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Chip Scale Review May • June • 2018

[ChipScaleReview.com]

Biodegradable and recyclable materials in

semiconductor packaging

By Randy H.Y. Lo, Andrea S. Chen

[Siliconware USA, Inc.]

nvironmental consciousness

has pushed reusability of

mat e r ia l s i n a l l a spe c t s

of societ y, whet her it be recycli ng

aluminum beverage cans and plastic

water bottles, or re-purposing vehicle

t i r e s . To d a t e , t he i mpu l s e t o go

“green” in semiconductor packaging

has been ref lected by eliminating the

use of lead (Pb)-based solders and by

eliminating halogens like bromine and

antimony as molding compound f lame

retardants. There has been minimal

discussion, however, in the literature

and t rade press about recycli ng or

taking apart said packages in a more

environmentally-friendly manner. One

logical reason is due to the compound

nature of an IC package—with so many

component elements and the use of

many disparate materials, both organic

and inorganic in nature.

Given t he sit uat ion , t he re cou ld

be plenty of opportunities to utilize

novel ma t e r i a l s i n o r de r t o ma ke

a semiconductor package i nto less

hazardous waste. Areas of research

i n c l u d e s u b s t i t u t i n g t h e e p ox i e s

i n mo l d i n g c omp o u n d s a n d d i e

attach adhesives with biodegradable

versions, or f inding substit utes for

silver f lakes in conductive die attach,

or perhaps using cellulose ( paper)-

based materials instead of fiberglass

for subst r at e s. As for conduct ive

wi r i ng, r e s e a r che r s might look t o

iron, which is considered non-toxic

and more environment ally-f r iendly

than gold, silver or copper. Or better

still, one might look to an electrically-

conductive polymer to create an all-

organic materials package system.

Th i s pap e r look s a t s ome ide a s

a nd c on c e p t s t h a t m i g h t b e u s e d

t o develop more env i ronment al ly-

f r ie nd ly e ng i ne e r ed ma t e r i a l s fo r

semiconductor packages. The intent

here is to consider var ious thought

e x p e r i m e n t s o n w h a t m i g h t b e

possible in reducing waste in the area

of electronics packaging.

Introduction

While societies in advanced economies

have made moves towards recycling,

reusing and being envi ronment ally

conscious in general, some things have

proven more difficult than others in those

efforts. For instance, materials used in

semiconductor packaging tend not to fit

any of the green categories, though there

were successful steps to restrict the use of

Pb and other hazardous materials through

the implementation of the European

Commission’s Restriction of Hazardous

Substances (RoHS) Directive back in the

early 2000s [1]. Admittedly, compliance

to the RoHS directive took several

years to implement, which continues to

the present day as standards undergo

continuous updates [2] (see the

sidebar

).

G i v e n t h e i m p l e m e n t a t i o n

precedence noted above, it has been

generally difficult to substitute more

biodegradable and recyclable materials

in a semiconductor package, both due to

the stringent reliability requirements and

the heterogeneous structures inherent in

said packages, as illustrated in

Table 1

and

Figure 1

, respectively. Which is not

to say that is should not be attempted.

The intent of this paper is to look at the

possibilities to improve the materials

used in semiconductor packaging from an

environmentally-friendly perspective.

Research into biodegradable and

recyclable electronic materials

The l it e r at u r e a nd news r epor t s

s h ow t h a t t h e r e i s c o n s i d e r a b l e

interest and research into the topic of

environmentally-friendly electronic

materials [5,6], but much of the existing

work is looking into novel uses rather

than replacing existing materials in

established packaging bills of materials.

Examples include sof t and f lexible

disposable sensors that can be worn on

the skin’s surface, perhaps to collect and

store certain health data for a patient, or

even implantable health sensors. In these

cases, the materials would need to be bio-

compatible as well as biodegradable. The

end result is the ability to decompose

the electronics into inert materials that

are safe for the environment. One of

the examples cited used a weak acid,

like vinegar, to dissolve the conductive

polymer into non-toxic components and

using iron for the conductive circuitry

because iron oxide (rust) is considered

relatively non-toxic.

Also, it has been shown that carrier

trays and tape for semiconductor packages

can be made from biodegradable plastics

without sacrificing functionality [7].

Table 2

shows the attributes comparison

for different types of biodegradable

plastics. However, it may prove difficult to

substitute biodegradable organic materials

into the existing bill of materials used

for semiconductor packaging, though

perhaps not be impossible to find suitable

subst it utes for the epoxies used i n

molding compound, die attach adhesives

o r ch i p u nde r f i l l s . As me n t ione d

previously, however, the performance

requirements could prove daunting,

whether technologically or economically,

not to mention the additional complexity

E

Figure 1:

a) Generic cross-section illustration of a

wire bonded quad-flat no leads (QFN) package; and b)

of a flip-chip QFN [4].