particular program or piece of equipment. This forces program managers to guess as to the quantity of parts that will be required across the life span of a particular product so that they can go buy all the parts initially available and put them in a warehouse for downstream use. This problem spans the entire mil-aero industry.
Similar to board fabricators and assemblers, there are not a lot of FPGA vendors who want to go through the certification process necessary to supply components for mil-aero projects. As an example, the FPGAs that go into satellites are built on sapphire such that they are RAD hardened for the outer space environment. Finding manufacturers who can and want to undergo this process can be challenging.
The mil-aero vertical market segment has a lot of different aspects to it that can be difficult to address and maintain. For naval applications the primary concern is developing PCBs that can withstand the harsh corrosive aspects of a salt air environment. Any particular PCB development company that wishes to participate in a mil-aero project should carefully evaluate all the contract specs and requirements in order to ensure that they can satisfy these requirements in a cost-effective and timely manner.
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