IPC-TM-650 EN 2022 试验方法.pdf - 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 edge to via edge spacings are: 0.26 mm,…

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

Figure 1 Layouts of Two Versions of the CAF Test Boards

Area of PTHs for Test Wire Attachment

a) IPC-9253 b) IPC-9254

IPC-TM-650

Number

2.6.25

Subject

Conductive Anodic Filament (CAF) Resistance Test: X-Y Axis

Date

02/21

Revision

Page2of11

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 shall 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

Table 1 Test Structures A1 through A4 Design Rules

A1 A2 A3 A4

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 only, bias

applied between:

J1, J5 J2, J5 J3, J5 J4, J5

IPC-2625-2

Figure 2 Manhattan Distance (Shortest Orthogonal)

"Manhattan Distance" = a+b

IPC-TM-650

Number

2.6.25

Subject

Conductive Anodic Filament (CAF) Resistance Test: X-Y Axis

Date

02/21

Revision

Page3of11

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,

Table 2 Test Structures B1 through B4 Design Rules

B1 B2 B3 B4

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 only, bias

applied between:

J7, J11 J8, J11 J9, J11 J10, J11

IPC-2625-3

Figure 3 CAF Test Board PTH-PTH Spacing Design

Staggered Hole to Hole (Section B)

In-Line Hole to Hole (Section A)

IPC-2625-4

Figure 4 BGA Device I/O Pin Assignment

928 Signal Pins

500 Power/ GND Pins

IPC-TM-650

Number

2.6.25

Subject

Conductive Anodic Filament (CAF) Resistance Test: X-Y Axis

Date

02/21

Revision

Page4of11