Military Connectors Stepping to a Commercial Beat
By Rick Lewis, Bishop & Associates Inc.

Connectors that are fully compliant with military specifications have failed to keep pace with the needs of weapon system OEMs. For years, military OEMs have been forced to use technically obsolete buses and interfaces because of the need to be fully mil-spec compliant. This has put military systems in a position of significantly trailing behind state-of-the-art commercial products. To bring military weapon systems in line with advances in the commercial industry, the military had to develop a new set of militarized standard buses and connectors, or select or adapt standards presently used in the commercial industry.

The solution chosen was the latter. The decision was not difficult. Industry is now years ahead of the military. The only way for the military to catch-up—or even come close—was to adopt the standards of the commercial industry.

The military is no longer the technology leader: It lost that title more than 25 years ago. There were very few electronics in the consumer segment before that time, with the exception of radios and later TV sets. Computers were used mainly by the government to support the military. In the early 1960s very few companies actually owned computers. If a computer was needed, time would be leased from companies like GE and Westinghouse who were working on military and government agency projects. The military controlled most of the electronics development.

All that changed in the ‘80s when the microprocessor came on the scene. In just a few short years the commercial marketplace exploded, not just with the development of PCs, but with computers that controlled everything from toasters to automobiles. The internet fueled the fires and suddenly the military was no longer the primary user of sophisticated electronic technology.

The connector industry went through its own metamorphosis. Originally developed to support the military, early commercial connectors differed little from their military counterparts. The telecom industry was the second largest user and had requirements similar to the military. Early PCs used connectors built to similar specifications. Because of their low cost (relative to the system), connectors received little attention. It was not until the price of computers began to drop that connectors were thoroughly analyzed. The life cycle for a PC was just a few years while the connectors being used in the PC were being made to last a few decades. The life of the connector was closely tied to the thickness of the gold plating. A shorter life span meant that connectors could get by with significantly less gold plating, immediately impacting price. In cases where connectors were not often unmated, even “gold flash” was sufficient. Simpler contact designs emerged where stamped and formed contacts were substituted for screw machine parts. The commercial and military parts diverged, and international competition drove the pricing of the commercial connectors.

Meanwhile, the military connector market experienced very little change. Unlike the commercial world, where investment in R&D and new product development are crucial to survival, the mil-spec world uses tooling that has been around for many years. The basic Mil-DTL-38999 (thirty-eight, triple nine) series is decades old, but continues to be used in equipment developed for the military. Much of the R&D associated with mil connectors is centered on new contacts for the existing shells.

Life Cycles
The platform development process has changed very little. Military programs still have long development times. Major systems, such as aircraft programs, can easily take 10 years to complete. For example, the F-22 (Raptor) started in 1986 and is just going into production at this time. It has also been mentioned as a candidate for elimination in the latest proposed budget cutbacks. According to Lockheed, the assembly plant is only able to turn out around 15 airplanes per year.

For connector manufacturers, the quantity of connectors on these major programs is quite modest. Even if the quantity of connectors on an aircraft is in the thousands, the numbers are not substantial when only 15 units a year are being built. But, the total number of connectors bought across all programs is significant. Many, if not most of the connectors being purchased are for systems already in inventory. Many of these systems are 20 years old—or even older. These systems go through multiple updates over the life of their deployment and updates often retain the full mil-spec requirements originally imposed. It is easy to see why the solid, unchanging mil-spec connectors have survived and why commercial connectors might have problems in this environment.

However, as earlier stated, the mil-spec varieties of connectors can no longer meet the needs of new technology in equipment required by the military. With the rapid rate of change in the technology sector and the long development cycles of military equipment, a new set of mil-spec connectors would probably be obsolete by the time the first set was fielded.

Opening the Military Market to Commercial Suppliers
As a result of a 1994 directive by then Secretary of Defense William Perry, the military is seeking to utilize existing commercial standards to lower the cost of military systems acquisitions. This directive became known as the COTS (Commercial Off-The-Shelf) Initiative. Secretary Perry reversed the traditional reliance on mil-specs in favor of commercial standards and performance specifications. Rather than arbitrarily imposing mil-spec requirements, Secretary Perry’s directive required a waiver to use mil-specs. The directive required justification to explain why a COTS solution could not be used.

In the past, the military procurement offices took the “safe and easy” approach of simply imposing mil-specs on everything. (Remember the $750 dollar hammer and $100 ash trays?) The new directive required that the environment in which the equipment or component needed to operate be defined and the OEM be allowed to meet that specific environment with the least expensive approach.

This has resulted in a significant reduction in equipment being procured with full military specifications imposed. The ramifications have been felt throughout the supply chain. For the connector industry, it means that the potential for sale of standard products is greatly enhanced and that even connector companies without full mil-spec parts may have an opportunity in what was once a closed market.

Other countries have followed suit to some degree. In 1999, the British Ministry of Defense (MOD) issued guidance to Integrated Project Teams (IPTs) on Off-The-Shelf (OTS) procurement. Regarding the British initiative, an article in the COTS Journal reported, “The use of COTS is now an integral part of the procurement process, but even though it is in its infancy, there are unique military specifications that cannot be met by commercial systems.”

Because of the relationships that have built up over the years, the new non-mil-spec connectors are coming primarily from traditional mil-spec vendors. But with the change in policy to allow non-mil-spec designs, opportunities are no longer closed to previously commercial-focused connector manufacturers.

COTS ≠ Non-Mil-Spec
It should be pointed out that COTS does not directly equal non-military. In the original interpretation of COTS, a commercial off-the-shelf part should be just that. It is a part that presently exists in the manufacturer’s catalog and has been sold in sufficient quantities to develop a price history. It is assumed that if the part is in the commercial marketplace, its price has been determined by market forces. But many of the "COTS" solutions end up being sole source because of modifications to meet environmental or performance requirements. Though these are often referred to as COTS, they are simply non-mil spec parts. Their price often reflects its low volume, sole source status, more than the reference to the COTS heritage would infer.

The movement to COTS connectors is happening and the transformation is occurring quickly. In some instances, it is happening too quickly. Some OEMs claim to have gotten “burned” when connectors failed during environmental testing and designs had to be redone. COTS connectors are typically not tested in the same manner as mil-spec connectors and the lack of data often spells trouble. A batch of connectors may perform well, but another batch—well within the tolerances of the commercial application—may fail in the military application. This has led to more connectors being procured with specifications and requirements rather than genuine off-the-shelf products. Terms like MOTS (Military Off-The-Shelf) and GOTS (Government Off-The-Shelf) are appearing to differentiate a product with a commercial origin that is used for military applications.

Initially, many viewed connectors as low-tech devices that could easily be replaced by commercial parts. While such thinking is common, in reality, modern connectors are a lot more complicated and critical. This is especially true in the high speed/high density (HS/HD) connectors which are a mainstay in the digital backplanes of today’s sophisticated equipment.

Digital circuits often involve high numbers of parallel signal paths that require high-density connectors to allow signals to travel from one circuit board to the next. The commercial world has addressed these problems and developed connectors that meet these needs. The military now has similar needs, but it must often deal with additional requirements such as temperature extremes outside the normal realm of commercial equipment. It must also address issues with electrostatic discharge (ESD) resistance, and the need for more robust construction to withstand shock and vibration. Until recently, some form of the DIN connector has sufficed; however, as the frequency of the backplane signals rises, the need for more sophisticated impedance-matched connectors grows.

The Bigger Problem
The current commercial HD/HS connectors fail to meet all the previously mentioned parameters: ESD protection, robustness, and temperature resistance. This situation is made worse by the small quantity of connectors that any one military program procures, due to high development costs and low volume. The prohibitive development cost of environmentally robust HD/HS connectors for low-volume applications has led to conditioning the hardware to shield the components from experiencing environmental extremes.

Military OEMs have installed elaborate liquid cooling systems that keep circuit cards at temperatures lower than those experienced in commercial applications. Shock-absorbing materials and hardware are applied and various techniques are employed to eliminate electromagnetic interference (EMI). Even with these techniques, the applicability of multi-sourced connectors is limited.

This has resulted in a number of connectors specifically developed to operate in the “less than mil-spec, but more than commercial” environment. While these products cost less than a full-mil version, some of these connectors cost $700 to $800 or more per mated pair, and that’s with the military OEMs contributing to the non-recurring engineering (NRE) costs.

Some applications can not be conditioned to allow application of non-military style connectors and may rule out the use of connectors altogether. Even in the commercial world, companies making mainframe computers have soldered memory cards in place to prevent momentary signal interruptions from vibration in relatively benign environments. Due to its stringent requirements, the military often finds a need to do the same. In avionics systems, the use of sockets to connect integrated circuit packages to the PC board is almost non-existent. Similarly, memory cards seldom plug into sockets, unless supplemented by some form of physical attachment. PC cards that interface through a backplane connector typically use a connector that incorporates a screw-type retention mechanism to ensure they stay securely mated. Thus, even if a military application uses a commercial processor, it may not use a socket.

When they can be employed, connectors usually use multiple points of contact between the pin and the socket to further assure a secure connection. This is seen in the many contact technologies employed in the MIL-C-55302 rectangular connector system. Some manufacturers use contacts that have four mating surfaces, while Amphenol uses what its website calls a “Bristle Brush Bunch” (B3), a descriptive name for the “multiple strands of high tensile strength wire that are bundled together to form the brush-like contact. By intermeshing two multi-strand wire bundles, an electrical connection is made. The ‘B3‘ contact design results in low, normal contact site forces and significantly reduces mating and unmating forces.”

The packaging of military systems is also contributing to the need to move away from mil-spec connectors. In the past, systems were configured around LRUs (Line Replaceable Units or “Black Boxes”) that were interconnected by cables which used mil-spec circular connectors for I/O. New systems are being built using LRMs (Line Replaceable Modules) which plug into a backplane which eliminates cabling and facilitates maintenance. This further dictates a HS/HD backplane solution.

The use of LRMs is also affecting the RF connectors. The desire for line replaceable RF modules has led to the development of blindmateable RF connectors that operate up to 23 GHz.

Conclusion
All of this adds up to increased opportunities for the non-military connector supplier. Dealing with the government however, does add a level of complexity. Because of the long life-cycles of government programs, supplying connectors often means insuring an ongoing supply of product for 10 or more years, which is usually outside of the commercial viability of a part. Government contracts are another issue.