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Chip Scale Review September • October • 2018

[ChipScaleReview.com]

Effective, scalable EMI protection for semiconductor

packages

By Xinpei Cao, Jinu Choi, Junbo Gao, Dan Maslyk, Andrew Sun, Qizhuo Zhuo

[Henkel Corporation]

he connectivity of everything

and growth of the Internet of

Things (IoT) have fueled the

massive expansion of wireless,

memory and data processing components,

enabling consumers to enjoy historic levels

of convenience, connection and control.

With an increase both in the quantity and

functionality of these radio-frequency

(RF) emitting devices alongside their

miniaturization, however, comes the need

for more effective isolation to protect against

electromagnetic interference (EMI) from

other components in close proximity, as well

as within devices that contain multiple chips

such as a system-in-package (SiP) device,

for example.

To be su re, t here is now g reater

integration at the package level than ever

before. Devices have much smaller and

thinner profiles to accommodate shrinking

end-product dimensions and it is not

uncommon to have chips with different

operating frequencies within the same

package. Without segregation of wireless-

enabled devices, unwanted cross-talk

among components can cause electrical

performance degradation and/or failures.

Therefore, to ensure functional reliability,

it is essential to address electromagnetic

compatibility (EMC) through the elimination

of noise at the component level.

Conventional solutions for

EMI shielding

Historically, EMI shielding has been

achieved through the use of metallic cans

that cover a component or an assembly

and attach to grounding pads on the

substrate (

Figure 1

). However, with today’s

high-density designs dictating thinner,

smaller components placed within tighter

dimensions, conventional metal enclosures

are not practical for many applications due

to their size and the board layout restrictions

required to accommodate them.

Miniaturization has, therefore, driven

the use of package-level solutions such

as physical vapor deposition (PVD) –

also known as sputtering – to deposit

metal coatings on package exteriors for

interference protection. PVD, though, is

not without its shortcomings in terms of

processability and cost. It is well understood

that this technique has operational

challenges that include surface treatment

requirements, limited material selection,

low units per hour (UPH) rates, stringent

maintenance, a large equipment footprint,

and high costs. Until recently, however,

coping with PVD’s drawbacks have been the

tradeoff for its thin EMI protection. And,

while PVD offers external package shielding

to protect against outside interference, it

obviously does not prohibit cross-talk within

multi-chip devices.

Next-generation EMI shielding

developments

To tackle the industry need for thinner,

more adaptable EMI solutions with greater

process f lexibility, two new material

technologies have been developed. The first

is a conductive, silver-based ink platform that

is applied via spray-coating using readily-

available spray technology, and the second

is a conductive paste solution that is used to

effectively isolate chips housed within the

same device. The sections below discuss

conformal coating of spray-coated metal

inks and high-viscosity compartmental

shielding paste.

Conformal coating spray-coated metal

inks.

Two key elements of the conformal

coating of spray-coated metal inks are

(A) processing and (B) performance as

discussed below.

(

a

)

Processing

Compatibility with any commercially

available spray technology makes the new

metal inks extremely versatile, allowing

for cost-effective deployment within

manufacturing operations that may already

have spray technology onsite, can easily and

T

Figure 1:

Traditional metal cans enclose components

to protect against electromagnetic interference.

Figure 2:

Component configuration and spray coating

of new EMI shielding conformal coatings.

Table 1:

Material properties of the conformal coating metal ink as tested.