IPC-CM-770D-1996.pdf - 第131页

IPC-CM-770

Januaty

1996

Straight for

1

D

but not

less

than 0.8mm

"

Flush

to

0.635mm [0.25]

Max

Cqonductor

IPC-1-00363

L

Figure 25-2 Component Modifications for Surface

Mounting Applications

chip components between the parts. Also, machine head

clearances must be considered.

IPC-1-00355

I

Figure 25-3 Placement Machine Considerations

In the example shown, the chip resistors would be placed

first and probably attached through reflow soldering. The

design must provide adequate clearances for the machine

that assembles and clinches the leads for the

axial

leaded

components. Without proper knowledge of machine clear-

ances or considerations included into the design, manufac-

turers would have to insert components semi-automatically

or use manual techniques.

25.1.4 Component Securing

Techniques for shock and

vibration mounting of intermixed assemblies do not vary

dramatically from techniques previously described for

boards that have only through-the-board components or are

all surface mounted.

One aspect of the intermixed assembly is the fact that,

although components can take the shock of the final assem-

bly, certain components and their joints may not take the

shock of a secondary assembly operation. As an example,

if chip components are mounted on the underside of the

board and attached using some form of adhesive, the next

assembly operation should not impart additional shocks to

the assembly

so

that the parts that have been secured to the

underside are dislodged.

The characteristic of shock from secondary assembly

operations is even more important when parts that have

previously been mounted are attached using soldering tech-

niques. Now the shock and vibration is not just on the part

itself, shock and vibration can also affect the reliability of

the soldered joint.

Special fixturing should normally be provided during the

assembly operation to insure that no damage is imparted to

those parts that have been previously mounted or attached.

25.1.5 Assembly Sequence

Although this guideline

deals primarily with the mounting of components and not

the joining process, in intermixed assemblies, the two can-

not be separated. In some sequencing operations, parts

must be secured or attached permanently before the next

level of component mounting can be accomplished. J-STD-

001

covers the requirements for solder joints used to attach

electronic parts.

In considering the design process, each component has its

own unique characteristics for component mounting. These

have already been previously described in this guide in

Sections

5

through

18.

In general, component types that

mount through- the-board are shown in Figure

25-4

and

components that mount on the board surface are shown in

Figure

25-5.

During assembly sequencing another major item to con-

sider is whether the component placement will be done

singularly

(1

component at a time) or whether multiple

components will be placed by the equipment. The primary

concerns in these areas are the tool head clearances for

automatic placement and the set up procedures that are

necessary in order to insure that the placement of one com-

ponent does not dislodge or disturb the placement of a pre-

viously set part.

Previous sections have identified that electronic assemblies

can be divided into two types-those types that have com-

ponents mounted on only one side (type

1)

and those that

have components mounted on both sides (type

2).

As stated

earlier, components that are mounted through-the-board

usually are only of the type

1

variety; whereas surface

mounted components, or intermixed component mounting

techniques, can use both sides of the printed board for

component mounting surfaces.

In addition, the type of board or packaging interconnection

structure used to interconnect the components can also play

a dramatic role in the sequencing of electronic component

5-28

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

A. Axial Parts

(2

Leads)

B.

Radial Parts

(2

Leads)

C. Radial Parts

(3/4

Leads)

E. Single ln-Line Packages

F.

Dual ln-Line Packages

G.

Pin Grid Arrays

H.

Sockets and Connectors

D. TO-5 ICs

D.

QE.

F.

H

I.

Others (Transformers, Chokes, Coils, Trim Pots, etc.)

.

..

=El===

A.

W

G.

L.

IPC-1-00353

J.

Discrete-Rectangular, Square

K.

Discrete-Cylindrical Ends Caps

L. Small-Outline Transistors

M.

Small-Outline ICs (SOC)

N.

Plastic Chip Carrier (leaded PCCs)

O.

Ceramic Leaded Chip Carrier (LCC)

P. Ceramic Leadless Chip Carrier (LLCC)

Q.

Flat Packs

R. Quad Packs

S.

Other Connectors (Coils, Sockets)

L.

Q

N.

O.

P.

Q.

c

J.

IPC-1-00354

Figure

25-5

Surface Mount Component Types

mounting. Figure 25-6 shows the various techniques for

that contains the single layer

of

copper circuitry.

If

all

of

component mounting on a single-sided printed board or

the components are surface mounted, the component side

P&I structure. In Figure 25-6A all components are

and solder attachment side become one and the same (Fig-

mounted through- the-board and interconnected on the side

ure 25-6B).

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

A. All

through hole

B.

All

surface mounting

IPC-1-00357

I

the total quantities of assemblies do not justify the set up

time required for automated component mounting.

A.

Mixed assembly

B.

Mixed assembly

IPC-I-

Figure

25-6

Single-sided Board Assemblies

Figure 25-8 Mixed Technology Assemblies

A. All

through hole

B.

All

surface mounting

IPC-1-00354

Figure

25-7

Double-sidedlmultilayer Board Assembly

In an intermixed assembly (Figure 25-S), components

mounted through-the-board are usually positioned on one

side; whereas, components mounted on the underside of

the board are usually those of the surface mounted variety.

In this technique, the surface mounted components are usu-

ally attached to the board using an appropriate adhesive

after which the through-the-board components are auto-

matically inserted, and then the entire assembly is passed

through a solder wave.

The technique for the assembly operation can vary,

depending on the type of component, the quantity of differ-

ent components being mounted, and the techniques being

used for mounting. It should be understood that if a single

part is surface mounted amidst a large variety of through-

the-board mounted components, the surface mounted part

becomes a minor part of the assembly operation. The same

holds true if the through- the-board parts are in the minor-

ity. In these instances, manual techniques or semi-

automated techniques are usually employed, especially

if

When the intermix of parts is such that there is an equal

number of through- the-board and surface mounted compo-

nents, the tooling concept for automated component

mounting must take into account the need for special fix-

turing or attachment techniques.

Double-sided or multilayer printed board structures have

similar characteristics for the mounting of parts. Figure

25-7A shows a double-sided or multilayer board with

through-hole mounted components. Major differences

between the single-sided board and double-sidedmultilayer

assembly is that leads of through-the-board components are

usually in plated-through-holes. The tolerances associated

with plated-through- holes must be more liberal to allow

for the plating build-up; therefore, the component mount-

ing process is sometimes more restricted, based on the

manufacturing allowances incorporated into the plated-

through-hole printed board. The attachment techniques for

through-the-board components are usually some form of

wave soldering.

When parts are surface mounted to double-sided or multi-

layer printed boards, the surface mounted parts may be

J

mounted all on one side, or mounted on both sides, as

shown in Figure 25-7B. The attachment techniques for all

surface mounted boards are usually some form of reflow

soldering.

When components are intermixed on double-sided or mul-

tilayer printed boards or printed board structures; the inter-

mixing may take several forms. Figure 25-8 shows a few

examples of mixed assemblies where the components are

mounted. Figure 25-SA shows a few examples of mixed

assemblies where the components are mounted on only one

side (type

1).

Figure 25-SB shows the mixed assembly with

components on both sides (type 2).

5-30

COPYRIGHT Association Connecting Electronics Industries

Licensed by Information Handling Services

COPYRIGHT Association Connecting Electronics Industries

Licensed by Information Handling Services