IPC-TM-650 EN 2022 试验方法.pdf - 第528页

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 (S…

The layout of the disc structure is shown in Figure 3-4. The

red text is on the external surface for pad identification pur-

poses. In a multi-signal layer cross section, disks can be

‘‘stacked’’ vertically to facilitate later cross-sectioning if

desired (e.g., the disc for layer 6 is directly under the disc for

layer 3). The voltage planes around each disc are connected

together at the reference PTH and isolated from the rest of the

test vehicle through the use of a voltage divider.

3.3.4.3 SPP Test Coupon Design An example is shown of

a typical coupon layout with 3 cm and 10 cm [1.18 in and

3.94 in] long lines and the 12.7 mm [0.5 in] disc in Figure 3-5.

The contacts are shown using the SMA connectors described

in Figure 3-3. This is a minimum configuration. Additional lines

would need to be added for differential line testing. The layout

in Figure 3-5 requires 2.0 cm x 16 cm [0.8 in x 6.3 in] of card

space.

3.3.5 SET2DIL Test Lines The SET2DIL test coupons

shall contain one DUT (Device Under Test) for each

impedance/layer combination being controlled, and a ‘‘thru’’

reference structure.

3.3.6 FD Test Lines The FD test sample shall contain one

transmission (or interconnect) test line per layer. The reference

line shall be between 1.27 cm [0.5 in] and 2.54 cm [1 in].

The test line shall be between 15.24 cm [6 in] and 30.49 cm

[12 in]. The recommended line is 1.27 cm [0.5 in] for the ref-

erence line and 20.32 cm [8 in] for the test line. The specific

length shall be specified by printed board customers or ven-

dors.

3.3.7 Surface Finish No matter what surface finish is

used, one should ensure the surface of the launch/capture

structure is clean and that the contact of the probes is not

affected by residues and/or oxides. OSP (organic solderability

preservative) finishes may inhibit probing of fine-pitched

probes and may need to be removed from the probe area.

In the lab based qualification/verification assessment, one can

facilitate this by slight burnishing (a pencil eraser often works

well), followed by cleaning with isopropyl alcohol (IPA).

In production floor assessments, the probe design should be

designed to break through any potential oxides or contami-

nants.

4 Apparatus

4.1 Differential and Single Ended Measurements

Both

single ended and differential measurement can be applied to

all the test methods. The measurement process for a differen-

tial measurement is identical to that of a single ended test. For

Figure 3-4 SPP Disc Structure

IPC-25512-3-5

Figure 3-5 Example of Test Coupon for Single Line Case

10 cm

3 cm

ø=1.27 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

Page7of24

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