New power conversion standard provides direction

New power conversion standard provides direction

The IPC-9592 standard creates a set of consistent specifications and methods for the electronics industry

BY DAVE TORP
IPC, Bannockburn, IL
http://www.ipc.org

Power conversion devices (PCDs) are used throughout the computer and telecommunications industries, but until now there was no defined standard for these devices. A standard was needed to improve these devices’ field performance, reduce their overall qualification interval, and provide customer requirements for consumer and telecommunications grade PCDs. Thus, IPC — Association Connecting Electronics Industries, published the first-ever power conversion standard, IPC-9592, Requirements for Power Conversion Devices for the Computer and Telecommunications Industries, in September 2008.

Power conversion devices are used in the electronics industry to provide conversion of main power sources, which are usually alternating current (ac), to lower direct current (dc) voltages either for direct use of electronic circuits, or as a secondary source for additional dc/dc PCDs in order to provide several dc voltage levels for various electronic devices in a product. The IPC-9592 standard refers to three categories of PCDs:

Category 1 . Dc output power supplies to be embedded in equipment, whether the input power is ac or dc.

Category 2 . Board-mounted dc/dc converters including both isolated and non-isolated converters.

Category 3 . Ac/dc power supplies used as adapters and chargers external to the equipment being powered.

The PCD purpose

The purpose of IPC-9592 is to create a set of consistent specifications and methods to assure suitability, quality, safety and reliability of PCDs for the electronics industry. These specifications apply to suppliers of PCDs and provide guidelines for the end user to ensure adequate specs for use of these PCDs in their products. It sets the requirements for design, qualification testing, conformance testing, and manufacturing quality and reliability processes. All the specifications and requirements defined in this standard are intended to be part of the supplier’s PCD certifications outlined by the customer and should ship with first article and any design changes to the PCD on request by the user.

Product specifications and documentation requirements should follow specific guidelines and appear in a delineated format. The supplier must provide the user with pertinent documentation in a reasonable time frame, before the evaluation of engineering first article samples, and with appropriate nondisclosure agreement protection executed.

Such documentation may include the theory of operation; applicable schematics; qualification test plan; reports for electromagnetic compatibility (EMC), sample qualification tests, design verification testing (DVT), highly accelerated life testing (HALT), SMT power module solder attachment reliability, and derating; reliability data and calculation; design checklist; failure mode and effect analysis (FMEA) for custom products; bill of materials (BOM); approved supplier list for all components; PCB artwork; component drawings, including magnetic; manufacturing drawings; regulatory reports (if applicable); change history; and mechanical dimension measurements. The level of documentation will differ between custom and standard PCDs, as agreed by the user and the supplier; with custom PCDs typically requiring significantly greater detail (ex. BOM and PCB artwork may not be required for standard PCD).

The datasheet should provide complete specifications of form, fit, and function, including electrical specifications and whether it is a Class 1, general or standard PCD, or Class 2, enhanced or dedicated service PCD. The date and revision level should be marked at the bottom of the sheets. Items to be addressed are input power logic, indicator, control, and output specifications; reliability, safety, and regulatory factors; physical dimensions and electrical specifications and requirements; and material control and labeling.

In addition, the PCD supplier needs to implement a documented, capable material control system for all incoming, in-process, and outgoing materials and make available documentation of a material control plan.

Design for reliability means that industry best practices to specify, design, and document PCD performance and reliability are in place. Expected reliability of a PCD and the conditions under which the reliability is specified should be defined by the supplier. There should be a documented process in place to select all components for product designs including information on all components and all component suppliers. IPC-9592 defines the factors that should be incorporated into the component selection process.

Derating guidelines

An important part of IPC-9592 involves derating documentation requirements and setting derating guidelines. To provide a reliable power conversion product, the standard document sets forth a method of component derating to use in all electrical designs. It describes derating methods, conditions, and results.

Derating is a technique used to ensure that component ratings are not exceeded, either under steady state or transient conditions. The intent of component derating is to improve reliability of electrical components in electronic products by compensating for many variables inherent in a design. Proper component derating will lower failure rates through reduced stresses; reduce the impact of material, manufacturing, and operational variability; and enable continued circuit operation with long term part parameter shifts.

When there is a custom PCD design on new topologies or architectures with no previous design failure modes and effects analysis (DFMEA), or in cases where there are new technology components, the supplier should provide a DFMEA to the customer with results of the analysis and of any corrective actions. DFMEA is to be performed early in the power supply development cycle. DFMEA activities are designed with three aims: to recognize and evaluate the potential failure modes of each component in a product and its effects on the product, to identify actions that could eliminate or reduce the chance of the potential failure occurring and to document the process for improvement of future designs.

Design and qualification testing is a central and detailed focus of IPC-9592. The testing described has two main purposes.

First, design verification testing and electromagnetic susceptibility testing, including electromagnetic interference (EMI) and electrostatic discharge (ESD) testing, are intended to provide assurance that the device will function according to its specification.

Second, environmental stress testing, including HALT, is intended to provide a measure of assurance (not proof) that the device is robust enough to operate in its intended environment without damage or degradation that would affect its operation.

IPC-9592 was developed by the Power Conversion Devices Standard Subcommittee (9-82) of the IPC OEM Management Council Steering Committee (9-80). It comprised representatives from leading original equipment manufacturers (OEMs) and power conversion equipment suppliers, such as Alcatel-Lucent, Cisco Systems, Dell, Emerson Network Power, Hewlett-Packard, IBM, Lineage Power, and Murata Power Solutions. There was such urgency for the document that it was released as soon as the core features of it were in place, with work on a revision in progress even before the original standard was in print.

According to Neil Witkowski, technical manager at Alcatel-Lucent, and formerly vice chair and now chair of the IPC Power Conversion Devices Standard Subcommittee, “There are a variety of reasons for the revision. There is a need for clearer requirements with respect to moisture sensitivity and corrosion and the higher temperatures associated with lead-free manufacturing need to be addressed.

The current language on HALT is not enough to give suppliers clear guidance that would ensure meeting customer requirements, so more guidance and examples will be included with respect to HALT testing. In addition, there will be an increased focus on customers in countries such as China and India.”

T. Paul Parker, vice chair of the committee, said, “IPC-9592 is a needed standard in the power supply industry. It has come about due to a collaborative effort between major OEMs and power supply vendors. The resulting document provides a cohesive direction for best practices in design and test of power products and clearly establishes a uniform set of qualification and manufacturing test requirements. This has not existed prior to now and will prevent suppliers from having to perform unique sets of tests for each customer.” ■

Copies of IPC-9592 can be purchased through www.ipc.org/onlinestore. Call IPC Customer Service for more information at 847-597-2862.