IPC-CM-770D-1996.pdf - 第78页

IPC-CM-770 Table 16-1 Socket Types 16.1.2.2 Chip Carrier Sockets Sockets such as shown in Figure 16-9 can be used with most ceramic chip carriers. They can be surface mounted or through-hole mounted. In the surface mount…

Januaw

1996

IPC-CM-770

FlJNNEL

FLAT

HOLLED

IPC-1-00243

Figure 16-6 Styles of Low-Profile Grip Devives

provided for an extremely wide assortment of component

types. The major use, however, is for semiconductor pack-

age styles. These semiconductors and most other compo-

nent styles are defined extensively in EIA (Electronic

Industry Association) standards and won't be repeated

within this document.

Although sockets are normally associated with the inserted

component names, they most generally fall into several

broad socket contact categories which vividly describe

their type.

Component named sockets utilizing these different contact

types are listed in Table 16-1. Contact styles vary with each

socket dependent on the supplying vendor. Figure 16-7

shows a cross section of various socket types available.

16.1.2.1 DIP Sockets

Sockets of this type are designed

for low cost, high density production packaging. They have

universal mounting and packaging capabilities. Sockets are

available with a "solder tail" in 14-, 16-, 24- and 28-lead

configurations. They are generally designed to resist solder

wicking into the socket cavity. Sockets of this type may be

inserted into a printed board manually or automatically.

Many are designed with standoffs which allow for ease and

thorough cleaning after application to the printed board and

are ventilated to assist cooling of components. IC leg tar-

get areas or lead-in should be large and target areas

1.1

1.5

mm or larger are not uncommon. Large "lead-in"

facilitates IC leg entry.

Many factors affect IC socket performance. Consider con-

tact plating materials (gold, tin and tin-lead alloys); socket

body construction; insulating materials (thermoplastic and

thermoset plastics); standard profile-8.3 mm versus low

profile-4.44 mm; and the retention force needed for a par-

ticular application.

Housing length is dependent upon the number of lead con-

figurations. Average force to insert a package or a printed

board varies from 7 pounds on an 8-position part to 13

pounds on a 16-position part. (See Figure 16-8.)

TContact

Houslng

Slngle Wlpe

Devlce-

~ Single wipe. slde gulde

~ Dual wlpe D ~

Box

~ Screw machlne

losed Posltlon

Rest

Posltlon

Cam

Horlzontal beam

"J"

lead

~ Bellows

~ Zero Insertion J ~ Leaf

IPC-1-00244

Figure 16-7 Contact Configurations

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IPC-CM-770

Table 16-1 Socket Types

16.1.2.2 Chip Carrier Sockets

Sockets such as shown in

Figure 16-9 can be used with most ceramic chip carriers.

They can be surface mounted or through-hole mounted. In

the surface mount version, land patterns are on 1.27 mm

centerlines. Through-hole versions require hole patterns on

2.54 mm centers.

IPC-I-

I I

Figure 16-8

DIP

Socket

Sockets for plastic leaded chip carriers are available for 44,

68, 84, and

100

position devices. They can be surface

mounted on 1.27 mm centers or through-hole mounted on

2.54 mm centerlines. The land pattern of the surface mount

Januaty 1996

Normal

Grid System

(Inches)

100

300

min.

100

400

min.

100

600 min.

100

900 min.

100 min.

100

100 min.

50 min.

Speced

0.200

0.160

0.175

0.075, 0.100,

0.125, 0.062

CHIP

CARPIER

(PRESSURE

ONLY

RETAINER SCREW

THRUSTER

CLIP

STRUCTURE

(PRESSURF

ONLY

IPC-I-

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IPC-CM-770

16.1.2.3 Pin Grid Array (PGA) Sockets

Sockets for

PGAs are designed to match pin configurations of the

packages. In situations where polarization is desired, a non-

active pin serves the function. Three types are available

including a standard, low insertion force and zero insertion

force. PGAs and corresponding sockets are available in

sizes from

to 215 x 25. At higher pin counts, zero

insertion force types are preferred. The use of high tem-

perature materials adds utility to the zero insertion force

(ZIF) style for test, conditioning, and bum-in applications.

16.1.2.4 PGA Socket

Figure 16-10 shows the various

types of pin grid array (PGA) sockets. These are available

in a wide variety of grid sizes and patterns. They are typi-

cally manufactured in an economy type (LIF) version, or a

more expensive but easier to use and durable (ZIF) produc-

tion type socket suitable for test and bum in. Note the cam

handles or levers on the ZIF designs. A typical bum in

socket is normally rated at 25000 durability cycles and

150°C

continuous operating temperature. A bum in socket

normally has a very large opening in the contact area for

ease of accepting the pin on the chip carrier.

Another type of grid device is the leadless grid array

socket. This socket, instead of mating with a pin, mates

with a pad or land on the package. This eliminates the pin

on the package but requires hold downs on the socket to

maintain normal force on the terminal.

assurance that the part is supplied as requested. The best

guarantee is a preproduction trial run of the assembly.

Preparation should focus attention on:

A. Packaging and Handling

Inadequate or improper

methods damage lead sets which will force line delays.

Terminal Surface

They should be provided with tinned

or gold plate. Terminals without must be pretinned.

C. Length

Terminals

The terminals should not protrude

beyond the board more than

0.15

mm (nor less than

0.8

mm.

not provided in this fashion, they will require clip-

pin(trimming).

Seals

The assembly (solder, cleaning, etc.) dictates the

degree to which the component must be closed. Standard-

precaution, however, requires use of a closed entry bottom

terminal exit or a plate to achieve the same effect. When

the socket face is to be sealed this may be accommodated

by special tapes or a pallet tool.

Cleanliness

Wave solder assembly cleaning tactics are

normally adequate to assure part cleanliness. Periodic

examination, however, of preassembly components is a

normal procedure.

Sockets such as that shown in Figure 16-9 can be used in

through-hole (non-surface mounting) applications. How-

ever, since the terminals of the chip carrier are not on 2.54

Zero Insertion Force (ZIF) Socket

IPC-I-

Figure 16-1

Pin Grid Array Sockets

Figure 16-11 shows a leadless grid array socket with sur-

face mount leads shown in cross section. Leadless grid

array sockets are available on a 2.54 mm centerline grid

pattern (in both thru hole and surface mount versions).

16.2 Through-Hole Mounting

Sockets normally have

pre-set leads and are usually supplied by Vendor prepared

for assembly into the board. This being the situation,

preparations should be focused into two areas. Selection of

the component (and its options) for particular assembly and

mm centers, a contact similar to the one shown in Figure

16-12 is used to provide the desired transition. A polariz-

ing boss can be provided on the connector to mate with a

corresponding hole in the printed board structure.

Figure 16-12 shows a section through the short contact. A

dog-leg in the solder tail serves as a friction retaining

device. This prevents the connector from being lifted off

the mounting structure during the wave soldering opera-

tion.

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