fiXtress Deep Dive: PCB Reliability Prediction and Automated Schematic Review

The Cost of Late Reliability Discovery

A reliability defect found during field deployment costs orders of magnitude more to fix than the same defect caught at the schematic level. An overstressed capacitor in a power supply filter, a transistor operating beyond its safe operating area under worst-case input voltage, a voltage regulator with insufficient thermal margin at maximum ambient temperature, these are design errors that will not appear in a functional verification test. The board will power up, pass all functional tests, and ship.

Six months later, field failures begin.

The root cause of most reliability-related field failures is not component quality, it is design margin. The component is used correctly according to the datasheet absolute maximum ratings, but the actual operating stress (voltage, current, power dissipation, junction temperature) leaves insufficient margin for the statistical variation in component parameters, environmental conditions, and aging effects. Catching these margin violations requires a systematic stress analysis at the schematic level, before the PCB is laid out and fabricated.

BQR’s fiXtress is the only commercially available tool that integrates automated schematic review, electrical stress calculation, thermal analysis, stress derating verification, and MTBF prediction in a single platform that operates as an add-on to existing EDA tools.

Automated Schematic Review (ASR)

fiXtress’s Automated Schematic Review module applies a database of design rules to the schematic netlist, checking for electrical errors that are invisible to standard Design Rule Checks (DRC). Standard DRC verifies connectivity, are all pins connected, are there floating nets, are there short circuits? ASR goes further: it checks whether the connections are electrically correct.

The rule database includes 17 major groups with approximately 15 sub-groups each, covering signal integrity, power distribution, protection circuits, bypass capacitor placement, pull-up and pull-down sizing, reset circuit design, clock distribution, and bus termination. Rules are not individual scripts that run sequentially, fiXtress evaluates all rules simultaneously, accounting for the interdependencies between components. A pull-up resistor’s stress depends on the bus voltage, the number of loads, and the input leakage current of each load. fiXtress resolves these dependencies automatically.

Engineers can extend the rule database with custom rules for application-specific requirements, ESD protection verification, safety-critical redundancy checks, or customer-specific derating standards.

Electrical Stress Analysis

The electrical stress modules, Rapid (calculation-based) and Precise (simulation-based), determine the actual voltage, current, and power dissipation for every component in the circuit under specified operating conditions. This requires knowing the input conditions: the power supply voltages (including tolerance), the signal characteristics at each connector (defined by the Interface Control Document or ICD), and the load characteristics.

fiXtress uses the ICD signals and their tolerances to perform a real stress analysis, not an approximation. This is a critical distinction. Tools that do not use the ICD assume nominal conditions at every interface, which misses the worst-case stress combinations that cause field failures. fiXtress propagates the actual power supply voltages and signal levels through the circuit, calculating the stress on every component under the defined operating conditions.

The Stress Derating Analysis (SDA) module compares the calculated stress against the applicable derating standard, MIL-STD-975, ECSS-Q-ST-30-11C, ESA/SCC, or a custom organizational standard. Every component that exceeds its derated limit is flagged with a quantified margin violation, enabling the designer to prioritize corrections by severity.

Thermal Analysis

fiXtress includes a thermal analysis module that estimates the average temperature rise over the PCB cold-plate or heatsink. This is not a full CFD thermal simulation, it is an analytical estimate that accounts for component power dissipation, board area, copper coverage, and cooling conditions. The purpose is to provide a first-order junction temperature estimate for the MTBF prediction, which is strongly temperature-dependent for most component failure rate models.

For designs where thermal management is critical, fiXtress’s thermal estimate identifies the components and board regions that require detailed thermal simulation with dedicated CFD tools. This triage approach saves engineering time by focusing expensive thermal simulation on the areas that matter.

MTBF Prediction

fiXtress supports all major MTBF prediction standards: MIL-HDBK-217F (Parts Count and Parts Stress methods), Telcordia SR-332 (RIAC 217Plus), IEC 62380, FIDES (2009 and 2014 editions), and NSWC Mechanical (for non-electronic components). The prediction uses the actual electrical and thermal stress calculated by the stress analysis modules, not assumed nominal conditions.

This integration between stress analysis and MTBF prediction is fiXtress’s key differentiator. Most standalone MTBF prediction tools require the engineer to manually enter the stress values for each component, a tedious, error-prone process for boards with hundreds or thousands of components. fiXtress calculates the stresses automatically and feeds them directly into the prediction model.

The resulting MTBF prediction is audit-ready for compliance with IEC 61508 (functional safety), ISO 26262 (automotive), and DO-254 (aerospace) certification frameworks. The prediction report includes the component-level failure rates, the stress factors, and the environmental adjustment factors, all the data a certification authority or customer reliability reviewer needs to verify the prediction.

Integration With CARE and apmOptimizer

fiXtress’s component-level failure rate and failure mode data exports directly to BQR’s CARE platform for system-level RAMS analysis, FMEA, FMECA, Fault Tree Analysis, and Reliability Block Diagrams. This eliminates the manual data transfer between design-phase reliability prediction and system-level safety analysis, reducing errors and maintaining traceability from component stress to system-level safety case.

Why Buy BQR fiXtress From GSAS

GSAS is BQR’s authorized engineering partner in India, providing fiXtress licenses with INR invoicing, installation, and application support. Our team in Bengaluru, Hyderabad, Chennai, Pune, Mumbai, and Delhi NCR assists with initial setup, EDA tool integration, custom derating standard configuration, and training for design and reliability engineers.

Contact sales@gsasindia.com or call +91 80 6590 1783 to discuss your reliability engineering requirements.