IPC-CM-770D-1996 - 第136页

IPC-CM-770 Januaty 1996 5-34 COPYRIGHT Association Connecting Electronics Industries Licensed by Information Handling Services COPYRIGHT Association Connecting Electronics Industries Licensed by Information Handling Serv…

January

1996

IPC-CM-770

IPc-I-00050

Figure 25-11 Panel Assembly Tooling Holes

IPC-1-00361

Figure 25-12 Positive Symbol Machine Correction

PCB

Layout:

Spacing

Wave Solder

-7

&%?I

IPC-1-00362

Figure 25-13 Chip Placement

5-33

Licensed by Information Handling Services

IPC-CM-770

Januaty

1996

5-34

Licensed by Information Handling Services

January 1996 IPC-CM-770

Part

Six

Related Subjects

26.0 HANDLING AND STORAGE

26.1 General Considerations

The following general

rules should be practiced when handling printed board

assemblies:

Work stations should be kept clean and neat.

There should be no eating or drinking in the work area,

to prevent contamination of the board assemblies.

Handling of the edgeboard contacts should be avoided.

Hand creams and lotions containing silicone should not

be used since they can result in solderability problems.

Lotions formulated specially for use in solder assembly

areas are available.

Stacking of board assemblies should be avoided to pre-

vent physical damage to components. Special racks are

normally provided in assembly areas create contamina-

tion; therefore, changes should be made as frequently as

necessary.

In areas where electrostatic discharge may damage sensi-

tive components, all handling and assembly should be

performed at an antistatic work station.

Caution: Certain substrates and unsealed components such

as some switches, power modules, adjustable devices, etc.,

may be damaged by cleaning agents. Care must be taken to

identify and protect these types of components through the

cleaning process.

26.2 Electrostatic Discharge (ESD) Protection

ESD is

the abbreviation for the term “Electrostatic Discharge,” a

phenomena produced by contact and separation of unlike

materials. Some common examples of activities which gen-

erate ESD are:

Walking across carpet

Combing hair

Rubbing wool against nylons

a result of these phenomena, high voltages (upward of

5,000

volts) are created which, when touching another con-

ductive surface, may create a discharge capable of damag-

ing miniature electronic components and components

mounted on printed boards.

The potentially damaging effects of ESD can be avoided

by:

Grounding personnel and components to avoid an electro-

static charge buildup.

Ionizing sources

Humidity control

Proper handling procedures

The approximate range of susceptibility to damage by

static discharge for several components is shown in the

Table

26-

Table 26-1 Susceptibility Ranges of Various Devices

Exposed to Electrostatic Discharge from a Person or

Electronic Equivalent

Range

Minimum

ESD

Device Type

Susceptibility (Volts)

VMOS

1000 to 2500 Schottky TTL

680 to 1000 SCR

500 to 1500 ECL (PDC Board Level)

380 to

7800

Bipolar Transistors

300 to 3000 Film Resistors (Thick, Thin)

300 to 2500 Schottky Diodes

250 to 3000 CMOS

190 to 2500 OP AMP

150 to 500 SAW

140 to 7000 J FET

100 PLUS EPROM

100 to 300 GaAsFET

100 to 200 MOSFET

30 to 1800

Some do’s and don’ts for proper handling are:

A. Do:

Keep paper, non-conductive plastic, plastic foams or

cardboard off the conductive benchtop. Placing a compo-

nent of printed circuit card on top of any of these mate-

rials effectively insulates the component from ground and

defeats the purpose of the conducting surface.

Keep handcreams and food away from the conductive

work surfaces. If spilled on the benchtop, these materials

will contaminate and increase the resistivity of the work

area.

Be especially careful when using soldering guns around

conductive work surfaces. Solder spills and heat from the

gun may melt and damage the conductive mat.

Check the grounding strap connections daily. Make cer-

tain they are snugly fitted before starting work with the

components and printed boards.

Touch conductive work surface before touching any

components. This drains off any static buildup from the

operator.

Licensed by Information Handling Services