Packaging method for an electronic element

A packaging method for an electronic element, comprising the steps of:

• etching portions of a top surface of a metal board made of copper to form several recesses between raised unetched segments and filling the recesses with a dielectric material of high metal density polymer while keeping the raised unetched segments exposed;
• forming multiple solder balls in contact with the raised unetched segments by printing;
• coating the solder balls with a thin metal paste layer;
• bonding contacts on a die respectively to the solder balls with the thin metal paste layer;
• injecting an underfill between the die and the metal board;
• sealing the die with an outer encapsulant;
• etching a bottom surface of the metal board to form multiple metal leads;
• coating the metal leads with a metal layer;
• attaching an isolator between the metal leads;
• coating the bottom surface of the metal board other than the metal leads with a solder resist;
• and
• conducting a continuity test.