IPC-TM-650 EN 2022 试验方法.pdf - 第529页

Note: Equipment drift may occur as a function of time and environment; check with equipment manufacturer for proper calibration frequency. 4.2 EBW, RIE, and SET2DIL Apparatus EBW, RIE, and SET2DIL utilize a TDR measureme…

the RIE, SPP, and EBW methods the differential voltage mea-

surement is used where the single ended measurement is

specified. For SET2DIL, a slightly different algorithm is used

for single-ended (S21) vs. differential (SDD21) signals. For the

FD (VNA) method, SDD21 is used in place of S21.

4.1.1 TDR Differential Channel Synchronization The

two excitation channels need to be synchronized and have

the same amplitude. One recommended method is to use an

oscilloscope that has timing adjustments both in the TDR

heads and in the detector heads. Such a setup is performed

on a short pair of lines or zero-delay configuration. The steps

are as follows:

1) Channel 1 on the source side is propagated and detected

by Channel 3 on the detect side. The pulse or step is

recorded and displayed on the screen. Next, Channel 2 on

the source side is propagated to Channel 3 on the detect

side. The new pulse or step is overlapped with the one on

the screen. If there is a difference, the differential TDR skew

is adjusted until they are coincident. This makes sure that

the two sources do not have any difference in time, as

illustrated in Figure 4-1.

2) Next, the detector channels are adjusted. Channel 1 on the

source side is propagated and detected at this time by

Channel 4 on the detect side. This is compared to the

pulse or step obtained by the path of 1 going into 3. If they

are not synchronized, the Horizontal Skew Adjustment is

used to bring the timings together. Similarly, Channel 3 (or

4) is used as a source into channels1&2;channel 2’s

horizontal skew is adjusted to bring the timings together,

see Figure 4-2. If there is any amplitude difference due to

detector amplification difference, the Channel 4 (or 2)

attenuation can be adjusted to match the waveform of

Channel 3 (or 1).

Both setup steps are needed for TDT and SPP; the first step

alone is enough for TDR used in RIE and EBW; and only step

2 is required for SET2DIL. Step 1 is repeated for Odd-Mode

and for Even-Mode measurements in the differential case.

Note: Channel 2’s excitation must be in the same mode that

will be used during measurements (even or odd) during syn-

chronization; the pulse timing may vary, depending on the

excitation mode. Using a math function to invert the waveform

at the receiver might be necessary for odd mode excitation.

IPC-25512-4-1

Figure 4-1 TDR Pulse Synchronization for Differential

Application

IPC-25512-4-2

Figure 4-2 TDR Receiver Horizontal Skew Adjustment

IPC-TM-650

Number

2.5.5.12

Subject

Test Methods to Determine the Amount of Signal Loss on

Printed Boards

Date

07/12

Revision

Page8of24

Note: Equipment drift may occur as a function of time and

environment; check with equipment manufacturer for proper

calibration frequency.

4.2 EBW, RIE, and SET2DIL Apparatus EBW, RIE, and

SET2DIL utilize a TDR measurement system which shall be

composed of a step generator, high-speed sampling oscillo-

scope, and all the necessary accessories for connecting the

TDR unit to the test specimen depicted in Figure 4-3. IPC-

2141 provides a short discussion of the TDR system architec-

ture, system considerations, and the TDR measurement

process.

4.3 SPP Apparatus SPP utilizes a TDR measurement sys-

tem with the addition of one more sampling output head and

impulse forming networks placed between the TDR Sample

head and on probe. This type of setup comprises a TDT sys-

tem as shown in Figure 4-4.

Three general probing solutions may be used. These include:

microprobes, SMA connectors, and handheld probes. Each of

these methods embodies a test structure(s) in near proximity

and on the same printed board layer.

4.4 Measurement System Requirements

4.4.1 System Calibration

Follow the TDR instrument

manufacturer’s recommendation for the frequency of factory

calibration. TDR system ‘‘field’’ checks are to be performed at

regular intervals to ensure proper operation of the test sys-

tembetween the less regular factory calibrations. Field checks

are required for the following reasons:

a) TDR instrument specifications vary with temperature.

b) TDR instrument specifications vary with time (drift).

c) TDR instrument specifications vary due to minor ESD dam-

age.

d) TDR instrument factory calibration may not include auxiliary

components (e.g., cables, probes, etc.).

TDR system field checks should also be performed after a

change of any system component (such as, cable, probes,

etc.). Ensure that the TDR instrument has been operating for

at least 30 minutes prior to any field check or test measure-

ment procedure. Use proper ESD control methods to avoid

damage to the TDR instrument in all field check and test

IPC-25512-4-3

Figure 4-3 TDR Measurement Components

IPC-25512-4-4

Figure 4-4 SPP TDT/IFF Measurement Components

TDR

Low Frequency

Impedance

Analyzer

Impulse

Forming

Network

IPC-TM-650

Number

2.5.5.12

Subject

Test Methods to Determine the Amount of Signal Loss on

Printed Boards

Date

07/12

Revision

Page9of24

measurement procedures. ESD control components can

include static dissipative mats, deionizer systems, and opera-

tor gowning.

4.4.2 Premeasurement Checks The test measurement

should be performed after the completion of the field check

process. Ensure that the plane of the signal line of a microstrip

(or embedded microstrip) structure is at least a distance equal

to six times the width of the microstrip signal line from any

material (such as the testing table) that can affect the dielec-

tric environment of the microstrip line. If the tests are being

conducted with hand probe(s), care must be taken to ensure

that the hands and/or arms of the operator do not contact any

surface of the printed board over the transmission line being

tested. Probes should be applied to the test points with suffi-

cient force to ensure proper electrical contact between the

conductor and the probe assembly. Consistent application

(that is, force, angle of placement, etc.) of the probes onto the

test points is important to ensure repeatable measurement

results. Before recording any measurement results, ensure

that the TDR waveform is stable (that is, not drifting in ampli-

tude or time) otherwise measurement error will occur. Ensure

that the temperature and humidity of the test environment are

within TDR instrument specifications and are stable.

4.4.3 Method for Evaluation of Measurement Repeat-

ability

Measurement repeatability is described in IPC-TM-

650, Method 1.9. This method also describes a process to

evaluate the reproducibility of a measurement system for mul-

tiple operators, on different days, and when using different

instruments. This evaluation process should be followed and

a precision-to-tolerance ratio acceptable to the customer

obtained.

4.4.4 TDR Requirements In general, the following

describes minimum TDR requirements. Improvement to these

requires agreement between customer and vendor.

4.4.4.1 EBW: TDR Requirements The voltage measure-

ment resolution of the TDR unit shall be at least 1% of the

step amplitude. Step aberrations should be ± 3% or less over

the zone 10 ns to 20 ps before step transition; +10%, -5% or

less for the first 300 ps following step transition; ±3% or less

over the zone 300 ps to 5 ns following step transition; ± 1%

or less over the zone 5 ns to 100 ns following step transition;

0.5% after 100 ns following step transition. The time base

accuracy shall be less than 2 ps.

4.4.4.2 RIE: TDR Requirements The voltage measure-

ment resolution of the TDR unit shall be within 1% of the step

amplitude. Step aberrations should be ± 3% or less over the

zone 10 ns to 20 ps before step transition; +10%, -5% or less

for the first 300 ps following step transition; ± 3% or less over

the zone 300 ps to 5 ns following step transition; ± 1% or less

over the zone 5 ns to 100 ns following step transition; 0.5%

after 100 ns following step transition. The time base accuracy

shall be less than ± 1% of full scaled used. The captured time

shall be at least twice the transit time and shall contain at

least 2000 samples. The time between samples shall also be

less than 25 ps.

4.4.4.3 SPP: TDR Requirements The voltage measure-

ment resolution of the TDR unit shall be at least 1% of the

step amplitude. Step aberrations should be ± 3% or less over

the zone 10 ns to 20 ps before step transition; +10%, -5% or

less for the first 300 ps following step transition; ± 3% or less

over the zone 300 ps to 5 ns following step transition; ± 1%

or less over the zone 5 ns to 100 ns following step transition;

0.5% after 100 ns following step transition. The time base

accuracy shall be less than 2 ps for delays less than 100 ns.

4.4.4.4 SET2DIL: TDR Requirements The voltage mea-

surement resolution of the TDR unit shall be at least 1% of

the step amplitude. Step aberrations should be ± 3% or less

over the zone 10 ns to 20 ps before step transition; +10%,

-5% or less for the first 300 ps following step transition; ± 3%

or less over the zone 300 ps to 5 ns following step transition;

± 1% or less over the zone 5 ns to 100 ns following step tran-

sition; 0.5% after 100 ns following step transition. The time

base accuracy shall be less than 1 ps.

4.4.5 TDR Risetime Requirement The procedure

depicted in Figure 4-5 can be used to determine the rise time

or maximum slope of the TDR measurement system through

the probe tip. This is done to ensure that there is sufficient

high frequency content within the step pulse that is to be

injected into the device under test (DUT) for the respective test

method.

Note: The SIU is a static isolation unit designed to eliminate

static damage to the TDR sampling head. It may be included

within the TDR instrumentation.

4.4.5.1 EBW Risetime The rise time (10%-90%) for EBW

shall contain sufficient spectral content as agreed upon

between vendor and customer base on the printed board

application with the open tip of the probe. For EBW, hold the

probe in air see Figure 4-5 and measure the maximum slope

of the rise time of the step response (in Megavolts/second)

and/or the risetime. This value should be compared to the

IPC-TM-650

Number

2.5.5.12

Subject

Test Methods to Determine the Amount of Signal Loss on

Printed Boards

Date

07/12

Revision

Page 10 of 24