IPC-TM-650 EN 2022 试验方法.pdf - 第86页

3.3 Operating Conditions. The evaluation of the plated- through holes shall be performed at room temperature (68 ° to 75 ° F) and the printed wiring boards to be evaluated shall be stabilized at that temperature for appr…

1.0

Scope

1.1

nondestructive inspection method for determining the

quality of plated-through connections in printed wiring boards.

1.2 Theory. Copper will display a resistivity of known value

depending upon the geometry of the shell and the conductiv-

ity of the copper. If the shell is not uniform, defects such as

cracks, voids, or thin spots in the copper will cause the mea-

sured resistance to be higher than the theoretical value. This

value is computed by using the equation given in Fig. 1.

2.0

Applicable Documents

IPC-TC-500

Specification

for copper plated through hole,

two-sided boards, rigid.

3.0

Test Specimen

3.1 Description of Specimens.

The

following types of

specimens can be tested using the equipment specified

herein:

(1) Printed wiring boards, either two-sided or multilayer,

which can fit properly within the neck of the test meter.

NOTE:

testing of plated-through holes in two-sided or

multilayer printed wiring boards, the measurement is the resis-

tance of the plating in the hole only and is not related to any

interconnected circuit terminating in that hole, unless there is

an electrically parallel circuit, i.e., two or more holes located

within 0.25″ of each other.

(2) Printed wiring boards up to 3/8’’ in thickness.

(3) Plated-through connections of any diameter which can

be spanned conveniently by the probes.

3.2

Specimen Preparation.

Insulating

materials such as

flux, conformal coatings, encapsulating compounds, adhe-

sives, mold release compounds, etc., shall be removed from

the terminal areas to allow a positive metal-to-metal contact to

be made between the probes and the plated-through hole

terminal area. Closely spaced conductors shall be masked to

prevent the probes from bridging between the terminal areas

and adjacent conductors. Whatever material is used to mask

the conductors shall be located in such a manner that the

probes are not separated from the hole to be measured.

Figure

1 Resistance Calculation of Plated-Through

Connection

The

Institute for Interconnecting and Packaging Electronic Circuits

2215 Sanders Road • Northbrook, IL 60062

IPC-TM-650

TEST

METHODS MANUAL

Number

2.2.13.1

Subject

Thickness,

Plating in Holes Microhm Method

Date

1/83

Revision

Originating Task Group

Printed Board Test Methods Task Group (7-11d)

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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3.3

Operating Conditions.

The

evaluation of the plated-

through holes shall be performed at room temperature (68° to

75° F) and the printed wiring boards to be evaluated shall be

stabilized at that temperature for approximately one hour prior

to evaluation.

4.0

Apparatus

4.1 Description of Equipment.

The

microhm resistance

meter used in the nondestructive testing employs the stan-

dard four*probe technique. The equipment is portable and

suitable for bench operation. The equipment consists of two

essential parts:

(1) the mechanical portion for providing physical attachment

with the test specimen and

(2) the electrical-electronic portion for providing the microhm

readout of the through connection being measured

The probes are tension-suspended to ensure positive interfa-

cial contact with the termination areas over a range of mate-

rial thicknesses.

4.2

The

meter impresses a constant ac current into the

through connection, and the voltage that develops across

the, hole is sensed. This voltage is amplified and observed

visually on a suitable meter or a digitized readout. See circuit

diagram in Fig. 2A.

5.0

Procedure

5.1 Calibration of Equipment.

order to provide valid

resistance measurements, the equipment must be calibrated

as specified in the manufacturers’ instruction manual

5.2

Test Steps.

The

steps to be performed in evaluating

the quality of plated-through holes in printed wiring board∼ are

as follows:

5.2.1 Calibrate

the equipment.

5.2.2

Prepare

and condition the specimen(s) to be

inspected per 3.2.

5.2.3

Position

the printed wiring board between the probes

as shown in Fig. 2B.

5.2.4

Depress

the upper probes until they Awes. come

locked over the plated-through hole.

Figure

2A Circuit for Resistance Measurements

Figure

2B Ideal Probe Placement on Pad

IPC-TM-650

Number

2.2.13.1

Subject

Thickness,

Plating in Holes Microhm Method

Date

1/83

Revision

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NOTE:

steady reading indicates that the probes am mak-

ing good contact. Trial settings to obtain the minimum resis-

tance value will indicate when the probes are properly located

over the interconnection.

5.2.5

poor electrical contact is evidenced, relocate the

probes until a minimum resistance is indicated.

NOTE:

During the microscopic inspection (30X) of the edges

of the plated-through hole and the adjacent areas on the ter-

minal area, there shall be no detectable damage to the sur-

faces by contact with the probes during testing. In the

absence of such surface defects, the microhm testing can

assuredly be considered nondestructive.

5.2.6

Read

and record the microhm value.

5.2.7

Compare

the microhm value with the plating thickness

of the standardization curve as illustrated in Fig. 3. The theo-

retical curves shown in Fig. 3 indicate to within 0.2-rail thick-

ness the plating in the through connection and for all practical

purposes are representative of the resistance-plating thick-

ness relationships encountered in practice.

NOTE:

This

comparison shall indicate if the plating thickness

of the through connection meets the acceptable thickness

requirements

5.2.8

When

this method is used, any reading above the

specified allowable microhm reading shall be reason for fur-

ther investigation of the defect for conformance to the require-

ments of the applicable fabrication specification.

5.2.9

Plating

thickness curves shall be generated by the

user.

6.0

Resistance Curves

6.1

Curves

for the resistances of plated-through holes of

three different diameters in 1/16’’ printed wiring boards are

presented in this test method (Fig. 3). Over coatings of gold,

tin-lead, etc., can have an effect on the micro-ohm readings

depending on the electrical resistance relative to the copper.

Resistivity of tin-lead is approximately ten times that of cop-

per, while gold is of the same resistivity.

6.2

eliminate material and equipment variables, the user

should develop thickness-resistance curves for his particular

condition based on metallographic cross-section measure-

ments (TM-650 Method 2.2.13). These curves may be used

as guides for acceptance of product.

IPC-TM-650

Number

2.2.13.1

Subject

Thickness,

Plating in Holes Microhm Method

Date

1/83

Revision

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