Aloka ProSound Alpha 10, Руководство по обслуживанию, Страница: 17 / 405

MN2-2008
SECTION 2
PRECAUTIONS
2 - 4
2-10 Handling of S.M.D. PCBs
It is an Aloka's policy that neither repair nor modification of PCBs used for S.M.D. is made in the field
as a rule because of the following reasons:
[REMARKS] PCB does not need repairing or modifying in the field as a rule.
When handling a PCB, do not touch the IC unless it is necessary.
IC soiled with worker’s hands may cause corrosion. Additionally, foreign particles such as fine solder
dust could be the cause of short-circuited IC lead wires whose pitch is smaller than that of the traditional
ones.
# CAUTION #
When handling a PCB, avoid touching the IC and connector pins on the
devices to prevent ESD (Electro Static Discharge) damage.
A service person should preferably wear an ESD wrist strap correctly
grounded when handling a PCB.
Do not give excessively large shocks to the PCB.
When replacing the ROM (Read Only Memory) on the PCB, attempting to force the ROM into its
socket would cause the PCB to be subjected to an undue force, and the following faults may :
1) Damage to PCB intermediate-layer patterns,
2) Peeling of chip devices (resistor, capacitor, diode, etc.),
3) Damage to a junction between electrode and internal element of chip devices,
4) Peeling of patterns (especially those for mounting the parts) together with chip devices since those
patterns are rather fragile compared with PCBs used before now, and
5) Damage to parts on the reverse side in the case of PCBs of both-side mounting type.
Also, a PCB mounted improperly or a warped PCB mounted as it is may cause the chip devices to come
off and the fine patterns to be cut.
Additionally, reuse of chip devices (including resistors, capacitors, diodes, etc.) is strictly inhibited
because of the following reason:
Since the chip devices are lacking in lead wires, such as those found in the traditional component parts,
heat given to the PCB will be directly conducted to the inside of chip devices.
As a result, a thermal
stress will occur due to a difference in thermal expansion coefficient between each chip device and PCB,
giving rise of the possibility of cracks inside of or on the surface of chip devices or the possibility of
thermal breaking (internal burning).
Very thin wiring patterns require extreme care in handling of the PCB.
Be sure to observe the precautions mentioned above also to prevent the secondary accidents.