520.495/580.495 Microfabrication Laboratory

Laboratory Assignment #9

The final step in our process is the packaging of the pressure sensors. The chips will be separated from the wafer, then epoxied into packages. Our packages will be simple printed circuit boards with copper wire patterns etched on them. The wire bonder will be used to make connections from the bond pads on the chip to the leads of the package. The wafers have been scribed using a wafer scriber, a device which drags a diamond tipped tool across the wafer to score the surface. When flexed sufficiently the wafer will break along this line.

I. Dicing the wafer

1.         Place your wafer (or what remains of it!) face down on a clean filter paper, on a piece of rubber mat, noting the orientation and location of the scribe lines. Position a pencil over the scribe line and press down gently. Rock the pencil back and forth while increasing the downward pressure until the wafer breaks. Repeat this until the individual chips are obtained.

2.         Inspect the individual chips and try to pick the best one or two for packaging.

II. Mounting the chip in the package

1.         Mix up the epoxy following the instructions provided by the TA.

2.         Place the chip face down on a clean piece of filter paper, and apply a small bead of epoxy around the rim of the cavity. You should use just enough epoxy to insure a leakproof seal between the bottom of the chip and the package. Using tweezers, carefully place the chip in the package.

3.         Cure the epoxy at the time and temperature specified by the TA.

III. Wire bonding

1.         Instructions on the use of the wire bonder will be provided during the lab session.