Non-Contact Height Monitor
Original Publication Date: 1985-Oct-01
Included in the Prior Art Database: 2005-Feb-19
Variations in the height of surface features can be determined without direct contact by detecting the change in quantity of infrared radiation emitted from a limited surface area that is selectively heated by a remote energy source of fixed focus. In the figure, substrate 1 having a raised surface element 2, such as a solder pad, is moved under an infrared radiation detector 3 that provides an output signal proportional to the sensed energy. An infrared emitter 4, for example, a pulsed laser, is focused to heat a spot on the top surface of substrate 1 that lies wholly and directly under detector 3. When the surface height changes to that of the solder pad 2 only a fraction of the emitted radiation from the pad is detected because of the misalignment of detector 3 and heated spot.