The
Background
For 20 years, the information revolution has been built
on the sand silicon based chip. Each year, by cramming more circuits
on a memory or microprocessor chip, engineers have made computing
technology cheaper, more plentiful and more adaptable to new uses.
Smaller has always been better, yet never good enough. With the chip
becoming the size of a thumbtack, the size of printed circuit boards,
or PCBs, is also getting smaller.
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The Process
The circuit board in it's simplest form is a piece
of insulating material, such as epoxy or phenolic resins, on which
chips (integrated circuits) and other electronic components are
mounted and interconnected to form a circuit. Most modern circuit
boards use patterns of copper foil to interconnect the components.
The foil layers may be on one or both sides of the board and, in
more advanced designs, in several layers within the board.
Photosensitive polymer compounds
called photo-resistors are applied to the surface to selectively
mask circuit lines for the etching process. The hygroscopic nature
of these compounds can cause the adsorbed moisture to make cuts
in the bridging of microscopic circuit lines, resulting in circuit
failures. The relative humidity of air in the photolithography clean
rooms where etching is done is therefore maintained at controlled
levels. For best results clean rooms are generally maintained at
20% to 35% Relative Humidity at 20ºC.
Moisture control is also absolutely essential when
quartz crystals are incorporated with the printed circuit boards.
The quartz crystal boards, after assembly, are put through an aging
process during which time the humidity level must be carefully controlled
to prevent the crystal from absorbing water vapour.
The Problem
Exposure to high humidity can lead to corrosion on
the surface of the circuits. This is known as microscopic corrosion.
Even minute layers of corrosion can increase electrical resistance
and decrease capacitance, affecting performance. Excessive
moisture, therefore, causes adhesion failures, surface defects and
decreased performance. In fact, the smaller and denser the microcircuit,
the larger the problem in performance.
The Solution
Desiccant Dehumidifiers provide the ideal low humidity
environment in the manufacture, assembly and storage of these precision,
high quality electronic Printed Circuit Boards, since they are capable
of maintaining RH as low as 1% or even lower at a constant level,regardless
of ambient conditions.
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