IPC-TM-650 EN 2022 试验方法.pdf - 第603页

3.1 Conductor Any high resistance conductor used in HDI applications (polymer thick film, via fill, metal, metal compos- ites, transient liquid phase sintering, organometallic, conduc- tive polymer, etc.). Copper foils u…

Scope

This

test method covers the two-wire resistance

test for the determination of the volume resistivity of polymer-

based conductive pastes and other conductive materials used

in HDI. This test is valid for conductive materials with volume

resistivity on the order of 10

-5

Ω-cm

or higher. For measuring

resistivity on highly conductive materials or any material that

cannot be patterned into a circuit pattern, a four-wire (Kelvin

Probe) test method, such as IPC-TM-650, Method 2.5.14, is

recommended.

1.1

Definition

Volume

resistivity is a material property that

can be utilized to calculate the resistance in a circuit design.

For materials with high resistivity, a two-wire resistance test

may be used to measure the volume resistivity.

The resistance in any sample (R in units of Ω) is related to the

dimensions of the test circuit and the volume resistivity (ρ)

inherent in the material (see Figure 1).

R =ρ

(

)

W, and t are the length, width, and thickness respectively

of the test circuit (in cm). The quantity L/W is called a square,

([). The volume resistivity can then be expressed as:

ρ=

(

)

[

with

units of ohms-cm (Ω-cm).

Applicable Documents

IPC-TM-650

Test

Methods Manual

2.5.14 Resistivity of Copper Foil

Test Specimen

The

test specimen is a 0.5 mm wide

serpentine circuit pattern (see Figure 2) with a length of

between 200 [ and 1000

(length

equal to 200 to 1000

times the width) prepared by screen printing or other meth-

ods. Specimens may be prepared by other methods, as long

as they have measurable dimensions. If materials cannot be

prepared in a circuit pattern, see 6.2.

IPC-2-5-17-2-1

Figure

1 Resistivity Diagram

Conductor

Length = L

Current Flo

Width = W

Thickness = t

IPC-25172-2

Figure

2 Serpentine Pattern

The

Institute for Interconnecting and Packaging Electronic Circuits

2215 Sanders Road • Northbrook, IL 60062

IPC-TM-650

TEST

METHODS MANUAL

Number

2.5.17.2

Subject

Volume

Resistivity of Conductive Materials Used in

High Density Interconnection (HDI) and Microvias,

Two-Wire Method

Date

11/98

Revision

Originating Task Group

HDI Test Methods Task Group (D-42a)

Material

in this Test Methods Manual was voluntarily established by Technical Committees of the IPC. This material is advisory only

and its use or adaptation is entirely voluntary. IPC disclaims all liability of any kind as to the use, application, or adaptation of this

material. Users are also wholly responsible for protecting themselves against all claims or liabilities for patent infringement.

Equipment referenced is for the convenience of the user and does not imply endorsement by the IPC.

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3.1

Conductor

Any

high resistance conductor used in HDI

applications (polymer thick film, via fill, metal, metal compos-

ites, transient liquid phase sintering, organometallic, conduc-

tive polymer, etc.). Copper foils used in HDI should be tested

according to IPC-TM-650, Method 2.5.14.

3.2

Substrate

Unless

otherwise specified, the substrate

shall be a PCB laminate, etched to remove all copper. Other

acceptable substrates (when specified) may be plate glass,

insulated metals, or flexible circuit base material.

3.3

Screen

For

materials that are screen printed, unless

otherwise specified, the screen shall be as outlined in 3.3.1

through 3.3.3.

3.3.1

Type

200

mesh, stainless steel, 35 µm wire

3.3.2

Emulsion

<15

µm emulsion build up

3.3.3

Wire Angle

22.5°

to 45°

3.4

Typical Patterns

3.4.1 Pattern

Serpentine

with 0.5 mm wide lines and

spaces and 200 [ to 1000 [ long (10 cm to 50 cm). The

larger the number of squares, the higher the resistance and

more accurate the measurement.

3.4.2

1.25

mm snapoff

0.2 Kg to 1.0 Kg squeegee pressure per cm squeegee length

2.5 cm/sec. to 12.5 cm/sec. draw speed

3.5

Cure Conditions

The

conductor shall be cured

according to the manufacturer’s specifications. Parts are

allowed to cool to room temperature, after which they are

measured for resistance.

Equipment/Apparatus

4.1

digital multimeter capable of resolving 0.1 Ω resis-

tance is required. This unit must be accurately calibrated. An

example would be a Fluke 70 series digital multimeter. For

improved accuracy in this measurement, a larger number of [

and/or a more sensitive multimeter can be utilized.

4.2

screen printer capable of making 0.5 mm line/space

circuitry, or any other method for preparing the desired circuit

pattern

4.3

Equipment

to measure the test circuit conductor length,

width, and thickness. If the number of squares is accurately

known (length/width of circuit) from the artwork and standard

process conditions, then only the thickness needs to be mea-

sured on each specimen. Thickness can be determined by

various methods: cross-section/optical microscopy, profilo-

meter measurement, or calculation from deposition weight

and material density. If the circuit thickness is very uniform,

then optical sectioning is the preferred method for obtaining

the thickness. If the circuit thickness is thought to be non-

uniform, thickness may then be determined by averaging pro-

filometer readings or determining average thickness from the

weight of the material deposited (knowing the length, width,

and density that the thickness can be determined).

Procedure

5.1 Samples

Prepare

a minimum of five test specimens

according to 3.1 through 3.5.

5.2

Conditioning

Condition

the specimens at 23°C ± 5°C,

50% RH (± 5%) for 24 hours.

5.3

Measurement

5.3.1

Measure

the circuit length, width, and thickness using

the equipment described in 4.3.

5.3.2

Apply the digital multimeter leads to the pads at each

end of the circuit. Measure and record the resistance in ohms.

For a resistance less than 2 Ω, see 6.1.

5.3.3

Measure

the resistance of a minimum of five speci-

mens and average the values.

5.4

Calculation

Calculate

the volume resistivity for each

specimen from the equation below:

(

)

where:

= average resistance of a single specimen in ohms

t = thickness of the conductive specimen in cm

L = length conductive specimen in cm

W = width conductive specimen in cm

Note: The ratio L/W is the number of squares.

IPC-TM-650

Number

2.5.17.2

Subject

Volume

Resistivity of Conductive Materials Used in High Density

Interconnection (HDI) and Microvias, Two-Wire Method

Date

11/98

Revision

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Calculate

the average resistivity from the sum of the specimen

volume resistivities:

ave

ρi

where:

= number of specimens measured

Note: The units of resistivity are Ω-cm.

5.7

Report

5.7.1

Report

the volume resistivity in units of Ω-cm.

5.7.2

Report

the substrate used in the test.

5.7.3

Report

the test circuit length, width (or squares), and

thickness.

6 Notes

6.1

Low Resistance Measurements

For

test circuits with

a resistance less than 2.0 Ω, the contact resistance between

the probe and the pads will be significantly relative to the

resistance arising from the test circuit. The 2.0 ohm lower

limit, in combination with the 0.1 ohm sensitivity of the multi-

meter, provides for a minimum error of 5%.

One solution is to increase the length of the circuit (increase

the number of squares) to increase the resistance. Another

solution for measuring resistivity on a highly conductive mate-

rial is to change to a four-wire (Kelvin Probe) test method,

such as IPC-TM-650, Method 2.5.14.

6.2

Test Circuit Specimens

is anticipated that some

materials cannot be formed into a uniform test circuit, as

called out for in this test method. It is recommended that

these materials be tested with a four-wire method (IPC-TM-

650, Method 2.5.14) and an alternative construction.

For example, a thin film of conductive material (i.e., paste or

conductive film) can be placed between two metal plates and

the resistivity may be determined using the four-wire (Kelvin

Probe) method. The material thickness and contact area must

be known, and the material must be sufficiently compliant to

completely wet (contact) the two plates.

6.3

Other References

Gilleo,

Ken, Polymer Thick Films, Van Nostrand Reinhold,

1996

IPC-TM-650

Number

2.5.17.2

Subject

Volume

Resistivity of Conductive Materials Used in High Density

Interconnection (HDI) and Microvias, Two-Wire Method

Date

11/98

Revision

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