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36

Chip Scale Review November • December • 2018

[ChipScaleReview.com]

performance. eWLB can achieve the

minimum interconnection length and

excellent electrical performance up to

mmWave frequencies. The conversion

gain and the noise figure of the mixer

affect the performance of the overall

system. Therefore, a high-transmission

performance of the mmWave signal is

very important in the design of a package.

With the push toward autonomous

driving and automated vehicles, the

research and development programs for

sensors enabling the above mentioned

t e ch nolog ie s h ave gone i nt o h ig h

gear over the last several years. SRR,

MRR and LRR sensors are essential

components for the overall sensors

needed for the complete implementation

of automated vehicles. Many packages in

these segments use advanced packaging

options such as fan-out eWLB, with

lower parasitics at 77GHz [14].

For radio frequency (RF) and high-

f r equency dev ice s , eWLB showed

less parasitic electrical interference,

t he refore, sign if icantly improv i ng

overall device electrical performance.

In one example, a 77GHz SiGe mixer

p a c k a g e d w i t h eWL B a c h i e v e d

excellent high-f requency elect r ical

performance due to the small contact

dimensions and short signal pathways

o r i n t e r c on ne c t i on l e ng t h , wh i ch

decreased parasitic effects [15,16].

The sections below demonstrate the

advantages of the eWLB packaging

s o l u t i o n f o r t h e mmWave d e v i c e

or h igh -f r equency appl icat ion s a s

compared to subst rate or laminate-

based packaging, such as f lip chip or

wire bonding.

I nt erconne c t i on l eng t h .

eWLB

enables integration where the distance

has to be as shor t as possible (loss

increases with distance) to minimize

loss (assuming both technologies have

the same material loss).

Conductance loss.

Plated Cu used

i n organ ic subst r at e mat e r ials ha s

large surface roughness because of the

process used to improve adhesion and

plating process control. eWLB uses

a thin-f ilm fab process for the seed

layer and a well-controlled Cu plating

to achieve a smooth Cu RDL surface,

which is more effective for skin effect

i n h ig h -f r e que ncy r a nge s (i.e., a t

100GHz, Cu skin depth is ~0.2mm).

Dielectric loss.

Organic substrate

ma t e r i a l s h ave h ig h lo s s e s i n t he

m mWa v e r a n g e . F u r t h e r m o r e ,

het e rogeneou s mat e r ia l set s br i ng

complex it y i n t e r ms of ele c t r ic a l

b e h a v i o r s . eWLB u s e s mo l d i n g

compou nd a nd low-los s d iele c t r ic

materials that enable the achievement

of less dielectric loss.

Design f lexibility.

eWLB provides

more design flexibility for less routing

interference with fine line width (LW)

and line spacing (LS) capability (less

than 10/10µm LW/LS).

One key element for the change from

a rather complex and expensive solution

t o a n e a s y- t o - u s e a nd , t he r e fo r e ,

inexpensive and affordable product

is the use of standard surface mount

device (SMD) packaging technology.

The eWLB package is SMD attached,

t he r eby simpl i f y i ng t he up s t r e am

assembly process and has already been

proven in a few mmWave applications.

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