IPC-CM-770D-1996 - 第70页

January

1996

IPC-CM-770

Part Four

Electromechanical and Interconnect Components

15.0 CONNECTORS

This section provides the details on selection, description

and technical considerations for mounting electrical con-

nectors. Through mount, surface mount and mixed mount-

ing situations are addressed as well as automation.

Interconnection needs must be considered during the initial

phases of printed board design and process design. This

section reviews basic connector selection criteria by con-

sidering requirements for performance, packaging and pro-

cessing.

15.1 Performance Considerations

The required perfor-

mance of an electrical connector can be sub-divided into

mechanical, electrical and environmental categories.

15.1.1 Mechanical

These factors are important because

they affect electrical and environmental performance.

Mechanical aspects of a connector include normal force,

insertion/extraction forces, wipe length, and shock and

vibration.

“Normal force” is the force a contact beam exerts on a

mating half in a direction normal to the surface of the mat-

ing half. In the case of multi-beam systems, a normal force

is not additive. For example, if a contact has four beams

each exerting

100

gms. normal force, the normal force for

that contact is designated as

100

gms.-not

400

gms. Nor-

mal force must be sufficient to maintain contact pressure to

maintain electrical requirements through environmental

exposures.

Normal force affects insertiodextraction forces. Therefore,

a proper balance must be considered. For example, as the

number of I/Os increases on a connector, the total mating

force could increase to the point where special equipment

would be required to mate. An alternative would be to

select a connection containing terminals that have lower

insertion/extraction forces. This would reduce the total

mating force for the same number of I/Os.

Wipe length is an important connector requirement because

connectors are often bowed. Therefore, as connector length

increases, the possibility of not mating at the ends of the

connector increases. Adequate wipe length eliminates this

problem.

The shock and vibration performance of a connector sys-

tem is significantly dependent on the supporting structure

or framework of the chassis or cabinet where utilized. Con-

nectors are available with a variety of hold-downs for

applications where high vibration loading is anticipated. In

applications where extreme density is required, the normal

force of the contact may be the only means of retaining the

component or mating half of a connector. Hence, rudimen-

tary analysis in these situations may dictate the selection of

an appropriate connector. MIL-STD-202 is the predomi-

nant document in describing vibration tests for connectors.

15.1.2 ElectricallElectronic Considerations

Contact

resistance, capacitance and inductance (impedance) are sig-

nificant variables in the selection of connectors in high

speed applications. Power rating coupled with millivolt

drop and temperature rise carry equal significance in power

oriented applications. Special note is given to published

power ratings since test conditions significantly affect

actual performance. Dominant variables include the pres-

ence of a housing, housing population density, housing

materials, contact materials, ambient temperatures and air

flow. Recent rulings by the Federal Communications Com-

mission (FCC), pertinent to EMCRFI control, embodied in

Docket 20780 are accepted as a controlling application

document. Shielded and/or filtered connectors provide one

solution for the equipment manufacturer.

15.1.3 Environmental Requirements

Connectors must

retain their performance requirements in their designed

environment. Therefore, connector durability and electrical

performance should be evaluated through environmental

exposures. Data are typically published regarding perfor-

mance in standard corrosion tests (such as nitric acid), in

on-site exposure tests, and in simulated accelerated envi-

ronmental requirements.

15.2 Selection Considerations

Design philosophy in

equipment design often puts severe limitations on connec-

tor selection. Key issues include, system performance,

goals, board design, space allocations, process and safety

considerations.

15.2.1 Polarization

Whenever it is possible to install a

connector on the printed board improperly or install a con-

nector on the wrong board, a polarization feature is some-

times cut into the board to assure proper installation.

Polarization features may be provided in the connectors to

preclude improper installation. (See Figure

15-1.)

15.2.2 Keying

Keying a connector enables the same

basic connector to be used with different signal patterns

without the possibility of mix-up. This feature is an advan-

tage of two-part connector systems and is illustrated in

Figure 15-2.

4-

1

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Licensed by Information Handling Services

COPYRIGHT Association Connecting Electronics Industries

Licensed by Information Handling Services

IPC-CM-770

Januaty

1996

I I

insulation displacement slot, press fit pin, or solder. Note

IPC-I-O0062

Figure 15-1 Typical Polarization

that housing can be designed to provide some board

support.

15.3.1.1 Plug (Card Edge) Connectors

These connec-

tors use conductors at the edge of the board as a portion of

the connector. The arrangement may be similar to that in

15.3.1.2

or directly to cable or discrete wire connector.

Examples are shown in Figures

15-3

and

15-4.

15.3.1.2 Receptacle Connectors

A

most common and

versatile arrangement is the use of a card cage.

A

large

board is provided with male pins and appropriate intercon-

nection circuits or solderless wrapping connections. Subcir-

2

54

mm

(O

100

In)

(O

400

In)

10 16

mm

TYP

Dia

Ref

IPC-I-O0228

L

Figure 15-2 Connector with Keying and Polarization

15.2.3 InputdOutputs

In order to minimize board space

required by connectors, consideration must be given to

high pin count connectors, or connectors with reduced cen-

terline spacing.

15.2.4 Processing

The processing a connector is

exposed to plays a major role in selection. Elevated tem-

perature exposure adds constraints to plastic selection. Mis-

matches in the coefficient of thermal expansion (CTE)

I

IPC-I-O0229

Figure 15-3 Card Edge Connector to Ribbon Cable

between the connector and substrate affect selection and

lead design. Cleaning processes effect connector selection

due to design considerations and chemical compatibility.

15.3 Part Type Descriptions

When discussing board

I!

-,

mounted connectors, they can be divided into two general

categories, card edge, integral, and two-part. Variations of

;i

each type include through and surface mount, male and

y

female and press-fit.

15.3.1 Integral (One-Piece) Connectors

Card edge or

integral connectors use the conductor paths of the printed

board as contacts. The connector serves to provide a suit-

Figure 15-4 Card Edge Connector for Discrete Wiring

able interface between the printed board and a cable, dis-

crete wires, or another printed board. Generally, the non- cuits are connected to this mother board by card connectors

separable interface is created by means of a crimp, as shown in Figure

15-5.

A

similar design can be used with

- -

.

.\

IPC-I-

4-2

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Licensed by Information Handling Services

COPYRIGHT Association Connecting Electronics Industries

Licensed by Information Handling Services

January

1996

IPC-CM-770

internal connectors, but the special board preparation usu-

ally results in higher costs.

wrap, press-fit pin or solder. Housing enhancements may

include card support, printed board, or connector latches

(locks) and polarizationkeying features. (See Figure

15-7.)

-1-00085

Figure 15-5 Card Guide Connector

15.3.2 Discrete-Contact (Two-Part) Connectors

In

recent years, two-part connector systems have become

quite popular as a means of interconnecting mother boards

to daughter boards. The system consists of a permanently

mounted male on one board and a mating permanently

mounted female on the other board. Male headers can be

soldered or press fit into the board. Another variation is to

put pins into the board (solder or press fit), and then press

a shroud over the pins to form a header. Female recep-

tacles are usually soldered to the board. Both straight and

right angle versions are common. Examples of a two-part

system are shown in Figure

15-6.

r

Figure 15-6 Two-piece Connector System

15.3.2.1 Pin Contact (Male) Connectors

Contacts char-

acterized by a pin at the separable interface are male con-

nectors. The opposite or permanent inter- face may utilize

such methods as crimp, insulation displacement slot, wire

IPC-1-00232

Figure 15-7 Header Connectors

15.3.2.2 Socket-Contact (Female) Connectors

Female

connectors consist of some type of socket terminals within

a dielectric housing. There are an infinite variety of styles

to provide necessary requirements. The terminals can be

arranged for mating of boards which are parallel or at right

angles to each other. Examples of female receptacles are

shown in Figure

15-8.

15.4 Through-Hole Mount Connectors

Through-hole

mount connectors are designed to mount to the printed

board with the leads extended through the board. The leads

are then typically soldered in place to permanently mount

the connector to the board. A variety of connectors,

employing a compliant section in a pin are available. The

compliant section allows installation in a plated through-

hole without the need for soldering. The interference fit

between the compliant section of lead and plated-through-

hole achieves a reliable gas tight interconnection. Installa-

tion of this type requires the use of an arbor press with

suitable tooling. An example can be seen in Figure

15-9.

Connectors may be mounted to the printed board by solder-

ing, welding, crimping, press fitting or other means; leads

may be extended through-hole or contact may be made to

circuit lands provided on the board, holes may be plated

through or simply drilled. The exact method will depend on

the connector design. Board size and weight are important

factors in choosing connector mounting hardware, and in

deciding whether the board will be mounted horizontally or

vertically. It is common practice to mount the connector

4-3

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Licensed by Information Handling Services

COPYRIGHT Association Connecting Electronics Industries

Licensed by Information Handling Services