1. Current Rating Difference: BTA08 (8A RMS) offers a 33% higher steady-state current capability than BTA06 (6A RMS). If the original design's load current exceeds 6A or approaches 8A, direct substitution may cause BTA06 to overheat and fail. The actual operating current must be confirmed with sufficient margin maintained (recommended for applications ≤4.8A). 2. Gate Trigger Sensitivity Difference: BTA06 features a logic-level gate (Igt ≤ 5mA, Vgt ≤ 1.3V), while BTA08 has a standard gate (Igt ≤ 35mA, Vgt ≤ 1.1V). BTA06 can be driven directly by a microcontroller or digital logic circuit, whereas BTA08 typically requires an isolated driver circuit. The trigger circuit must be redesigned for substitution: if the original circuit has weak drive capability (e.g., MCU direct connection), BTA06 is preferable; if the original circuit has strong drive (e.g., via a pulse transformer), BTA06 may require a current-limiting resistor to prevent gate overstress. 3. Surge Current Capability Difference: BTA08's Itsm (90A @60Hz) is significantly higher than BTA06's (60-63A). In surge scenarios such as capacitive loads or motor startup, BTA06 has weaker transient overload capability and may be damaged by inrush current. The load's transient characteristics must be assessed. 4. Holding Current Difference: BTA06's Ih (10mA) is lower than BTA08's (35mA). BTA06 maintains conduction more easily under low-current loads but is more sensitive to circuit leakage current during turn-off, potentially causing unintended latching in low-power resistive loads or low conduction angle applications. Substitution Recommendation: Substitution is only viable when the actual operating current is ≤6A and the trigger circuit is compatible with a logic-level gate. Focused verification of surge protection and turn-off reliability is essential. If the original design relies on high Itsm or high Ih characteristics, the substitution risk is significant.