Hybrid circuit and module technology has been evolving for more than 60 years, and now modules are available in COTS (commercially available), designed to reduce design cycles, reduce obsolescence and address SWaP (size, weight and power) challenges. Significant contribution. Let's review the history of this technology and explore some of the factors that are important to the aerospace and defense industry.
Early hybrid circuit
In the late 1950s, the field of computing using discrete transistors made great strides, but boards became increasingly complex, sometimes with thousands of interconnected transistors, diodes, resistors, and capacitors. Therefore, a solution is needed to increase density and reliability. Government agencies have funded various hybrid circuit concepts.
In 1958, the US-funded RCA company proposed the concept of "micro-modules." The approach taken by this concept is to use cubes that are configured externally and of uniform size so that the cubes can be fixed to each other. Internally, the chiplets of the various discrete components are vertically stacked and interconnected at their edges. In terms of volume, component density has more than doubled, reliability has increased by a factor of six, and further investment has been made in the next few years. In 1962, a 10-component module cost $52, which is about 2.5 times the price of a conventional discrete PCB (printed circuit board) solution.
Despite the high price, RCA's micro-modules are very successful, but life is very short, the birth of integrated circuits (ICs) has undoubtedly contributed to this module giving way. The price of early ICs was nine times that of hybrid solutions. These ICs were often the beneficiaries of government-funded projects. A famous project in 1962 was Raytheon's Apollo guidance for NASA. Computer (ApolloGuidance Computer).
With the rapid development of ICs, people soon realized the advantages of ICs over hybrid circuits and modules. In this respect, it seems surprising that hybrid circuit technology still exists. However, governments often have broader considerations, including product stability and long-term availability, reliability, and usability, relative to innovation and complex operational requirements. These factors combined with the specific technical advantages of hybrid circuits and modules are undoubtedly one of the reasons why hybrid circuit technology has been used continuously for the past 50 years.
During this time covered by this article, ASIC technology brought an industry revolution. Initially, hundreds of gate arrays provided the government with a way to increase digital integration. With the rapid increase in gate density and improvements in development tools, the days of hybrid circuits seem to be few.
In the late 1980s, defense equipment designers recognized the success of digital ASICs and tried to apply the same approach to mixed-signal circuits. Their motives are mainly dominated by miniaturization requirements, because defense requires more and more complex systems, and at that time such systems have large budgets. However, it is difficult to adjust the design tools that are completely customized for the customer's use, and the analog design is complex. This difficulty and complexity means that the mixed-signal ASIC will still consume resources very intensively for a completely custom-designed design. And highly dependent on the design team of the semiconductor manufacturer.
Despite tremendous advances in analog ASIC design tools and techniques, real-world simulation problems are wide-ranging and still difficult to solve with off-the-shelf semi-custom circuits. As a result, hybrid circuits provide a way to integrate high-performance analog and signal link functions fabricated using different process technologies into a single package when off-the-shelf products do not work.
Performance defense and aerospace systems are typically designed based on modular subsystems. For example, the Field Replaceable Unit (LRU) simplifies service and operational support. LRU interconnects rely on standards such as the MILSTD-1553 bus interface. Implementing these features with hybrid circuits, modules, ASIC macros, or on standard-format boards has become the preferred method. In fact, they are specialized standard products.
(ASSP) and basic building blocks.
This highlights two important factors. First of all, there is no merit in unnecessary reinvention, and it is more effective to let the designer focus on the core intellectual property of the system. Second, according to today's standards, the defense and aerospace industries are small users of semiconductors, and developing module or board-level solutions is a more realistic proposition than developing single-chip IC-level ASSPs.
Traditionally, the performance requirements of power modules have been well aligned with hybrid module technology. The sealed metal can package used in this technology meets the power density and heat management requirements of high temperature, high reliability defense applications. As power requirements for larger FPGAs and microprocessors increase, the pursuit of more efficient power architecture and point-of-load (POL) regulation has led to new modular solutions.
Applications such as radar have long relied on hybrid circuits and modules to implement RF and microwave solutions. Only in recent years has a single-chip IC product that has begun to meet this type of demand, but now, the new highly parallel phased array radar has once again focused on modular solutions.
Outdated product elimination is a very serious problem for the defense industry. Project life spans of 30 to 50 years are common, so defense and aerospace equipment suppliers are constantly looking for ways to reduce risk. Hybrid circuits and modules have always been a way to try to isolate the rapid changes in the defense industry and the semiconductor industry. Memory modules are a particular area of interest because DRAM and SRAM technology have a particularly short life span.
The concept of standard form factor and pin layout can be maintained while the memory chips within the module can be updated. It's much easier to write than it actually is, in part because of ongoing advances in access time, architecture, and supply voltage. On the other hand, using a standard format embedded processor board provides a more advanced approach if space permits. However, the concept of standard form factor is the core of many outdated elimination management strategies and is undoubtedly a major factor affecting the longevity of hybrid and modular solutions.
Hybrid circuits and modules also have advantages because fully custom modules can be used to hide valuable intellectual property associated with hardware design, making reverse engineering more difficult to implement. Looking at only the number of devices on the package is not enough to decode the hardware design. In addition, some semiconductor chips are not easily available on the open market.
From full customization to today's COTS
Previous views on continuing to use hybrid circuits and modules in defense systems are still valid. However, it is important to recognize that commercial equipment pressure from defense equipment manufacturers is greater than ever, especially in terms of cost and time to market.
Fully custom hybrid designs are expensive and take a relatively long time to develop. Alternative single-chip IC solutions are increasing year by year. Although large defense companies are still developing new hybrid designs, as production declines, manufacturing outsourcing trends are perceived.
The situation of the module is completely different. Driven by technical and commercial factors, module-based solutions have seen significant momentum. Switching power supplies and signal links are two types of applications that are particularly well-suited for use in modules, because high-efficiency design requires expertise, which is scarce in today's defense design teams.
Sixty years ago, hybrid circuits and modules were the technology of choice for miniaturization of electronic circuits and improved reliability of electronic circuits. As the semiconductor industry becomes more and more commoditized, the product life cycle and the equipment life cycle of the defense industry are becoming more and more different, and hybrid circuits and modules have found new use in reducing the problem of obsolescence. While ASICs are the preferred method of digital electronic circuit integration, hybrid modules can play a role in the small specialized market that solves simulation challenges.
At the same time, COTS modules come in the form of ApplicationSpecific Standard Products, especially for power supplies, processors, signal links and interfaces. These specialized standard products have also been widely adopted as defense equipment providers strive for new competitive advantages and recognize the importance of focusing scarce design resources on enhancing core competencies.
Today's defense budget pressures and shorter design cycles may make fully custom hybrid circuits increasingly a legacy solution, but there is no doubt that COTS modules are increasingly becoming the technology of choice for the defense and aerospace industries.