IPC-CM-770D-1996.pdf - 第40页

January

1996

IPC-CM-770

Figure 8-7 Straight-through Lead, Unclinched Can

IPC-1-00161

Figure 8-8 Offset Lead Can Mounting

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Figure 8-9 Transistor Mounting (Unsupported Holes)

Where spacers or spreaders are used, they should deter-

mine the height of the component above the board. The

feet of the spacer should be against the board.

When using spacers, the spacer should be installed in inti-

mate contact to both component and printed board mount-

ing surfaces

so

as to preclude any axial play between the

component body, spacer and the board. Spacers with pro-

trusions on one side should be mounted with the protru-

sions against the board.

A

typical method for mounting of a “TO” component with

a spacer is shown in Figure 8-10. The effect of spacers on

the leadcan seal and on lead forming should be evaluated

before their use is determined.

Spacer

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Figure 8-10 Transistor Mounting (with Spacer)

The use of multiple lead can spreaders, Figure 8-11, serve

a similar function for offset can mounting as do spacers for

straight-thru can mounting. Leads may be terminated in the

straight-thru method or the clinched lead method.

SPREADER

IPC-1-00164

Figure 8-11 Can Mounting Spreader

In installations where flux must be removed, a clearance of

0.38 to 3.2 mm should be allowed between the board and

the base of the component. The base of the component

should be parallel to the board.

Suitable fixturing should be provided to help assure that the

component is retained in proper position throughout the

soldering operation. Where no spacer is used, a temporary

spacer may be required until the component has been sol-

dered. Tab or index locations must be closely observed to

assure proper orientation in mounted position.

8.2.4.2 Horizontal Mounting

When transistors in TO

style cans are mounted horizontally, mounting clips should

be used.

A

typical method of mounting a transistor of this

type is shown in Figure 8-12.

Plastic power transistors are designed such that the mount-

ing hardware may also be a part of the active circuit.

A

typical mounting of such a device is shown in Figure 8-13.

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IPC-CM-770

Januaty

1996

Lead bend radius requirements should also be followed

when mounting these devices.

8.2.4.3 Electrical Insulators and Thermal Conductors

When electrical insulators are also thermal conductors, the

device mounted on thermal conductors should have a maxi-

mum space of

0.05

mm between the transistor and thermal

conductor, and between the thermal conductor and the

board. However, the transistor should be in contact with the

electrical insulator/thermal conductor and the electrical

insulator/thermal conductor should be in contact with the

board at some point.

SIDE VIEW

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END VIEW

IPC-1-00153

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OPTIONAL SPACER

Figure 8-14 Mechanically Secured Transistor

Allow for adequate cleaning after soldering.

Minimize possibility of solder shorts to the component

case.

Minimize thermal expansion induced stresses on the sol-

der joints.

8.3 Surface Mounting

General surface mount consider-

ations that apply to multiple-lead components and assem-

blies are discussed in Section

22.

8.4 Mixed Technology

The general techniques and

sequences for mixed assembly are discussed in Section

25.

Figure 8-1 2 Horizontal “TO” Mounting

8.5 Manual Assembly

Special tools and equipment are

not normally needed or used for manual insertion of mul-

tilead radial components. General manual assembly tech-

niques are discussed in Part

5.

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8.6 Automated Assembly

There are few standards for

automatic insertion of “TO” can type components because

very few are inserted automatically. There are two general

methods for automatic insertion of transistors: axial where

the part is handled by the leads, and radial where the part

is handled by the body.

8.6.1 Design Considerations

Figure 8-1 3 Transistor Can Horizontal Mounting

8.2.4.4 Mechanical Securing

Transistors which are to

be mechanically secured should have proper stress relief in

their mounting procedures.

A method for mounting of a transistor which must be

mechanically secured to the surface of the board is shown

in Figure

8-14.

In this configuration it is essential to:

8.6.1.1 Hole Diameter

A factor to be considered with

the radial insertion is the uncertainty of lead position,

caused by the fact that leads cannot be guided directly into

the board holes. Generally, the component hole diameter

must be increased at least an additional

0.25

mm to allow

for lead position variation.

8.6.1.2 Location Considerations

Both axial and radial

insertion require tooling clearances. Above the board clear-

ances similar to Figure

8-15

must be used in the axial

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January

1996

IPC-CM-770

method. The radial method requires a clearance around the

body diameter of approximately 2.0 mm larger than the

body.

FRONT

VIEW

PLAN

VIEW

.O70

4

.O70

Spacing

on

two-lead

side

may

be

.100/.125"

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Figure 8-15 Transistor Assembly Tools

8.6.2 Radial Method

The component body is held during

the insertion process for means of inserting and locating

the part on the board. After the leads are prepped, the major

problem with the radial technique is that the physical con-

figuration of the parts vary substantially from batch to

batch, and from manufacturer to manufacturer.

8.6.3 Axial Method

The axial method of automatic inser-

tion is used the transistor is treated like an axial-leaded

component. This system for handling TO-92, TO-18, and

similar transistors, is based on forming the leads as shown

in Figure 8-16 and taping them on conventional lead tape,

just like and axial-leaded component.

Since the physical configuration of the component can vary

due to manufacturers' processes, it is advisable to obtain

parts on reels with thick interliners. This would ensure the

handling of one size part only. (See Figure 8-16.)

Once on tape, the insertion problem becomes one of com-

patible wire diameter-since the part is handled only by

the leads and a body clearance to a maximum envelope. As

a result, nearly all vendors' devices can be used by a single

insertion head without retooling. Spans from 7.6 to 10.2

mm are possible.

8.7 Handling and Storage

The handling and storage of

multiple-radial-lead components should be in accordance

with the guidelines of Section 26.

8.8 Soldering

General soldering techniques applying to

all types of components are described in Section 27.

8.9 Cleaning

General techniques for cleaning applying

to all types of components are discussed in Section 28.

8.10 Conformal Coating

General techniques for confor-

mal coating for all types of assemblies are described in

Section 29.

Notes:

1. Heavy Kraft

or

single ply

"A*

type corrugated interliner to be used.

2. Lead length in contact with tape, each side-,120" minimum.

3.

Leads must be straight within ,015" between body and tape.

4.

Component bodies

must

be in line withil .015"

5.

No

more than one component may be missing at a gap.

6.

Distance between tapes may not go below minimum shown.

Variation of

,060"

over reel permisslble.

7.

Both In-line leads (TO-92, TO-98, etc.) and TO-18 pin conflgurations

suitable for this process.

8. Insertion spacmg

IS

a function of part width.

For example: for

,235

"

width, it is

,400'

Certain plastlc devices can be handled down to

300'.

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Figure 8-16 Taping Specifications (Only Inches Shown)

9.0 SMALL OUTLINE COMPONENTS

Small outline

(SO)

components are available in a series of

molded plastic packages with .025" pitch and up to

.050"

pitch. They are designed to be surface mounted to the PCB

or to other substrates and therefore are supplied with gull-

wing or

J

shaped lead configuration.

9.1 Part Type Description

9.1.1 SOIC Packages

Small outline integrated circuit,

(SOIC) packages can have eight, fourteen, sixteen, twenty,

twenty-four or twenty-eight leads and fall into two groups.

The leads are arrayed as two rows of leads with adjacent

leads spaced 1.25 mm apart. It the smaller component

group, consisting of SO-8, SO-14, and SO-16 packages, the

rows are spaced about 6.0 mm apart while in the group of

larger components, consisting of S0-16L, SO-20, SO-24

and SO-28 packages, the rows of leads are about

10.0

mm

apart. A typical SOIC package is illustrated in Figure 9-1.

9.1.2 SOT Packages

Three leaded components are des-

ignated SOT packages. There are two common SOT pack-

ages: SOT-23 and SOT-89. In general, SOT packages are

used with diodes, transistors and small I/O devices (devices

with only a limited number of input-output lead require-

ments). SOT packages are illustrated in Figure 9-2.

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Licensed by Information Handling Services