IPC-CM-770D-1996 - 第45页

January 1996 IPC-CM-770 Heat sinks may be required and should be properly secured to the board so that they do not stress the subsequent sol- der joints. A resilient spacer may be used as shown in \\V “Resilient spacer /…

IPC-CM-770

Januaty

1996

110.16

mm1

[.400"] max

2.54

OO"]

max

.25

[.O1

O"]

non

accum

IPC-I-O0042

Figure 10-1 16-Lead DIP

IPC-1-00373

Figure 10-2 Single In-line Component

and through the printed board such that deformation does

not cause clearance spacings to be reduced beyond the

minimum. Slanting, bowing and bending of leads in any

direction should not exceed

of the lead width (or diam-

eter) nor should leads be twisted more than

15".

10.2.2 Land Patterns

DIP layouts usually follow a rect-

angular grid pattern and reasonable densities are possible,

such as that shown in Figure

10-3.

10.2.3 Lead Configuration After Assembly

The maxi-

mum clinched lead length is dependent upon the length of

lead that is available for cutting and clinching and the

thickness of the printed board.

nominal clinched lead

ength is

1.25

mm although a range from

0.75

mm mini-

mum to

2.25

mm maximum is attainable. In all cases the

land diameter should be large enough to accommodate the

clinched lead to minimize solder bridging. (See Figure

10-4.)

minimum of two

(2)

diagonally opposite leads should be

clinched for part retention as shown in Figure

10-4.

10.2.4 Mounted Configuration

The base of the device

should be parallel to the surface of the printed board to the

All

lines 0.3

[0.012]

Plated hole

1.0 [0.040]

All

line spacing 0.2 [0.010]

Lands 1.5 [0.06]

Component centers 12.5 [0.5]

22.5 [0.9]

Component area 19.6 [0.785]

8.3 [0.332]

........

9 lines 7.5 10.31

lin es^^^^^^

-5 lines 5.0 [0.2]

........*

5.0 [0.2]--1 200

IPC-1-00169

Figure 10-3 A Typical Dual In-line Layout

View

IPC-I-O0201

Figure 10-4 Lead Configuration (After Assembly)

extent that minimum lead protrusion and maximum com-

ponent body height from the board is maintained (see IPC-

A-610).

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January

1996

IPC-CM-770

Heat sinks may be required and should be properly secured

to the board

that they do not stress the subsequent sol-

der joints. A resilient spacer may be used as shown in

\\V

“Resilient spacer

IPC-I-O0203

Figure 10-5 Resilient Spacer to Heat Sink Frame

Figure

10-5.

The lead-to-body seals of mounted devices should be

undamaged. Body chipouts that extend to or into the glass

seal and chipouts that expose a normally encased area of a

lead, are unacceptable. Hairline cracks in either the seal or

the body are not acceptable.

10.3 Surface Mounting

For whatever reason the deci-

sion is made to use through-hole components in combina-

tion with surface-mount components, there must be a will-

ingness to compromise some of the advantages of a totally

surface mount assembly. Modified through-hole compo-

nents do not provide the space savings that components

intended for surface mounting provide. However lead

modification may be the only reasonable approach to sur-

face mounting, if the required components are not available

in surface mounted packages.

10.3.1 Component Preparation

One method for mount-

ing both through-hole and surface mounted components on

the same board is to modify the leads

that they can be

surface mounted and soldered.

10.3.1.1 DIPS

Where only a few DIPs are involved on an

otherwise surface mounted assembly, the leads may be

formed to resemble a SOIC package. (See Figure

10-6.)

For production, machines are available which cut and form

IC leads into a “gullwing”-type configuration. (See Figure

10-6.)

Another method of modifying DIPs for surface mounting is

the “Butt” mounting technique. This involves simply cut-

ting the DIP leads to a shorter length and placing the

device on a land pattern to be soldered along with the other

surface mounted devices.

10.3.1.2 SIPS

SIPs lead forming is shown in Figure

10-7.

Take care to assure the coplanarity of the reformed

leads, especially if the assembly is to be vapor phase

reflow soldered. Leads may be carefully formed by hand

for low volume or prototypes. For production, machines

are available which cut and form IC leads into SOIC type

configuration.

Dip, thru-hole mount

Dip, modified

“SOIC”

type mount

(gull-wing lead)

Dip, modified

“BUTT”

mount

(“I”

lead)

IPC-I-O0206

Figure 10-6 Modifying DIP for Surface Mounting

10.3.2 Land Patterns

Land patterns for DIPs and

SIPs

that are surface mounted depend on the lead shape of the

parts. The gullwing lead shape uses the same land pattern

concepts for SOICs described in Section

When using

DIPs with the “1”-lead, the land pattern should be suf-

ficient to provide a minimum of

0.25

mm on all sides of

the lead.

Figure 10-7 Gull-Wing Lead for SIP-type Component

10.3.3 Lead Configuration After Assembly

The lead

configuration for surface mounting for SIPs and DIPs

remain the same after assembly as before assembly. If

reflow soldering techniques are used, the leads must be in

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IPC-CM-770

Januaty

1996

contact with the solder paste or tin/lead plating being

reflowed. Proper handling is required

that components

do not move prior to the reflow soldering operation.

I-

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

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.

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.

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.

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