A single unpackaged silicon die, cut straight from a wafer, is glued directly onto the circuit board. Skipping the usual plastic package makes the calculator cheaper, lighter and thinner.

A wire bonder welds fine wire leads from each pad on the die to traces on the board. These leads are far too delicate to touch afterward.

A drop of epoxy is dispensed over the die and its wires and cured hard. That black bump is what you see if you open a cheap calculator, and it keeps out moisture and fingerprints.

Silicone rubber is compression molded into a single mat of keys, each on a thin flexing web. A conductive carbon pill on the underside of every key touches two interleaved traces on the board when pressed.

A small liquid-crystal display is clamped above the board with a rubber connector between them. Its stripes alternate thin conductive and insulating layers, so each pad on the glass finds its matching pad on the board without solder.

A strip of amorphous silicon solar cell is wired in above the display, a button cell is clipped in below, or both. An LCD and a low-power chip need so little current that indoor light can be enough.

The keypad, board and display stack into a molded plastic case with printed key legends. The back clips or screws on, and each unit is tested key by key.