IPC-TM-650 EN 2022 试验方法--.pdf - 第749页

each ap prox imately 0.7 in x 5 in. Layers 5 and 6 have no trace routing, so removing them provides an 8 layer coupon. Con- versely, by d uplicating layers 5 and 6, a 14-layer or h igher layer count coupon can be obtaine…

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

IPC-TM-650

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Page

each approximately 0.7 in x 5 in. Layers 5 and 6 have no trace

routing, so removing them provides an 8 layer coupon. Con-

versely, by duplicating layers 5 and 6, a 14-layer or higher

layer count coupon can be obtained. Note: Inner layer copper

filling (similar to external layer copper thieving) can be applied

to inner layers. These two CAF test coupons have additional

features for identifying root cause failure site(s). Design data

should show the drill sizes to be used (example: 0.37 mm or

0.0145 in), but not the finished hole sizes after plating. Solder-

mask application is not required for these CAF test coupons.

• IPC-9256 CAF coupon evaluates the A2, A3 and A4 hole

wall to hole wall structures, with controlled spacings

between the adjacent plated through holes in both X and Y

in-line dimensions so good CAF test data is obtained even if

the laminate material machine direction lay-up is done incor-

rectly.

• IPC-9255 CAF coupon evaluates the A2, A3 hole wall to

hole wall structures, with controlled spacings between the

adjacent plated through holes in both X and Y in-line dimen-

sions (so good CAF test data is obtained even if the laminate

material machine direction lay-up is done incorrectly). This

coupon also evaluates the B2 structure where hole wall to

hole wall spacings are diagonal and useful for determining

the quality of the CAF testing performed (reference CAF test

method user guide).

[NOTE: These coupons can be run on production board lots

on unused portions of the working panel, allowing more cost-

effective on-going process and/or product monitoring of CAF

resistance.]

As a general rule, there should be enough CAF test boards

run within each sample test lot to have at least the equivalent

number of potential CAF failure sites as on a single targeted

specific application PWB.

4 Equipment/Apparatus or Material

4.1 Environmental Test Chamber

A clean test chamber

capable of producing and recording an environment of 65 ±

2 °C [149 ± 3.6 °F] or 85 ± 2 °C [185 ± 3.6 °F] and 87 +3/-2%

relative humidity, and that is equipped with cable access to

facilitate measurement cables to be attached to the speci-

mens under test.

4.2 Measuring Equipment

A high resistance meter

equivalent to that described in ASTM D-257, with a range up

to 10

ohms and capable of yielding an accuracy of ± 5% at

ohms with an applied voltage of 100 ± 2 VDC, or an

ammeter capable of reading 10

-10

amps and capable of yield-

ing an accuracy of ± 5% in combination with 100 ± 2 VDC

power supply. The values of resistors used

be verified

by reference resistors traceable to known industry or national

standards such as NIST.

4.3 Power Supply

A power supply capable of producing a

standing bias potential of 10 VDC up to 100 VDC with a

tolerance of ± 2 VDC, and current supply capacity of at least

1 Ampere (Amp).

4.4 Current Limiting Resistors

Tight control of the total

current limiting resistance value is critical for this test method.

One 10

ohm resistor in series be used for each current

path. Insert the current limiting resistors in series with the ter-

minating leads going to each test pattern. Note that some test

equipment has current limiting resistors built into the testing

systems. For the purposes of this standard test, excluding the

current limiting resistor and for each CAF test circuit, the total

series resistance of the measuring equipment and wires

be more than 200 ohms. A lower total resistance value

will increase potential for damage to the test board when a

CAF failure occurs. A higher total current limiting resistance

value for each test net removes test conditions further from

actual field conditions and is not recommended.

4.5 Connecting Wire

Use PTFE- or PFE-insulated copper

wires and solder the copper wire directly to the board to con-

nect test points for each test board to the measurement

apparatus. The insulation material should not outgas during

testing.

IPC-2625-3

Number

2.6.25

Subject

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

Date

02/21

Revision

IPC-TM-650

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4.6 Other Dedicated Fixtures

Hard-wiring is the default

connection method. Other dedicated fixtures may be used,

provided that the fixture does not change the resistance by

more than 0.1 decade compared to a comparable hard-wired

system when measured at the test conditions. These fixtures

should be checked for their resistance values frequently.

5 Procedure

5.1 Test Specimen Preparation

5.1.1 Sample Identification

Use a method for identifying

each test board that does not cause contamination, such as

a scribe, making marks away from the biased area(s) of the

specimen. Test boards

be handled by the edges of the

board only, and the use of noncontaminating gloves is recom-

mended. Each board

be clearly marked to identify the

simulated assembly reflow and reword processing, and other

differentiating parameters, completed prior to CAF resistance

testing.

5.1.2 Prescreen fo r Opens and Shorts

Perform

as-received insulation resistance measurements using a mul-

timeter to make connection to each net, and check for gross

defects. Check for shorts at a 1.0 megohm setting. No opens

are allowed in connected nets.

5.1.3 Simulated Assembly & Rework

CAF test samples

go through representative assembly and rework thermal

cycling for the application. Default lead-free simulated assem-

bly and rework is 6X at 260 °C. Default simulated eutectic tin-

lead assembly and rework is 6X at 230 °C. For reference see

IPC-TM-650, 2.6.27 (method for assembly simulation).

5.1.4 Cleaning

Entirely clean each sample (CAF test

board) per IPC-TM-650, Method 2.3.25, Detection and Mea-

surement of Ionizable Surface Contaminants by Resistivity of

Solvent Extract by immersion washing until the level of ionic

contamination is reduced to less than 1.0 microgram NaCl

equivalent per square centimeter and for a maximum of 20

minutes. Boards not achieving this level of cleanliness within

20 minutes

be scrapped for the purposes of this test.

See IPC-TM-650, Method 2.6.27, Thermal Stress, Convection

Reflow Assembly Simulation.

5.1.5 Connecting Wire

Plated through holes near one

edge of the board may be used for connecting wire to each

test circuit. The test board

be covered with noncontami-

nating film to prevent flux spattering during the wire attach

process. After stripping back the wire insulation, use water

white rosin (per J-STD-004, Type B) and best soldering tech-

nique (per J-STD-001, Class 1 or 2) to solder (per J-STD-006,

Type Sn63) PTFE- or PFE-insulated wires to the connection

points on each test board. Ensure against damaging PWB

laminate material adjacent to the plated holes during soldering

by using appropriate time/temperature parameters for the sol-

dering iron.

5.1.6 Cleaning After Attachment

Perform appropriate

local cleaning and rinsing after the attachment of the connect-

ing wires. Isolation resistance between connecting wire

attachment sites should remain excellent through 96 hours

conditioning. Note: Each CAF test failure that does occur dur-

ing subsequent testing should be checked to determine

whether the connecting wire attach area is the low resistance

site. If the connecting wire attach area rather than the daisy

chain area is the low insulation resistance site, then that test

sample is no longer valid for data analysis.

5.1.7 Dry

Bake sample boards for a minimum of 30 min-

utes in a clean oven at 105 ± 2 °C [221.0 ± 3.6 °F].

5.1.8 Precondition

Precondition test board samples in a

bias-free state (no electrical potential applied to any test pat-

tern) for 30 minutes minimum at 23 ± 2 °C [73.4 ± 3.6 °F] and

50 ± 5% relative humidity prior to any initial insulation resis-

tance measurements [measuring insulation resistance of each

daisy-chain net on each test board before starting the first 96

hours (± 30 minutes) of bias-free temperature and humidity

conditioning].

5.1.9 Temperature/Humidity/Bias ( T/H/B ) Chamber

Place the specimens in the environmental test chamber in a

vertical position such that the air flow is parallel to the direc-

tion of all test boards in the chamber. Allow at least approxi-

mately 2.5 cm [nominally 1.0 in] between each test board.

Place the test boards, as much as possible, toward the cen-

ter of the chamber to help ensure against nonoptimum air flow

and/or drops of condensation falling onto the test boards.

Dress all wiring away from the test patterns, keeping the wires

away from the test patterns as they are routed to the outside

of the chamber. Also, wire should not impede airflow around

the samples. Set the chamber temperature and humidity with

a ramp rate of one hour.

Number

2.6.25

Subject

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

Date

02/21

Revision

IPC-TM-650

shall

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