Page 152 - Sensors and Control Systems in Manufacturing

Classification and Types of Sensors
engineers can use them to carefully quantify the effects of variables 113
such as probe force to determine the best operational window for
their process.

2.11.3 Probe-Mark Inspection Requirements
The probe-mark inspection process must be capable of evaluating a
number of quantitative and qualitative characteristics. Quantitative
measures include size, location within the pad, proximity to the
edge of the pad, orientation relative to the center of the pad, and
orientation trends across the wafer. Qualitative indicators include
over-etch and under-etch, pitting, corrosion, abrasion, roughness,
and punch-through. Advanced automatic defect classification (ADC)
that makes efficient use of all available input to provide fast accurate
classification is a practical requirement for probe-mark inspection in
a production environment.

2.11.4 Multi-Chip Packages
The use of multi-chip packages is increasing, driven primarily by
consumer demand for larger memory, multifunction handheld
devices, and increased electronic capabilities in automobiles. The pri-
mary first-level interconnect technology in multi-chip packages is
wire bonding. Probe marks created by electrical testing are a primary
cause of failure in wire bonds. Probe-mark inspection is playing an
increasingly important role in maintaining the yield and reliability of
wire.

2.12 Understanding Laser Sensors
Two theories about the nature of light have been recognized. The par-
ticle theory was the first presented to explain the phenomena that
were observed concerning light. According to this theory, light is a
particle with mass, producing reflected beams. It was believed that
light sources actually generated large quantities of these particles.
Through the years, however, many phenomena of light could not be
explained by the particle theory, such as reflection of light as it passes
through optically transparent materials.
The second theory considered that light was a wave, traveling
with characteristics similar to those of water waves. Many, but not all,
phenomena of light can be explained by this theory.
A dual theory of light has been proposed, and is presently consid-
ered to be the true explanation of light propagation. This theory sug-
gests that light travels in small packets of wave energy called photons.
Even though photons are bundles of wave energy, they have momen-
tum like particles of mass. Thus, light is wave energy traveling with
some of the characteristics of a moving particle. The total transmitted
as light is the sum of energies of all the individual photons emitted.