ABC's of Ultrasonics

Scanning 

Acoustic 

Microscopy 

Training 

This presentation and images are copyrighted by 

Sonix, Inc. They may not be copied, reproduced, 

modified, published, uploaded, posted, transmitted, 

or distributed in any way, without prior written 

permission from Sonix. 

8700 Morrissette Drive 

Springfield, VA 22152 

tel: 703-440 

440-02220222 

fax: 703-440 

440-9512 

e-mail: info@sonix.com

This presentation serves as a brief 

introduction into the theory and 

operation of scanning acoustic 

microscopes. 

2 

Copyright Sonix, Inc

Ultrasound Inspection, 

Using an Acoustic Microscope… 

• Ultrasound 

What does this 

thing do 

•Non-Destructive Testing 

•Example Images 

3 


Ultrasound 

MEDICAL 

SONAR 

University of California Medical Center 

San Francisco, California 

What are are Ultrasonic Waves 

Ultrasonic waves refer refer to to sound waves above 20 20 kHz kHz 

(not (not audible to to the the human ear) ear) 

4 


Non-Destructive Testing 

NDT utilizes various non-invasive 

measurement techniques, such as 

ultrasonics and radiography to 

determine the integrity of a 

component, structure, or material 

without destroying the usefulness 

of the item. 

5 


Where an Acoustic Microscope is utilized. 

•Failure Analysis 

•Reliability 

•Process Control 

•Vendor Qualification 

•Production 

•Quality Control 

•Research 

6 


Common Applications 

•Plastic encapsulated IC IC packages 

•Flip Chips 

•Bonded Wafers 

•Printed Circuit Boards 

•Capacitors 

•Ceramics 

•Metallic 

•Power Devices/Hybrids 

•Medical Devices 

•Material Characterization 

7 


Examples 

Lid seal voids 

Delamination 

BGA die attach 

Die Crack 

8 


Examples 

Die Top 

Delamination 

Mold compound voids 

Flip Chip Underfill 

Voids 

9 

Die Tilt, B-Scan 

Die Pad delamination 

Copyright Sonix, Inc 

Die Attach Voids

Ultrasound Inspection 

•Theory 

•System Components 

•Transducers 

10 


Ultrasonic Waves 

Characteristics of of Ultrasonic Waves 

•• Freely Freely propagate through liquids liquids and and solids solids 

•• Reflect Reflect at at boundaries of of internal internal flaws flaws and and 

change change of of material 

•• Capable of of being being focused, straight straight 

transmission 

University of California Medical Center 

San Francisco, California 

•• Suitable for for Real-Time processing 

•• Harmless to to the the human human body body 

•• Non-destructive to to material 

11 


Ultrasonic Inspection 

Ultrasound 

•• A transducer transducer produces produces a high high 

frequency frequency sound sound wave wave which which 

interacts interacts with with the the sample. sample. 

•• High High frequency frequency sound sound waves waves 

can can not not propagate propagate through through air. air. 

•• Couplant- Couplant-A material material used used to to 

carry carry the the high high frequency frequency sound sound 

waves. waves. 

•Water •Water is is the the most most common common 

couplant couplant for for immersion immersion 

testing. testing. 

Inspection Modes 

•Pulse •Pulse Echo Echo 

•Through •Through Transmission 

Transmission 

Transducer 

H 2 O 

Coupling 

Receive 

12 


Scanner 

The scanner consists of a three axis system, X, Y, and Z. The 

motor controller directs the movement of these axes. 

F 

o 

c 

u 

s 

Z 

A 

x 

i 

s 

X-Axis 

Y-Axis 

Step 

13 

ScanCopyright Sonix, Inc

Transducers 

High Frequency 

Short Focus 

Low Frequency 

Long Focus 

1. 1. Higher Higher resolution resolution 

2. 2. Shorter Shorter focal focal lengths lengths 

3. 3. Less Less penetration penetration 

(Thinner (Thinner packages) packages) 

1. 1. Lower Lower resolution resolution 

2. 2. Longer Longer focal focal lengths lengths 

3. 3. Greater Greater penetration penetration 

(Thicker (Thicker packages) packages) 

General 

General 

rules: 

rules: 

• 

• 

Ultra 

Ultra 

High 

High 

Frequency 

Frequency 

(200+ 

(200+ 

MHz) 

MHz) 

for 

for 

flip 

flip 

chips 

chips 

and 

and 

wafers. 

wafers. 

• 

• 

High 

High 

Frequency 

Frequency 

(50-75 

(50-75 

MHz) 

MHz) 

for 

for 

thin 

thin 

plastic 

plastic 

packages. 

packages. 

(110MHz-UHF) 

(110MHz-UHF) 

for 

for 

flip 

flip 

chips. 

chips. 

• 

• 

Low 

Low 

Frequency 

Frequency 

(15 

(15 

MHz) 

MHz) 

for 

for 

thicker 

thicker 

plastic 

plastic 

packages. 

packages. 


14

Transducer Beam Profile 

Depth of Field 

The purple region 

is referred to as the 

focal area or depth 

of field of the 

transducer beam. 

15 


Typical Transducer Selection 

Sample Application 

Transducer 

16 

T/X Receiver 

PLCC, QFP, PQFP 

Power Pak 

BGA Top 

Capacitors 

TSOP 

Flip Chip Underfill 

Flip Chip Interconnect 

Bonded Wafer 

Bonded Wafer 

10 MHz w/0.75” focus 



50-75 MHz w/12mm focus 

75 MHz w/12mm focus 



UHF w/ 5.9 mm focus 


UHF w/ 5.9 mm focus 


ABC’s Of Acoustics 

•Acoustic Reflections 

•Acoustic Waveforms 

•Image Display 

17 


Acoustic Properties 

Material Density LongitudinalWave Acoustic Impedance 

(g/cm 3 ) Velocity (m/s) (kg/m 2 s) (x10 6 ) 

Water (20 0 C) 1.00 1483 1.48 

Alcohol (20 0 C) 0.79 1168 0.92 

Air (20 0 C) 0.00 344 0.00 

Silicon 2.33 8600 20.04 

Gold 19.3 3240 62.53 

Copper 8.90 4700 41.83 

Aluminum 2.70 6260 16.90 

Epoxy Resin 1.20 2600 3.12 

Resin (for IC pkg) 1.72 3930 6.76 

Glass (Quartz) 2.70 5570 15.04 

Alumina (AL 2 O 3 ) 3.80 10410 39.56 

18 


Sound Reflection 

•Acoustic Material Properties 

•density (r) 

•velocity of sound in material (c) 

•acoustic impedance (Z= rc) 

19 


Sound Reflection 

Whenever a sudden change in 

acoustic impedance is encountered, 

like at a material boundary, a portion 

of sound is reflected and the 

remainder propagates through the 

boundary. 

20 


Reflection vs. Transmission 

Incident Energy 

Z= ρC 

Water Z 1 

Plastic Z 2 

Z 1 

= ρ C where: 

ρ=1.00 gram/cm 3 

C= 1.5 x 10 6 

Z 1 

= 1.5 x 10 6 

Reflected Energy 

Transmitted Energy 

Z 2 

= ρ C where: 

ρ =2.00 gram/cm 3 

C= 2.00 x 10 6 

Z 2 

= 4.00 x 10 6 

T 

T 

T 

= 

= 

= 

2 ( Z 

1 

) 

( Z + Z ) 

2 

2 ( 1 . 5 ) 

( 4 . 0 + 1 . 5 ) 

( 3 . 0 ) 

( 5 . 5 ) 

1 

45% of the 

sound entering 

the boundary is 

reflected. 

R 

R 

R 

= 

= 

= 

( Z 

2 

− Z 

1 

) 

( Z + Z ) 

( 4 

( 4 

( 2 

( 5 

2 

. 0 

. 0 

. 5 

. 5 

) 

) 

− 

+ 

1 

1 

1 

. 5 

. 5 

) 

) 

21 

T 

= 

. 55 

Copyright Sonix, IncR 

= 

. 45

Reflected Sound Information 

Measuring the reflected 

ultrasound can provide: 

• Amplitude Information 

• Polarity Information 

• Time Information 

22 


ABC’s of Acoustics 

A-Scan- The raw ultrasonic data. It is the received RF signal 

from a single point (x,y). 

B-Scan- A line of A-scans. (Vertical cross-section) 

23 

C-Scan-Data from a specified depth over the 

entire scan area. (Horizontal cross-section. 


A-SCAN 

Initial Pulse 

Transducer 

Front surface 

Interface of 

interest 

Sample 

Back surface 

24 


Ultrasonic Waveforms 

The Black signal is commonly 

referred to as the initial pulse or the 

main bang. This signal occurs at 

Zero microseconds. 

The Red signal is commonly referred 

to as the front surface. This 

represents the first interface the sound 

encounters. 

1 

2 

The Green signal would be considered 

the area of interest. A data gate would 

be positioned over this signal or group 

of signals for evaluation. 

1 2 

The Blue signal is commonly referred to 

as a back wall echo or back surface. 

Just as the name implies it is the back 

or bottom of the sample. 

25 


A-SCAN 

100% 

+ Phase 

Amplitude %FSH 0% 

-100% 

_ 

Phase 

Time / Depth 

A-Scans provide the following information: 

1. Amplitude / % of full screen height (FSH) 

2. Phase / positive or negative peak 

3. Time / Depth 

26 


C-SCAN 

IP 

Front surface 

Back surface 

Area of interest 

The red box (data gate) indicates 

the depth of information. 

27 


B-Scan 

Front surface 

Signal from 

indication 

Back surface 

The blue line (B-scan gate) represents the depth 

of information recorded. 

Front surface 

28 

Signal from 

indication 

Back surface 



•Pulse Echo 

•Through Transmission 

29 



Pulse-Echo 

Through Transmission 

Transmit 

Transmit 

& 

Receive 

Receive 

30 

Pulse-Echo 

Pulse-Echo 

- 

- 

One 

One 

Transducer 

Transducer 

Through 

• 

• 

Ultrasound 

Ultrasound 

reflected 

reflected 

from 

from 

the 

the 

sample 

sample 

is 

is 

used. Through 

Transmission 

Transmission 

- 

- 

Two 

Two 

Transducers 

Transducers 

used. • 

• 

• 

Can 

Can 

determine 

determine 

which 

which 

interface 

interface 

is 

is 

delaminated. • 

Ultrasound 

Ultrasound 

transmitted 

transmitted 

through 

through 

the 

the 

delaminated. sample 

• 

• 

Requires 

Requires 

scanning 

scanning 

from 

from 

both 

both 

sides 

sides 

to 

to 

inspect sample 

is 

is 

used. 

used. 

inspect • 

all 

all 

interfaces. 

• 

One 

One 

Scan 

Scan 

reveals 

reveals 

delamination 

delamination 

at 

at 

all 

all 

interfaces. 

interfaces. 

• 

• 

Provides 

Provides 

images 

images 

with 

with 

high 

high 

degree 

degree 

of 


spatial 

interfaces. 

spatial • 

detail. 

• 

No 

No 

way 

way 

to 

to 

determine 

determine 

which 

which 

interface 

interface 

is 

is 

detail. 

delaminated. 

• 

• 

Peak 

Peak 

Amplitude, 

Amplitude, 

Time 

Time 



Flight 

Flight 

(TOF) 

(TOF) 

and 

delaminated. 

and • 

Phase 

Phase 

Inversion 

Inversion 

measurement 

• 

Less 

Less 

spatial 

spatial 

resolution 

resolution 

than 

than 

pulse-echo. 

pulse-echo. 

measurement 

• 

Copyright • 

Commonly 

Sonix, Commonly 

used 

Inc used 

to 

to 

verify 

verify 

pulse-echo 

pulse-echo 

results. 

results.


Pulse-Echo 

Front Surface 

Back surface 

1 

2 

Transmit 

& 

Receive 

1 

Front Surface 

Air Gap 

Air Gap 

2 

31 




1 

1 

2 

3 

Transmit 

2 

Receive 

3 

32 


Focusing Sound 

33 


Too Close 

1 

Focusing the Transducer 

Too Far 

Focused 

Too Close 

Focused 

2 

3 

2 

1 

Too Far 

3 

34 

Focusing an ultrasonic transducer is similar to focusing an 

optical microscope. 

When optimum focus is reached the signal will reach a 

maximum peak. (See the A-scans images to the left) 


De-focused-- too close 

Water path 

Correct focus 

28% 

1. Note the 

time in 

microseconds 

of the signal 

at the different 

focus 

locations. 

(Red arrow) 

De-focused-- too far 

85% 

33% 

2. Also note 

the amplitude 

of the signal. 

(white box) 

When the 

signal is not 

in focus the 

amplitude is 

lower 

compared to 

that of correct 

focus. 

35 


*The ultrasound is focused on the surface of the penny.

Focusing Sound 

De-Focused - Too Close 

Focused on Die 

De-Focused - Too Far Away 

Amplitude = 42% Time =10.5 us Amplitude = 82% Time = 14.5 us Amplitude = 55% Time = 18.5 us 

36 


Practical Application 

•Digital Oscilloscope 

•Front Surface Follower 

•Data Gates 

37 


Digital Oscilloscope 

Initial pulse 

1st Echo 

2nd Echo 

3rd Echo 

38 

The 1st set of echoes is the 

area of interest, gate placement 

will be on this group. 


Multiple Echoes

Gates 

Gates Gates are are used used to to collect collect information information at at 

desired desired interfaces interfaces within within the the sample. sample. 

•The •The gate gate is is placed placed over over the the signal signal or or 

signals signals of of interest. interest. 

•The •The absolute absolute value value of of the the highest highest 

amplitude amplitude signal signal which which breaks breaks the the gate gate 

threshold threshold within within the the gated gated region region is is 

recorded. recorded. (Figure (Figure 1) 1) 

•If •If no no signal signal breaks breaks the the gate gate threshold threshold 

no no data data is is recorded. recorded. (Figure (Figure 2) 2) 

•Signal •Signal amplitude amplitude can can be be increased increased or or 

decreased decreased by by adjusting adjusting gain. gain. 

1 

2 

Gate Threshold 

Highest Amplitude signal 

No data recorded 

39 


Practical Application 

•Image Data 

•Peak Amplitude 

•Time of Flight (TOF) 

•Phase Inversion 

40 


Peak Amplitude 

Peak amplitude imaging is used 

when defects result in changes in 

the amount or strength of 

ultrasound reflected. It is the most 

common type of imaging 

technique. 

41 




100 

78 

75 

50 

X1 

25 

0 

Signal height is measured in absolute 

value for Peak Amplitude images. 

42 

Amplitude 

Copyright 

78% 

Sonix, Inc

Time Of Flight 

Time of Flight (TOF) imaging 

works by measuring changes in 

the time it take sound to reflect off 

a particular interface. Most 

commonly used to measure die 

tilting. 

43 


Time Of Flight 

1 

X2 

X1 

2 

Time of Flight images provide a 

relative depth within a sample. 

Structures which appear white or 

light gray are closer to the surface 

of the sample. 

Structures which appear darker 

shades of gray or black are deeper 

within sample. 

44 

The peak signal for location 1 occurs at 

14.2 microseconds (light gray) while the 

peak signal for location 2 occurs at 14.6 

microseconds (dark gray). 


Peak Amplitude vs. TOF 


Time of Flight 

X2 

X2 

X1 

X1 

Amplitude =73% Time =14.2 microseconds Amplitude =67% Time =14.6 microseconds 


45

Phase Inversion 

Phase Inversion imaging is used when 

defects cause changes in polarity (phase) 

of the signal. Most commonly used for top 

and back side imaging of plastic 

encapsulated devices. 

Do not use phase inversion imaging for flip 

chip, bonded wafer or die attach imaging. 

46 


Phase Inversion 

Normal 

Phase Inverted 

47 


X 

Phase Gate 

X 

RED 

Yellow 

Sonix Sonix uses uses a 

proprietary proprietary algorithm algorithm 

to to detect detect phase phase 

inversion. inversion. This This 

method method is is 

independent independent of of signal signal 

amplitude amplitude as as long long as as 

the the signal signal is is not not 

saturated saturated (100% (100% 

screen screen height). height). 

X 

48 


Image Comparison & Correlation 


Peak Amplitude Image 

of Die Top 

Phase Inversion Image 

of Die Top 

Peak Amplitude Image 

of Die Attach 

49

ABC's of Ultrasonics

You also want an ePaper? Increase the reach of your titles

Delete template?

Save as template?