IPC-CM-770D-1996 - 第47页

IPC-CM-770

Januaty

1996

contact with the solder paste or tin/lead plating being

reflowed. Proper handling is required

so

that components

do not move prior to the reflow soldering operation.

í

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I-

o-

I’

IPC-I-O0270

Figure 10-8 Dual-in-line Package Gripping Tools

10.3.4 Mounted Component Configurations

The

mounting configuration for SIPS and DIPs are such that the

body of the part is parallel with the printed board to which

the part is attached.

10.4 Mixed Technology

SIPS and DIPS are normally

intended to be through-hole mounted. If parts are to be sur-

face mounted the requirements of Section

10.3

and Section

22

on surface mounting apply. In a mixed assembly, one

that contains both surface mounted and through-hole

mounted components, the decision of how to mount these

part types is determined during the design phase and is

usually based on the number of parts of a given type with

the intentions to reduce the number of assembly or process

steps. Land patterns must be available for the type of

attachment technique specified.

10.5 Manual Assembly

The sequence of equipment

mounting steps used for mixed assemblies is covered in

Section

25,

and should be such that no detrimental influ-

ence from any assembly operation is imposed on previ-

ously assembled components. Special fixtures or bending

techniques may be required to maintain component

placemendposition integrity prior to the solder process.

As

an alternative, partial assembly and soldering may be

required before a second set of electronic components are

mounted to the

packaging/interconnection

structure. Figure

10-8

shows part holders and dispensers, and dual-in-line

package gripping tool.

I

IPC-I-O0208

Figure 10-9 DIP Clearances

10.6 Automated Assembly

Dual-Inline-package (DIP)

integrated circuits are among the most common electronic

devices to be processed. The obvious advantages of auto-

matically inserting DIPs are speed, volume, and accuracy.

In nearly all cases of printed board design where DIPs are

used, it is recommended that all DIPs be inserted in a

single orientation.

The component space requirements for DIP components

are similar to axial lead components in that the general

rules for axial lead component layout apply whenever they

are intermixed with DIPs on the same board. The DIP to

DIP clearances for the tooling fingers are shown in Figure

10-9.

In all cases of board design because the DIP is

located by the front leads, it is recommended that all DIPs

be laid out in a row or column fashion, starting at the front

or “operator” side of the board (refer to Figure

10-10).

The DIP leads should be uniform and not bent too far from

the specified positions. Machines do form and straighten

the leads within the machine, but leads bent too

far

out of

tolerance cannot be formed and will cause jams in the

machine.

3-10

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

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