IPC-CM-770D-1996 - 第48页

January

1996

IPC-CM-770

PROGRAM

ZERO

IPC-I-O0209

I

Figure

10-10

DIP Layout in

Rows

and Columns

For automatic insertion, the DIP components should be

obtained from the supplier in slide magazines (see Figure

10-11)

for feeding into the insertion machines. Each slide

magazine can hold from 20 to

50

DIP components. The

capacity of the slide magazine will depend upon the length

of the DIP.

IPC-I-O0210

I

L

Figure

10-11

DIP Slide Magazines

DIP modules may be inserted into sockets mounted on the

printed boards as well as directly into predrilled holes.

Wherever it is desired to insert into sockets rather than

directly into the circuit board, the cut and clinch mecha-

nism can be disabled. In the case of wire wrap sockets the

cut and clinch mechanism may be completely removed to

provide the necessary clearance for the socket leads.

10.7

Soldering

General soldering techniques applying to

all types of components are described in Section 27.

10.8

Cleaning

General information for cleaning apply-

ing to all types of components are described in Section 28.

10.9

Conformal Coating

General techiques for confor-

mal coating for all types of assemblies are described in

Section 29.

11

.O

RIBBON-LEAD COMPONENTS

Flatpacks and quad packs are similar to

“SO”

devices (see

Section 9), but with a number of important differences.

These devices are normally supplied by the vendors with

the leads extending straight out from the body on two

opposite sides, or from all four sides. Although this

requires the user to form the leads, this permits either sur-

face mounting or through-the-board mounting techniques.

(“SO”

device leads are pre-formed by the vendor for sur-

face mounting only.)

These devices are available in both hermetically sealed and

molded plastic styles. Hermetically sealed devices are

packaged in metal, ceramic, glass, or combinations of these

materials.

“SO”

devices are normally available only in

molded plastic cases.

Multiple-ribbon-lead components are highly suitable for

high density printed board applications due to their close

lead spacing, 1.25 mm, and small body sizes. The wide

variety of flatpack configurations permits a wide variety of

mounting methods.

The basic flatpack mounting technique can be categorized

as being either the through-the-board mounting or surface

mounting. These can be further divided into:

Through-the-board, unclinched lead.

Through-the-board, clinched with circumscribing full

land.

Through-the-board, clinched with offset land.

Surface land.

Surface post.

A number of discrete devices (transistors and diodes) are

also available as ribbon leaded devices. Most of these have

been designed specifically for high frequency, stripline

mounting.

11.1 Part Type Descriptions

11.1.1 Flatpacks

One of the smallest of the presently

existing multiple lead component type is the flatpack. The

body of these components can be as small as 3.2 mm wide,

6.4

mm long, and 0.8 mm thick. The component leads are

normally flat ribbons

0.5

x 0.25 mm or smaller, and are

located on 1.27 mm centers. Flatpacks are presently avail-

able with up to

50

leads. Various approaches are used to

facilitate the securing of these to carriers:

Form leads to fit a staggered hole-land pattern, using pot

or wave soldering.

Weld or solder leads to lands or tabs.

Form leads with stress relief bends to protect the glass

seals, then weld or solder to lands or tabs that are 0.8 mm

wide x 1.9 mm long. In an alternate method, all leads are

simultaneously solder coated and then reflow-soldered

3-11

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

with semiautomatic insertion equipment.

Flatpacks must be insulated when placed over conductive

traces. Unless the user has control over the particular pack-

age material, it may be appropriate to provide insulation

between the bottom of the flatpack and any conductive

traces, regardless of the case material being used.

Users of flatpacks have had problems from non-standard

shipping containers. Another flatpack problem is that the

automated assembly cost is very high compared to other

packages, owing to the fragile leads and the special care

required in assembly.

Flatpacks devices are usually of the outline depicted in

Figure

11-1.

Dimensions of standard flat pack devices are

listed in MIL-M-38510 and in JEDEC publication 95-83.

E

IPC-I-O0212

Figure 11-1 Flatpack Outline Drawing

A.

Flat Pack Device Type

One of the smallest multiple lead components is the flat

pack. The body of these components can be as small as

3.18 mm wide, 6.35 mm long, and 0.79 mm thick. The

component leads are normally flat ribbons

0.5

x 0.25 mm

or smaller, and are located on 1.27 mm centers.

Flat packs are secured several ways:

Form leads to fit a staggered hole-land pattern, using pot

or wave soldering.

Weld or solder leads to lands or tabs.

Form leads with stress relief bends to protect the glass

seals, then weld or solder to lands or tabs that are 0.79

mm wide x 1.9 mm long. In an alternate method, all leads

are simultaneously solder-coated and then reflow-

soldered with semiautomatic insertion equipment. As with

all metal cased components, flat packs must be insulated

when placed over the particular package material, it may

be appropriate to provide insulation between the bottom

of the flat pack and any conductive traces, regardless

of

the case material being used.

Non-standard shipping containers for flat packs have

caused problems. Another flat pack problem is the very

high automated assembly cost, compared to other pack-

ages, due to the fragile leads and the special care required

in assembly.

Flat pack devices are usually similar to the outline depicted

in Figure

11-1.

Dimensions of standard flat pack devices

are listed in MIL-M-38510 and in JEDEC publication 95.

B.

Quad Pack Device Type

Four-sided flat packs, i.e., quad packs (Figure 11-2), are

used to increase the

Il0

capacity of the device without sig-

nificantly increasing the component size. In this respect,

they closely resemble leaded chip carriers.

C. Discrete Device Type

Ribbon leaded discrete devices are also very small leaded

discrete devices. The case is normally no larger than nec-

essary to provide mechanical support for the leads. These

devices were originally developed for use on stripline

boards, where the part body is recessed into the board such

that the part leads are aligned with the stripline circuit

traces.

The special characteristics of these devices (small lead

inductances, low capacitance between leads, and small

physical size) have made these devices useful in non-

stripline applications also. Figure 11-3 is typical of the rib-

bon leaded transistors available. JEDEC publication 95

lists the dimensions of ribbon leaded discrete devices.

t-

-1

Figure 11-2 Quad Pack Configuration

11.2 Through-Hole Mounting

11 2.1 Component Preparation

Through-hole mounting

of flatpacks is accomplished as illustrated in Figure

11-4

.

Lead bending is normally accomplished using fixed dies,

which will bend all leads simultaneously.

Hand held tooling is also available, which will bend all

leads on one side of the device at one time. All tooling

should protect the device seals by supporting the lead

3-12

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

-”

IPC-I-O0213

2t

but

not

less

than

L

Mar

-

Maxlrnurn

Body

length

or

wldth (including

extensions

such

as

lead fillets (both sides),

glass

seals,

etc.]

W

-

Nominal lead mdth

t

-

Nominal lead lhlcknew

I

IPC-1-00216

Figure 11-3 Typical Ribbon Leaded Discrete Device

Outline Drawing

Figure 11-5 Through-hole Mounting. “MO” Flatpack

Outline Drawing

pack mounting method with unclinched leads the flat leads

are formed at a

90”

angle and inserted in mounting holes

in the printed board (see Figure

11-6).

SUGGESTED

SIZES

(IN

i

I

Figure 11-4 Staggered Hole Pattern Mounting. “MO”

Flatpack OutlineDrawing (Only Inches Shown)

between the body and the bend. Lead bending and forming

requirements for typical packages are shown in Figure

11-5.

11.2.2 Land Patterns

Typical land patterns for through-

hole mounting are included in Figure

11-4.

The inline

mounting pattern is much more restrictive regarding toler-

ances and position because of the limited space between

the leads.

The staggered lead arrangement of Figure

11-4

permits

hole sizes of

0.75

mm, which will accommodate

“F”

out-

line devices under all combinations of hole diameter toler-

ance and lead size tolerances.

11.2.3 Lead Configuration After Assembly

11.2.3.1 Unclinched Leads

In the through-the-board flat-

PLATED-THROUGH

HOLE

/

Figure 11-6 Through-the-board board Mounting with

Unclinched Leads

As

can be seen from Figure

11-3,

the in-line mounting

restricts the hole diameter to about

0.5

mm which, in turn,

restricts the maximum width of the lead to less than

0.5

mm. Under these conditions, selection of devices with

small leads may be required.

A. Circumscribing Land

In the through-the-board,

clinched lead with full circumscribing land flatpack mount-

ing method, an additional lead clinching operation is per-

formed (see Figure

11-7).

11.2.3.2 Clinched Leads

A. Circumscribing Land

through-the-board, clinched lead

with full circumscribing land flatpack mounting method, an

additional lead clinching operation is performed (see Fig-

ure

11-7).

The advantages of using this type of flatpack mounting are:

The flatpack is positioned to withstand the forces exerted

upon it during the mass soldering operations.

The hole-to-lead clearance is not as critical.

Solder connections may be more reliable than unclinched

mounting due to additional mechanical contact.

Supported (plated-through) mounting holes need not be

3-13

COPYRIGHT Association Connecting Electronics Industries

Licensed by Information Handling Services

COPYRIGHT Association Connecting Electronics Industries

Licensed by Information Handling Services