IPC-TM-650 EN 2022 试验方法.pdf - 第533页

These are the TDR waveforms used in the RIE loss calcula- tion. It is recommended to be positioned within 80% of the vertical screen scale in reference to the representative waveform. The signal on the screen must have a…

4.4.11 TDR ESD Protection TDR equipment shall pro-

vide ESD protection commensurate with the test environment.

It is recommended that samples be grounded to remove any

residual static to protect against static discharge with in the

test environments.

Static can be built up on samples prior to test and can dam-

age the sampling heads in the TDR/TDT equipment. There-

fore, it is recommended that ESD protection be used. Such

protection must be supplied internally to the TDR system.

Samples should be grounded to remove any residual static

and/or passed through some type of deionization device prior

to testing. This can be done by shorting each line to ground

with a simple connection between one end of the lines and

the instrument ground. Keeping the relative humidity in the

test area between 45% and 55% may minimize the buildup of

static. Operators are always required to have a grounding

strap around one wrist havinga1MΩ resistor in series with it.

Special waxing can be used on the lab floor to prevent body

charge build-up. Always use a grounded, conductive table

mat. Always wear a heel strap. Always ground the center con-

ductor of a test cable before making a connection to static-

sensitive equipment.

4.5 SPP Test Apparatus

4.5.1 Other SPP Equipment Requirements

An LCR

meter is required that can measure capacitance at 1 MHz.

4.5.2 SPP Software The following software is required for

implementation of the SPP technique:

a) Gamma-Z software for signal processing or equivalent

b) 2D field solver such as CZ2D, which can be downloaded

from: www.alphaworks.ibm.com/tech/gammazandcz2d,

or equivalent

4.6 FD Test Apparatus The measurement equipment

needed includes a VNA, cabling, a probing solution, and a

calibration structure and calibration coefficients that are

acquired from the probe or connector manufacturer. The

probing solution should match the test sample chosen from

the above described samples. High performance connectors

and cables are recommended in performing VNA measure-

ments. Optionally, a TDT system may be used in place of a

VNA to acquire frequency domain attenuation and loss data.

5 Procedures

5.1 EBW Measurements Procedure

5.1.1 Measurement Process

This procedure will measure

the maximum slope of the rise time of the combined measure-

ment system and DUT and determine a loss factor. Recom-

mended resolution is 4000 points with a horizontal scale of

200 ps/div.

Step 1 – Probe the interconnect (see Figure 5-1) and measure

the maximum slope of the step response in Megavolts/second

(e.g., 430 Megavolts/second). The maximum slope may be

directly acquired from TDR equipment with that capability.

Step 2 – Report the Loss Factor at the test system bandwidth

(as measured within 4.4.5.1) (e.g., 430 Megavolts/second @

14.5 GHz).

5.2 RIE Measurement Procedures Figure 5-2 summa-

rizes the RIE measurement procedure.

The RIE method utilizes a comparison between a reference

loss (line) measurement and a test conductor (line) measure-

ment. The reference measurement may be a calibration stan-

dard or short length of conductor in the neighborhood and on

the same layer as the conductor to be measured.

5.2.1 TDR – Open or Unterminated Line Requirement

The RIE method requires a measurement of lines where one

end is a probe launch and the other end is left unterminated

or open. The probe injects a fast step at the launch point in

much the same manner specified in IPC-TM-650, Method

2.5.5.7. The injected step causes a wave to propagate down

the line; most of the wave is reflected by the open end of the

line and travels back to the source where it is measured as the

superposition of the incident wave and all the reflections.

IPC-25512-5-1

Figure 5-1 Measurement of Maximum Slope of Step Rise

Time at Open end of DUT

TDR Instrument

probe

SIU

Maximum

risetime

DUT

(interconnect)

Time

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 12 of 24

These are the TDR waveforms used in the RIE loss calcula-

tion.

It is recommended to be positioned within 80% of the vertical

screen scale in reference to the representative waveform. The

signal on the screen must have a resolution of at least 5% of

the measured signal.

Figure 5-3 specifies two time regions. T0 and T1. The sum of

T0 and T1 represents the time range for the captured wave-

form. Figure 5-3 specifies the point between T0 and T1 which

corresponds to the point where the probe contacts the

printed board, or where the rising edge would be if the probe

were disconnected from the sample. The TDR specification

for T0 and T1 is found in Table 5-1.

Each TDR waveform is averaged on the TDR instrument at

least 16 times. The time base and offset remain the same for

all measurements.

5.2.2 Measurement and Processing Two TDR wave-

forms are captured. One corresponds to a reference and the

second corresponds to the test line.

The measured waveforms require post-processing. TDR

waveform is processed as follows:

a) Filtering

b) Cubic spline fit

c) Using derivative to find impulse response

d) Calculating RIE loss ratio

5.2.2.1 Recursive Digital Filtering of Spline Data The

two TDR waveforms are filtered using the method prescribed

in Equation 5-1.

Let S

j,0

= A

for k = 1 to N

j,k

2,k +

i=1

(

i-1

⋅ S

i,k

)

Assign B

= S

j,N

[5-1]

Where:

N is the number of filtering iterations

is the j

point of the on of the acquired TDR waveforms

Sj,k is the j

point of the k

filtered waveform

j is an index for the waveform points

Bj is the j

point of the filtered waveform

The number of filter iterations depends on the number of

samples in the acquired TDR waveform and specified in Table

5-2.

5.2.2.2 Resampling with a Cubic Spline Fit The next

step is to resample the filtered TDR data to 10,000 points (J).

This is accomplished with a cubic spline fit.

5.2.2.3 Impulse Response The impulse response of the

reference and test specimen, respectively I_R

and I_T

is cal-

culated by taking the derivative of the respective resample

step waveforms RB

and TB

. One method to perform this

Figure 5-2 RIE Flowchart

RIE TDR PROCESS

Acquire TDR response for one reference and line under test

Averaging filter of re-sampled TDR waveforms

Cubic spline re-sampling of TDR waveforms

Perform Derivative of filtered TDR waveforms

Determine RIE loss from reference Sample

Determine RIE loss from test Sample

Determine RIE loss ratio

IPC-25512-5-3

Figure 5-3 Waveform Position on TDR Screen

Voltage

Time

Corresponds to probe launch

T0 T1

TDR Display Window for RIE

Table 5-1 RIE TDR Time Range Speciﬁcations

T0 50 ps (typical)

T1 At least twice the transit delay

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 13 of 24

operation is specified in Equation 5-2.

I_R

− RB

j−1

− t

j−1

I_T

− TB

j−1

− t

j−1

[5-2]

5.2.2.4 RIE Results The reference structure, RIE

reference

,is

the square root of the square of the integral of the square of

the impulse response I_R, and can be calculated from J

samples as show in Equation 5-3. The test structure, RIE

test

is the square root of the square of the integral of the square

of the impulse response I_T, and is calculated from J samples

as show in Equations 5-3 and 5-4.

RIE

reference

√

j=1

I_R

− t

)

[5-3]

RIE

test

√

j=1

I_T

− t

)

[5-4]

The RIE loss in dB, RIE

loss_dB

, is calculated by dB ratio of the

RIE

test

to RIE

reference

as show in Equation 5-5.

RIE

loss_db

= 20 * log

(

RIE

test

RIE

reference

)

[5-5]

5.3 SPP Procedure Figure 5-4 summarizes the SPP mea-

surement extraction process.

5.3.1 Selecting Optimum SPP Transmission Lines SPP

utilizes measurements on two lines of different lengths such as

2.0 cm and 8.0 cm. The pair shall be designed to be identi-

cal in every way except for length. The SPP is used to extract

parameters such as α(f) β(f), Γ(f) and Z

(f) by utilizing the dif-

ference between the two specimen line lengths. Effects due to

the connectors, cables, probes, and oscilloscope circuitry can

be minimized using this method. Screening the two lines

improves accuracy. Figure 5-5 illustrates lines of similar

design. Accuracy is improved when the slope and deviation

along the lengths of overlaid portions of the respective TDR

waveforms are coincident.

5.3.1.1 Additional SPP Step for Differential Lines There

are a few additional steps needed when analyzing differential

lines. The TDR screening still needs to be performed first. In

Table 5-2 Filter iterations, N, vs.

number of points, n, in TDR capture

Number of Points

in TDR capture (n)

Number of

Filtering Iterations

(N in Equation 5-1)

0>n≥750 1

750>n≥1500 2

1500 > n ≥3000 6

> n >3000 21

Figure 5-4 SPP Flowchart

TDR

Select best candidates for line pairs

Low Freq

TDT

disc

Determine

1MHzε

and Tan δ

(LCR meter)

Determine

Capacitance/unit

length (LCR meter)

Determine

Resistance/unit

length ρ and

(LCR meter)

Lines

Acquire Impulse response for 2 lines of 2 lengths

Window and filter Impulse response

FFT to get Propagation Constant Γ (Attenuation and Phase)

Use itrative matching of Γ, Att, and low freq

parameters to determine tline modeling parameters

IPC-25512-5-5

Figure 5-5 Example of Similar TDR Responses for

Different Lengths of Lines

0.3

0.2

0.25

1.5 2.5

Time (nsec)

Voltage (V)

3.52

1=2 cm

1=5 cm

1=8 cm

1=9.8 cm

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 14 of 24