Environmental and Human Inputs#

A circuit on the bench exists in a controlled environment. The room temperature is 22°C. The air is still. The power comes from a lab supply with sub-millivolt ripple. The only signals present are the ones deliberately applied. The only loads are the ones intentionally connected. Nothing is vibrating, nothing is corroding, and no one is unplugging cables during data transfers.

A system in the field exists in an uncontrolled environment. Temperature varies by 60°C between seasons (or by 40°C between morning and afternoon in a vehicle). Power comes from a wall outlet, a battery, a solar panel, or a generator — each with its own voltage range, noise profile, and transient behavior. The air carries humidity, salt, dust, and conducted vibration from nearby machinery. Cables are connected and disconnected by people who don’t read specifications. The environment is an input to the system whether the design accounts for it or not.

Temperature#

Temperature affects nearly every electrical parameter. Resistance changes with temperature (positive tempco for metals, negative for most semiconductors). Capacitance changes with temperature (ceramics can lose 50% or more of their capacitance at temperature extremes, depending on dielectric class). Semiconductor parameters shift — threshold voltages decrease with increasing temperature, leakage currents increase exponentially, and gain-bandwidth products change. Crystal oscillator frequencies drift. Battery capacity decreases in cold. Solder joints fatigue under thermal cycling.

The practical range matters enormously:

Consumer electronics: 0°C to +40°C ambient. Components specified for commercial temperature range.
Industrial equipment: −40°C to +85°C ambient. Components specified for industrial temperature range. The full range is 125°C span — every temperature-sensitive parameter shifts significantly across this range.
Automotive: −40°C to +125°C (or +150°C near the engine). Extended temperature range components required. The combination of wide range and thermal cycling creates reliability challenges that don’t exist in benign environments.

Temperature doesn’t just shift parameters — it creates gradients. One side of a PCB may be 20°C hotter than the other due to proximity to a heat source. Thermal gradients across a precision resistor network create thermoelectric voltages (Seebeck effect) that appear as DC offsets — microvolts per degree of temperature difference across dissimilar metal junctions. In precision analog circuits, thermal gradients can introduce errors larger than the circuit’s intended resolution.

Vibration and Mechanical Stress#

Electronic systems experience mechanical forces: vibration from motors, fans, vehicles, and building infrastructure; shock from drops, door slams, and transportation; sustained mechanical stress from mounting hardware, cable weight, and thermal expansion.

Mechanical forces affect electronics through several mechanisms:

Solder joint fatigue. Thermal cycling and vibration create cyclic mechanical stress on solder joints. BGA (ball grid array) packages are particularly susceptible because the solder balls are the only mechanical connection between the IC and the PCB, and thermal expansion mismatch between the IC substrate and the PCB creates shear stress on every thermal cycle. After enough cycles — hundreds to thousands in harsh environments — the solder balls crack, creating intermittent connections.

Microphonics. Mechanical vibration modulates the electrical characteristics of components. Ceramic capacitors are piezoelectric — mechanical stress generates voltage, and voltage generates mechanical stress. A ceramic capacitor on a supply rail that experiences vibration generates a voltage signal at the vibration frequency. This effect is typically small (microvolts) but can be significant in high-gain audio circuits or precision sensor circuits. MEMS devices (accelerometers, gyroscopes, microphones) are intentionally sensitive to mechanical input but can’t distinguish between intended and unintended vibration sources.

Connector reliability. Connectors experience insertion and removal forces, vibration, and corrosion. Each mechanism degrades the contact resistance over time. A connector with increased contact resistance creates a voltage drop that varies with current — an intermittent and load-dependent failure that’s extremely difficult to diagnose remotely.

Power Quality#

Bench power supplies deliver stable, clean power. Field power sources deliver whatever the physics of the installation provides:

AC mains power varies in voltage (nominally ±10% but wider during brownouts and surges), carries high-frequency noise from other equipment on the same circuit, and can have brief interruptions (sags and swells) lasting milliseconds. Lightning strikes on the distribution network create transients of thousands of volts lasting microseconds. AC-DC power supplies must handle all of these conditions and present a stable DC output to the system — a demanding filtering and regulation task.

Battery power varies with state of charge (a lithium-ion cell ranges from 4.2 V fully charged to 3.0 V discharged), with load (internal resistance causes voltage sag under high current), and with temperature (internal resistance increases in cold, reducing the effective voltage under load). Battery-powered systems experience a slowly declining supply voltage that the circuit must tolerate across the full range, plus transient sags during high-current events.

Vehicle power (12 V or 24 V automotive systems) is notoriously hostile: load dump transients (up to 60 V or higher when a large inductive load is disconnected), cranking voltage sags (down to 4–6 V during engine start), and alternator ripple. Automotive electronics must survive conditions that would destroy components designed for benign environments.

Industrial power may include ground loops between equipment, conducted noise from variable-frequency motor drives, and power interruptions during load switching. The power environment in a factory is defined by everything else connected to the same electrical infrastructure.

Humidity and Corrosion#

Moisture affects electronics through several mechanisms:

Leakage current. Water condensation on a PCB creates conductive paths between traces. At board-level spacings (0.1–0.5 mm), even a thin moisture film provides a leakage path that can draw microamps — enough to affect high-impedance circuits, bias sensitive inputs, or drain battery-powered systems. The leakage is resistance-dependent on the contamination level: a clean board with condensation has higher resistance (megohms) than a board contaminated with flux residue, salt, or finger oils (kilohms or less).

Corrosion. Sustained humidity accelerates electrochemical corrosion of copper traces, solder joints, and connector contacts. Corrosion increases resistance, introduces noise (the corroded junction behaves as a poor contact), and can eventually cause open circuits. Salt-laden environments (coastal, marine, road salt exposure) dramatically accelerate corrosion.

Dielectric absorption and degradation. Moisture absorbed into PCB substrate materials changes the dielectric constant and loss tangent, affecting high-frequency signal propagation and increasing dielectric losses. In extreme cases, moisture absorption leads to delamination — separation of PCB layers — which can crack internal vias and traces.

Human Inputs#

Humans interact with electronic systems in ways that are difficult to fully anticipate:

Hot insertion. Connecting or disconnecting cables and modules while the system is powered. Hot insertion creates transients — the contact bounce of the connector generates rapid voltage changes, the cable’s capacitance presents a sudden load that the supply must charge, and the ground connection may be established before or after the signal connections (depending on pin lengths), creating a period of undefined reference.

Incorrect connections. Reversed polarity, wrong cables, incorrect pin assignments. Despite keyed connectors and labeling, incorrect connections happen. The system’s response to incorrect connections — surviving without damage versus suffering immediate destruction — depends on protection circuitry that’s part of the system design.

Out-of-sequence operations. Turning on equipment in the wrong order, pressing buttons at unexpected times, removing storage media during write operations. Human operators don’t follow power sequencing specifications — they follow convenience, habit, and impatience.

Maintenance and modification. Replacing components with incorrect substitutes, cleaning with solvents that damage conformal coatings, using ESD-unsafe procedures. Each human intervention introduces a potential for altered conditions that the original design didn’t anticipate.

Tips#

Environmental specifications should be derived from the actual deployment conditions, not assumed from the component ratings. A device using commercial-temperature components deployed in an industrial environment will eventually encounter temperatures outside its capability — the specifications must match the environment, not the component catalog.
For systems operating in variable-temperature environments, test at the temperature extremes simultaneously — hottest conditions with maximum load, coldest conditions with startup. Many failures occur only at the combination of extreme temperature and specific operating conditions.
When deploying in environments with poor power quality, measure the actual power conditions at the installation site before specifying the power input requirements. Assumptions about “typical” mains quality or “typical” battery voltage don’t cover the transients, sags, and noise that exist in specific installations.
Conformal coating, potting, and environmental sealing protect against humidity and contamination, but they also affect thermal management. Coating a PCB reduces convective cooling from the board surface. This tradeoff must be evaluated — protecting against moisture while overheating is not a net improvement.

Caveats#

Component ratings are not system ratings — A component rated for −40°C to +85°C operating temperature guarantees the component meets its specifications across that range. It does not guarantee the system works across that range. The system’s temperature margin depends on all components’ deratings, their interactions, and the thermal management design.
Environmental failures are often intermittent — A thermal-cycling fatigue crack in a solder joint opens and closes with temperature. A moisture-related leakage path dries out in warm conditions. A vibration-related connector failure depends on the vibration frequency and amplitude. These intermittent failures are among the hardest to diagnose because they can’t be reproduced on command.
Environmental testing in a chamber doesn’t replicate the field — A temperature chamber provides uniform, controlled temperature. The field provides thermal gradients, air movement, sun exposure, and vibration — simultaneously. Chamber testing validates individual environmental parameters; field exposure validates the combination.
Human behavior can’t be fully specified — No amount of documentation, labeling, or training eliminates the possibility of incorrect human interaction. System design should assume that every connector will be plugged in wrong at least once, every button will be pressed at the wrong time, and every removable component will be removed at the most destructive moment.