IPC-CM-770D-1996 - 第50页

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

IPC-CM-770

Januaty

1996

used; components can be more readily desoldered and

removed.

a

IPC-I-O0218

Figure 11-7 Through-the-board Mounting with Clinched

Leads and Circumscribing Land

B. Offset Land

A common variation of the through-the-

board, clinched lead flatpack mounting method just

described is that in which the land is offset, instead of

circum- scribing the hole (Figure 11-8).

IPC-I-O0219

Figure 11-8 Through-the-board Mounting with Offset

Land

11.2.4 Mounted Component Configuration

11.2.4.1 lnline Leads

The mounting pattern shown in

Figure 11-3 employs “inline” leads and lands for through-

the-board mount devices. Although such inline lead

arrangements simplify lead forming requirements, they

result in very closely spaced lands (approximately 0.8 mm

clearance) and therefore require the use of close tolerance

manufacturing processes for fabrication and assembly, par-

ticularly for through-the-board mounting.

Another disadvantage of the inline arrangement is the lim-

ited space available for conductor routing between terminal

areas.

11.2.4.2 Staggered Leads

Some of the disadvantages

associated with inline patterns can be overcome by the use

of “staggered” lead arrangements (see Figure

11-4).

In

these mounting patterns the lead hole and lands for adja-

cent leads on the same side of the flatpack are offset by

some convenient distance from the inline axis. Although a

staggered lead arrangement requires somewhat more board

area per device than the inline arrangement, it provides

several advantages:

Tolerances are less critical.

Larger lands can be used.

More space is available for routing conductors between

adjacent lands.

Larger component lead holes can be used to simplify

component insertion.

In the staggered lead arrangement a good compromise

between loss of available board area and the increase in the

number of through conductors can be achieved by the use

of an

2.5

mm offset between adjacent land area. With this

arrangement conventional manu- facturing tolerance are

applicable, and a

2.5

mm annular ring (a practicable mini-

mum) is possible. The maximum offset that can be

achieved with flatpack leads of

6.4

mm length is 3.8 mm.

When this maximum offset is used, only the through-the-

board type of mounting is practicable.

11.3 Surface Mounting

11.3.1 Component Preparation

Component preparation

for surface mounting requires only than an off- set be

formed in the leads to provide contact with the mounting

surface and prevent stress on the component seals. Lead

bending requirements are illustrated in Figure

11-9.

As

with the through-hole mounting configura- tions, lead

forming for surface mounting can be accomplished using

either fixed tooling which forms all leads at the same time,

or hand held tooling which will form all leads on one side

at a time.

21

but

not

less

than

0.4

mm

[0.16”]

7

I

112

W

-

1/2

W

Land Spacing

+

L

Max

=

Maxlmurn Body length

or

wldth [includmg

extensions such as lead fillets (both sides),

glass seals, etc

]

W

=

Normnal lead width

t

=

NomInal lead thickness

IPC-I-O0221

Figure 11-9 Lead Bending Requirements for Surface

Mounting

Two major considerations must be addressed when select-

ing tooling: the extent of the offset, and coplanarity. The

offset in the leads must account for the distance from the

lead exit from the package to the bottom of the package,

the thickness of any insulation under the flatpack, and the

thickness of any adhesive or other spacers under the

device. Coplanarity is important to assure that stresses are

equalized on each lead. A value of

k0.05

mm is recom-

mended.

11.3.2 Land Patterns

With the surface mounted method

of flatpack attachment, the connections to the device on the

component side of the printed board assembly can be

3-14

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

attached to either (a) a solid metal post, or

(b)

a conven-

tional land as illustrated in Figure

11-10.

(a)

"Post" Method

TINNED

LEAD

(b)

"Surface

Terminal Area

Method"

IPC-1-00381

Figure 11-10 Surface-mounted Flatpacks

The surface land method of flatpack mounting, Figures

11-10b and

11-11,

terminate the flatpack leads to lands

which are an integral part of the conductor pattern formed

on the component side of the structure.

11.3.3 LeadlLand Configuration After Assembly

11.3.3.1 Soldered Terminations

Part placement, fabri-

cation, and assembly processes should permit the final

product to meet the requirements illustrated Figure

11-12,

11-13,

11-14,

and J-STD-001.

Part leads should have a minimum of

0.75

mm for soldered

type type connections and a minimum of

1.14

mm for

welded type connections in contact with the land (Figure

11-12).

Part leads should be axially parallel to land areas

whenever possible. (see Figures

11-13

and

11-14).

11.3.3.2 Welded Terminations

For some applications of

integrated circuits it may be necessary or desirable to use

welded rather than soldered connections to the devices.

Figure

11-15

shows two methods which may be used for

making such welded connections. In general, the mechani-

cal space considerations described in J-STD-O01 for sol-

dered connections (lead bending, tolerances, etc.) apply

equally for welded connections.

11.3.4 Mounted Component Configuration

The surface

I

IPC-I-O0222

Figure 11-11 Typical Surface Land Flatpack Mounting

0.030

rnin

soldered

0.045

rnin

welded

(INCHES SHOWN)

IPC-1-00057

Figure 11-12 Minimum Planar Lead Contact

RECOMMENDED

L

030

mlnlsolder

045

mln

weld

NOT

RECOMMENDED

I

RECOMMENDED NOT RECOMMENDED

Pan lead centered

or

edge

of

lead

does not

Edge

of

lead overhangs land

overhang land

area

by

more

than

005 Inch

(INCHES SHOWN)

IPC-1-00056

Figure 11-13 Axial Alignment

land method of flatpack mounting has the following advan-

tages over the through-the-board mounting methods:

Drilling of holes is not required.

Bending or special forming of the flat leads is minimized.

High component packaging densities are possible; greater

conductor routing on the circuit side of the printed board

structure; component mounting is possible on both sides

of the assembly. One disadvantage of the surface mount-

ing method is that the flatpack must be located accurately

and held in position during the soldering operation.

3-15

COPYRIGHT Association Connecting Electronics Industries

Licensed by Information Handling Services

COPYRIGHT Association Connecting Electronics Industries

Licensed by Information Handling Services