IPC-TM-650 EN 2022 试验方法.pdf - 第105页

all steps recommended for full curing. For resin coated cop- per (RCC) foil, after laminating the foil, cure as per manufac- turer’s instructions, then etch the copper layer and proceed as for other deposited dielectric …

Scope

The

object of a planarity measurement is to deter-

mine the effectiveness of a polymer thin film in smoothing

topological features created by underlying layers of circuitry or

etch patterns. In this case, the polymer thin film is a dielectric

material for use in High Density Interconnect (HDI) and

microvia technologies.

1.1

Test Structure

Schematics

given in Figure 1 (end view)

and Figure 2 (top view) depict the essential features of a rec-

ommended test structure for measuring the planarity as a

function of feature size.

In the finished test structure, ‘‘d’’ is the step height over the

circuit trace after the polymer has been deposited and cured.

The planarity is dependent on the trace height, ‘‘b,’’ the poly-

mer coating thickness, ‘‘c,’’ and the trace width, ‘‘a.’’ Rather

than fully characterizing this relationship for each polymer

coating, it is best to use simplified standard procedures for

measurement and for comparing different types of coatings.

Planarity is also affected by the proximity of the line feature

being used for measurement to any neighboring topological

feature in the test structure. Planarity is generally much lower

for isolated features. Therefore, in order to consider the

‘‘worst case’’ conditions, isolated lines are preferred in the

test structure. To satisfy this requirement, no neighboring fea-

tures can be within fewer than 15 line widths of the line in

question.

The test pattern in Figure 2 is recommended as one that pro-

vides planarity characterization over a broad range of feature

sizes. All lines are isolated in accord with the above guideline.

It is recommended planarity be determined over the complete

range of these widths (but the specific nominal values within

that range are not important). Normally, one finds the planar-

ity is high over narrow lines, but it progressively rolls off in pro-

ceeding toward wider ones. The roll-off rate is important, and

it varies from polymer to polymer. Thus any report of planarity

must include the line width measured and, preferably, a plot of

planarity versus line width should be reported.

Applicable Documents

IPC-DD-135

Qualification

for Deposited Organic Interlayer

Dielectric Materials for Multi-Chip Modules

Test Specimens

3.1 Prepare Test Coupons

Prepare

the surface of the test

structure for polymer deposition in accordance with the pro-

cedure recommended by the manufacturer of the dielectric

coating (follow all procedures for cleaning the surface and for

deposition of a coupling agent if one is recommended). Coat

the polymer resin in accordance with the manufacturer’s rec-

ommended procedure to provide an average film thickness of

63.5 µm (± 10%) for 18 µm copper over the substrate surface

when the cure is completed. Cure the polymer thin film using

IPC-2-2-21-1

Figure 1 Cross-Section Planarization Diagram

IPC-2-2-21-2

Figure

2 Top View of Planarization Structure

The

Institute for Interconnecting and Packaging Electronic Circuits

2215 Sanders Road • Northbrook, IL 60062

IPC-TM-650

TEST

METHODS MANUAL

Number

2.2.21

Subject

Planarity

of Dielectrics for High Density

Interconnection (HDI)/Microvia Technology

Date

11/98

Revision

Originating Task Group

HDI Test Methods Task Group (D-42a)

Material

in this Test Methods Manual was voluntarily established by Technical Committees of the IPC. This material is advisory only

and its use or adaptation is entirely voluntary. IPC disclaims all liability of any kind as to the use, application, or adaptation of this

material. Users are also wholly responsible for protecting themselves against all claims or liabilities for patent infringement.

Equipment referenced is for the convenience of the user and does not imply endorsement by the IPC.

age1of4

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all

steps recommended for full curing. For resin coated cop-

per (RCC) foil, after laminating the foil, cure as per manufac-

turer’s instructions, then etch the copper layer and proceed

as for other deposited dielectric materials (see Figure 3).

Equipment/Apparatus

This

method uses profilometer

measurements providing topological height variations as a

function of displacement across the surface of a standard test

structure.

Use a TENCOR Profilometer (Model: Alpha Step 200). Substi-

tutions are acceptable, provided they can measure feature

heights in the range used to within ± 2% and can provide a

linear scan of at least 10 mm.

Note:

an alternate method, where a profilometer is not

available, the measurements can be collected by cross-

sectioning the test structures. This method will require one

cross-section for each trace width in order to collect data for

trace width effects.

Procedure

Prior

to the polymer deposition, scan the pro-

filometer stylus across all copper lines in the test structure,

scanning in the direction indicated by the arrow in Figure 2.

Measure and record the dimensions depicted as ‘‘a’’ and ‘‘b’’

in Figure 1 for each of the lines.

After polymer deposition and cure, measure the polymer film

thickness at a location distant (at least 15 line widths) from any

of the test structure’s copper lines. In order to do this, a ‘‘win-

dow’’ must be imaged in the dielectric down to the substrate.

A ‘‘window’’ to the substrate may be opened by photo-

imaging, chemical dissolution, laser ablation, or other appro-

priate method (see Figure 4). The sweep must allow measure-

ments of the thickness of the dielectric entering and exiting

the ‘‘window.’’ These measurements should be within ± 0.2

µm of each other. Record this dielectric thickness as dimen-

sion ‘‘c.’’

Finally, measure the dimension shown in Figure 1 as the fea-

ture step height ‘‘d’’ of the polymer; use the profilometer, not

an optical method. In measuring ‘‘d,’’ take the difference in

height between the highest point on top of the copper line and

the lowest point at least 15 line widths from the line to be

measured.

5.1

Conditions of Test

5.1.1

Calibrate

the profilometer before making measure-

ments using the calibration procedure specified by the manu-

facturer of the equipment.

5.1.2

Measure

at ambient room temperature and humidity.

IPC-2-2-21-3

Figure

3 Pattern of One Test Board Showing Three Test Substructures (Board is 150 mm sq.)

IPC-TM-650

Number

2.2.21

Subject

Planarity

of Dielectrics for High Density Interconnection (HDI)/

Microvia Technology

Date

11/98

Revision

age2of4

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5.1.3 To

standardize measurements, use test structures in

whichb=18µm,c=63.5 µm, and the ratio of c/b is 3.5 ±

0.2. If a dielectric film is used, which has been produced at a

fixed thickness other than that outlined above, maintain a c/b

ratio as described. If the standard construction with this

defined ratio cannot be maintained, the actual metal and

dielectric thickness must be reported.

5.1.4 Make

triplicate measurements and average the results

at each line width.

5.2

Calculation of Planarity

5.2.1

Planarity

for an individual trace, P

can be defined by

the following equation:

(1 - d/b)100

where ‘‘a’’ is the trace width, ‘‘d’’ is the bump height over the

trace, and ‘‘b’’ is the copper trace height. For an ideal planar

structure, the value of P is equal to 100%.

5.2.2

Average

planarity, P

ave

for a given trace width is cal-

culated using the triplicate measurements:

ave

=(P

)/3

5.2.3

Total average planarity, P

total

, is the average planarity

for all widths of traces (where n = number of traces widths

measured):

total

ave1

ave2

.......+ P

ave

)/n

5.3

Report

5.3.1

Report

the average planarity for each trace width

measured (see 5.2.2).

5.3.2

Report

the total average planarity as a single average

percentage of all seven trace width averages (see 5.2.3).

5.3.3

Also

report the technique, profilometer or cross-

section, used to obtain the measurements.

This calculation can be performed for each trace width to

develop a planarity plot.

6 Notes

6.1

Cross Section Method

Due

to the field of view

required for the larger trace widths (> 0.8 mm), accurate mea-

surements of the dielectric ‘‘bump’’ may not be possible due

to the low magnification. One option is to use a higher mag-

nification and measure the total dielectric and copper trace

height from the substrate surface and subtract the minimum

dielectric height over the substrate alone.

6.1

Planarity Test Method Sample

example of a pla-

narity test method is given in Figure 5.

IPC-2-2-21-4

Figure

4 Cross Section of Window Used for Dielectric

Thickness Measurement

ofilometer Stylus

Direction

of Scan

Height at Exit

Dielectric

Height at Entry

``Window´´ in Dielectric

IPC-TM-650

Number

2.2.21

Subject

Planarity

of Dielectrics for High Density Interconnection (HDI)/

Microvia Technology

Date

11/98

Revision

age3of4

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