What is an electronics packaging system? Which components are included in it? What role do standards play? What functionality is provided? How does it differ from an office PC, an industrial PC, a box PC or programmable logic controller, etc? What is the interaction between the various components? We answer these and other questions in a new seven-part series and present the entire system in detail with all its individual components.

Schroff understands a system to be a combination of mechanical components such as a subrack or case, electronic components such as backplane and PSU and where necessary a cooling system and a system management module. A functioning system without active PCBs (function modules)(Fig. 1). Such a system is used as a computer, e.g. for measurement, for the control of machines, whole systems and automated processes in an industrial environment. Today cameras are being used increasingly e.g. in industrial applications for process monitoring. The raw camera data is sent to the system where it is vectorised for further processing and evaluated in the system. The results are used in turn to control an action such as e.g. the rejection of defective parts by a deflector.

Standards „standardise” products, define uniform requirements for production processes and specify comparable quality criteria and agreed component interfaces, such as e.g. a connector, including pinout, software protocol and also the dimensions of the function modules (PCBs). The user then has the possibility of combining products from different manufacturers, since the interfaces are clearly defined.

Electronics packaging standards include standard dimensions and criteria for physical integration, electromagnetic compatibility and thermal management. Dimensional compatibility in electronics packaging is mainly governed by six IEC standards (IEC 60297-3-101, IEC 60297-3-102, IEC 60297-3-103, IEC 61969-2-1, IEC 61969-2-2 and IEC60917-2-X). Of primary relevance for physical integration, earthquake resistance, electromagnetic compatibility and thermal management are the five IEC standards IEC 61587-1, IEC 61969-3, IEC 61587-2, IEC 61587 3 and IEC 62194, ed. 1. In addition to the IEC standards there are definitions and specifications that apply to specific market sectors. Examples are VITA (VMEbus International Trade Association), the body that defined the bus specifications for VMEbus, VME64 Extension, VXS, etc, and PICMG (PCI Industrial Computer Manufacturers Group), responsible for CompactPCI, AdvancedTCA, MicroTCA and much more. PICMG primarily creates specifications for the industrial automation and telecommunications sectors. VITA concentrates more on ruggedized and military applications.

Further standards specify how high levels of environmental protection and health and safety can be attained and assured, both technically and in organisational terms. Most important for electronics packaging in this regard are earthing (grounding), fire protection, IP (internal protection, IEC 60529) and ESD protection. The special protection requirements in respect of dangerous voltages, mechanical parts and heat sources through to fire protection are documented in IEC 60950 and IEC 61010. The same applies to IP protection of enclosures against the entry of dust and water and also to the protection of persons against electrical risks in the enclosure.

The standards place similar importance on the testing of specific characteristics. Product details that can be derived from these guidelines and requirements enable the user to compare the characteristics of competing products. The three-part series of IEC 61587 standards covers climate control, mechanics, safety and earthquake tests plus a function test for electromagnetic shielding.

Schroff has participated actively since 1978 in the "Mechanical Structures for Electronic Equipment" standardisation work of the international IEC organisation. The company also takes a leading part in certain activities of the VITA and PICMG committees. As an international enterprise Schroff shares in the responsibility for developments in standardisation - the implementing of the latest technologies and their realisation in standard product platforms.

In function terms an electronics packaging system is basically a computer and is event-driven in operation. It responds to events, calls up appropriate function blocks and executes these. Such a system is a suitable choice for large data volumes, for signal processing and for calculations e.g. in image processing, optical quality control or image-generating diagnosis procedures in medical applications.

Electronics packaging systems are based on standardised 19" technology. This ensures that the dimensions that are required for interface definition with the next highest or lowest component plane are fixed. These are in particular the connecting dimensions between chassis and plug-in units and for electronics cabinets in which the chassis or completed system may be installed. All function boards are arranged parallel to one another (horizontally or vertically) as 19" plug-in boards in the system, inserted into and removed from the system from the front. This ensures a high degree of modularity and expandability. Multiprocessor systems and also redundant systems can be constructed in accordance with the relevant specifications.

This construction also allows a defined direction for the flow of cooling air and thus efficient cooling without the risk of hot spots. The plug-in boards can be exchanged without dismantling the system and indeed while the system is in operation (hot swap). This is significant for the ease of maintenance of a system.

All system components are designed for industrial use: mechanically robust (chassis and connectors), durable (e.g. high MTBF for fans and PSUs) and with long-term availability. The system offers high shock and vibration resistance and a suitable level of EMC shielding. Of equal importance is the long-term availability of the components used. An availability of 7 to 10 years is normally guaranteed; by special agreement with the user, up to 15 or 20 years is possible.

Also of increasing importance is system management, which, depending on the specification, can be realised in an electronics packaging system up to board level.

Programmable logic controllers (PLCs) work cyclically. At the start of a cycle the PLC reads the values of all inputs, runs the stored program and provides the outputs at the end of the cycle. Then the cycle starts again; the program has no end. The cycle is controlled by the operating system permanently stored by the manufacturer. Programmable logic controllers are mounted on lipped horizontal rails in switchgear cabinets. They are particularly suited to simple control and regulating tasks with low data volumes and a large number of I/Os. Since such areas of use have little overlap with those of computers, we will not make a detailed comparison here.

The differences between electronics packaging systems and office, industrial or box PCs are primarily their construction type, modularity and expandability and their suitability for industrial use (Table 1). The functionality is however basically the same.

An electronics packaging system can be constructed on various platforms for different bus technologies. Possibilities include VME, VME64x, VXS, VPX, CompactPCI, CompactPCIe, CompactPCI Plus, AdvancedTCA and MicroTCA.

VMEbus is a bus system for 19" systems whose specification was announced by VITA (VMEbus International Trade Association) in 1994. While the original VMEbus (VITA1) is of decreasing importance for new projects, systems and backplanes based on the VITA 1.1 update (VME64x, 1997) are still commonly used. A VITA31.1 backplane is based on a standard VME64x backplane and is expanded only by two serial ports, so that e.g. a gigabit Ethernet link (1000Base-T) can be connected to two switches for each. A VITA41 backplane (VXS) is based on a VME64x backplane. However, the P0 connector differs from that of the VME64x backplane. This allows transmissions in the region of 10 Gb/s. The standard defines many high-speed protocols that can be sent over these connections, e.g. Rapid I/O, Ethernet and InfiniBand. Backwards compatibility to VME64 extensions is still preserved. The VPX standard goes another step further and implements the complete high-speed slot connectors, capable of transmitting 10 Gb/s per port. VPX backplanes are then no longer compatible with VME64x backplanes because of the connectors. However, simple hybrid backplanes can be produced under VITA46.1 that can accept VME64x, VXS and VPX boards. VPX backplanes allow transmission of high-speed signals in all connector areas in order to increase transmission bandwidth. However, even the classic parallel VMEbus or even PCI buses can still be accommodated here. VMEbus and/or its successors are used, for example, in military applications and in aviation and space travel.

CompactPCI (CPCI) is a standard of PICMG (PCI Industrial Computer Manufacturers Group) for high-end systems in 19" configuration with passive backplane (Fig. 2) for demanding applications in terms of performance, robustness and failure safety. CompactPCI can be built flexibly and is based on the Euroboard format. The electrical specifications are based on the PCI standard defined for office PCs. Unlike the ordinary PCI bus, CompactPCI boards can be swapped during operation (hot swap). CompactPCI was supplemented in 2005 by its successor CompactPCI Express. Decisive factors for this were the developments in the world of PCs and the replacement of the PCI bus, which is the foundation of CompactPCI, by PCI Express. CompactPCI Express continued to draw on the technological, availability and cost advantages of the PC world and also offered still higher data rates. CompactPCI Express now uses serial rather than parallel data transmission.

The current CompactPCI standard provides no serial interfaces such as PCI Express, Serial Advanced Technology Attachment (SATA), Ethernet or USB via the backplane. The original successor CompactPCI Express lacks decisive factors such as support for SATA, USB and Ethernet. In order to continue to accept CompactPCI boards in CompactPCI Express systems a PCIe-to-PCI bridge is required, either on the backplane or in the form of a plug-in board. In CompactPCI Express the number of rear I/O connections is also too small. It is expected that the new CompactPCI Plus standard will compensate for these and other restrictions. CompactPCI Plus (Cplus.0) is the future of industrial embedded computer systems. And the PICMG 2.30 CPLUS I/O specification allows a "soft" migration path from CompactPCI to the future. Both specifications - each still at the draft stage - represent the logical further development of CompactPCI, supported by today's data transport mechanisms - PCI Express (PCIe), SATA, USB II & III and Ethernet Base-T.

AdvancedTCA (Advanced Telecom Computing Architecture, PICMG 3.x) is a PICMG standard primarily for high-performance communications servers that can meet the needs of increasing data traffic with new data services. The ATCA concept is a scaleable, high-performance architecture that has proved itself in terms of high performance, availability and future compatibility and on whose platform many forward-looking applications can be realised (Fig. 3). While AdvancedTCA is used in core and capillary networks, the more compact MicroTCA standard will be used in access networks.

MicroTCA stands for "Micro Telecommunications Computing Architecture" and is also a modular standard agreed by PICMG. The MicroTCA specification defines the requirements of a system that PICMG AdvancedMCs drives directly on a backplane. MicroTCA complements PICMG3.0 Advanced Telecommunications Computing Architecture (AdvancedTCA). While AdvancedTCA was designed for high capacity and high-performance applications, MicroTCA is focussed on cost-sensitive, physically smaller applications with less capacity and lower performance and possibly less stringent availability requirements (Fig. 3). MicroTCA provides a high-speed system platform that is sufficient for both the high demands of the telecommunications sector and the less demanding requirements of industrial applications.

So that all the components of an electronics packaging system work smoothly together in one system, so-called 'interoperability workshops' are regularly held e.g. for AdvancedTCA and MicroTCA, at which developers from participating manufacturers can test their components with one another under real conditions. The need for such workshops began with the introduction of the AdvancedTCA standard. The design of these systems is highly complex, and becomes more so with the MicroTCA standard. Above all, communication and management within a system is substantially more comprehensive than in, for example, VMEbus or CompactPCI. The specification defines the management with great precision but also allows some room for interpretation. At the workshops, individual component manufacturers can collaborate on the scope for interpretation available to them and establish standards.

Further contributions will appear here regularly that discuss the individual components such as mechanics, cooling, backplanes, power supply systems, system management and applications and the future of electronics packaging systems in detail.