Electronic Hardware Reliability - davi.ws

1 2001 by CRC Press LLC 22 Electronic Hardware Reliability Int roduction Product Requirements and Constraints The Product Life Cycle Environment Characterization of Materials, Parts, and Manufacturing Processes Parts Selection and Management Candidate Part and Part Manufacturer Selection Manufacturer, Part, and Distributor Assessment Performance Assessment Reliability Assessment Assembly Issues Assembly Compatibility Routing Compatibility Test and Rework Acceptability Life Cycle Mismatch Assessment Risk Management Failure Modes and Mechanisms Design Guidelines and Techniques Protective Architectures Stress Margins Derating Redundancy Qualification and Accelerated Testing Virtual Qualification Accelerated Testing Manufacturing Issues Process Qualification Manufacturability Process Verification Testing Summary Defining Terms References Further Information Introduction

2 Reliability is the ability of a product to perform as intended ( , without failure and within specifiedperformance limits) for a specified time, in its life cycle application environment. To achieve productreliability over time demands an approach that consists of a set of tasks, each requiring total engineeringand management commitment and enforcement. These tasks impact Electronic Hardware reliabilitythrough the selection of materials, structural geometries and design tolerances, manufacturing processesand tolerances, assembly techniques, shipping and handling methods, operational conditions, and main-tenance and maintainability guidelines.

3 1 The tasks are as follows:1. Define realistic product requirements and constraints determined by the life cycle applicationprofile, required operating and storage life, performance expectations, size, weight, and cost. Arun Ramakrishnan University of Maryland Toby Syrus University of Maryland Michael Pecht University of Maryland 2001 by CRC Press LLC The manufacturer and the customer must jointly define the product requirements in the light ofboth the customer s needs and the manufacturer s capability to meet those Define the product life cycle environment by specifying all relevant assembly storage, handling,shipping, and operating conditions for the fielded product.

4 This includes all stress and Characterize the materials and the manufacturing and assembly processes. Variabilities in materialproperties and manufacturing processes can induce failures. A knowledge of the variability isrequired to assess design margins and possible trade-offs with weight, size, and Select the parts required for the product, using a well-defined assessment procedure that ensuresthat the parts selected have sufficient quality and integrity, are capable of delivering the expectedperformance and Reliability in the application, and will be available to sustain the product through-out its life Identify the potential failure sites and failure mechanisms by which the product can be expectedto fail.

5 Critical parts, part details, and potential failure modes and mechanisms must be identifiedearly in the design, and appropriate measures must be implemented to assure design architectural and stress interactions must also be defined and Design to the usage and process capability of the product ( , the quality level that can be controlledin manufacturing and assembly), considering the potential failure sites and failure design stress spectra, the part test spectra, and the full-scale test spectra must be based on theanticipated life cycle usage conditions. The proposed product must survive the life cycle environ-ment, be optimized for manufacturability, quality, Reliability , and cost-effectiveness, and be availableto the market in a timely Qualify the product manufacturing and assembly processes.

6 Key process characteristics in all themanufacturing and assembly processes required to make the part must be identified, measured,and optimized. Tests should be conducted to verify the results for complex products. The goal ofthis step is to provide a physics-of-failure basis for design decisions, with an assessment of allpossible failure mechanisms for the anticipated product. If all the processes are in control and thedesign is valid, then product testing is not warranted and is therefore not cost-effective. Thisrepresents a transition from product test, analysis, and screening to process test, analysis, Monitor and control the manufacturing and assembly processes addressed in the design, so thatprocess shifts do not arise.

7 Each process may involve screens and tests to assess statistical Manage the life cycle usage of the product using closed loop management procedures. This includesrealistic inspection and maintenance procedures. Product Requirements and Constraints A product s requirements and constraints are defined in terms of customer demands and the company score competencies, culture, and goals. If the product is for direct sale to end users, marketing usuallytakes the lead in defining the product s requirements and constraints through interaction with thecustomer s marketplace, examination of the current product sales figures, and analysis of the , if the product is a subsystem that fits within a larger product, the requirements andconstraints are determined by the product into which the subsystem fits.

8 The results of capturing productrequirements and constraints allow the design team to choose product parts that conform to product-specific and company objectives. The definition process begins with the identification of an initial set of requirements and constraintsdefined by either the marketing activity (or in some cases by a specific customer), or by the product intowhich the subsystem fits. The initial requirements are formulated into a requirements document, wherethey are prioritized. The requirements document needs to be approved by several groups of people, ranging 2001 by CRC Press LLC from engineers to management to customers (the specific people involved in the approval will vary withthe organization and the product).

9 Once the requirements are approved, the engineering team preparesa preliminary specification indicating the exact set of requirements that are practical to between the requirements document and the preliminary specification become the topic oftrade-off analyses (usually cost/performance trade-offs), and if, after analyses and negotiation, all therequirements cannot be implemented, the requirements document may be modified. When the require-ments document and the preliminary specifications are agreed upon, a final specification is prepared andthe design begins. The Product Life Cycle Environment The product life cycle environment goes hand in hand with the product requirements.

10 The life cycleenvironment affects product design and development decisions, qualification and specification processes,parts selection and management, quality assurance, product safety, warranty and support commitments,and regulatory product life cycle environment describes the assembly, storage, handling, and scenario for the useof the product, as well as the expected severity and duration of these environments, and thus containsthe necessary load input information for failure assessment and the development of design guidelines,assembly guidelines, screens, and tests. Specific load conditions may include steady-state temperatures,temperature ranges, temperature cycles, temperature gradients, humidity levels, pressure levels, pressuregradients, vibrational or shock loads and transfer functions, chemically aggressive or inert environments,acoustic levels, sand, dust, and electromagnetic radiation levels.