IPC-7351-2005_表面贴装焊盘布局设计和标准通用要求.pdf - 第39页

ｗｗｗ．ｂｚｆｘｗ．ｃｏｍ the board handling and ﬁxturing equipment. These dimen- sions should be obtained from the process equipment manufacturer before board or panel design (see Figure 3-19). Special tooling and ﬁxturing holes ar…

ｗｗｗ．ｂｚｆｘｗ．ｃｏｍ

IPC-7351-3-17

Figure 3-17 Conductor Description

▼

LaminateX

▼

Etch Factor =

An etch factor of 1/1 is usually considered practical.

Higher factors may be specified for some applications.

Resist

▼

"B" (DCW)

"E" Outgrowth

▼

"C" Undercut

▼

"A"

(MCW)*

Overhang

Panel Plating (Liquid Resist)

▼

(OCW)*

▼

"D"

"B" (DCW)*

"E" Outgrowth

▼

(MCW)*

"A"

▼

Pattern Plating (Liquid Resist)

▼

"B" (DCW)

(MCW)*

"C" Undercut

& Overhang

Panel Plating (Dry Film Resist)

▼

"A"

▼

"D"

▼

"A"

(MCW)*

Overhang

Pattern Plating (Dry Film Resist)

▼

(OCW)*

"B" (DCW)*

▼

"E" Outgrowth

▼

"C" Undercut

▼

"B" (DCW)*

▼

"C" Undercut

▼

Thin Clad & Pattern Plating (Dry Film Resist)

A = MCW (Minimum Conductor Width) B = DCW (Design Conductor Width) D = OCW (Overall Conductor Width)

Table 3-17 Conductor Width Tolerances,

0.046 mm [0.00181 in] Copper, mm [in]

Feature

Producibility

Level A

Producibility

Level B

Producibility

Level C

Without

plating

± 0.06 mm

[± 0.00236 in]

± 0.04 mm

[± 0.00157 in]

± 0.015 mm

[± 0.0005906 in]

With

plating

± 0.10 mm

[± 0.00393 in]

± 0.08 mm

[± 0.00314 in]

± 0.05 mm

[± 0.0197 in]

Table 3-18 Feature Location Accuracy (units: mm [in])

Greatest

Board/ X,Y

Dimension

Producibility

Level A

Producibility

Level B

Producibility

Level C

Up to 300

[11.81]

0.30

[0.012]

0.20

[0.00787]

0.10

[0.00394]

Up to 450

[17.72]

0.35

[0.0138]

0.25

[0.00984]

0.15

[0.00591]

Up to 600

[23.62]

0.40

[0.0157]

0.30

[0.012]

0.20

[0.00787]

IPC-7351-3-18

Figure 3-18 Examples of Modiﬁed Landscapes

Corner Entry

Filleting

Key Holing

IPC-7351 February 2005

标准分享网 www.bzfxw.com 免费下载

ｗｗｗ．ｂｚｆｘｗ．ｃｏｍ

the board handling and ﬁxturing equipment. These dimen-

sions should be obtained from the process equipment

manufacturer before board or panel design (see Figure

3-19).

Special tooling and ﬁxturing holes are generally located

within the edge clearance areas. The clearance areas are

needed to avoid interference with board handling ﬁxtures,

guidance rails and alignment tools.

For accurate ﬁxturing, two or more nonplated holes are

located in the corners of the board to provide accurate

mechanical registration on board transfer equipment. Board

handling holes (typically 3.2 mm [0.126 in]) may also be

located in the clearance areas. These holes may be used by

automated board handling equipment or for test ﬁxture

alignment. Speciﬁc panel size should be obtained from the

equipment manufacturer or process engineer.

3.4.8.1 Board Size and Panel Construction In order to

fully utilize the automation technology associated with

surface mount components, a designer should consider how

a printed board or P&I structure will be fabricated,

assembled and tested. Each of these processes, because of

the particular equipment used, may require ﬁxturing, which

will affect or dictate certain facets of the board layout.

Tooling holes, panel size, component orientation and clear-

ance areas (both component and conductor) on the primary

and secondary sides of the board are all equipment and

process dependent.

To produce a cost-effective layout through optimum base

material utilization, a designer should consult with the

board manufacturer to determine optimum panel size. The

board should be designed to utilize the manufacturer’s sug-

gested usable area. Smaller boards can be ganged or nested

in a uniform panel format to simplify ﬁxturing and reduce

excessive handling during assembly. Panel layout is typi-

cally deﬁned by an assembly process specialist or the

manufacturing service provider.

IPC-7351-3-19

Figure 3-19 Typical Copper Glass Laminate Panel

▼

The keepout zone defined in this illustration is typical for in-line assembly automation using reflow and wave solder processes.

▼

Typical Finished Panel

for Automated SMT

Assembly Equipment

Showing two

Printed Board Assemblies

▼

300mm

[12.0 in]

▼

3.0mm

[0.12 in]

▼

5.0 mm

[2.0 in]

▼

10 mm [0.40 in]

▼

5 mm [0.20 in]

▼▼

▼

3.0 mm

[0.12 in]

Keep Clear

▼

Primary Component Side

Secondary Component Side

▼

12.0 mm

max.

[0.500 in]

5mm

[2.0 in] min.

DIRECTION OF FLOW

KEEPOUT ZONE

▼

February 2005 IPC-7351

ｗｗｗ．ｂｚｆｘｗ．ｃｏｍ

Panel construction may include several boards arranged in

a matrix or simply one board requiring additional material

retained for efficient assembly processing. The large board

or several smaller boards are retained in the panels and

separated after all assembly processes are completed.

Excising or separating the individual boards from the panel

must be planned as well. Several methods are used to retain

circuits in a panel, including V-groove scoring, NC routing

and routed slot with break-away tabs.

3.4.8.2 V-Groove Scoring V-groove scoring may be pro-

vided to enable post assembly separation. The groove fea-

ture is generally provided on both surfaces of the board and

only in a straight line. A small cross-section of board mate-

rial is retained at the break line. An allowance for the scor-

ing angle must be made as well. Conductors that are

located too close to the score groove will be exposed or

damaged, and rough edges must be sanded lightly to

remove burrs and rough fabric particles (see Figure 3-20).

3.4.8.3 Routed Slot and Tab Features The routed slot

and tab pattern is widely used for panel construction and

break-away tab extensions. Routing is more precise than

scoring, and edge surfaces are smooth, but the break-away

‘‘tab’’ points will require consideration. Tabs can be cut

and ground ﬂush with the board edge or predrilled in a pat-

tern. The drilled pattern furnishes a low stress break point

on the ‘‘tab.’’ If the hole pattern is recessed within the

board edge, secondary sanding or grinding can be bypassed

(see Figure 3-21).

3.5 Outer Layer Surface Finishes

3.5.1 Solder Mask Finishes

Solder mask coatings are

used to protect the circuitry on the printed board. Solder

mask coatings are available in two forms, liquid and dry

ﬁlm. The polymer mask material is applied using several

process methods and is furnished in varying thicknesses.

As an example, liquid materials will have a ﬁnished thick-

ness of 0.02 mm [0.0079 in] to 0.025 mm [0.00984 in]

while the dry ﬁlm products are supplied in thicknesses of

0.04 mm [0.016 in], 0.08 mm [0.0315 in], and 0.10 mm

[0.0394 in]. Although screen type printing for solder mask

is available, photo-imaged soldermask is recommended for

surface mount applications.

The photo process provides a precise pattern image and

when properly developed eliminates mask residue from

land pattern surfaces. The mask thickness may not be a

factor on most surface mount assemblies but, when ﬁne

pitch (0.63 mm [0.0248 in] or less) IC devices are mounted

on the printed boards, the lower proﬁle soldermask will

provide better solder printing control.

3.5.2 Solder Mask Clearances A solder mask may be

used to isolate the land pattern from other conductive fea-

tures on the board such as vias, lands or conductors. Where

no conductors run between lands, a simple gang mask

opening can be used as shown in Figure 3-22.

For land pattern designs with routed conductors between

lands (see Figure 3-23), the solder mask pattern must

IPC-7351-3-20

Figure 3-20 Conductor Clearance for V-Groove Scoring

90˚

▼

Break Line

▼

60˚

▼

Conductors Must

Be Clear of Score

Zone

90˚ Score

Option

60˚ Score

Option

▲

IPC-7351 February 2005

标准分享网 www.bzfxw.com 免费下载