The complete μModule product line, power, interface and signal links are essential!

Hybrid circuit and module technology has been evolving for more than 50 years. Now, the module is in the form of COTS (commercially available), which has been designed to shorten design cycles, mitigate 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.

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 6 times, and further investment has been made in the next few years. In 1962, a 10-pack 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 miniature modules have been very successful, but life is very short, and the birth of integrated circuits (ICs) has undoubtedly contributed to this module giving way. Early ICs were nine times more expensive than hybrid solutions. These ICs were often beneficiaries of government-funded projects. A famous project in 1962 was Raytheon's Apollo guidance for NASA. Computer (ApolloGuidance Computer).

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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 the development of 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 the 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.

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 functions with hybrid circuits, modules, ASIC macros, or on standard-format boards has become the preferred method. In fact, they are specialized standard products (ASSPs) and basic components.

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 thermal 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. It’s only in recent years that monolithic IC products have begun to meet this type of demand, but now, the new highly parallel phased array radars are once again focusing 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 an attempt 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 power 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 customizable modules can be used to hide valuable intellectual property associated with hardware design, making reverse engineering more difficult to implement. Viewing only the number of devices on the package is not sufficient to decode the hardware design. In addition, some semiconductor chips are not easily available on the open market.

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 with the COTS 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.

The μModule product is an example of today's COTS module. Launched in 2005, the first product has a complete 12A DC/DC regulator in a 15 mm2 surface mount package (Figure 1).

Figure 1 LTM4601AHV 12 A μModule DC/DC Regulator

Next, we developed a complete μModule product line that includes a variety of power, interface, and signal link products, such as the recently introduced LTM9100 (Figure 2) and the ADAQ7980 (Figure 3).

Figure 2 High-voltage isolated switch controller LTM9100 with telemetry

Figure 3 16-bit 1Msps data acquisition subsystem ADAQ7980

Similar to surface mount ICs, each μModule regulator includes a complete system-in-package solution that simplifies design and minimizes external components. Internally, layout and design are optimized for improved electrical performance and thermal efficiency. Developed to the highest standards in the industry, these μModule products offer outstanding reliability and are close to standard ICs. Available in LGA (pad grid array) packages with gold coated pads and BGA (ball array) packages with SAC305 or SnPb solder in various temperature grade versions.

Figure 4. Two μModule Regulators in LGA (Left) and BGA (Right) Packages

If required, the Defense Temperature Grade version of the μModule product provides 100% electrical testing at -55 °C and +125 °C to provide guaranteed data sheet performance.

Hybrid circuits and modules were the technology of choice for miniaturization of electronic circuits and improved reliability of electronic circuits 50 years ago. 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. Although 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 Application Specific 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, 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.