Echelon Series 6000 Chip databook - Manual (Page 160)

because they appear as intermittent failures or as degraded performance. Static damage can
often increase leakage currents.
CMOS devices are not immune to large static voltage discharges that can be generated
during handling. For example, static voltages generated by a person walking across a waxed
floor have been measured in the 4 kV – 15 kV range (depending on humidity, surface
conditions, and so on). Therefore, you should observe the following general precautions:
1. Do not exceed the maximum ratings specified by the data sheet.
2. All unused device inputs should be connected to V
DD
or GND.
3. All low-impedance equipment (for example, pulse generators) should be connected to
CMOS inputs only after the device is powered up. Similarly, this type of equipment
should be disconnected before power is turned off.
4. A circuit board containing CMOS devices is merely an extension of the device, and
the same handling precautions apply. Contacting connectors wired directly to
devices can cause damage. Plastic wrapping should be avoided. When external
connections to a PC board address pins of CMOS integrated circuits, a resistor should
be used in series with the inputs or outputs. The limiting factor for the series
resistor is the added delay caused by the time constant formed by the series resistor
and input capacitance. This resistor will help limit accidental damage if the PC
board is removed and is brought into contact with static-generating materials. For
convenience, Figure 55 describes equations for added propagation delay and rise-time
effects due to series-resistance size.
5. All CMOS devices should be stored or transported in materials that are antistatic.
Devices must not be inserted into conventional plastic “snow,” Styrofoam ® , or plastic
trays. Devices should be left in their original container until ready for use.
6. All CMOS devices should be placed on a grounded bench surface and operators
should ground themselves prior to handling devices, because a worker can be
statically charged with respect to the bench surface. Wrist straps in contact with
skin are strongly recommended. See Figure 56.
7. Nylon or other static-generating materials should not come in contact with CMOS
circuits.
8. If automatic handling is being used, high levels of static electricity can be generated
by the movement of devices, belts, or boards. Reduce static build-up by using ionized
air blowers or room humidifiers. All parts of machines that come into contact with
the top, bottom, and sides of IC packages must be grounded metal or other conductive
material.
9. Cold chambers that use CO
2
for cooling should be equipped with baffles, and devices
must be contained on or in conductive material, or soldered onto a PCB.
10. When lead-straightening or hand-soldering is necessary, provide ground straps for
the apparatus used and be sure that soldering ties are grounded.
11. The following precautions apply during wave-solder operations:
a. The solder pot and conductive conveyor system of the wave-soldering
machine must be grounded to an Earth ground.
b. The loading and unloading work benches should have conductive tops which
are grounded to an Earth ground.
c. Operators must comply with precautions previously explained.
148 Handling and Manufacturing Guidelines