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[6] Handling Guide
115
3.6 Protecting Devices in the Field
3.6.1 Temperature
Semiconductor devices are generally more sensitive to temperature than are other electronic
components. The various electrical characteristics of a semiconductor device are dependent on the
ambient temperature at which the device is used. It is therefore necessary to understand the
temperature characteristics of a device and to incorporate device derating into circuit design. Note
also that if a device is used above its maximum temperature rating, device deterioration is more rapid
and it will reach the end of its usable life sooner than expected.
3.6.2 Humidity
Resin-molded devices are sometimes improperly sealed. When these devices are used for an
extended period of time in a high-humidity environment, moisture can penetrate into the device and
cause chip degradation or malfunction. Furthermore, when devices are mounted on a regular printed
circuit board, the impedance between wiring components can decrease under high-humidity
conditions. In systems which require a high signal-source impedance, circuit board leakage or leakage
between device lead pins can cause malfunctions. The application of a moisture-proof treatment to the
device surface should be considered in this case. On the other hand, operation under low-humidity
conditions can damage a device due to the occurrence of electrostatic discharge. Unless damp-proofing
measures have been specifically taken, use devices only in environments with appropriate ambient
moisture levels (i.e. within a relative humidity range of 40% to 60%).
3.6.3 Corrosive Gases
Corrosive gases can cause chemical reactions in devices, degrading device characteristics.
For example, sulphur-bearing corrosive gases emanating from rubber placed near a device
(accompanied by condensation under high-humidity conditions) can corrode a device’s leads. The
resulting chemical reaction between leads forms foreign particles which can cause electrical leakage.
3.6.4 Radioactive and Cosmic Rays
Most industrial and consumer semiconductor devices are not designed with protection against
radioactive and cosmic rays. Devices used in aerospace equipment or in radioactive environments
must therefore be shielded.
3.6.5 Strong Electrical and Magnetic Fields
Devices exposed to strong magnetic fields can undergo a polarization phenomenon in their plastic
material, or within the chip, which gives rise to abnormal symptoms such as impedance changes or
increased leakage current. Failures have been reported in LSIs mounted near malfunctioning
deflection yokes in TV sets. In such cases the device’s installation location must be changed or the
device must be shielded against the electrical or magnetic field. Shielding against magnetism is
especially necessary for devices used in an alternating magnetic field because of the electromotive
forces generated in this type of environment.