OBJECTIVES

You will learn proven, quick methods for designing and evaluating the reliability of electronic equipment that can also be used as a sanity check for computer analysis, such as:

• Finding the natural frequencies of many different beams, circuit boards and chassis.
• Estimating transmissibility, Q, values for different beams, circuit boards and chassis.
• Critical relationships between dynamic displacements, frequencies and accelerations.
• How to find the minimum desired PCB natural frequency for sine, random and shock.
• How to find component lead wire and solder joint forces, stresses and fatigue life.
• How the component type, size, orientation and location on PCB affect the fatigue life.
• Methods for improving reliability of commercial electronics in military environments.
• Seven basic equations that can solve 85% of your vibration and shock problems.
• Methods for quickly estimating fatigue life of many different types of components.
• Quick and easy methods for finding the fatigue life in random vibration environments.
• Why isolation systems are good for vibration and bad for shock, and visa versa.

WHO SHOULD ATTEND

Designers, engineers and managers from all the following functions:

Quality Assurance

Reliability

Test Engineer

Research & Development

Product Design

Production & Manufacturing

COURSE OUTLINE

Simplified Methods for Obtaining Natural Frequencies of Beams, Chassis, Plates and PCBs With Different Geometries and Supports.

• Quick Methods for Finding the Fundamental and Higher Natural Frequencies.
• Flexing Frequencies of Uniform and Variable Cross Section Beams and Chassis With Concentrated Loads and Different Combinations of Free, Supported and Clamped Ends.
• Simple, Proven Methods for Averaging Variable Cross section Moments of Inertia.
• Torsional Frequencies in Beams and Chassis With Bolted Interfaces.
• Why Most Chassis Failures are Due to Torsional Resonances.
• Rectangular Plates, Circular Plates, Triangular Plates, and Hexagonal Plates and PCBs With Various erimeter and Distributed point Supports.
• Composite Construction Beams, Plates and PCBs With laminated Metals and Plastics.
• Sample Problems to Demonstrate Methods of Evaluation.

Techniques for Determining the Minimum Required PCB Natural Frequency to Insure Reliable Operation In Various Sine Vibration, Random Vibration and Shock Environments Applications for a wide Variety of Surface Mounted and Through-Hole Mounted Components.

• Effects of Component Type, Size, Location and Orientation on Required Frequency.
• Why the Dynamic Coupling Effects Between the Chassis and PCBs Must be Examined.
• Methods For Estimating the Transmissibility (Q) values for PCBs and Chassis.
• How PCBs and Chassis Respond to Sine Vibration, Random Vibration and Shock.
• How to Find the Maximum Allowable Dynamic PCB Displacements to Prevent Failures.
• Sample Problems to Show How to Design Real Hardware.

Determining the Fatigue Life of Surface Mounted and Through-Hole Mounted Components.

• Dynamic Forces and Stresses in Lead Wires and Solder Joints of Heavy Components
• Fatigue Damage Accumulated During a Sine Sweep Through a Resonance, During a Sine Resonant Dwell, During Random Vibration, During Shock and During Thermal Cycling
• Using Miner's Cumulative Damage Criteria to Add up All the Fatigue Accumulated in Many Different Environments to Obtain the Resulting Fatigue Life
• How Component Mounting Methods Can Affect the Fatigue Life
• Effects of Stress Concentrations on Fatigue Properties of Lead Wires and Solders
• How Dynamic PCB Displacements Affect the Fatigue Life
• Sample Problems to Help Understand Concepts Presented

Relative Dynamics Displacements Between Component and PCB Induce Strains in Lead Wires and Solder Joints.

• Effects of Component Type and Size on Resulting Forces, Stresses and Fatigue Life.
• Effects of Component Location and Orientation on Fatigue Life.
• Why You Should Not Mount Large Components at the Center of a Plug-In PCB.
• Estimating the Component Fatigue Life in Sine and Random Vibration Environments.
• How the PCB Natural Frequency and Component Size Affects Relative Displacements.
• How the Lead Wire Geometry and Strain Relief Affect the Forces, Stresses and Fatigue life.
• Effects of Wire Strain Relief in Coining, Looping and Camel Humps on Fatigue Life.
• Sample Problems to Demonstrate Affects of Physical Factors Outlined Above.

Quick Methods for Evaluating PCB Fatigue Life in Random Vibration.

• Characteristics of Random Vibration Compared to Sine Vibration.
• Simplified 3 Band Techniques for Evaluating Random Probability Distribution Functions.
• How Plug-in PCBs Respond to Random Vibration.
• Why You Cannot Duplicate Random Vibration Failures With Sine Vibration.
• Quick Methods for Evaluating Input G RMS Acceleration Levels.
• Why Input Power Spectral Density (PSD) Levels Are More Important Than Input G Levels.
• Quick Method for Finding Random Vibration Fatigue Life in Electronic Systems.
• Sample Problems to Show How to Generate Reliable Designs for Random Vibration.

Cost effective Methods for Improving the PCB Fatigue Life of Commercial Hardware for Reliable Operation in Severe Military Environments.

• Solutions Such as Constrained Layer Damping Sounds Good, But it is Not Really Effective.
• Adding Stiffeners to PCBs Can Work if You Can Find Room Between the Components on Existing Hardware. Make Sure Ribs Do Not Interfere With Forced Convection Cooling.
• Adding Isolators Can Do a Good Job if They Are Designed for Vibration and Shock.
• Care Must Always Be Exercised to Make Sure Isolator Rocking Modes and ChassisResonances Are Well. Separated from PCB Resonances by Using the Octave Rule. Snubbers that are Properly Installed can Substantially Improve the Dynamic Fatigue Life Without taking up too Much Room and Without Interfering with the Cooling System.
• Sample Problems are Shown to demonstrate Cost Effective Applications.

How Poor Fixtures Designs and Poor Testing Methods can Ruin a Good Electronic Design.

• 13 Simple Fixture Design Rules that can Insure Reliable Testing Performance.
• Aluminum and Magnesium Fixtures can Add Stiffness Without a Lot of Weight.
• Welded magnesium Fixtures Sometimes Have Problems with Threaded Inserts.
• Screw and Glue Types of Fixtures can Have a Good Working History.
• Laminated Wooden Fixture can Provide Good Damping Properties.
• Hollow Tube Welded Fixtures Partially Filled with Sand Provide Good Damping.
• Proper Accelerometer locations and Attachment Methods are Needed For Good Results.
• The Use of a Strobe Light During Sine Tests can Reveal Critical Resonances.

Effects Of Poor Manufacturing Methods on the Reliability Of Electronic Assemblies.

• Improper Dimensioning of the PCB Thickness Tolerances Can Result in a Lower Natural Frequency which Can Substantially Reduce the Fatigue Life.
• Poor Wire Forming Dies Can Introduce Stress Concentrations and Reduce the Fatigue Life.
• Improper Forming Wire Strain Relief in Coining, Looping and Camel Humps Reduces Fatigue Life.
• Machining Very Small Radii in Shafts can Increase Stress Concentrations, Decreasing Life.
• Improper Abrading and Cleaning of Smooth Metal Surfaces Reduces Bonding Strength and Reduces Fatigue Life.
• Applying Polyurethane Conformal Coatings with a High Expansion Coefficient and Elastic Modulus which Wick Under Small Chip Capacitors and Resistors Cracking them in Temp. Cycling.

©2006 Hobbs Engineering