IPC-TM-650 EN 2022 试验方法.pdf - 第630页

6.1 Ground Measurement Determination of tip-to-ground resistance is accomplished by using a basic ohmmeter circuit as represented in Figure 2. It works by passing a current through the tip and its grounding circuit and m…

Scope

This

test method describes the measurement of

the DC tip-to-ground resistance of an electric hand soldering/

desoldering tool designed with a grounded tip. Measurement

of tip-to-ground AC reactance is outside the scope of this test

method. Also, measurement of soft grounded or equipment

with insulated tips is outside the scope of this test method.

There are three times when ground testing should be done:

• Equipment qualification for purchase

• Incoming inspection of new or repaired equipment

• Process monitoring (periodic checks)

Determination of tip-to-ground resistance is accomplished by

using a basic ohmmeter circuit, passing a current through the

tip and its grounding circuit and measuring the resultant volt-

age drop. The values used in this test eliminate error caused

by the Seebeck (thermocouple) effect.

Warning

This

is a laboratory test procedure that may, of

necessity, expose terminals that carry line voltages. All stan-

dard laboratory safety procedures regarding the setup and

performance of tests with line voltage equipment must be

observed at all times.

Caution

This

test is performed with soldering systems at

their normal operating temperature. Test personnel must take

adequate precautionary steps to protect themselves and oth-

ers from potential burns.

Applicable Documents.

ANSI/J-STD-001

Requirements

for Soldered Electrical and

Electronic Assemblies.

IPC-TM-650

Test

Methods Manual

2.5.33 Measurement of Electrical Overstress from Solder-

ing Hand Tools

Test Specimens

Test

specimens for this procedure are

detailed in Method 2.5.33.

Equipment/Apparatus

4.1

Test

electrode per Method 2.5.33

4.2

Constant

current source capable of providing 10 milli-

amps DC

4.3

millivoltmeter capable of measuring at least 60 mv

DC and having a resolution of 1 mv DC

4.4

Resistor,

4.99Ω 1% precision

⁄

or greater (any com-

mercially available brand carbon or metal film)

4.5

Preparation of Apparatus

Connect

the apparatus as

illustrated in Figure 1. The negative electrode of the test appa-

ratus shall make a good electrical connection to the ground

reference point of the Unit Under Test (UUT). The UUT shall be

turned on and adjusted (if applicable) to achieve normal oper-

ating temperature.

Note: The plug is in the receptacle during measurements.

It’s shown unplugged in Figure 1 for clarity. Non-US power

receptacles may be different from that illustrated.

4.6 Calibration and Standardization

The

apparatus is

checked by separately placing two resistive elements across

the test apparatus’s electrodes: a shorting wire (0.0Ω) and

4.99Ω 1% precision

⁄

or greater resistor. The combination

of the current source and the measuring/indicating device will

be accurate to within ± 0.2Ω (± 4% of upper limit).

Procedure

Once

the electrodes are in position and the

test apparatus is operating, touch the HOT tip of the UUT to

the tinned area of the test electrode. Apply solder to form a

good electrical contact. Wait for the reading to stabilize, then

record the reading.

5.1

Calculation and Interpretation of Results

Even

though

the meter reads out millivolts, using 10 ma DC for

excitation current results in the displayed numbers represent-

ing the resistance in ohms without calculation, except for

decimal place shifting (i.e., a readout of 30 mv dc indicates

3.0Ω).

The reading shall be equal to or less than 5.0Ω.

6 Notes

tracking test results, record the measured values

on a copy of the form found in Method 2.5.33.

The

Institute for Interconnecting and Packaging Electronic Circuits

2215 Sanders Road • Northbrook, IL 60062

IPC-TM-650

TEST

METHODS MANUAL

Number

2.5.33.1

Subject

Measurement

of Electrical Overstress from

Soldering Hand Tools - Ground Measurements

Date

11/98

Revision

Originating Task Group

Manual Soldering Task Group (5-22c)

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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6.1

Ground Measurement

Determination

of tip-to-ground

resistance is accomplished by using a basic ohmmeter circuit

as represented in Figure 2. It works by passing a current

through the tip and its grounding circuit and measuring the

resultant voltage drop. This test method recognizes the ther-

mocouple effect present due to the assembly comprising dif-

ferent metallic materials whose junctions operate at different

temperatures (including the test apparatus electrodes). Test-

ing using ohmmeters having too low excitation current has

resulted in the thermocouple voltage introducing a significant

error or even causing a negative resistance reading. Error from

the thermocouple effect is made insignificant by increasing the

excitation current, thus increasing the voltage drop. Testing

has demonstrated an excitation current of 10 milliamps suf-

fices.

The voltage measuring device must indicate the voltage drop

in such a manner that the reading the operator sees directly

reflects the resistance in ohms and tenths of ohms. No calcu-

lations other than decimal place shifting should be used.

6.2

Constant Current Source

The

constant current

source can be an off-the-shelf unit, a custom-built active cir-

cuit, or a simple passive circuit. Figure 3 shows a very simple

way to achieve a 10 ma source accurate enough for measur-

ing soldering systes.

This circuit works because the battery voltage is high com-

pared to the drop across the UUT. Assume a battery voltage

of 48 volts and a dropping resistor of 4800 ohms. When the

resistance of the UUT equals zero, the current will be 10 ma.

IPC-2.5.33.1-1

Figure

1 Test Apparatus

10 MA.

CURRENT

SOURCE

GROUND

REFERENCE

POINT

MILLI-

VOL

METER

ELECTRODE

( )

UNIT

UNDER

TEST (UUT)

TEST

ELECTRODE ( )

IPC-2.5.33.1-2

Figure

2 Block Diagram of Test Apparatus

UUT

10 MA

CURRENT

REGULA

TOR

MILLIVOLT

METER

IPC-TM-650

Number

2.5.33.1

Subject

Measurement

of Electrical Overstress from Soldering Hand

Tools - Ground Measurements

Date

11/98

Revision

age2of3

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the resistance of the UUT rises to the upper limit of 5Ω, the

current will be 9.989 ma, just outside 0.1% on the low side.

This inaccuracy is well within the limits of the stanard.

able 1 Examples for Battery, Dropping

Resistor, and Accuracy

R Accuracy

600 -0.8%

9 900 -0.6%

12 1200 -0.4%

24 2400 -0.2%

48 4800 -0.1%

IPC-2.5.33.1-3

Figure

3 Simple Constant Current Source

UUT

TO 5

OHMS

10 MA

CURRENT

MILLIVOLT

METER

IPC-TM-650

Number

2.5.33.1

Subject

Measurement

of Electrical Overstress from Soldering Hand

Tools - Ground Measurements

Date

11/98

Revision

age3of3

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