Metal-lined package cavity for fluid sensors

A sensing system, comprising:

• a semiconductor die including a device side and a fluid sensor in the device side;
• a first metal ring forming an opening configured to be in fluidic communication with the fluid sensor, the first metal ring having a first top surface, a first bottom surface, and a first inner surface extending between the first top surface and the first bottom surface, the first bottom surface being on the device side, and at least part of the first inner surface abutting the device side being plated with a first noble metal;
• a second metal ring around the first metal ring, the second metal ring having a second top surface, a second bottom surface, and a second inner surface extending between the second top surface and the second bottom surface, the second bottom surface being on the device side, and at least part of the second inner surface being plated with a second noble metal;
• and
• a mold compound covering the semiconductor die and a first portion of the second metal ring, in which a second portion of the second metal ring having the second top surface protrudes out of the mold compound.

A method for manufacturing a sensing device, comprising:

• depositing a photoresist layer on a first surface of a semiconductor die, the first surface including a sensor;
• exposing and developing the photoresist layer to produce a central photoresist member, a ring-shaped photoresist member surrounding the central photoresist member, and a ring-shaped cavity between the central photoresist member and the ring-shaped photoresist member, the central photoresist member contacting the sensor;
• plating a metal ring in the ring-shaped cavity, the metal ring including a first portion having a first lateral thickness and a second portion having a variable lateral thickness;
• removing the central photoresist member and the ring-shaped photoresist member;
• plating a noble metal on at least an inner surface of the metal ring abutting the first surface;
• and
• applying a mold compound to the first surface and to the metal ring, a top surface of the metal ring at least partially exposed through the mold compound.