tmp1940cyaf TOSHIBA Semiconductor CORPORATION, tmp1940cyaf Datasheet - Page 36

• Manufacturer Part Number: tmp1940cyaf
• Description: 32-bit Tx System Risc Tx19 Family
• Manufacturer: TOSHIBA Semiconductor CORPORATION

3.6
3.6.1
3.6.2
3.6.3
3.6.4
3.6.5
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.
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%).
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.
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.
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.
Protecting Devices in the Field
Temperature
Humidity
Corrosive gases
Radioactive and cosmic rays
Strong electrical and magnetic fields
3 General Safety Precautions and Usage Considerations
22