IPC-TM-650 EN 2022 试验方法-- - 第641页
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Figure 2 AC Power Entry Mounting Suggestion
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IPC-TM-650
Number
Subject Date
Revision
Page 2 of 3
2.5.33.4
Measurement
of
Electrical
Overstress
from
Soldering
Hand
Tools
-
Shielded
Enclosure
11/98
Figure 3 Test Electrode Mounting Suggestion
METAL
ENCLOSURE WALL
WIRE LOOPS
TO CONNECT SCOPE
PROBE AND GROUND CLIPS
OutsideInside
TEST
ELECTRODE
BOARD
DUAL READOUT
PANEL MOUNT
EDGE CARD CONNECTOR
IPC-TM-650
Number
Subject Date
Revision
Page 3 of 3
1 Scope
The Power Density Rating (PDR) for Embedded
Resistors test method covers procedures for the demonstra-
tion of the ability to operate the embedded device safely, with-
out a permanent change in the electrical characteristic of the
device. The procedure consists of monitoring a resistance
change from its nominal value as a function of the dissipated
power. During the test, the applied voltage or current stimulus
is held until the device temperature is stable, the steady resis-
tance reading is reached, and the dissipated power is mea-
sured. This process is repeated with higher dissipated power
until the measured resistance change exceeds the specifica-
tion limits. The results are presented in terms of the dissipated
power density rating (PDR) factor for the embedded resistive
device.
This document describes testing procedure for power density
rating of embedded resistive devices, which operate in com-
plex electrical and thermal environments, and for which exist-
ing procedures are not adequate or inapplicable.
2 Applicable Documents
Specification for Embedded Passive Device Resis-
tor Materials for Rigid and Multilayer Printed Boards
Test Methods Manual
1.3 Ambient Conditions
3 Terminology
When current passes through a resistor,
electrical energy is dissipated by the resistor in the form of
heat. A resistor can be used at any combination of voltage
and current as long as its dissipating power (P) does not
exceed the maximum power rating (P
max
) indicating how
much power the resistor can convert into heat and absorb
or/and transfer away without any damage to itself or to the
surrounding circuitry.
3.1 Electrical Resistance,
R = V / I (1)
R is a ratio of voltage V over current I, (Ohm’s law), the unit of
measure is ohm [Ω].
3.2 Dissipated Power,
Direct current (DC):
P = V I; P = V
2
/ R; P = I
2
R (2)
Alternating current (AC):
P = V* I* cos (ϕ) (3)
V* and I* are voltage and current amplitudes, and ϕ is the
phase angle between V* and I*.
3.3 Power Density Rating
The power density rating (PDR)
is defined as the total dissipated power normalized by the
effective surface area (heat flux cross sectional area).
PDR = P
max
/ S (4)
where, S is the area of the embedded resistor or device
defined as one-side of the heat flux area.
3.4 Power Density Rating Comments
• The power that can be dissipated by a resistor is limited by
the size of the resistor and the maximum operational tem-
perature of the resistive material.
• The power ratings depend on thermal management of the
heat generated from the resistor.
• The use of heat sinks can lower the device’s operating tem-
perature and consequently increase the power rating.
• Higher glass transition temperature laminate materials in
which the resistive device is embedded can allow higher
operating temperatures.
4 Test Specimen
This method recommends testing the
embedded resistors in configurations that reflect the actual
functional application (Figure 1).
The recommended geometrical attributes of the embedded
resistors are specified in the IPC-4811.
4.1 Sampling
The sampling procedure for the tested
specimen should be defined in the specification for that
device. The sampling procedure should provide sufficient data
to estimate the average quality and the variability of the lot
being examined.
4.2 Conditioning
The test results can be influenced by
temperature, moisture content and other electrically active
residuals originating from the processing conditions such as
3000 Lakeside Drive, Suite 309S
Bannockburn, IL 60015-1249
IPC-TM-650
TEST METHODS MANUAL
Number
2.5.34
Subject
Power Density Rating for Embedded Resistors
Date
07/12
Revision
Originating Task Group
Embedded Devices Test Methods Subcommittee
(D-54)
Association
Connecting
Electronics
Industries
IPC-4811
IPC-TM-650
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