News Contacts

HDBK 217 Plus

HDBK 217 PLUS Reliability Prediction

Upgrade from legacy MIL-HDBK-217 standards with RIAC 217Plus™. Calculate component and system-level failure rates using additive operational, non-operational, and thermal cycling models.

CORE COMPONENT FORMULA
217Plus Inherent Failure Rate

Combines operating, non-operating, and thermal cycling stress states:

λP = λOπDCO + λNπDCN + λCπCR
*Expressed in Failures Per Million Calendar Hours (FPMCH).
Mathematical Model & Formulation

Unlike legacy multiplicative models, 217Plus uses an additive profile model to prevent extreme over-estimation of failure rates.

1. Component Level Failure Rate

The component model accounts for environmental operating conditions, dormancy, and power/thermal switching:

λPart = πG • [ (λOB • πDCO • πTO) + (λEB • πDCN • πDT) + (λTCB • πCR • πDT) ]
  • λOB, λEB, λTCB: Base failure rates for Operating, Dormant, and Thermal Cycling states.
  • πDCO, πDCN: Operational and Non-operational Duty Cycles.
  • πCR: Cycling Rate factor (cycles per hour).
  • πG: Reliability Growth factor based on manufacturing year.
2. System Level & Process Factors

Base component failure rates are summed and modified by Process Grade Factors (πProcess) accounting for non-inherent system risks:

λSystem = (∑ λPart) • (πA • πD • πM • πS • πI)
  • πA (Assembly Grade): Manufacturing quality & soldering compliance.
  • πD (Design Grade): Margin testing, derating, and simulation practices.
  • πM (Manufacturing): Process control and screening effectiveness.
  • πS, πI: System Environment and Infant Mortality metrics.
Real Worked Example: Industrial Microcontroller

Step-by-step 217Plus failure rate prediction and calendar-to-operating hour conversion.

Scenario Specification

Industrial Plastic Encapsulated Microcontroller (2020 Manufacture)

Operational Profile: 30% Duty Cycle
Step 1: Define Parameters
  • Operating Duty Cycle (πDCO) = 0.30 (30%)
  • Non-Operating Duty Cycle (πDCN) = 0.70 (70%)
  • Cycling Rate (πCR) = 1 cycle / day (0.0417 cycles/hr)
Step 2: Compute Contributions

Stress state contributions per 106 hours:

  • Operating Contribution (λOp) = 10.0 FPMCH
  • Non-Operating Contribution (λNon-Op) = 4.0 FPMCH
  • Cycling Contribution (λCycle) = 1.0 FPMCH
Step 3: Calendar Failure Rate

Summing profile contributions:

λCalendar = 10.0 + 4.0 + 1.0 = 15.0 FPMCH

(0.000015 failures per calendar hour)

Step 4: Operating Hours Rate

Divide calendar failure rate by the 30% duty cycle (0.30):

λOperating = 15.0 / 0.30 = 50.0 FPMCH

Equal to an MTBF of 20,000 Operating Hours.

Frequently Asked Questions About 217Plus

Key insights into RIAC 217Plus™ reliability prediction methodology, additive models, and process factors.

How does 217Plus differ from legacy MIL-HDBK-217?
217Plus uses additive stress models, whereas MIL-HDBK-217 uses multiplicative models. Legacy MIL-HDBK-217 multiplies stress factors together, which often results in unrealistically high failure rates under extreme conditions. 217Plus sums independent operating, non-operating, and thermal cycling failure rate contributions to provide far greater empirical accuracy.
What are 217Plus Process Grade Factors (πProcess)?
Process Grade Factors account for system-level non-inherent failure causes outside component stress. 217Plus evaluates organizational processes across Design (πD), Manufacturing (πM), Assembly (πA), System Environment (πS), and Infant Mortality (πI) to adjust baseline hardware failure rates.
What is the difference between Calendar and Operating Failure Rates in 217Plus?
Calendar failure rate evaluates total elapsed time (operating + dormant hours), while operating failure rate accounts for active uptime. Because 217Plus factors in dormancy (πDCN) and power cycling (πCR), operating failure rate is obtained by dividing total calendar failure rate by the active duty cycle (πDCO).
Why does 217Plus include a Reliability Growth Factor (πG)?
The Growth Factor (πG) adjusts baseline failure rates according to the component's year of manufacture. As semiconductor fabrication and component manufacturing processes improve over time, modern parts exhibit higher intrinsic reliability than parts built in earlier decades.
How does 217Plus handle Plastic Encapsulated Microcircuits (PEMs)?
217Plus includes dedicated empirical models tailored for commercial Plastic Encapsulated Microcircuits. Unlike older standards that heavily penalized non-hermetic packaging, 217Plus reflects modern resin quality, moisture resistance, and packaging improvements used in commercial off-the-shelf (COTS) devices.
Can 217Plus calculations be automated across large BOMs?
Yes, automated software like ALD RAM Commander models complete BOM hierarchies instantly. RAM Commander maps electrical stresses, thermal environments, duty cycles, and process grade factors across thousands of parts automatically without manual matrix calculations.