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42

Chip Scale Review March • April • 2017

[ChipScaleReview.com]

materials and highlight two

a p p l i c a t i o n e x amp l e s o f

the technology.

Basics of functional inkjet

printing

To d a y , e v e r y b o d y i s

familiar with inkjet printing

because it is widely used

f o r g r a p h i c s p r i n t i n g i n

home and office printers,

i n l a rge - s ca l e p r oduc t i on

of magazines, bill boards,

a n d e v e n f o r a p p l y i n g a

design onto ceramic tiles.

That said, it is important

t o h i gh l i gh t s ome ba s i c s

o f t h e t e c h n o l o g y a n d

t h e d i f f e r e n c e s b e t we e n

g r a p h i c s p r i n t i n g a n d

functional inkjet printing

a s app l i ed i n e l e c t r on i c s

a n d s e m i c o n d u c t o r

manufacturing. All inkjet

p r i n t he ad s a r e ba s ed on

the principle of pushing a

low viscosity liquid out of

a numbe r o f i nd i v i dua l l y

addressable tiny channels, or

nozzles. The very small droplets that

are created in this way eventually form

the pattern on the substrate. In home

and office printers, a thermal pulse is

used to invoke a droplet. However, for

the application of printing electronic

materials, a much higher accuracy and

reliability is needed, which therefore

restricts the choice of print heads

to piezo-driven high-quality heads

a s u s e d i n i ndu s t r i a l , l a rge - s c a l e

graphics printers.

Figure 1

provides an

illustration of a droplet in flight.

Although they share the basic print

head technology, it should be noted,

that printing equipment for graphical

and for functional applications (such as

the example shown in

Figure 2

) also

have a lot of differences. The accuracy

and reliability requirements and the

diversity of applications and inks to

be processed have a large impact on

the machine design of a functional

printer. These specifications ask for

a high-precision motion platform,

precise pattern rendering, modular

design, adequate head inspection and

maintenance functionality, as well as

substrate handling.

Comparison between inkjet and

traditional technologies

The co s t r educ t i on po t en t i a l o f

inkjet printing becomes apparent when

comparing it to lithography. The ability

of inkjet printing to directly produce

patterned layers from a digital file avoids

the need for expensive lithography tools

and associated processes such as resist

coating, mask production, development

and etching. All these steps are typically

Inkjet-based additive manufacturing addresses

challenges in semiconductor packaging

By Wouter Brok, Henk Goossens, Klaus Ruhmer

[Meyer Burger]

r o w i n g d e m a n d f o r

s e m i c o n d u c t o r s i n

w e a r a b l e e l e c t r o n i c s ,

automotive and Internet of Things

( I o T ) a p p l i c a t i o n s , d r i v e t h e

deve l opmen t o f mi n i a t u r i z ed and

lower cost semiconductor devices.

Additive manufacturing and printed

electronics technologies like inkjet

printing of functional materials have

a numbe r o f un i que bene f i t s ove r

traditional semiconductor technologies

that enable further miniaturization and

process cost reduction.

J u s t l i k e t r a d i t i o n a l d i s p e n s e

technology, inkjet printing deposits

small droplets of functional liquid

ma t e r i a l s on t o a s ub s t r a t e . Wh a t

makes inkjet unique is that droplets

are much smaller (picoliter volume),

are jetted by thousands of individually

a d d r e s s a b l e n o z z l e s a t t h e s ame

t ime , and a r e depos i t ed i n a non -

contact manner. With this technique,

patterned and homogeneous layers

can be produced, also on 3D surfaces.

Even 3D structures can be printed

directly. These benefits are recognized

in many industries such as printed

circuit board, photovoltaics, display,

3D printing, and even pharmaceutics

where inkjet technology finds its way

into industrial manufacturing.

Where the feature size of inkjet

printing is not compatible with most

semiconductor front-end processes

be c au s e s ub -mi c r on pa t t e r n i ng i s

required, many wafer-based back-

end-of-line (BEOL) and strip-based

packaging process steps need features

of tens of microns up to millimeters,

and can benefit from inkjet technology.

Therefore, inkjet printing is being

a d o p t e d b y s ome o f t h e l a r g e s t

s em i c o n d u c t o r p r o d u c e r s i n t h e

world. In this article we will review

the advantages of inkjet printing in

comparison to traditional technologies,

give an overview of inkjet-compatible

G

Figure 1:

An inkjet droplet in flight in the first 200μs after the

piezoelectric excitation of a nozzle.

Figure 2:

Example of a functional inkjet printer for semiconductor

fabrication.