IPC-CM-770D-1996 - 第79页

January 1996 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.…

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-

4-10

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January

1996

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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IPC-CM-770

Januaty

1996

.a35

Section

fhru

Contact

Cuvitv

IPC-I-

Figure 16-11 Leadless Grid Array Socket

'ACT-

HOUS

STRUCTURE

?SOLDER

ING

OIN

P/I

STRUCTURE

COMPLIANT SECTION

LAND

IPC-I-

Figure 16-1 2 Section Through Socket Solder Contact

The low profile plastic leaded chip carrier socket serves as

a transition device to enable users to take advantage of the

benefits of four sided IC packages without making changes

in their current assembly procedures.

As previously mentioned, the chip carriers can have sur-

face mount leads on 1.27 mm spacing. The chip carrier

socket has flat spring input leads on 1.27 mm spacing to

accommodate the package, and straight solder tail output

leads on 2.54 mm spacing to meet the requirements for

standard through-hole mounting.

In pin grid array packages, the through-hole mounting is

the dominant choice. Sockets for pin grid arrays are

designed to match pin configurations.

There are three types of pin grid array sockets currently

available: the standard version which allows the component

to be pushed in; a low insertion force version which

employs a low force contact design; and a zero insertion

force, which makes use of a mechanical assist to maintain

contact pressure.

Through-hole mounting techniques are outlined in Section

21.

16.2.1 Land Patterns

The most appropriate board layout

for the component is usually offered by the socket supplier.

Automatic assembly will normally demand additional

clearance for greater positioning/placement allowance.

Sockets are somewhat unique to other board components in

that they serve as a connector for their components. As

such, they take much more stresdstrain on the fillet through

the terminal). It is strongly recommended therefore, that:

Surface land diameters be as large as allowable.

The RTH diameter should be designed to the lower side

to allow maximum capillary action, minimum hole solder.

Surface detail should allow at least two diagonally oppo-

site terminals to be clinched, or minimally to have reten-

tive mechanical actions.

See IPC-SM-782 for surface mount land patterns.

16.2.2 Lead Configuration After Assembly

Socket con-

tacts are normally stationary (nonformable), preset and

typically protrude orthogonally to the board surface. For

stamped contacts, where there is not a mechanical grip,

clinching is recommended. Clinches should be formed to

4-12

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