IPC-TM-650 EN 2022 试验方法.pdf - 第604页

Calculate the average resistivity from the sum of the specimen volume resistivities: ρ ave = Σ ρ i n n where: n = number of specimens measured Note: The units of resistivity are Ω -cm. 5.7 Report 5.7.1 Report the volume …

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

age3of3

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Scope

This

method describes the test procedures

required to measure the characteristic impedance of flat

cables.

To keep this test method as simple and straightforward as

possible, balanced and differential signal lines are not

addressed. Also, the effect of flat cable against a ground

plane is not shown, because of the difficulty in determining

what a lab standard ground plane should be.

1.2

General

Characteristic

impedance (Z

)

for high fre-

quency pulses is defined electrically as the square root of the

inductance divided by the capacitance (C). In equation form:

√

Accuracy

and consistency of impedance is required to match

the characteristics of the other electronic circuit components.

Variations and mismatches in impedance create undesirable

pulse reflections and pulse distortions. These reflections and

distortions increase attenuation and crosstalk. The character-

istic impedance of flat cables is primarily dependent upon the

dielectric properties of the insulation and the cable geometry.

It is directly proportional to conductor spacing and is inversely

proportional to conductor size and the effective dielectric con-

stant of the insulation. Therefore, consistency of impedance is

achieved by maintaining uniformity of the insulation dielectric

constant and by maintaining accurate control over conductor

dimensions and spacing of adjacent conductors.

Characteristic impedance (Z

)

is usually measured by time

domain reflectometry (TDR).

Measurement of Z

with

a TDR consists of sending a pulse

down a length of cable and then comparing the reflection

obtained to that obtained from a laboratory standard of known

impedance. Z

a cable is fully defined when three values

have been measured:

1. The average Z

for all signal lines in a length of cable when

the cable is suspended in air.

2. The maximum change in impedance (or reflection coeffi-

cient) at any point on any signal line of the cable when the

cable is suspended in air.

3. The maximum change in impedance when the cable is

clamped against a ground plane.

Measurement of the preceding values is performed by use of

the setup illustrated in Figure 1. The laboratory standard is

connected to the TDR generator output, and the cable with

unknown Z

is connected to the end of the laboratory stan-

dard. When a single-ended (unbalanced) cable is to be tested,

connection to the laboratory standard consists of (1) the cable

signal conductor to the laboratory-standard signal conductor,

and (2) the ground conductors associated with the cable sig-

nal conductor to the laboratory standard ground. The far end

of the cable may be left unterminated, or it may be terminated

with a precision resistor to verify the laboratory standard. Bal-

anced cable (which carries simultaneous positive and negative

pulses) cannot be directly tested for impedance in this man-

ner; however, a close approximation can be achieved by

selecting an axis of symmetry between two signal conductors

and then testing only one signal conductor and its associated

ground conductor.

The typical oscilloscope trace obtained when testing a cable

is illustrated in Figure 2.

Test Specimen

3.1

One

pre-production or production sample 0.9 m to 3 m

long. The number of test samples should be determined by

the manufacturer and/or user.

Equipment/Apparatus

IPC-2-5-18-1

Figure

1 TDR Test Set-up for Measuring Characteristic

Impedance

TRD

Ref Z Airline

Hang

Test Cable

in Air

RG 58 C

Cable

Connection

Device

Non-Metallic

Surface

The

Institute for Interconnecting and Packaging Electronic Circuits

2215 Sanders Road • Northbrook, IL 60062

IPC-TM-650

TEST

METHODS MANUAL

Number

2.5.18

Subject

Characteristic

Impedance Flat Cables (Unbalanced)

Date

7/84

Revision

Originating Task Group

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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