IPC-TM-650 EN 2022 试验方法-- - 第747页
45° angle results in a square 1.08 mm x 1.08 mm [0.04252 in x 0.04252 in] grid. Note: the sketches do not look square when tipped 45° but, the CAF Test Boards do. The resulting via ed ge to vi a e dge sp acin gs ar e: 0 …
IPC-9253 and IPC-9254 Test Structures A1 through A4
The four structures A1-A4 each have five rows of connected
vias. Within each structure each row has 42 vias with alternat-
ing rows being tied to positive or negative electrodes. The via
edge to via edge spacing is varied from one structure to the
next by using a different drilled hole size on the same 1 mm
[0.040 in] pitch between rows of daisy chain vias. The result-
ing via edge to via edge spacings are: 0.27 mm, 0.38 mm,
0.51 mm, 0.65 mm [0.0106 in, 0.0150 in, 0.0201in, 0.0256
in]. Other than the use of different drilled hole sizes and a small
change in pad sizes, the four structures are identical. The vias
in these four test structures A1-A4 are aligned with the glass
fibers. Since A1-A4 evaluate susceptibility to CAF in just one
direction, test coupons should be manufactured so that the
machine direction of the woven fiber laminate reinforcement is
perpendicular to the rows of same-net daisy chain vias
(machine direction tends to fail first).
For both A and B test structures the inner and outer layer
pads are the same, i.e., the same pad size is consistently
used within a given test structure, although it does change
from structure to structure. All via to electrode connections
are made on layer 2 and are repeated on layer 9 so that a
single etch-out will not affect results. Traces from via to elec-
trode are routed on internal layers rather than external layers
to minimize potential for surface insulation resistance failure.
Design details for each test structure A1-A4 follows in Table 1.
Note: ‘‘Manhattan Distance’’ is the shortest orthogonal
distance along the X- and/or Y- axes lines between adjacent
drilled hole features (corresponds to the orthogonal nature
of the laminate material’s woven glass fiber reinforcement
(Figure 2).
IPC-9253 and IPC-9254 Test Structures B1 through B4
The four ‘‘B’’ test structures have seven alternating rows of
vias. Within each structure, alternating rows have either 27 or
26 vias with the alternating rows being tied to either positive
or negative electrodes. The via edge to via edge spacing is
varied from one structure to the next by using a different
drilled hole size on the same 1.52 mm x 1.52 mm [0.05984 in
x 0.05984 in] via grid. The 1.52 mm x 1.52 mm [0.05984 in x
0.05984 in] grid has an interstitial via therefore, tipping at a
IPC-2625-1
Number
2.6.25
Subject
Conductive Anodic Filament (CAF) Resistance Test: X-Y Axis
Date
02/21
Revision
C
IPC-TM-650
—
b)
IPC-9254
A1
B1
A2
B2
A3
B3
A4
B4
C1
C3
C2
C4
D1
D2
Area
of
PTHs
for
Test
Wire
Attachment
Figure
1
Layouts
of
Two
Versions
of
the
CAF
Test
Boards
Page
2
of
11
45° angle results in a square 1.08 mm x 1.08 mm [0.04252 in
x 0.04252 in] grid. Note: the sketches do not look square
when tipped 45° but, the CAF Test Boards do. The resulting
via edge to via edge spacings are: 0.26 mm, 0.37 mm,
0.51 mm, 0.62 mm [0.0102 in, 0.0146 in, 0.0201 in,
0.0244 in]. Other than the use of different drilled hole sizes
and a small change in pad sizes, the four structures are iden-
tical. The vias in the ‘‘B’’ test structure are not aligned with the
glass fibers. If the failure mode is along glass bundles it is rea-
sonable to expect the ‘‘B’’ test structure to perform better
than the ‘‘A’’ structure for equivalent via edge to via edge
spacings. Within a given test structure, the inner and outer
layer pads for all 10 layers are the same, i.e., the same pad
size is consistently used within a given test structure although,
it does change from structure to structure. All via to electrode
connections are made on layer 1 and are repeated on layer 10
so that a single etch-out will not affect results.
A conceptual representation of the ‘‘B’’ test structure of
the coupons in Figure 1 is shown to the upper right.
Design details on each of the four ‘‘B’’ test structures follows
in Table 2.
3.2 Other Structures
Section C is designed to evaluate
plated-through hole (PTH)-to-plane layer spacings. It is rec-
ommended to use the registration coupon per test board (IPC
Test Pattern F) when CAF testing includes this region. Section
D in the IPC-9254 design is for layer-to-layer Z-axis CAF test-
ing. Section D in the IPC-9253 is for evaluating CAF resis-
tance in a press-fit compliant pin connector application. The
feature in the D region is an optional feature that is present
automatically with the design. However, the A, B and C
regions
remain as designed in order to provide a stan-
dard basis of comparison.
The CAF test board with 10 layers is designated to evaluate
thin single-ply constructions typically used on high perfor-
mance boards. This board construction stackup can be
reduced down to: (a) four layers by eliminating layers 3
through 8 and (b) only test structures A and B, when just
evaluating differences between laminate materials.
3.3 CAF Test Board Design
This 10-layer CAF test board
for evaluating the insulation resistance between internal con-
ductors within a printed wiring board has the following key
features for evaluating hole-hole CAF resistance (Figure 3).
Holes In-Line (in-line with glass fiber direction): There are two
rows of 42 signal-1 vias intermeshed with three rows of 42
Outer layer pad size 0.86 mm [0.0339 in] 0.81 mm [0.0319 in] 0.75 mm [0.0295 in] 0.69 mm [0.0272 in]
Inner layer pad size 0.86 mm [0.0339 in] 0.81 mm [0.0319 in] 0.75 mm [0.0295 in] 0.69 mm [0.0272 in]
Drilled hole size 0.74 mm [0.0291 in] 0.63 mm [0.0248 in] 0.51 mm [0.0201 in] 0.37 mm [0.0146 in]
Via edge to via edge
(shortest distance)
0.27 mm [0.0106 in] 0.38 mm [0.0150 in] 0.51 mm [0.0201 in] 0.65 mm [0.0256 in]
Via edge to via edge
(Manhattan Distance)
0.27 mm [0.0106 in] 0.38 mm [0.0150 in] 0.51 mm [0.0201 in] 0.65 mm [0.0256 in]
On IPC-9254
, bias
applied between:
J1, J5 J2, J5 J3, J5 J4, J5
IPC-2625-2
Number
2.6.25
Subject
Conductive Anodic Filament (CAF) Resistance Test: X-Y Axis
Date
02/21
Revision
C
IPC-TM-650
—
Table
1
Test
Structures
A1
through
A4
Design
Rules
A1
A2
A3
A4
only
"Manhattan
Distance"
=
a+b
Figure
2
Manhattan
Distance
(Shortest
Orthogonal)
shall
Page
3
of
11
signal-2 vias; for a total of 168 potential in-line PTH-PTH fail-
ures for each spacing distance.
Holes Staggered (closest PTH-PTH spacing in diagonal direc-
tion): There are three rows of 26 signal-1 vias intermeshed
with four rows of 27 signal-2 vias; for a total of 312 potential
diagonal PTH-PTH failures for each spacing distance.
3.4 CAF Test Coupon/Board Quantity
The CAF testing
data analysis technique recommended for either of these CAF
test coupon/board designs requires a minimum 25 CAF test
boards to be run per sample lot per bias level for statistical
significance. This provides a total of 4,200 potential in-line
hole-hole CAF failure sites and 7,800 potential diagonal hole-
hole CAF failure sites for each unique sample/condition set.
For comparison, on a 1,428 I/O BGA device (Figure 4) there
are about 500 power/ground pins. So with an average of
slightly less than two adjacent power/ground pin spacings per
pin there are about 1,000 potential in-line hole-hole CAF fail-
ure sites per BGA device. For a production board with the
equivalent of three of these BGA devices and about 1200
passives or other components with close power/ground pin
spacings, the total number of opportunities for in-line CAF fail-
ure would then be about 4,200 (about the same as the entire
CAF test board sample lot of 25 pieces).
3.5 CAF Test Small Coupon Designs
The IPC-9255 and
IPC-9256 CAF test coupon designs (Figure 5) have 10 layers,
Outer layer pad size 0.94 mm [0.0370 in] 0.89 mm [0.0350 in] 0.84 mm [0.0330 in] 0.75 mm [0.0300 in]
Inner layer pad size 0.94 mm [0.0370 in] 0.89 mm [0.0350 in] 0.84 mm [0.0331 in] 0.75 mm [0.0295 in]
Drilled hole size 0.81 mm [0.0319 in] 0.71 mm [0.0280 in] 0.57 mm [0.0224 in] 0.46 mm [0.0181 in]
Via edge to via edge
(shortest distance)
0.26 mm [0.0102 in] 0.37 mm [0.0146 in] 0.51 mm [0.0201 in] 0.62 mm [0.0244 in]
Via edge to via edge
(Manhattan Distance)
0.37 mm [0.0146 in] 0.52 mm [0.0205 in] 0.72 mm [0.0283 in] 0.88 mm [0.0346 in]
On IPC-9254
, bias
applied between:
J7, J11 J8, J11 J9, J11 J10, J11
IPC-2625-3
IPC-2625-4
Number
2.6.25
Subject
Conductive Anodic Filament (CAF) Resistance Test: X-Y Axis
Date
02/21
Revision
C
IPC-TM-650
―
Table
2
Test
Structures
B1
through
B4
Design
Rules
B1
B2
B3
B4
only
Figure
3
CAF
Test
Board
PTH-PTH
Spacing
Design
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7
928
Signal
Pins
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Power/
GND
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Figure
4
BGA
Device
I/O
Pin
Assignment
Page
4
of
11