IPC-TM-650 EN 2022 试验方法.pdf - 第507页

3) Outside of the PB area and at the center or edge of the panel. If coupons are placed in all the locations listed above, a com- parison between a statistically significant sample set taken from each location over time …

assumption invalid and introduces errors in the reported

delay

b. Short test lines reducing the t

accuracy due to system

temporal limits (see 4.1.2)

c. Short test lines reducing ability to identify intentional dis-

continuities from signal launch

d. Long test lines detrimentally reducing amplitude of reflec-

tion signal due to large skin effect and dielectric losses

2 Applicable Documents

IPC-2141

Design Guide for High-Speed Controlled Imped-

ance Circuit Boards

IPC-TM-650 Test Methods Manual

1.9 Measurement Precision Estimation for Variables Data

2.5.5.7 Characteristic Impedance of Lines on Printed Boards

by TDR

3 Test Specimens The test specimen can take one of sev-

eral forms depending on the application, but it must contain at

least one transmission line (or interconnect) test structure and

be representative of the actual PB product. Four definite types

of specimens are described in 3.1.1 through 3.1.4. The trans-

mission lines to be measured may be of either stripline or

microstrip construction.

3.1 Test Specimen Examples

3.1.1 Example 1

Test specimens are representative PBs

selected out of a lot of fabricated product. In some cases, this

sample set may contain all PBs in the lot. Agreed upon func-

tional and nonfunctional transmission lines on the PB are used

as the test set for this specimen. The selection of lines that

form the test set must be based on these criteria (nonexclu-

sive):

a. Inclusion of the PB’s critical features

b. Accessible line terminations for measurements

c. Absence of line branching

d. Absence of impedance changes within the transmission

line under test

e. Representation of controlled characteristic impedance Z

signal layers

3.1.2 Example 2 Test specimens are representative fabri-

cated PB samples or entire lots as in 3.1.1. The test lines used

in these specimens are nonfunctional lines designed into the

PB for easy termination and connection to TDR equipment.

Such test lines should be designed to include critical features

typical of functional lines and should lie in the controlled Z

signal layers of the application.

3.1.3 Example 3 Test specimens are test coupons cut

from representative fabricated PB samples or entire lots. The

test coupons are cut from the master PB at the time the indi-

vidual PBs are separated. Such test coupons will have one or

more nonfunctional transmission lines with termination suited

for TDR testing. Such test lines should include critical features

typical of functional lines and will be fabricated in the same

configuration and structure as the master PB on the same

controlled Z

signal layers as the application.

3.1.4 Example 4 Test specimens are a sample of the sub-

strate laminate to be characterized before PB manufacturing

and fabrication. The test line fabrication on these specimens

may involve laminating several PB layers together in the same

manner anticipated for PB manufacture.

3.2 Identification of Test Specimen For specimens of

types called out in 3.1.1, 3.1.2, or 3.1.3, each specimen shall

be identified with no less than a PB part number, PB serial

number, and date code. Specimens of the type called for in

3.1.4 must include the lot or panel identification for the sub-

strate laminate being evaluated.

3.3 Conditioning Environmental conditioning prior to test

may be called for as part of the test. When conditioning is

required, test specimens shall be stored before testing at 23

+1/-5 °C and 50 ± 5% RH for no less than 16 hours. If a dif-

ferent conditioning procedure is required, it must be specified

and documented in test reports.

3.4 Test Interconnect Placement The ability to correlate

propagation delay values derived from measurements of non-

functional test lines to propagation delay values of functional

lines is directly related to the proximity of the nonfunctional

test structure to the functional lines. The closer the test and

functional lines, the more likely the nominal material properties

will be the same. The placement of test structures on the PB

or panel should be analyzed for each PB design and be based

on the propagation delay tolerance and practicality of the lay-

out. When deciding on the best test interconnect placement,

consider the following placement priorities:

1) Inside the functional area of the PB;

2) At the edge of the PB but outside the functional circuit

area; or

IPC-TM-650

Number

2.5.5.11

Subject

Propagation Delay of Lines on Printed Boards by TDR

Date

04/2009

Revision

Page2of16

3) Outside of the PB area and at the center or edge of the

panel.

If coupons are placed in all the locations listed above, a com-

parison between a statistically significant sample set taken

from each location over time can yield data that will relax

placement requirements without reducing confidence in test

results.

3.5 Test Interconnect Geometry The test structures

should use the same line width and conductor thickness, and

be located in the same dielectric environment (permittivity,

thickness, and layering) as the target functional interconnects.

Spacing between conductors should also match that of the

functional interconnects. If edge coupons are used, and pre-

vious studies have shown that conductors at the edge of the

panel experience different lamination from those in functional

panel areas, then a compensation factor may be needed to

adjust the propagation delay measurement for this difference.

3.6 Lengths for Two-Line Test Structure When using

two nonfunctional transmission lines as the test structures,

thenominal physical lengths of the transmission line pair

should be 76.2 mm [3.0 in] and 152.4 mm [6.0 in]. Variations

in test structure lengths shall be documented.

3.7 Transmission Line Termination Transmission lines

are to be terminated at both ends using PTHs to allow electri-

cal connections to both ends of the line. Additionally, PTH ter-

minations at both ends provide for DC and low frequency

measurements of resistance, capacitance, conductance, and

inductance as additional diagnostic tools in the event of an

out-of-specification condition.

3.8 Contact Land The contact land should comprise PTHs

and contact pads as shown in Figure 3-1. Reference contact

lands should be square to aid in visual identification. The

nominal hole diameter shall be 0.46 mm [0.018 in] and sur-

face land shall be 1.02 mm [0.040 in]. However, the PTH

should be of consistent dimensions to ensure repeatability

and reliability of the tests for the given measurement equip-

ment. Care must be used when specifying different hole sizes

and land pitches since their electrical properties may affect the

reported t

in a secondary manner. Hole size should be larger

only if required by plating/aspect ratio requirements. Ideally,

hole and pad size should be the same as those of functional

IPC-25511-3-1

Figure 3-1 Contact Lands

1.91 mm [0.075 in]

1.02 mm [0.040 in]

0.46 mm [0.018 in]

0.28 mm [0.011 in]

1.91 mm [0.075 in]

ø0.46 mm [0.018 in]

ø1.02 mm [0.040 in]

SINGLE-ENDED

(1.91 mm [0.075 in])

DIFFERENTIAL

(1.91 mm [0.075 in] SQUARE)

SIGNAL LANDS

REFERENCE

LANDS

IPC-TM-650

Number

2.5.5.11

Subject

Propagation Delay of Lines on Printed Boards by TDR

Date

04/2009

Revision

Page3of16

interconnects, but a practical issue of operator ability to use

hand-held probes may be considered. Test reports must

report any deviation from the nominal contact land and PTH

geometry.

3.9 Contact Land Pitch Whenever possible, the center-

to-center distance between the signal and reference lands

of the test interconnect should be consistent to simplify

probing requirements and ensure measurement repeatability

and reproducibility. Nominal center-to-center pitch shall be

1.91 mm [0.075 in]. The use of different contact and probe

pitches must be specified and documented.

3.10 Single-Signal Conductor Transmission Line The

single-signal conductor transmission line is also known as the

single-ended, unbalanced, and asymmetrical structure. The

probing area for these lines should consist of a contact land

(see Figure 3-2) for each signal line. The contact land should

provide connection to the reference, or ground, connection for

the test structure. This method requires the use of one con-

tact pitch to ensure measurement consistency between the

test structures of the specimen.

3.11 Orientation The contact land orientation (placement

and angle of the contact land of the signal line relative to the

contact land of the reference plane) must be the same for all

test interconnects of the specimen in order to ensure mea-

surement consistency between test interconnects.

3.12 Test Interconnect Routing

a. The test interconnects shall only be routed over and under

contiguous ground and voltage planes following controlled

line impedance guidelines (see IPC-2141). The test inter-

connects must not extend into PTH clearance areas.

b. The test interconnects shall be kept at least six times the

width of the signal conductor or 2.5 mm [0.0984 in],

whichever is greater, from any PTHs and any other inter-

connect on the same plane. All conductive material (such

as copper nomenclature, copper thieving, etc.) shall be

kept at least 2.5 mm [0.0984 in] from each test intercon-

nect.

c. Test interconnects shall be straight or contain gradual and

rounded bends.

3.13 Nomenclature Labeling of all test interconnect con-

tact lands on at least one surface layer is required for opera-

tor identification during manual probing operations. The label

shall minimally contain information about which signal layer

the test interconnect is modeling (for example, L1-3in, L1-6in,

etc.). Nomenclature should be etched in copper and be

spaced a minimum of at least six times the width of the signal

conductor (of the test interconnect) or 2.5 mm [0.0984 in],

whichever is greater, from the test interconnect area. When-

ever practical, the terminations at both ends of test intercon-

nect shall be marked.

IPC-25511-3-2

Figure 3-2 Transmission Line Structures

2.54 mm

[0.100 in] MIN

2.54 mm [0.100in] MIN

2.54 mm [0.100 in] MIN

1.91 mm [0.075 in]

152.4 mm [6.00 in] REF

76.2 mm [3.00 in] REF

1.91 mm [0.075 in]

L1/3.0 Layer One – 3 Inch Line

L1/6.0 Layer One – 6 Inch Line

L3/3.0 Layer Three – 3 Inch Line

L3/6.0 Layer Three – 6 Inch Line

L1/3.0

L1/6.0

L3/3.0

L3/6.0

L7/3.0

L7/6.0

THIEVING

NOTES:

PN#. LOT#.

SN#.

IPC-TM-650

Number

2.5.5.11

Subject

Propagation Delay of Lines on Printed Boards by TDR

Date

04/2009

Revision

Page4of16