IPC-CM-770D-1996.pdf - 第72页

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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COPYRIGHT Association Connecting Electronics Industries

Licensed by Information Handling Services

IPC-CM-770

Januaty

1996

lnrulallon Support

Wir.

Crimp

Rac*ptmclo

IPC-1-00233

Figure 15-8 Female Receptacles

IPC-1-00235

I

Figure 15-9 Connector with Press Fit Contacts

either to a mother board or to card racks or frames, then

insert the component board into the connector using appro-

priate guiding and support mechanisms. In general, if the

board is mounted horizontally, or if vibration is to be

encountered, the board should be attached to the connector

or supported by mechanical means other than contact

friction.

Press fit headers require special tooling to apply the header

to a board. Tooling can vary from simple hand fixtures to

elaborate presses depending on part size and connector

design.

Connectors with low line densities can be installed manu-

ally. Higher concentrations will require card ejectors, jacks,

or guide pins. So-called zero insertion force connectors are

available which require an auxiliary force to make connec-

tions after the card is inserted into the connector.

Note: Many versatile connectors are available for the

printed board designer to transfer signals or power to the

boards. Careful attention to the uses and requirements of

these devices will result in reliable interconnections.

Connectors with integral retention to the board are favored

for manufacturing ease. Connectors that cannot be snapped

or clinched in place prior to soldering require mechanical

fastening. This is primarily for positioning and the connec-

tor must then be soldered to assure electrical integrity.

15.4.1 Component Preparation

Examination of the

leads is recommended. The assembler should look for

grossly bent leads, poor plating, and loose debris.

15.4.2 Land Patterns

Connectors are available for a

variety of land patterns including inline and staggered.

Commercially available pitches are

0.127

mm and greater.

15.4.3 Lead Configuration After Assembly

Connector

leads are generally selectively crimped for retention.

15.4.4 Mounted Component Configurations

Lead and

hole location become more critical as the number of I/Os

increase. Chamfered leads are recommended for large con-

nectors. As in any multi-lead device, the true position of

pattern clusters becomes critical for reliable installation and

ease of manufacturing. The use of a secondary reference

such as a hardware hole is recommended. Connector manu-

facturers should be contacted for installation aids

availability.

15.5 Surface Mounting

Surface-mount connectors are

designed with compliant leads which are usually reflow

soldered to the lands located on the surface of a board.

Although not as popular, alternate methods of attachment

at the non-separable interface include pressure and conduc-

tive epoxy. Connectors designed for surface mount carry

the implicit qualities associated with high-temperature,

dimensionally stable materials. Examples of surface mount

connectors are shown in Figures

15-10

through

15-13.

Connectors for surface mounted substrates differ from

through mounted connectors in several important aspects.

The plastic insulator material must be chosen to withstand

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COPYRIGHT Association Connecting Electronics Industries

Licensed by Information Handling Services

January

1996

IPC-CM-770

IPC-1-00234

Figure

15-1

O

Surface Mount Connector

the high temperatures (215°C) encountered during reflow

solder processes.

The leads have been formed to make contact with the

lands on the board. The more intimate the contact is

between lead and land, the better.

The leads should be plated

so

as to assure good solder-

ability to the land. Solderability of leads can be checked

using simple tests described in MIL-STD-202, Method

208 or J-STD-002.

The connectors may require features for mechanical

attachment to the board. This is especially desirable for

longer connectors or connectors that are potentially sub-

jected to abuse during mating and unmating.

Alternative methods of surface mounting include the use of

pressure contacts to maintain electrical contact at the

board, as well as the separable interface. A point in these

applications is the need to provide board stiffening struc-

tures to neutralize the effect of "normal" forces.

An evolving technology is the use of conductive epoxies to

surface-mount a connector to board. Utilization of this

method affords the potential of lower processing tempera-

tures.

15.5.1

Component Preparation

Extra care should be

taken with surface mount connectors to assure that the

leads are not damaged prior to placement on the board.

15.5.2

Land Patterns

The size of the land on the board

is directly related to the size of the lead to be soldered plus

a tolerance needed to adapt to any inaccuracies in place-

ment. Generally, a land that is 0.25 mm larger on all sides

than the lead is recommended. The minimum land size

must be sufficient to provide a fillet on all sides of the lead.

15.5.3 LeadlLand Configurations After Assembly

Con-

nector leads are not reconfigured after surface mounting.

15.5.4

Mounted Component Configuration

The loca-

tion, or true position, of component leads becomes more

critical as the number of inputs/outputs increase. Board

hole tolerances and lead tolerances over the length of some

of the larger connectors can cause interference problems

when mounting. In such instances, mounting aids are

required and are provided by the connector manufacturer.

An important consideration with larger surface mounted

connectors is the difference in thermal expansion between

the connector plastic and the printed board. All commonly

used plastic materials have a coefficient of thermal expan-

sion (CTE) that exceeds that of epoxy glass boards by at

least

7

ppm/C"

(17

ppm/C" for ceramic substrates). The

mechanical connector design must be able to absorb this

CTE difference to avoid solder joint failures during thermal

cycling. Visual examination of leads of the mounted con-

nectors is recommended. Reposition individual leads if

required.

15.6 Mixed Technology

These assemblies generally are

wave soldered as the last attachment step. Standard

through-hole connectors can therefore generally be used for

mixed assemblies. These connectors should be applied

after the reflow solder process or must be chosen to be

compatible with the high temperatures seen during reflow

soldering.

15.7

Manual Assembly

Most connectors are inserted or

placed using manual techniques. Assembly may occur the

same time as other components or as a separate secondary

operation. Care should be exercised to not disturb previ-

ously assembled parts.

15.8 Automated Assembly

For many backplane assem-

blies, computer controlled machines are used which stake

individual pins into the backplane. Those pins that are actu-

ally needed are staked. Also, pin lengths can be selected for

staged mating of ground, power, and signal contacts.

Increasingly, robots are being used to place connectors.

Where robots are being used, it is important to specify

connectors with true position tolerances and other key

dimensions compatible with the board and robotic place-

ment system. Packaging should also be selected to make

delivery of the connector to the robot simple.

15.9 Handling and Storage

The handling and storage of

connectors should be in accordance with the guidelines of

Section 26.

4-5

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