Stress isolated bulk acoustic wave resonator dies

A semiconductor package, comprising:

• a portion of a lead frame;
• a first semiconductor die coupled to the portion of the lead frame, the first semiconductor die having a first device side in which first circuitry is formed and a first non-device side opposite the first device side;
• a second semiconductor die coupled to the first device side of the first semiconductor die, the second semiconductor die having a second device side in which second circuitry is formed and a second non-device side opposite the second device side, the second semiconductor die having four lateral surfaces orthogonal to the second device side;
• a polymer coat physically contacting the four lateral surfaces and the second non-device side, the polymer coat not covering an entirety of the second device side;
• a trench in the second device side and circumscribing the second circuitry;
• a cavity in the second semiconductor die and below the second circuitry;
• a polymer wall circumscribing the trench and extending vertically away from the second device side;
• a mold compound covering the first and second semiconductor dies and physically contacting an outer surface of the polymer wall;
• and
• an epoxy film contacting a top surface of the polymer wall and a top surface of the mold compound.

A method for manufacturing a semiconductor package, comprising:

• etching through a thickness of a semiconductor wafer using a patterned photoresist to form multiple semiconductor dies separated by multiple gaps, each of the multiple semiconductor dies having a device side in which circuitry is formed and a non-device side opposite the device side, each of the multiple semiconductor dies including a trench circumscribing the circuitry and a cavity in that semiconductor die between the circuitry of that semiconductor die and the non-device side of that semiconductor die;
• depositing a polymer material into the multiple gaps and on the non-device sides of the semiconductor dies;
• dicing through the polymer material in one of the multiple gaps to produce a first semiconductor die separate from the remaining ones of the multiple semiconductor dies;
• coupling a second semiconductor die to a portion of a lead frame;
• coupling the first semiconductor die to the second semiconductor die;
• and
• applying a mold compound to the portion of the lead frame, the second semiconductor die, and the first semiconductor die.