IPC-CM-770D-1996.pdf - 第24页

IPC-CM-770 Januaty 1996 1-10 COPYRIGHT Association Connecting Electronics Industries Licensed by Information Handling Services COPYRIGHT Association Connecting Electronics Industries Licensed by Information Handling Serv…

January

1996

IPC-CM-770

enhance the interconnection capabilities and to interface

with housings, supports, test equipment and other periph-

eral structures. The details of these special components are

contained in Sections

16,

and

18.

4.1 4 Packaging and Interconnecting (Printed Board)

Structures

Printed board structures include conventional

and modified organic printed boards, inorganic ceramic

printed boards, and supporting planekore structures.

Details concerning printed board structures are described in

Section

19.

4.1

TAB

Tape Automated Bonding (TAB) involves the

automated bonding of semiconductor devices (dies) to a

flexible lead frame in tape and reel format. The devices are

delivered to the assembly operation on tape where the indi-

vidual devices and part of the interconnecting lead frame

are excised, the leads formed and the devices directly

mounted to a printed board structure. TAB devices are fre-

quently encapsulated after mounting to the printed board

structure. Details are contained in Section

24.

4.16 Pad Grid Arrays

Pad Grid Arrays, also known as

Land Grid Arrays are surface mount packages where the

interconnections are distributed in an area array on the bot-

tom of the package. The interconnections are typically sol-

der columns connecting lands on the bottom of the pack-

age to a matching set of lands on a printed board structure

beneath it. Details of Pad Grid Arrays are contained in

Section

13.

1-9

Licensed by Information Handling Services

IPC-CM-770

Januaty

1996

1-10

Licensed by Information Handling Services

January

1996

IPC-CM-770

Part Two

Discrete (Two- and Three-Lead) Components

5.0 AXIAL-LEADED DISCRETE COMPONENTS

Axial leaded components with two leads are perhaps the

most common electrical components used in printed wiring

assemblies. The component body is usually cylindrical in

shape with two leads exiting from the opposite ends of the

component along its longitudinal axis. The lead is usually

round in cross section. Component identification as well as

polarity, when necessary, are generally marked on the body

of the component. Many resistors, capacitors and diodes

are supplied in this configuration (see Figure

5-1).

IPC-1-00173

Figure 5-1 Axial-leaded Component

Automatic processing technology and equipment handle

this type of com- ponent very effectively when the compo-

nents are provided in tape reels (see Figure 5-2).

U U

IPC-1-00136

Figure 5-2 Taped Axial-leaded Components

5.1 Part Type Description

In addition to Figure

5-1,

axial-leaded components (2 leads) can also come in polar-

ized component body styles (see Figure 5-3), and where the

center of gravity of the component is not CO- linear with the

leads. Size and material of component bodies and leads

range and vary widely, based on device characteristics,

electronic rating, and component package style techniques.

Figure 5-3 Polarized Axial Lead Component

5.2 Through-Hole Mounting

5.2.1 Component Preparation

Component preparation

is the processing step which generally includes forming

and cutting of component leads to facilitate subsequent

component assembly and/or minimize component damage

due to stress.

5.2.1.1 Lead Forming

The lead should extend approxi-

mately one forming allowance straight out from the body

of the component. This forming allowance is usually

expressed as “2 lead diameters” or a minimum of

1.5

[0.06

inch] prior to the start of the bend except that when

space is limited by high density packaging the minimum

may be

0.75

mm [0.03 inch]. The end of the body in this

application is defined to include any coating meniscus, sol-

der seal, solder or weld bead, or any other extension.

The minimum component center-to-center board lead spac-

ing can be represented by the equation: (see Figure 5-4)

L=Bmax+3D*+2FA

where:

Center to center lead spacing

Body length

Nominal lead diameter

Forming allowance (lead should not be disturbed

within this distance from the body)

*For lead diameters up to

0.7

mm, 4D for lead diameters

between

0.7

mm and 12 mm and SD for lead diameters

over 1.2 mm.

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