Motorola VSWR, Service Manual Supplement

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Devices sensitive to static
5th Feb 99
12
Service Manual Supplement: VSWR Monitor for M-Cell 6
68P02900W86-O
Devices sensitive to static
Introduction
Certain metal oxide semiconductor (MOS) devices embody in their design a thin layer of
insulation that is susceptible to damage from electrostatic charge. Such a charge applied
to the leads of the device could cause irreparable damage.
These charges can be built up on nylon overalls, by friction, by pushing the hands into
high insulation packing material or by use of unearthed soldering irons.
MOS devices are normally despatched from the manufacturers with the leads shorted
together, for example, by metal foil eyelets, wire strapping, or by inserting the leads into
conductive plastic foam. Provided the leads are shorted it is safe to handle the device.
Special handling
techniques
In the event of one of these devices having to be replaced observe the following
precautions when handling the replacement:
S
Always wear an earth strap which must be connected to the electrostatic point
(ESP) on the equipment.
S
Leave the short circuit on the leads until the last moment. It may be necessary to
replace the conductive foam by a piece of wire to enable the device to be fitted.
S
Do not wear outer clothing made of nylon or similar man made material. A cotton
overall is preferable.
S
If possible work on an earthed metal surface. Wipe insulated plastic work surfaces
with an anti-static cloth before starting the operation.
S
All metal tools should be used and when not in use they should be placed on an
earthed surface.
S
Take care when removing components connected to electrostatic sensitive
devices. These components may be providing protection to the device.
When mounted onto printed circuit boards (PCBs), MOS devices are normally less
susceptible to electrostatic damage. However PCBs should be handled with care,
preferably by their edges and not by their tracks and pins, they should be transferred
directly from their packing to the equipment (or the other way around) and never left
exposed on the workbench.