Hello dear Milan Kumar Bera,

You can try a caustic etching procedure, using a mixture of hexylene glycol and sodium hydroxide (Isoprep 177), at 95 °C for 1-3 minutes. Prior to caustic etching, you must clean Kapton surface to remove all impurities, soap cleaning follows by acetone/ethanol bath and air dry must be enough.

P.S. You can try different etching times according to your needs.

Regards!