Understanding Best Practices in Test Plan Development January 24, 2019 | Greg Caswell 9000 Virginia Manor Rd Ste 290, Beltsville MD 20705 | 301-474-0607 | www.dfrsolutions.com
Abstract • Preparing a viable test plan involves several steps to properly identify the requirements for the tests. This webinar will identify a methodology for this test plan approach. It will discuss the necessity for a BOM review to determine part limitations, assessing the field environmental conditions so they can be properly mapped to the tests implemented, and the impact of failure history, should it exist. • Next, it is necessary to generate the acceleration factors for the test protocols. Determining the acceleration factors involves identifying the failure mechanisms or the environments the unit has encountered. There are several formulas for ascertaining the acceleration factor based on the anticipated failure mechanism. Several will be discussed. • Next, identifying the correct activation energy for the materials being tested is also critical. .7eV has classically been the activation energy for integrated circuits, but is not applicable for all device types. • Finally, a test protocol that facilitates the accelerated testing is created. To do so requires an understanding of the reliability metrics for the product (e.g. reliability requirement, life expectancy, confidence level, sample size) is needed. The test plan can then be formulated where the specific test conditions and parameters are defined. These involve temperature range, humidity, cycles to failure, power (power cycling) and unusual stresses like dust or salt fog. • This webinar will address this flow and provide insight into the approach to take in developing your test plans. 9000 Virginia Manor Rd Ste 290, Beltsville MD 20705 | 301-474-0607 | www.dfrsolutions.com 2
Test Plan Approach • Determine Failure Mechanisms − Review BOM, conduct product tear down if possible − Determine part limitations. What are the maximum stresses the product can handle in test? − Determine the field environmental conditions − Assess failure history if it exists • The objective is to develop a test plan that does not stress the assembly to a level where a failure might not be experienced in the field 9000 Virginia Manor Rd Ste 290, Beltsville MD 20705 | 301-474-0607 | www.dfrsolutions.com 3
Test Plan Development – Define Use Environment • The critical first step is a good understanding of the shipping and use environment for the product. • Do you really understand the customer and how they use your product (even the corner cases)? • How well is the product protected during shipping (truck, ship, plane, parachute, storage, etc.)? • Do you have data or are you guessing? − Temp/humidity, thermal cycling, ambient temp/operating temp. − Salt, sulfur, dust, fluids, etc. − Mechanical cycles (lid cycling, connector cycling, torsion, etc.) 9000 Virginia Manor Rd Ste 290, Beltsville MD 20705 | 301-474-0607 | www.dfrsolutions.com 4
Test Plan Development – Define Use Environment Container and Ambient Temperature 75.0 Container Temp (°C) Outdoor Temp (°C) 65.0 Temp. 55.0 Variation Temperature (°C) 45.0 In a Trucking 35.0 Container 25.0 15.0 0 50 100 150 200 250 300 350 400 450 Hours 9000 Virginia Manor Rd Ste 290, Beltsville MD 20705 | 301-474-0607 | www.dfrsolutions.com 5
Example of Failure Inducing Loads • Temperature Cycling – Tmax, Tmin, dwell, ramp times – T and Sustained Temperature – exposure time • Humidity – Controlled, condensation • Corrosion – Salt, corrosive gases (Cl 2 , etc.) • Power cycling – Duty cycles, power dissipation • Electrical Loads – Voltage, current, current density – Static and transient • Electrical Noise • Mechanical Bending (Static and Cyclic) – Board-level strain • Random Vibration – PSD, exposure time, kurtosis • Harmonic Vibration – G and frequency • Mechanical shock – G, wave form, # of events 9000 Virginia Manor Rd Ste 290, Beltsville MD 20705 | 301-474-0607 | www.dfrsolutions.com 6
Humidity / Moisture (Rules of Thumb) • Non-condensing − Standard during operation, even in outdoor applications − Due to power dissipation • Condensing − Can occur in sleep mode or non-powered − Driven by mounting configuration (attached to something at lower temperature?) − Driven by rapid change in environment − Can lead to standing water if condensation on housing • Standing water − Indirect spray, dripping water, submersion, etc. − Often driven by packaging 9000 Virginia Manor Rd Ste 290, Beltsville MD 20705 | 301-474-0607 | www.dfrsolutions.com
Field Environment (BEST PRACTICE) • Use standards when… − Certain aspects of your environment are common − No access to use environment • Measures when… − Certain aspects of your environment are unique − Strong relationship with customer • Do not mistake test specifications for the actual use environment − Common mistake with vibration loads 9000 Virginia Manor Rd Ste 290, Beltsville MD 20705 | 301-474-0607 | www.dfrsolutions.com
Test Plan Development • Product test plans are critical to the success of a new product or technology • Stressful enough to identify defects • Show correlation to a realistic environment • DfR Solutions approach • Industry Standards + Physics of Failure • MIL-STD-810, • MIL-HDBK-310, • Results in an optimized test • SAE J1211, plan that is acceptable to management and • IPC-SM-785, customers • Telcordia GR3108, • IEC 60721-3, etc. • PoF! 9000 Virginia Manor Rd Ste 290, Beltsville MD 20705 | 301-474-0607 | www.dfrsolutions.com
KNOW YOUR ENVIRONMENT (CASE STUDY) • Leader in surgical systems for eyecare − Released latest system with foot pedal for ease of use • Failed to realize how customers would use foot pedal − Moving system across carpet without lifting up foot pedal created large static charges − Using foot pedal to pull system caused cable/connector failures 9000 Virginia Manor Rd Ste 290, Beltsville MD 20705 | 301-474-0607 | www.dfrsolutions.com
ELECTRICAL ENVIRONMENTS (CHARGING) • Often well defined in developed countries − Though, not as benign as always specified • Introduction into developing countries can sometimes cause surprises • Rules of thumb − China: Can have issues with grounding (connected to rebar?) − India: Numerous brownouts (several a day) − Mexico: Voltage surges 9000 Virginia Manor Rd Ste 290, Beltsville MD 20705 | 301-474-0607 | www.dfrsolutions.com
Failure History • Beta Determination Beta = 2.7628 Rho = 97.4 Beta of 3 for EOL if test data not available 9000 Virginia Manor Rd Ste 290, Beltsville MD 20705 | 301-474-0607 | www.dfrsolutions.com 12
Acceleration Factor • Determine the Acceleration Factor formula to use − The formula should be based on the failure mechanisms, but if not possible, then on the environments − Make it clear how the acceleration factor was determined − Determine the activation energy for the failure mechanism based on the materials involved. • Research may be necessary to determine the most applicable failure mechanisms depending on the environments. 9000 Virginia Manor Rd Ste 290, Beltsville MD 20705 | 301-474-0607 | www.dfrsolutions.com 13
Using Sherlock • In the Sherlock solder fatigue calculator you put in the information for the part most susceptible to failure. In this case a 2512 chip resistor. The calculation on the left defines a diurnal thermal cycle from 20-40C. The right a test cycle from -20 to 85C with 1 hour at each extreme. The diurnal calculation is 135,132 cycles to failure while the test is 4358 cycles. The acceleration is the diurnal divided by the test cycles = Af =31 14 9000 Virginia Manor Rd Ste 290, Beltsville MD 20705 | 301-474-0607 | www.dfrsolutions.com
Arrhenius H = t f A exp kT A = scaling constant H = activation energy (eV) = Boltzmann constant (8.62 x10 -5 eV/K) k T = temperature (K) • Widely used to describe variety of chemical reactions • Limited to temperature effects 9000 Virginia Manor Rd Ste 290, Beltsville MD 20705 | 301-474-0607 | www.dfrsolutions.com 15
Eyring H C E = + + + + + t f AT exp B S D S 1 2 kT T T • Extension of Arrhenius equation − Takes into account multiple stresses and synergy with temperature − Recommended by IPC SIR Handbook to determine acceleration factors for ECM • Too comprehensive? − Number of stresses undefined − Number of unknowns increases twice as fast as the number of stresses − Stress functions undefined (natural log, exponential, linear) 9000 Virginia Manor Rd Ste 290, Beltsville MD 20705 | 301-474-0607 | www.dfrsolutions.com 16
Peck ( ) − = − n t A RH f ( v ) exp E kT life 0 a t life = time to failure, A 0 = material constant RH = relative humidity, n = empirical constant (2.66) E a = activation energy, k = Boltzmann constant T = temperature, f(v) = voltage function (power law, ~1.5) • Galvanic corrosion of aluminum bond pads in encapsulated microcircuit Based on Eyring model – • Review of previous research Primary environments: 85/85, 110/85 – Voltages: 5 to 70 VC – 17 9000 Virginia Manor Rd Ste 290, Beltsville MD 20705 | 301-474-0607 | www.dfrsolutions.com
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