IPC-TM-650 EN 2022 试验方法.pdf - 第631页

If the resistance of the UUT rises to the upper limit of 5 Ω , 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. T able 1 Examples for Battery , Dr…

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

电子技术应用　　　　　　　ｗｗｗ．ＣｈｉｎａＡＥＴ．ｃｏｍ

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

电子技术应用　　　　　　　ｗｗｗ．ＣｈｉｎａＡＥＴ．ｃｏｍ

Scope

This

test method deals only with transients gener-

ated within the Unit Under Test (UUT) and not with transients

originating elsewhere (i.e., power line transients), which propa-

gate through the UUT.

This procedure measures transient voltage events appearing

at the hot tip of an electric hand soldering/desoldering tool,

which could be seen by the workpiece. The test electrode and

measuring equipment represent a workpiece having a high

impedance.

There are two times when transients testing should be done:

• Equipment qualification for purchase

• Incoming inspection of new or repaired equipment

A storage oscilloscope is used to observe and measure tran-

sient events. The test electrode is coupled to the vertical input

of the oscilloscope via a 10 MΩ probe. The UUT may be iso-

lated from ambient electronic noise by placing it in a screen

room or shielded enclosure and supplying filtered AC power.

Inside the shield, the hot tip of the UUT is touched to the test

electrode.

This test may be falsely influenced by radio frequency interfer-

ence and electromagnetic interference from lighting and

equipment found in the workplace and testing area. This will

normally be demonstrated by ambient transients of 1.5 V peak

being present. At a minimum, shielded test leads should be

utilized. To avoid these influences it may be necessary to per-

form the leakage and transient tests in a screen room. In lieu

of a screen room a separate test procedure, see Method

2.5.33.4, which makes a low cost shielded enclosure, which

should provide adequate shielding for the performance of

these test procedures.

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

2.5.33.4 Measurement of Electrical Overstress from Solder-

ing Hand Tools - Shielded Enclosure

Test Specimens

Test

specimens for this procedure are

detailed in Method 2.5.33.

Equipment/Apparatus

Apparatuses

utilized by the pro-

cedures that make up this test method are given in 4.1

through 4.5.2.

4.1

Test

electrode (see Section 3)

4.2

Storage

oscilloscope, 100 Mhz bandwidth or faster, 1

MΩ input vertical amplifier

4.3

Power

line filter, 20 ampere @ 115 VAC, 50 dB insertion

loss @ 5 Mhz/50Ω

4.4

Oscilloscope

probe - X10 Attenuation

4.5

Optional

4.5.1

Screen

camera, diskette, or hard copy waveform

printer

4.5.2

Screen

room or shielded enclosure capable of accom-

modating the entire UUT, cord, and handpiece. A filtered AC

power receptacle shall be available from within (see Method

2.5.33.4).

4.6

Preparation of Apparatus

Turn

on the oscilloscope

and allow it to warm up.

Connect the UUT to a shielded AC line filter assembly as

shown in Figure 1 and configure for typical operation.

Note: The

plugs are in power receptacles during measure-

ments. They are shown unplugged in Figure 1 for clarity.

The

Institute for Interconnecting and Packaging Electronic Circuits

2215 Sanders Road • Northbrook, IL 60062

IPC-TM-650

TEST

METHODS MANUAL

Number

2.5.33.2

Subject

Measurement

of Electrical Overstress from

Soldering Hand Tools - Transient 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.

age1of4

电子技术应用　　　　　　　ｗｗｗ．ＣｈｉｎａＡＥＴ．ｃｏｍ