When should I use Norris-Landzberg instead?

When test and field differ in cycling frequency or in peak temperature, not just in swing size. Plain Coffin-Manson assumes those are equivalent, and accelerated chambers usually cycle far faster than the field.

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Coffin-Manson Thermal Cycling Calculator

Coffin-Manson models fatigue driven by repeated thermal expansion mismatch — most commonly solder joint cracking under temperature cycling. Life is governed by the size of the temperature swing, not the absolute temperature, which is why it is a cycling model rather than a steady-state one.

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Formula

Cycles to failureNf = C · (ΔT)^(−n)

Acceleration factorAF = (ΔT_test / ΔT_field)^n

Norris-Landzberg extensionAF = (ΔT_test/ΔT_field)^n · (f_field/f_test)^m · exp[(Ea/k)(1/T_max,field − 1/T_max,test)]

Adds cycling frequency and peak-temperature effects. Typical m ≈ 1/3.

Worked example

A board is cycled −40 °C to +100 °C (ΔT = 140 °C). The field environment cycles 10 °C to 50 °C (ΔT = 40 °C). Solder fatigue exponent n = 2.5.

AF = (140 / 40)^2.5 = 3.5^2.5
ln(3.5) = 1.2528; × 2.5 = 3.1320
AF = exp(3.1320) = 22.9
1000 test cycles ≈ 22,900 field cycles

If the field sees one cycle per day, 1000 test cycles represent about 63 years — almost certainly an over-test. If it sees 20 cycles per day, the same test covers about 3 years, which is a realistic qualification. The field cycle count matters as much as the acceleration factor.

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How to interpret the result

n ≈ 1.9–2.0	Eutectic tin-lead solder, commonly cited.
n ≈ 2.3–2.7	SAC lead-free solder alloys.
n ≈ 4–6	Brittle materials, ceramic and some wire-bond mechanisms.

Common mistakes

Using ΔT of the chamber rather than ΔT experienced at the joint. Thermal mass means the component may never reach chamber extremes — instrument the board.
Ignoring dwell time. Creep damage accumulates during the dwell, so a fast cycle with no dwell under-tests the mechanism.
Applying a solder exponent to a non-solder failure mode.
Comparing test cycles to field cycles without knowing the actual field cycle count, which is where most over- and under-testing originates.

Frequently asked questions

When should I use Norris-Landzberg instead?: When test and field differ in cycling frequency or in peak temperature, not just in swing size. Plain Coffin-Manson assumes those are equivalent, and accelerated chambers usually cycle far faster than the field.

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Coffin-Manson Model is part of a suite of 126 reliability, maintenance and quality engineering tools covering life data analysis, accelerated testing, system reliability, FMEA and root cause, SPC, and design for reliability. It runs in the browser and as native iOS and Android apps, so the same calculation is available at a desk or in front of the asset.

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