The recommended replacement for the MD90F18 is the SXF20FF3. The recommended replacement for the MD90U25 is the SXF6523. If the diodes are operated at full rated voltage, the voltage stressed between leads will exceed the general design guideline of 10V/mil in air. It is recommended that the isolation voltage between leads be increased through the use of a conformal coating, the use of a dielectric liquid or vapor.