IPC-SM-782A 表面安装设计和焊盘设计标准(带BGA).pdf - 第63页

Sequential placement equipment (Figure 7–6) typically uti- lizes a software controlled X-Y moving table system. Com- ponents are individually placed on the printed board in succession. T ypical cycle times vary from 0.3 …

In-line placement equipment (Figure 7–4) employs a series

of ﬁxed position placement stations. Each station places its

respective component as the printed board moves down the

line. Cycle times vary from 1.8 to 4.5 seconds per board.

Simultaneous placement equipment (Figure 7–5) places an

entire array of components on the printed board at the same

time. Typical cycle times vary from 7 to 10 seconds per

board.

IPC-782-7-1

Figure 7–1 Typical process ﬂow for underside attachment type 2c (simple) surface mount technology

Insert/Clinch

Leaded

Thru-Hole

Components

▼

Invert

Board

▼

Apply

Adhesive

Cure

Adhesive

Place

Surface Mt.

Components

Invert

Board

Wave

Solder

Clean*

Test

▼

*Optional depending on flux and cleanliness requirements.

IPC-782-7-2

Figure 7–2 Typical process ﬂow for full surface mount type 1b and 2b surface mount technology

Solder Paste

Side 1

▼

Place

Components

▼

Clean*

Invert

Board

Clean*

Type 2 (Double Sided) SMT

Type 1 (Single Sided) SMT

▼

Solder Paste

Side 2

Place

Components

Dry

Paste**

Test

Reflow

Solder

Optional depending on flux

and cleanliness requirements

**Typically used for vapor phase soldering

Dry

Paste**

Reflow

Solder

IPC-SM-782A December 1999

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Sequential placement equipment (Figure 7–6) typically uti-

lizes a software controlled X-Y moving table system. Com-

ponents are individually placed on the printed board in

succession. Typical cycle times vary from 0.3 to 1.8 sec-

onds per component.

Sequential/simultaneous placement equipment (Figure 7–7)

features a software controlled X-Y moving table system.

Components are individually placed on the printed board

from multiple heads in succession. Simultaneous ﬁring of

heads is possible. Typical cycle times vary around 0.2 sec-

onds per component.

There are many autoplacement machines available in each

of the four categories. One must establish guidelines for

selection of a machine. For example, what kind of parts are

to be handled? Will they come in bulk, magazine, or on a

tape? Can the machine accommodate future changes in

tape sizes?

Selection and evaluation of tapes from various vendors for

compatibility with the selected machine is very important.

The off-line programming, teach mode, and edit capability

along with computer aided design/computer aided manu-

facture (CAD/CAM) compatibility may be very desirable,

especially if a company has already developed a CAD/

CAM data base. Special features such as adhesive applica-

tion, component testing, board handling, and reserve capa-

bility for further expansion in a machine may be of special

interest for many applications. Reliability, accuracy of

placement, and easy maintenance are important to all users.

IPC-782-7-3

Figure 7–3 Typical process ﬂow for mixed technology type 2c (complex) surface mount technology

''' '

''''

'''' '

'''

Solder Paste

Dry

Paste**

Reflow

Solder

Place

Surface Mt.

Components

Clean*

Clinch Leaded

Thru-Hole

Components

Insert

Thru-Hole

Components

Invert

Board

Invert

Board

Wave

Solder

Apply

Adhesive

Cure

Adhesive

Place

Surface Mt.

Components

Clean* Test

*Optional depending on flux and cleanliness requirements. If no flux is used for solder paste

and/or wave soldering, cleaning and cleanliness test may be omitted.

**Typically used for vapor phase soldering.

IPC-782-7-4

Figure 7–4 In-line placement equipment

•

Moving board/fixed head

•

Each head places one component

•

1.8 to 4.5 seconds/board

IPC-782-7-5

Figure 7–5 Simultaneous placement equipment

•

Fixed table/head

•

All components placed simultaneously

•

Seven to ten seconds/board

▼

December 1999 IPC-SM-782A

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7.4 Soldering

Like the selection of autoplacement

machines, the soldering process selection depends upon the

type of components to be soldered and whether or not they

will be used in combination with leaded parts. For

example, if all components are surface mount types, reﬂow

method (vapor phase, hot air convection or infrared) may

be desirable. However, for through-hole and surface mount

combinations, in mixed technology, a combination of wave

soldering and reﬂow soldering may be used. No process is

best for all soldering tasks. In addition, the number of sol-

dering processes discussed in the following text are by no

means complete.

7.4.1 Wave Soldering Wave soldering is an economical

method of soldering mass terminations. There are four

main process variables that must be controlled in the wave

soldering process: preheat, ﬂuxing, speed, and solder wave.

In preheat, allowance in the conveyer system must be made

for the thermal expansion of the board during preheating

and soldering to prevent board warpage.

In ﬂuxing, ﬂux density, activity and ﬂux foam/wave height

must be closely monitored. A system must be in place to

determine when the ﬂux activity has deteriorated and when

the old ﬂux must be replaced and the new ﬂux added.

Speed is the time sequence and duration of all of the steps

in soldering. By controlling the speed, more uniform and

better joints result. In controlling the conveyer speed, pre-

heating a packaging and interconnecting assembly in two

or three stages minimizes the thermal shock damage to the

assembly and improves its service life. Uniform preheating

is achieved by developing a solder schedule that speciﬁes

preheat settings and conveyer speed for each type of board.

The solder wave is an important variable. Wave geometry

is especially important for preventing icicles and bridges

and for the proper soldering of surface mounted compo-

nents. Wave geometries include uni- and bidirectional;

single and double; rough, smooth and dead zone; oil inter-

mix, dry, and bubbled, and with or without a hot air knife.

Special solder waves just for surface mounted components

are also available.

The concern generally expressed in wave soldering of sur-

face mount devices is damage to the components when

they go through the soldering wave at 260°C [500°F]. The

maximum shift in tolerance of resistors and capacitors is

generally found to be 0.2%. This is a negligible amount

considering the part tolerance of commonly used compo-

nents is +5 to 20%. The components generally spend about

three seconds in the wave but they are designed to with-

stand soldering temperatures of 260°C [500°F] for up to 10

seconds.

In wave soldering, outgassing and solder skips are two

other main concerns. The outgassing or gas evolution

occurs on the trailing terminations of chip resistors and

capacitors. It is believed to be caused by insufficient drying

of ﬂux and can be corrected by raising the packaging and

interconnecting assembly preheat temperature or time. The

other concern, solder skips, is caused by the shadow effect

of the part body on the trailing terminations. Orienting the

part in such a way that both terminations are soldered

simultaneously solves most shadow effect problems. Some

manufacturers use an extra land to serve as a ‘‘solder

thief’’ for active components.

The most common method for solving both outgassing and

shadow effect is by switching to the dual wave system

where the ﬁrst wave is turbulent and the second wave is

IPC-782-7-6

Figure 7–6 Sequential placement equipment

•

X-Y Movement table/head

•

Components placed in succession

individually

•

0.3 to 0.8 to 4.5 seconds/board

▼

IPC-782-7-7

Figure 7–7 Sequential/Simultaneous placement equipment

•

X-Y table/fixed head

•

Sequential/simultaneous firing of heads

•

0.2 seconds/component

▼

IPC-SM-782A December 1999

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