Okay, I understand now. This Toshiba chip is oddly robust for how ridiculously small it is. Just as Doc has suggested, your mileage may vary.
Since this chip has no thermal protection other than the package and 175C overtemp circuit, the "paste" or "tape" is irrelevant. All you want to do is protect the MCU from the "EMF" or current backlash (AC) from the motor(s). Doc may have some suggestions better than my 1N4001 diode on your PWM output, but I do believe you are on your own on such a small device (298s or 293s have much more built into the device). Maybe somebody can suggest where to put the diode to get your reverse back 