IPC-CM-770D-1996.pdf - 第75页

IPC-CM-770

Januaty

1996

15.1

O

Soldering

Care must be taken

so

that flux or sol-

der does not wick up into the contact. Some manufacturers

provide anti-wicking devices to prevent flux or solder

wicking.

If

connectors are not mechanically secured to the

board, suitable fixturing should be provided to prevent lift-

ing during soldering. This is especially important with

small lightweight connectors. General soldering guidelines

are discussed in Section

27.

15.1 1 Cleaning

Cleaning agents used after soldering

should not have any harmful effects upon the connector

housing material. Check with the connector manufacturer

to verify the compatibility of any cleaning agent with the

connector housing material. Any residue left on the contact

surfaces must be removed. When possible the open end of

the connector should be turned with the opening downward

so

that the cleaning agent can drain out of the connector

body to facilitate drying.

Ideally, connectors should be provided with standoffs and

should not have blind holes, to permit cleaning agent to

pass between the connector and the printed board.

15.1

2

Coating

Care must be exercised to prevent coat-

ings from getting on the contact surfaces. Wicking can

present a problem, and it may be necessary to seal around

the connector to prevent it.

cessing temperature extremes.

Two classes of sockets are available; namely, low insertion

force and zero insertion force. Low insertion force

describes disconnects where the insertionlextraction forces

associated with the normal forces and component loading

actions are present. Since the magnitude of the force is

additive and related to the number of leads per device, the

maximum size of socket is limited. In situations where high

forcelpin counts are encountered, zero insertion force con-

nectors are used. These are characterized by the presence

of a cdlever arrangement which relieves the normal force

created by the fixed spring segments of connectors.

Synonymous with this is the implication that appropriate

clearances must be provided for the camllever actuation.

The use of a socket carries the inherent cautions associated

most component namely:

Assembly reliability does not deteriorate as a result of

process incompatibility.

Contaminants are not trapped to promote the degradation

of materials in the system.

Proper selection by engineering.

Added costs.

Sockets may be classified in two categories; namely, dis-

IPC-I-

L

Figure 15-11 D-subminiature Surface Mount Connector

16.0 DISCRETE COMPONENT SOCKETS

Sockets are passive interconnecting devices which serve to

create a readily separable interface between discrete com-

ponents such as DIPS, chip carriers, displays, axial compo-

nents, etc. The socket is usually soldered to the board and

embodies a plated fixed spring element which exerts nor-

mal force on an appropriate segment of an active discrete

component. Sockets have a broad range of utility including

ease of component replacement due to failure, system

updating, component substitution due to conditioning

andor testing, and protection of active devices from pro-

Crete or loose piece and array assemblies. Discrete sockets

are individually applied components which are inserted

independently at various board locations. Array style sock-

ets utilize a carrier such as a housing or tape to carry indi-

vidual contacts and ease the manufacturing task of socket

installation to the board.

16.1 Part Type Description

There are several types of

sockets used in printed board applications for the attach-

ment of discrete component leads. They generally fall into

one of the following categories.

4-6

COPYRIGHT Association Connecting Electronics Industries

Licensed by Information Handling Services

COPYRIGHT Association Connecting Electronics Industries

Licensed by Information Handling Services

January

1996

IPC-CM-770

Figure 15-1

2

Surface Mount Receptacle

Figure 15-1

3

Box-contact Surface Mount Receptacle

A.

Stake-to-the-Board Devices

that are mounted horizon-

tally or vertically. They are usually manufactured as either

dual or multimetal devices, or as singular metal devices.

B. Low Profile Pluggable Devices

assumes positive reten-

tion to the printed board prior to soldering. They usually

are designed with a cup and spring extension that allows

solder to be drawn to the top surface of the board, produc-

ing a solder fillet on the component side land without over-

flow into the socket.

C. Low Profile Grip Type Devices

are miniature connec-

tors with a singular metal device that has a portion acting

as a temporary retention device for discrete component

leads,

so

that they may be eventually soldered and, if nec-

essary,eventually removed easily without damage to the

board or to the component being removed.

16.1.1 Individual Component-Lead Sockets

16.1.1.1 Low Profile Sockets

One such device is a plug-

gable socket that assumes positive retention in the board

prior to soldering, and spring to board electrical contact

after soldering. The design of the cup and spring extension

allows solder to be drawn to the top surface of a two-sided

board, producing a solder fillet on the top land without

overflow into the socket. Soldering may be done by the

usual methods of wave soldering or hand soldering.

The socket shown is of two-part design having a heat

treated spring assembled into a drawn cup. Spring provides

multiple cycle life with high contact forces.

Many of these components come with an elastomer seal to

keep out contaminants during the soldering, washing cycles

as well as throughout its life and care must be taken during

insertion into the board

so

as not to destroy this seal. The

seal is normally left in position throughout the life of the

socket and discrete components are mounted or inserted

through it without detrimental effects. See Figures 16-1 and

16-2.

The profile of this type of device above the printed board

usually is less than

0.8

mm and can be used on centerline

spacings as close as 2.54 mm minimum center to centerline

distance. Product is available for nominal hole sizes of

1.07

4-1

COPYRIGHT Association Connecting Electronics Industries

Licensed by Information Handling Services

COPYRIGHT Association Connecting Electronics Industries

Licensed by Information Handling Services

IPC-CM-770

Januaty

1996

INSERTED

OMPONENT

ELASTOMERIC

SEAL

P

IPC-1-00238

Figure 16-1 Low Profile Pluggable Devices

Figure 16-2 Low Profile Devices

mm, 1.32 mm,

1.57

mm, 1.83 mm and 2.54 mm which

should be maintained for retention purposes in soldering

operations.

Devices of this type can accommodate round lead sizes

from 0.254 mm to 1.65 mm and square or rectangular

devices with equivalent diameters.

Four styles of product can be used in each of the hole sizes.

Closed Bottom

to accommodate standard applications

which are compatible with hand, wave or vapor phase sol-

dering. (See Figure 16-3.)

Open Bottom

for feed thru applications which are hand

soldered.

Knockout Bottom

for feed thru applications which

allow the use of wave or vapor phase soldering-the pres-

heared bottom is removed after soldering to complete the

feed thru application.

Bullet Nose

design allows greater positional tolerance

for high speed applications on bench or numerically con-

trolled equipment.

16.1.1.2 Low Profile Grip Type Device

This type of

miniature connector is a singular metal device having a

portion acting as a temporary retention device for compo-

nent leads

so

that they may be eventually soldered and, if

necessary, eventually removed easily without damage to

the board. They are designed to reduce or eliminate many

of the problems associated with component mounting prior

to solder reflow or solder processing.

They give a mechanical through connection that will resist

impact, vibration and thermal shock. They are retained in

I

IPC-1-00383

Figure 16-3 Closed Bottom Socket

the board by flaring of the lower edge, the upper edge hav-

ing been flared in manufacture. They may be used in plated

through or non-plated through-holes, multisided or single-

sided boards and may be hand or machine inserted. See

Figure 16-4.

I

Before flaring After flaring

Cross

section

IPC-I-O0240

Figure 16-4 Low Profile Grip Type Device

These devices help resist component movement which in

turn reduces solder defect failures. They assist in the reduc-

tion of damage when replacing components.

IPC-I-O0242

I

Figure 16-5 Use of Low Profile Grip Devices

In many cases, it is not necessary to use spacers since the

device retains a firm hold on conductors throughout normal

produc- tion handling at the depth inserted. Heat sensitive

components are held at a safe distance from the board. See

Figures 16-5 and 16-6.

16.1.2 Multiple-Lead Component Sockets

Sockets are

4-8

COPYRIGHT Association Connecting Electronics Industries

Licensed by Information Handling Services

COPYRIGHT Association Connecting Electronics Industries

Licensed by Information Handling Services