IPC-SM-782A-表面贴装焊盘图形设计标准.pdf.pdf - 第32页

3.6.1.9 Fiducial Mark Design Specifications The Sur- face Mount Equipment Manufacturers Association (SMEMA) has standardized on the design rules for ﬁdu- cials. These rules are supported by the IPC and consist of: A. Sha…

opening size prior to manufacturing the stencil to change

the volume of solder paste which is deposited on the lands.

3.6.1.7 Component Stand Off Height for Cleaning The

minimum component stand off height for cleaning is based

on the distance across the diagonal of the component. This

dimension implies a component surface area that may trap

contamination if care is not exercised. Table 3–7 shows the

relationship for recommended component standoff dis-

tances.

If the minimum stand off cannot be achieved, proper clean-

ing under the component may not be possible. In this case

it is recommended that a no clean ﬂux be used.

3.6.1.8 Fiducial Marks A Fiducial Mark is a printed art-

work feature which is created in the same process as the

circuit artwork. The ﬁducial and a circuit pattern artwork

must be etched in the same step.

The Fiducial Marks provide common measurable points for

all steps in the assembly process. This allows each piece of

equipment used for assembly to accurately locate the cir-

cuit pattern. There are two types of Fiducial Marks. These

are:

A. Global Fiducials

Fiducial marks used to locate the position of all circuit

features on an individual board. When a multi image

circuit is processed in panel form, the Global Fiducials

are referred to as Panel Fiducials when present for the

panel. (See Figures 3–11/3–12.)

B. Local Fiducials

Fiducial marks used to locate the position of an indi-

vidual component requiring more precise placement.

(See Figure 3–11.)

A minimum of two global ﬁducial marks is required for

correction of translational offsets (x and y position) and

rotational offsets (theta position). These should be located

diagonally opposed and as far apart as possible on the cir-

cuit or panel.

A minimum of three ﬁducial marks is required for correc-

tion of non linear distortions (scaling, stretch and twist).

These should be located in a triangular position as far apart

as possible on the circuit or panel.

A minimum of two local ﬁducial marks are required for

correction of translational offsets (x and y position) and

rotational offsets (theta position). This can be two marks

located diagonally opposed within the perimeter of the land

pattern.

If space is limited, a minimum of one local ﬁducial mark

may be used to correct translational offsets (x and y posi-

tion). The single ﬁducial should be located inside the

perimeter of the land pattern with a preference for the cen-

ter.

The minimum size for local, global or panel ﬁducials is 1.0

mm. Some companies have chosen a larger ﬁducial (up to

1.5 mm) for panel ﬁducials. It is a good practice to keep all

ﬁducials the same size.

Table 3–7 Component Stand Off

Component

Diagonal

Component

Surface Area

Component Stand

Off

< = 50 mm < = 2500 mm

> = 0.5 mm

<=25mm <=625mm

> = 0.3 mm

<=12mm <=144mm

> = 0.2 mm

<=6mm <=36mm

> = 0.1 mm

<=3mm <=9mm

> = 0.05 mm

IPC-782-3-11

Figure 3–11 Local/global ﬁducials

Global fiducial

Local fiducial

▼

IPC-782-3-12

Figure 3-12 Panel/global ﬁducials

Panel fiducial

▼

Global fiducial

▼

December 1999 IPC-SM-782A

3.6.1.9 Fiducial Mark Design Specifications The Sur-

face Mount Equipment Manufacturers Association

(SMEMA) has standardized on the design rules for ﬁdu-

cials. These rules are supported by the IPC and consist of:

A. Shape

The optimum ﬁducial mark is a solid ﬁlled circle. See

Figure 3–13.

B. Size

The minimum diameter of the ﬁducial mark is 1 mm

[0.040 in]. The maximum diameter of the mark is 3

mm [0.120 in]. Fiducial marks should not vary in size

on the same PB more than 25 microns [0.001 in].

C. Clearance

A clear area devoid of any other circuit features or

markings shall exist around the ﬁducial mark. The size

of the clear area shall be equal to the radius of the

mark. A preferred clearance around the mark is equal

to the mark diameter. (See Figure 3–14)

D. Material

The ﬁducial may be bare copper, bare copper protected

by a clear anti oxidation coating, nickel or tin plated,

or solder coated (hot air leveled).

The preferred thickness of plating or solder coating is

0.005 mm to 0.010 mm [0.0002 to 0.0004 in]. Solder

coating should never exceed 0.025 mm [0.001 in].

If solder mask is used, it should not cover the ﬁducial

or the clearance area. It should be noted that oxidation

of a ﬁducial mark’s surface may degrade its readabil-

ity.

E. Flatness

The ﬂatness of the surface of the ﬁducial mark should

be within 0.015 mm [0.0006 in].

F. Edge Clearance

The ﬁducial shall be located no closer to the PB edge

than the sum of 4.75 mm [0.187 in] (SMEMA Standard

Transport Clearance) and the minimum ﬁducial clear-

ance required.

G. Contrast

Best performance is achieved when a consistent high

contrast is present between the ﬁducial mark and the

PB base material.

It is good design practice to locate global or panel ﬁducials

in a three point grid based datum system as shown in Fig-

ure 3–15. The ﬁrst ﬁducial is located at the 0,0 location.

The second and third ﬁducials are located in the X and Y

directions from 0,0 in the positive quadrant. The global

ﬁducials should be located on the top and bottom layers of

all printed boards that contain Surface Mount as well as

Through Hole components since even Through Hole

assembly systems are beginning to utilize vision alignment

systems.

All Fine Pitch components should have two local ﬁducials

system designed into the component land pattern to insure

that enough ﬁducials are available every time the compo-

nent is placed, removed and/or replaced on the board. All

ﬁducials should have a soldermask opening large enough to

keep the optical target absolutely free of soldermask. If

IPC-782-3-13

Figure 3-13 Fiducial types for vision systems

Solid round dot typically 1.5mm Dia.

Preferred

Solid square typically 2.0mm on a side

Solid diamond typically 2.0mm on a side

Single cross hair typically 2.0mm high

Double cross hair typically 2.0mm high

Other

IPC-782-3-14

Figure 3-14 Fiducial clearance requirements

Clearance

Minimum Preferred

▼

IPC-SM-782A December 1999

soldermask should get onto the optical target, some vision

alignment systems may be rendered useless due to insuffi-

cient contrast at the target site.

The internal layer background for all ﬁducials must be the

same. That is, if solid copper planes are retained under

ﬁducials in the layer below the surface layer, all ﬁducials

must have copper retained. If copper is clear under one

ﬁducial, all must be clear.

3.6.2 Conductors

3.6.2.1 Conductor Width & Clearances

Increased com-

ponent density on SMT designs has mandated the use of

thinner conductor density and clearance between conduc-

tors with increased PB layer counts requiring the use of

more vias to make the necessary connections between the

additional layers. Figure 3–16 shows the effects of SMT

and Fine Pitch Technology (FPT) on printed board geom-

etries.

Conductor width/clearances of 0.15 mm [0.006 in] have

become commonplace today, and have basically replaced

the 0.3 mm [0.012 in] line/ space as a commonly used

geometry (see Figure 3–17). As more ﬁne pitch (including

Tape Automated Bonding) devices are used on printed

boards, the 0.125 mm [0.005 in] geometry may be used in

more SMT boards to reduce layer counts. Figure 3–18

IPC-782-3-15

Figure 3–15 Fiducial locations on a printed circuit board

Locate all fiducials and tooling holes on the appropriate grid.

Locate fiducials on both primary and secondary side of board.

Standard tooling hole diameters: 2.4mm, 2.8mm, 3.2mm

Global fiducials should be 5.0mm Min from board edges.

Global fiducials

/0 Point of origin

Fine

Pitch

Component

▼

Local fiducials

IPC-782-3-16

Figure 3–16 Packaging and geometries

GEOMETRY

PIN COUNTS

PLACEMENT TOLERANCE

CONDUCTORS/CLEARANCE

LANDS

HOLES

ANNULAR RING

8 TO 64

.25mm

.3mm

1.5mm

1.0mm

.25mm

8 TO 124

0.125mm

0.15mm

0.75mm

0.4mm

0.2mm

84 TO 244

0.05mm

0.125mm

0.63mm

0.40mm

0.125mm

2.54mm Pitch 1.25mm Pitch 0.63mm Pitch

December 1999 IPC-SM-782A