How the rate of temperature change affects screen strength

Screen strength is the probability that a thermal-cycling screen precipitates a given latent defect. In the RADC (Rome Air Development Center) model used for environmental stress screening, screen strength rises with the temperature range, the number of cycles and the rate of temperature change at the product: a faster rate reaches the same screen strength in fewer cycles, so the screen takes less time.

The calculator below uses the RADC thermal cycling model as published in MIL-HDBK-344A, Environmental Stress Screening of Electronic Equipment. The chart shows how many cycles a screen needs to reach 90% screen strength as the rate of change rises, and the tables give screen strength for 2 to 6 cycles.

For more on what sets a product’s temperature change rate, read Understanding the temperature change rate factors.

Screen strength calculator

The RADC thermal cycling model, as used in MIL-HDBK-344A. Enter your screen; the result is the probability that it precipitates a latent defect the model applies to.

SS = 1 − exp(−0.0017 (R + 0.6)^0.6 [ln(e + r)]³ N), where R is the temperature range in °C, r the rate of temperature change in °C/min and N the number of cycles.

Faster rate, fewer cycles

Cycles a thermal cycling screen needs to reach 90% screen strength over a 100 °C temperature range, from the RADC model. The orange line marks the Hanse VTC product change rate*.
*Measured 4" above center of table, −65 °C to +100 °C.

Chart data

Rate of change (°C/min)	5	10	15	20	25	30	40	50	60	70
Cycles to 90%	10.0	5.2	3.6	2.8	2.3	2.0	1.6	1.4	1.2	1.1

Screen strength tables

Screen strength for 2 to 6 cycles by rate of change and temperature range, from the same model.

2 cycles

Screen strength for 2 cycles
Rate (°C/min) \ Range (°C)	20	40	60	80	100	120	140	180
5	0.1633	0.2349	0.2886	0.3324	0.3697	0.4023	0.4312	0.4809
10	0.2907	0.4031	0.4812	0.5410	0.5891	0.6290	0.6629	0.7173
15	0.3911	0.5254	0.6124	0.6752	0.7232	0.7612	0.7920	0.8388
20	0.4707	0.6155	0.7034	0.7636	0.8075	0.8407	0.8665	0.9037
30	0.5878	0.7359	0.8160	0.8659	0.8992	0.9226	0.9395	0.9616
40	0.6689	0.8100	0.8790	0.9184	0.9429	0.9589	0.9698	0.9829
50	0.7279	0.8585	0.9168	0.9477	0.9656	0.9767	0.9838	0.9917
60	0.7725	0.8918	0.9409	0.9651	0.9784	0.9861	0.9908	0.9957

3 cycles

Screen strength for 3 cycles
Rate (°C/min) \ Range (°C)	20	40	60	80	100	120	140	180
5	0.2346	0.3308	0.4000	0.4545	0.4996	0.5379	0.5710	0.6260
10	0.4026	0.5388	0.6263	0.6890	0.7366	0.7740	0.8042	0.8497
15	0.5248	0.6730	0.7587	0.8149	0.8544	0.8833	0.9052	0.9353
20	0.6149	0.7616	0.8385	0.8851	0.9155	0.9364	0.9512	0.9701
30	0.7353	0.8643	0.9211	0.9509	0.9680	0.9785	0.9851	0.9925
40	0.8095	0.9172	0.9579	0.9767	0.9863	0.9917	0.9947	0.9978
50	0.8581	0.9468	0.9760	0.9880	0.9936	0.9964	0.9979	0.9992
60	0.8915	0.9644	0.9856	0.9935	0.9968	0.9984	0.9991	0.9997

4 cycles

Screen strength for 4 cycles
Rate (°C/min) \ Range (°C)	20	40	60	80	100	120	140	180
5	0.2999	0.4147	0.4939	0.5543	0.6027	0.6427	0.6765	0.7305
10	0.4969	0.6437	0.7308	0.7893	0.8312	0.8624	0.8863	0.9201
15	0.6292	0.7748	0.8498	0.8945	0.9234	0.9430	0.9567	0.9740
20	0.7198	0.8522	0.9120	0.9441	0.9629	0.9746	0.9822	0.9907
30	0.8301	0.9302	0.9662	0.9820	0.9898	0.9940	0.9963	0.9985
40	0.8904	0.9639	0.9854	0.9933	0.9967	0.9983	0.9991	0.9997
50	0.9260	0.9800	0.9931	0.9973	0.9988	0.9995	0.9997	0.9999
60	0.9482	0.9883	0.9965	0.9988	0.9995	0.9998	0.9999	1.0000

5 cycles

Screen strength for 5 cycles
Rate (°C/min) \ Range (°C)	20	40	60	80	100	120	140	180
5	0.3595	0.4880	0.5731	0.6359	0.6846	0.7238	0.7560	0.8059
10	0.5763	0.7247	0.8061	0.8572	0.8918	0.9162	0.9340	0.9575
15	0.7107	0.8448	0.9065	0.9399	0.9597	0.9721	0.9803	0.9896
20	0.7962	0.9083	0.9521	0.9728	0.9837	0.9899	0.9935	0.9971
30	0.8909	0.9642	0.9855	0.9934	0.9968	0.9983	0.9991	0.9997
40	0.9369	0.9843	0.9949	0.9981	0.9992	0.9997	0.9998	1.0000
50	0.9614	0.9925	0.9980	0.9994	0.9998	0.9999	1.0000	1.0000
60	0.9753	0.9962	0.9992	0.9998	0.9999	1.0000	1.0000	1.0000

6 cycles

Screen strength for 6 cycles
Rate (°C/min) \ Range (°C)	20	40	60	80	100	120	140	180
5	0.4142	0.5522	0.6400	0.7025	0.7496	0.7864	0.8160	0.8601
10	0.6431	0.7873	0.8603	0.9033	0.9306	0.9489	0.9617	0.9774
15	0.7742	0.8931	0.9418	0.9657	0.9788	0.9864	0.9910	0.9958
20	0.8517	0.9432	0.9739	0.9868	0.9929	0.9960	0.9976	0.9991
30	0.9299	0.9816	0.9938	0.9976	0.9990	0.9995	0.9998	0.9999
40	0.9637	0.9931	0.9982	0.9995	0.9998	0.9999	1.0000	1.0000
50	0.9799	0.9972	0.9994	0.9999	1.0000	1.0000	1.0000	1.0000
60	0.9882	0.9987	0.9998	1.0000	1.0000	1.0000	1.0000	1.0000

Constant temperature screens

For a screen held at one temperature (burn-in), the RADC model uses the temperature range and the time instead of cycles and rate.

SS = 1 − exp(−0.0017 (R + 0.6)^0.6 t), where R is the temperature range in °C and t the time in hours.