IPC-CM-770D-1996 - 第93页

IPC-CM-770 Januaty 1996

17-24). The number of turns required will depend on the

gauge of the wire used.

Wrapost

Apex

Wrapost

2

3

Level

Wrapper Turn

Insulated Wire

2

Level

-

2

1

Level

IPC-1-00273

Figure 17-23 “Wrapping Terminology”

Modified solderless wrapped connection is shown in Fig-

ure 17-25. In addition to the length of uninsulated wire

wrapped around the wrapost as defined for the conven-

tional solderless wrapped connection, an additional mini-

mum wrap of insulated wire in intimate contact with three

comers of the wrapost should be wrapped around the

wrapost to help insure better vibration characteristics.

Turn Requirement. (Table 17-3.) Each connection should

have the minimum number of complete turns given in

Table 17-3 in order to be acceptable.

Wire Size. (Table 17-4.) Unless otherwise specified, the

wire size in Table 17-4 will be used for all wire wrapping.

Wire wrapping tools may be manual, pneumatic, battery,

or electrically operated. To assure consistent results, only

pneumatic or electrically powered wire wrapping tools

should be used on Class 3 equipment.

Insulated or

Uninsulated Wire

Reference Corner

I

IPC-1-00274

L

Figure 17-24 Conventional Solderless Wrapped

Connection

Insulated Wire

I’

4

Corners

of

Contact

of

Insulated Wire

t

”2

Turn or

3

Corners

of

Contact

of

Insulated Wire

(2

IPC-1-00275

Figure 17-25 Modified Solderless Wrapped Connection

Table 17-3 Turns Requirement

Wire Gage

Insulated Wire* Uninsulated Wire AWG

Minimum Turns

of

Minimum Turns

of

I

30

I

7

I

28

6 26

7

I

24

I

5

I

22

I

5

I

20

I

4

I

Sufficient

for intimate

contact

of 3 corners

of the

wrapost

*Required for Modified solderless wrapped connections only

Table 17-4 Wire Size (in inches)

Wi re Uninsulated

AWG Wire

0.D

0.0420 +.O02 0.201 +0.0006/-0.0002 24

Insulation

0.D

0.0265 +0.0015 0.159

+

0.0004/-0.002 26

I

28

I

0.0126

+

0.0004/-0.0001

I

0.230 +0.0015

I

30

I

0.010

+

0.003/-0.0001

I

0.0195 +0.001

I

17.2.4 Guidelines for Mounted Component Configura-

tion

Except as noted in Section 17.3, the devices and

materials described in this Section have been designed for

throughhole mounting, and are used for electrical as well as

mechanical purposes. Reliable assemblies are the result of

proper design for the use of these devices. Design consid-

erations include proper hole diameters to permit solder

flowthrough (in plated-through-holes), adequate land sizes

to permit filleting between the land and the component, and

suitable finishes on the printed board and the component.

All areas to be soldered should be tin or tin-lead plated and

reflowed. Areas to be wire-wrapped or probed (as in test

points) are usually gold plated.

17.3 Surface Mounting

With the exception of wires,

these devices are not suitable for surface mounting. Wires

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January 1996 IPC-CM-770

may be surface mounted (lap soldered) to a printed board

trace, conductor, or land under the following conditions:

The attachment area meets the requirements defined in

Section 22. The land width should be 1-1/2 times the wire

diameter, and the length of the connection should be five

times the wire diameter.

The connection must be protected from peeling stresses,

either by external clamps, or by adhesives to attach the

wire to the board.

17.4 Mixed Technology

Mixed assembly technology has

no unique requirements for these components.

17.5 Manual Assembly

A. Terminals

Terminals are often installed manually. Ter-

minal swaging tools are available from each terminal

manufacturer to permit funnel or roll swages as required.

Elliptical swages, after suitable tool modification, can also

be performed manually.

B. Pins

Pins may be installed manually; however, it

should be noted that pressing the pins into the printed

board and achieving a uniform insertion depth manually is

difficult.

Tooling should be provided to control the depth of inser-

tion. This is a minor problem when using insertion tooling

similar to that shown in Figure 17-26. Another method of

controlling the insertion depth of the pins is to use pins

with a “board stop” which will contact the board or other-

wise indicate proper insertion.

C. Wire and Cable Preparation

Sufficient insulation shall

be stripped from the wire or leads to provide for insulation

clearances as specified. Chemical stripping agents shall be

used for solid wire only and shall be neutralized or

removed prior to soldering. After insulation removal, defor-

mation of remaining insulation shall not exceed 20% of the

insulation thickness. In stripping insulation, care should be

taken to avoid nicking or otherwise damaging the wire or

the remaining insulation. For Class

1

or 2 assemblies, the

number of damaged or severed strands in a single wire

shall not exceed the limits given in Table 17-5. For wires

used a potential of

6kV,

or greater, or for Class

3

assem-

blies, there shall be no broken strands; nicked strands shall

be per Table 17-5. Insulation discoloration resulting from

thermal stripping is permissible.

Table 17-5 Nicked or Broken Strand Limits

Maximum allowable nicked or

Number

of

Strands broken strands

Fewer than 7

O

7-1 5

37-40

4 26-36

3 19-25

2 16-1

8

1

5

41 or more 6

D.

Bus Bars

Because of the size of the bus bars, these

devices are usually installed manually. The bars are

inserted in the appropriate holes, and pins are clinched to

retain the bus bar.

E.

Test Points

Test points can be installed manually.

17.6 Automated Assembly

A. Terminals

Tooling is available to install and flare most

terminals automatically.

B. Pins

Pins are most often installed automatically. Pins

are available with carriers which feed the pins to the tool-

ing, which inserts the pins to a uniform depth.

C. Wire

Wire is usually installed manually with the

exception of jumpers and wire wrap. Wire wrap connec-

tions can be installed automatically by wire wrap machines

which can follow preplanned wire lists, install the wire

wraps, and route the wires between the connections.

D.

Bus Bars

Bus bars are not normally installed auto-

matically. The size of the bars and the tolerances involved

normally precludes automating installation of these

devices.

E.

Test Points

Test points may be installed automatically.

17.7 Handling and Storage

The handling and storage of

interconnect components should be in accordance with the

guidelines of Section 26.

17.8 Soldering

Soldering of devices in this Section fol-

low the guidelines outlined in Section 27.

17.9 Cleaning

Cleaning techniques are covered in Sec-

tion 28.

17.1

O

Conformal Coating

Conformal coating techniques

are covered in Section 29. In addition, the devices in this

Section may require masking. Care must be taken to apply

and remove the masking without contaminating the device.

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Licensed by Information Handling Services

IPC-CM-770

Januaty

1996

18.0 MECHANICAL COMPONENTS

contain provisions which permit the heat sink and compo-

This section provides information concerning Some of the nent leads to be soldered directly to the board. See Figure

many types of components that are used for the transfer-

18-2.

ence of heat, securing of parts to an assembly, maintaining

a prescribed space between part and surface, providing

electrical insulation between parts and guides used for

installing plug in assemblies. (Note: screws, rivets, wash-

ers, nuts, etc., are mentioned only in the application

required.)

18.1 Part Type Description

18.1.1 Heat Sinks

Heat sinks are devices used to absorb

and/or transfer heat away from heat sensitive parts. Heat

sinks come in many styles, shapes, sizes and may be

designed for mounting on printed boards, on a component

or a series of components. They can be mounted by

rivetingholting to the component or the circuit board or by

clipping to a mounted component. Some common types are

depicted in Figure

18-

1.

Figure 18-2 Solderable Heat Sink

I

1

n

o

*

n

U

I

U

9

IPC-1-00277

Figure 18-1 Common Component Heat Sinks

To facilitate heat sinking of components which must be

electrically insulated from heat sinks, chassis, washers,

etc., thermally conductive epoxy compounds and adhe-

sives, silicone grease, silicone rubber and other materials

are available. The silicone rubber and other sheet material

is usually provided in the shape of the various devices. The

effectiveness of heat sinks can be improved by forced air

convection. Heat pipes are also used for heat sinking,

spreading hot spots or causing several components to oper-

ate at the same temperature. Recently, heat sinks have

become available which permit mounting of the active

componentlheat sink combination. These can then be

mounted to the printed board. Some of these heat sinks

18.1.2 Spacers

Spacers are provided to maintain a com-

ponent above the mounting surface for electrical clearance,

increase soldering capabilities, improve air flow on heat

dissipative parts, provide mechanical support, facilitate and

minimize thermally cleaning induced stresses.

Spacers are manufactured from non-conductive materials,

(plastic, nylon, teflon) and materials that will dissolve dur-

ing the cleaning process. Spacers are usually used on mul-

tileaded radial devices (three or more leads), such as tran-

sistors, or amps, potentiometers, etc. Some examples are

depicted in Figure

18-3.

18.1.3 Component-Lead Spreaders

The use of multiple

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