IEC 62368-1 Edition 3.0 is an international standard that deals with safety requirements of audio/video, information and communication technology equipment. Clause 5.4.4 of the standard is about solid insulation. Even though sub-clause 5.4.4.2 says that there is no minimum DTI requirement for basic insulation and 0.4 mm minimum DTI for reinforced insulation but in the following sub-clause 5.4.4.4 which deals specifically with solid insulation requirements of semiconductor devices, the standard makes it absolutely clear that there is no minimum DTI requirement for reinforced components as long as they pass type tests and inspection criteria of clause 5.4.7 which basically subjects three samples to thermal cycling sequence. After thermal cycling, one sample is subjected to the electric strength test of clause 5.4.9.1 but the test voltage is multiplied by 1.6. In other words, a 60% margin is added on top of the already high transient voltage which could be 4kV_PEAK, 6 kV_PEAK or 8 kV_PEAK, for example. The other two samples are subjected to the same high voltage test with 60% margin after additional humidity conditioning test.

As an example, if we take a semiconductor component with material group I mold compound that has minimum 8 mm creepage and clearance distances and we try to determine its maximum basic and reinforced insulation working voltages at an altitude up to 2000 m, then we need to turn to Table 12 of IEC 62368-1 partially represented by Table 5-1. In this paper, we’ll assume that the intended end equipment operates in overvoltage category II and pollution degree 2 environment. Overvoltage category II equipment refers to pluggable or permanently connected equipment that is supplied from the building wiring. Pollution degree 2 refers to an environment where only non-conductive pollution occurs except that occasionally a temporary conductivity caused by condensation is to be expected.

AC mains voltage and thus semiconductor component’s working voltage goes up to 600 V_RMS according to Table 5-1 of IEC 62368-1 but we can refer to IEC 60664-1 for higher working voltages as this is allowed by the standard. Table 5-1 shows relationship between basic working voltage with respect to transient voltage. For overvoltage category II, 600 V_RMS working voltage corresponds to 4000 V_PEAK transient voltage for basic insulation. For reinforced insulation, the transient voltage has to be increased by one level to 6000 V_PEAK. Thus applying 60% margin to the transient voltage, we get 9600 V_PEAK or 6789 V_RMS voltage level that the 3 samples have to pass after thermal cycling and humidity conditioning tests in order to claim 600 V_RMS reinforced working voltage per IEC 62368-1. Similarly, for a higher working voltage, we refer to Table F.1 of IEC 60664-1 which has the next higher working voltage of 1000 V_RMS or V_DC and the corresponding overvoltage category II impulse withstand voltage is 6000 V_PEAK for basic insulation.

Therefore, this semiconductor device can claim 600 V_RMS reinforced and 1000 V_RMS basic insulation as long as it can pass 6789 V_RMS voltage withstand test after thermal cycling and humidity conditioning tests. To check that clearance and creepage requirements are also satisfied, we turn to Table 14 and Table 17 of the standard. According to Table 14, 6000 V_PEAK and 8000 V_PEAK withstand voltages are required for a component with minimum clearance of 8 mm for reinforced and basic insulation respectively. Similarly, Table 17 allows components with 8 mm creepage to have a maximum working voltage of 800 V_RMS for reinforced insulation and 1600 V_RMS for basic insulation. As we saw earlier, Table 5-1 further limits the working voltage based on overvoltage category and dielectric strength of the component with 60% margin applied.

In summary, as long as the semiconductor component can meet this stringent criteria of thermal cycling followed by 60% higher voltage withstand compared to rated voltage, it does not need to have a minimum DTI for basic or reinforced ratings.