IPC-SM-782A-表面贴装焊盘图形设计标准.pdf.pdf - 第193页
smaller for pitches less than 1.0 mm. Refer to the manufac- turer specification before finalizing land pattern array and geometry. 4.4.1 Copper Defined Land Pattern The land patterns described are defined by the etched c…
contacts is typically 1.0 mm, 1.27 mm and 1.5 mm. The con-
tacts accommodate the electrical and mechanical interface
between device and host interconnecting structure (printed
board). The contact material will allow conventional reflow sol-
der or other attachment processes.
3.2 Marking The Ball Array device families are generally
marked with the manufacturers name or symbol, part number,
date code and orientation mark in the corner near contact
location A1.
3.3 Carrier Package Format Devices may be furnished in
matrix tray or tape and reel packaging formats. Tape and reel
packaging is generally preferred for high volume assembly.
Plastic trays and reels must be transported and stored in
moisture proof containers. When plastic array devices are
exposed to the environment for an extended period of time,
moisture may absorb into the device. The absorbed moisture,
if excessive, may expand (when exposed to higher tempera-
tures typical of reflow solder process), causing cracking and
other physical damage.
3.4 Assembly Process Conditions The Grid Array
devices are typically attached to the host interface structure
using eutectic solder alloy however, optional methods of
attachment may include electrically conductive epoxy or poly-
mer. Array package assembly should not require specialized
equipment or processes beyond that used for vision assisted
SMT pick and place.
4.0 GENERAL CONFIGURATION ISSUES
4.1 Device Outlines
The Grid Array package outlines
detailed in this document are furnished in JEDEC Publication
95. The overall outline specification for the array device allows
a great deal of flexibility as far as lead pitch, contact matrix
pattern and construction. The JEDEC standards allow for die
attachment on either side of the interface structure (cavity up
or cavity down). Refer to J-STD-013 for further definition and
interconnect schemes for BGAs.
The example shown in Figure 4-1 illustrates two 225 I/O
devices with a common package outline but, with the variation
of contact pitch, a unique matrix format is provided.
4.2 Contact Matrix Options Contacts may be distributed
in a uniform pattern, however the matrix is always centered
about the centerline of the package (see Figure 4-2). Contact
depopulation is permitted at the discretion of the device
manufacturer. Contact patterns can usually be described in
the following methods: full even matrix, full odd matrix, perim-
eter matrix, or staggered matrix.
4.2.1 Full Matrix For a given package size, there are two
full matrix possibilities: even and odd. One of them is the larg-
est matrix that theoretically could fit on the package, given the
size and pitch of the contacts. The other matrix is smaller by
one row and column. See Figure 4-2.
4.2.2 Perimeter Matrix A perimeter matrix is achieved by
removing an array of contacts from the center of the matrix.
Center-depopulation does not affect the centerline of the
matrix. See Figure 4-3. In addition, Perimeter matrices are
usually described by the number of contact perimeters.
4.2.3 Thermally Enhanced Matrix A thermally enhanced
matrix is a perimeter matrix with contacts added back in the
center. See Figure 4-3.
4.2.4 Staggered Matrix A staggered matrix is defined by
the removal of every other contact in an interstitial pattern.
This provides an effective minimum center-to-center contact
spacing of
√
2 x pitch of the full matrix. See Figure 4-4. In
order to retain the A1 contact position, the staggered matrix
must be developed using a full odd matrix.
4.3 Selective Depopulation In addition to depopulation
methods which lead to the matrices described above, con-
tacts may be removed selectively. Selective depopulation can
be accomplished in any manner as long as the pattern matrix
is not shifted from the center of the package outline. See Fig-
ure 4-5.
4.4 Attachment Site Planning The attachment site or
land pattern geometry recommended for BGA devices is
round with the diameter adjusted to meet contact pitch and
size variation. The diameter of the land should be no larger
than the diameter of the land at the package interface and is
typically 20% smaller than the normal diameter specified for
the ball contact for pitches greater than 1.0 mm and 10%
IPC-782143-2
Figure 3-2 Examples of plastic BGA package
configurations
IPC-SM-782A
Subject
Components with Ball Grid Array Contacts
Date
4/99
Section
14.0
Revision
—
Page2of6
smaller for pitches less than 1.0 mm. Refer to the manufac-
turer specification before finalizing land pattern array and
geometry.
4.4.1 Copper Defined Land Pattern The land patterns
described are defined by the etched copper. Solder mask
clearance should be a minimum of 0.075 mm from the etched
copper land. For applications requiring a clearance that is less
than recommended, consult with the printed board supplier.
4.4.2 Solder Mask Defined Land Pattern If solder mask
defined patterns are used, then adjust land pattern diameter
accordingly. See Section 6.0.
4.5 Defining Contact Assignment Array contact identifi-
cation is assigned by the column and row location. For
example, A1 contact position is always at an outside corner
position with alpha characters arranged in a vertical (row) pat-
tern from top to bottom. Numeric characters are assigned in
a horizontal (column) axis (I, O, Q, S, X and Z are omitted). See
Figure 4-6.
The designer should note that the A1 position is at the upper
left hand corner when the device is viewed from the top. Con-
tact pattern is defined when viewed from the bottom. The land
pattern provided on the host substrate is opposite of the con-
tact pattern (with A1 contact position again at the upper left).
IPC-782144-4
Figure 4-4 Staggered
matrix
IPC-782144-5
Figure 4-5 Selective
depopulation
IPC-782144-1
Figure 4-1 Bottom view of BGA devices
IPC-782144-2
Figure 4-2 One package size, two full matrices
IPC-782144-3
Figure 4-3 Perimeter and thermally enhanced matrices
IPC-SM-782A
Subject
Components with Ball Grid Array Contacts
Date
4/99
Section
14.0
Revision
—
Page3of6
5.0 HANDLING AND SHIPPING
For information on trays and shipping containers refer to
ACH:EIA-481-A, ACH:EIA-481-3, JEDEC CO-028, and
JEDEC CO-029.
6.0 LAND PATTERN ANALYSIS
The following provides an analysis of tolerance assumptions
and result in solder joints based on the land pattern dimen-
sions shown in Figure 4-6. The variations that exist in deter-
mining these land patterns include the diameter of the indi-
vidual ball, the positional accuracy of the ball in relationship to
a true position on the component and the board, and the
manufacturing allowance that can be held for the land on the
substrate that mount the particular ball. The land pattern of
the component (where the ball is attached) and the land pat-
tern of the substrate mounting structure (printed board)
should be as similar as possible. Component manufacturers
have made their determinations that the land pattern of pad
on the component should be less than the ball diameter. They
base their conclusions on the resulting nominal ball diameter
with a slight reduction in the land approximation. Pitch plays a
large role in the determination of what ball diameters can be
used in various combinations. Table 6-1 shows the character-
istics of those balls that are used with pitches of 1.5 mm
through 1.0 mm, as well as future ball sizes whose pitches fall
between 0.80 mm and 0.25 mm.
6.1 Land Approximation In each instance, component
manufacturers and board designers are encouraged to
reduce the land size by some percentage of the nominal ball
diameter. The amount of reduction is based on the original
ball size, which is used to determine the average land. In
determining the relationship between nominal characteristics,
a manufacturing allowance for land size has been determined
to be 0.1 mm between the Maximum Material Condition
(MMC) and Least Material Condition (LMC). Table 6-2 shows
the reduction characteristics, the nominal land size, and the
target land dimensions, as well as future approximations for
ball diameters of 0.40 mm and below.
6.2 Total Variation The total variation of the system con-
siders three major issues: positioning, ball tolerance, and sub-
strate tolerance. All three attributes added together result in a
worst case analysis, however as with other land patterns in
the standard, a statistical average is determined by using the
RMS (root, mean, square) value. Table 6-3 shows the total
variation in the system for each of the four ball sizes identified
in the standard.
It should be noted that the target value for lands on the sub-
strate of the component or the board should be at Maximum
Material Condition. The variation from the Maximum Material
Condition indicates that ball-to-land misalignment is achieved
IPC-782144-6a,b & c
Figure 4-6 Device orientation and contact A1 position
Table 6-1 Ball Diameter Sizes
Nominal Ball
Diameter (mm)
Tolerance
Variation (mm) Pitch (mm)
0.75 0.90 - 0.65 1.5, 1.27
0.60 0.70 - 0.50 1.0
0.50 0.55 - 0.45 1.0, 0.8
0.45 0.50 - 0.40 1.0, 0.8, 0.75
0.40 0.45 - 0.35 0.80, 0.75, 0.65
0.30 0.35 - 0.25 0.8, 0.75, 0.65, 0.50
0.25 0.28 - 0.22 0.40
0.20 0.22 - 0.18 0.30
0.15 0.17 - 0.13 0.25
IPC-SM-782A
Subject
Components with Ball Grid Array Contacts
Date
4/99
Section
14.0
Revision
—
Page4of6