Non-destructive acoustic micro imaging of package seals

Non-destructive acoustic micro imaging of package seals by Tom Adams Seals, which close a medical or pharmaceutical package, are designed to maintain

The ultrasonic frequencies used cover a wide

its contents in a sterile condition until use. Imperfections in the seals can allow

range.

bacteria or other contaminants to reach the contents, with potentially dangerous

frequency of 10 MHz are used when a package

consequences. The technology of acoustic micro imaging, which has become

is relatively

widely used in the microelectronics industry, has recently demonstrated its ability

provide better penetration.

Transducers thick,

Transducers

to image and analyze seal integrity non-destructively.

penetration In microelectronics,

acoustic

employed

for defects

circuit

to look

micro imaging is in integrated

packages, the familiar black ‘computer

chips’ found

in computers

and innumerable

several thousand

Ultrasound gasses,

will not travel through so the

or a vacuum,

coupled

times per second.

to the sample

air, other

transducer

by a liquid,

is

usually

water. The sample may be placed in a tank, or

other systems. Medical

receiving

and pharmaceutical

packages have

a tiny ‘waterfall’ nozzle, which

rides on the

circuit

transducer, may be used to create a small water

packages than merely the term ‘package.’ The

jet, which greatly reduces the exposure of the

materials

sample to water.

more

in

common

with

frequently

and metals -

integrated

used - various polymers

are similar.

So is the layered

polymer

structure. Acoustic

micro

imaging

suitable for high-speed packaging

of

pharmaceuticals, design

medical

not

lines in the

devices

and

but it is extremely useful in the of packages

of production.

used in microelectronics

throughput

is probably

production

and prototyping

batch-sampling

and

in

It is, however,

production

lines, where

the

acoustic

commonly

used transmission

which

scans

the

alternately pulsing ultrasound

mode,

package

while

into the package

The rapid scanning motion of the transducer is possible because the speed of ultrasound directions

metres

is very high -

per second

Ultrasound reflected,

is

in plastics,

pulsed

transducer

into

around

switches

Sealing Technology No. 76

While between

in

3000

for example. the

package,

first

between

layers of

will travel downward

layer -

the

metal

foil -

sending back any return echoes.

But

when ultrasound

reaches the interface between

the

and

metal

portion the

foil

the

of the ultrasound

transducer

and

polymer

below,

is reflected

is

ultrasound

collected.

continues

a

back to The to

travel

because

low

lower frequencies

above 200 MHz are used when

is not critical

and when a high-

improves as frequencies move up. Gap-type defects containing air or another gas at any depth will reflect all of the ultrasound. the

bulk

of a polymer

contains

voids,

ultrasound

even

the

layer,

voids

if the

If

for example,

will

reflect

boundaries

the

of

the

polymer layer are well bonded to other layers. This is why paper materials cannot usually be penetrated

by ultrasound;

the

paper

itself

contains thousands of tiny voids. But ultrasound can usually penetrate a material which is bonded to paper.

Voids and channels Voids and other

anomalies

medical or pharmaceutical

in the seal of a

package may not be a

threat unless they can form a channel by which

downward, where it will be reflected by deeper

bacteria

interfaces.

protection

or

contaminants

which

can

breach

the

the package is designed

A significant

channel

to

may be very

Gaps generate strong echoes

features

These events occur only if the metal foil and the

are likely to be noticed

polymer are well bonded to each other.

capable of detecting features which are too small

narrow. At high frequencies, ultrasound images

If there

disbond, or void -

between the two layers, all of the ultrasound is reflected transducer

back

to the transducer.

is scanning

the package

measure

as little

Even at lower frequencies,

Since

the

at high

as several microns. significant

features

because ultrasound

is

to be resolved. Figure 1 is the reflection-mode of a blister pack constructed

1ayers. In reflection-mode

acoustic image of two polymer

imaging, the display

speed, it rapidly collects the very strong echoes

image can be made using only those return

sent back by gap-type defects.

echoes from a specified depth in the sample.

In the display

in

acoustic image, gap-type defects will be visible

Echoes

scanning,

the

in the highest contrast, and well bonded internal

technique,

pulsing

and

features will be visible in medium contrast.

make this image; gating was on the seal between

and travels back to the transducer

a few microseconds.

without

the

is a gap - a delamination,

and receiving the return echoes.

both

metallic foil. Ultrasound through

consist of a

at the very

image is needed, because resolution

provide.

micro imaging employs an ultrasonic

transducer,

for example,

layer sandwiched

remaining

speeds are less.

High speed reflection of ultrasound In

A package might,

resolution

pulsing

from other

depths

called electronic

are ignored.

This

gating, was used to

0

The

same blister

Thru-Scan

pack, but imaged by the

technique,

is shown in Figure

Black areas are acoustic gaps

which

reaching

shadows representing

prevented

the collecting

blister pack.

ultrasound transducer

connecting

below the

In addition,

one blister

Low

to

there are irregular gaps

frequency

This image displays

less detail in the bonded internal interface, it

makes

significant

defects

much

but more

conspicuous. A portion package

is shown

performed bright

of the seal of a two-layer in Figure

by the Thru-Scan

feature

is

the

seal;

For best resolution,

The

long

imaging

The

highest

200

MHz)

the highest frequency which

has

development

in

the

already

of acoustic

semiconductor

yielded

very small features.

packages

are, very roughly,

pharmaceutical

method.

The

capable

consist

of

similar

packages,

a larger

in overall medical

and

number

materials

of

Semiconductor

to the seals of many

dissimilar

micro

industry

techniques

imaging

was

unbonded regions on either side of the seal.

(above

used.

3. Imaging

are

for

will penetrate to the depth of interest is generally

thickness

areas

MHz,

(10

low resolution.

transducers

foil

dark

transducers

penetrate less, but permit very high resolution.

which extend from both rhe inner and outer edges of the sealed area.

frequency

example) penetrate relatively thick materials, but have relatively

from

The blisters themselves are black,

as are the channels another.

2.

of

that

or

frequently layers

of

medical

pharmaceutical

package seals.

Application packages

in semiconductor

or

There are no outright breaks in the seal, but the width of the seal varies, and in a few places channels lead partway into the seal. Figure 4 shows a similar seal, here imaged in the two polymers.

The large black circles are the

A frequent

Two anomalies have been

semiconductor

packages

induced in the seal.

One, in the upper half of

multiple

in the

voids

the image, nearly breaks through the seal; the

connection

but the irregular white areas, which reflected all

second, in the bottom

around

of the ultrasound, are delaminations

through.

blisters.

Grey areas of the seal are well bonded,

two layers.

between the

Some of the delaminations

form

channels running from one blister to the next.

half, breaks completely

The interior of the package (the large

Acoustic micro imaging is most frequently used in the reflection mode, but a second technique, called Thru-Scan,

has been found to be very

useful

imaging

when

medical

pharmaceutical

packages.

reflection-mode

acoustic microscope

developed by Sonoscan

and

Thru-Scan,

and the itself, were

Inc (Elk Grove Village,

inch

a few tens of microns.

in the seal.

medical

Even very narrow channels enter a package.

micron in a can

How narrow a channel can be

of

of a solder

(100

microns);

the

Investigations

into

and food package seals have imaged leakers with widths range.

in the 1 to 10

In all of these instances,

Thru-Scan

ultrasound; however,

mode, some

consist

represent

part on the frequency

routinely imaged.

used.

blocks)

all

semiconductor

the

of

the

features,

not of gaps but of features

which are out of place.

imaged by acoustic micro imaging depends in of the transducer

in

channel is a gap-type defect which reflects (or,

may constitute

pathway by which bacteria or contaminants

bonding

imaging imaging

where the diameter of the bond is 0.004

grey area) is filled with air, as are the two breaks

Imaging very small defects

micro is the

individual voids in this case are on the order of

channel

Finding gaps at any depth

use of acoustic

the reflection mode.

well bonded

Such features, which internal

interfaces,

are

Illinois, USA). In reflection-mode the

various the

interfaces,

package.

imaging, after

ultrasound,

exits from

Thru-Scan below scanning

while

reflected

the upper

ultrasound,

Since

ultrasound

defects, will

will

resulting quick,

an

travel

very effective

whether

ultrasound, by

the

through

upper

gap-type

void, or other gap

acoustic

Thru-Scan

the

collects

surface.

any delamination,

produce

This of

transducer

pulsed

not

of

a second

bottom

collects

which exits the bottom transducer

the bottom

package.

the

of

through

places

the

transducer transducer, package

a portion

travelling

image.

shadow

in

Thru-Scan

method

the is a

of determining

a defect exists at any depth within

a

package. In imaging medical and drug packages, Thru-Scan

is often

used first;

identified, reflection-mode

if a defect

is

imaging is then used

to gate to a specific depth and examine the fine details of the defect.

@

Sealing Technology

No. 76

Acoustic X-rays

micro imaging micro

imaging

and x-ray

methods, while superficially internal

features

fundamentally an internal void

similar in that they

very different

or

delamination

-

if the

a void - or

makes

it very

for x-ray to detect the small change in

intensity.

Very

however,

detects

high

defects no matter sectioned ultrasound thin

S onoscan ultrasound

frequency

voids

and

electron

samples

0.1 has

other

gap-type Some

micrographs

demonstrated

was completely as

ultrasound,

what the thickness.

years ago scanning

as

X-ray can image

Too thin

enough.

are

and overlap only

void (to pick one example)

is thick

difficult

imaging

non-destructively,

slightly in their applications.

disbond

Several methods testing,

Acoustic depict

versus

micron. recently

is completely

of that

reflected from gaps New

research

suggested reflected

at that

by gaps as

thin as several hundred Angstroms.

- dye penetrants,

destructive

determine

analysis

the existence

Acoustic Image

vacuum

are used

of anomalies

seals of drug and medical packages. these methods

can establish

to

in the

Generally

the existence

of a

channel or a leak, but they are less successful at characterizing

the location

and structure

of an

anomaly.

Advantages imaging

of acoustic

The advantage of acoustic that

it

images

destructively,

the

micro imaging is

internal

in the more analytical acoustic

micro

anomaly

both in the Thru-Scan

imaging,

reflection

the package

non-

mode and

mode.

After

remains

intact

and is available for other types of analysis. Because the imaging process is both rich in data

and

non-destructive,

acoustic

micro

imaging is ideally suited for two environments _ setting up new production lines and batch sampling

from existing lines.

In characterizing

Transmitter

-

technology

sealing anomalies. from existing system

new production

rapidly

which

identifies

and

In batch sampling

lines, the analyzes of seals

lines, it serves as a monitoring finds

potentially

troublesome

defects in seals. Contact: Steve Martell, technical manager, Sonoscan Inc, 2149 East Pratt Blvd. Elk Grove Village IL 60007. USA. Tel: +I 847 437 6400; Fax: +l 847 437 1550; EL mail: smartelIQsonoscan.com.

Transducer

4 + 77 Water

Lens _

We are extremely happy m consider industrial and technical newt items and technical articles for publication in Sealing T~cbnologv,the only newsletter dedicated CO developments in the global scaling indusuy. Ideally, articles should be between 1500 and 2000 words and news items between 100 and 500 words. If you are interested in submitting any items then please contact Scaling TEchnoia~~ editor, Lara Mynors, ar the address below for &her details and authors’ guidelines. ElsevierAdvanced Technology PO Box 150, Kidlington, oxford, OX5 lAS, UK Tel: +44 1865 a43745 Fax: +44 1865 843971 Ed:

Sealing Technology No. 76

[email protected].&

@