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47

Chip Scale Review May • June • 2018

[ChipScaleReview.com]

Commercialization challenges

There are many issues that would need to be

addressed before any potential material could

be used commercially in a semiconductor

package. Due to the heterogenous nature

of IC package technology, changes in one

component may result in unintended effects

or consequences to the entire system. Many of

these issues have been alluded to earlier in this

paper, but described next is an example with

epoxy molding compounds. Epoxy molding

compounds are generally an epoxy thermoset

resin filled mostly with fused silica and some

additives like catalysts and hardeners. In

the past, small amounts of bromine (Br) and

antimony (Sb) were added to the mixture as

flame retardants but RoHS declared those

elements as harmful to the environment and,

therefore, needed to be eliminated.

The unintended consequences discussed

above resulted from the alterations to

molding compound formulations to make

the end package RoHS-compliant. Those

changes also made the molding compound

“stickier” during the molding process, and

thereby harder to remove the excess material

from the mold surfaces and subsequently

increased wear on metal mold platens and

plungers (see

Figure 2

for an illustration of a

transfer mold press) during production. This

means that more time must be devoted to

cleaning the mold press to prevent defective

packages. Additionally, the working life

of the mold surfaces in contact with the

molding compound are all reduced, which in

turn reduces manufacturing efficiency and

increases operation costs [14].

Therefore, perhaps the lesson here is that

the path to a more environmentally-friendly

end product may be filled with unanticipated

costs and issues. That should not preclude

pursuing research and development to find

such materials to be used in semiconductor

packaging, but researchers should be

aware of the risks and issues that can come

from altering a stable system. Reducing

e-waste and harm to the environment are

all admirable goals, but they do not come

without risks or a price.

Table 3:

Die shear strength readings for re-workable thermosetting underfill materials [10].

Figure 2:

Transfer mold press [15].

Table S-1:

Materials used in semiconductor packaging [21].

Materials used in semiconductor packaging [21]

This section lists different types of materials used in semiconductor packaging.

Table S-2:

Influence of molding compound ingredients on physical properties [22].

Molding compounds, die attach adhesives and underfills

A molding compound’s properties are a balance between ease of use in a high-

volume manufacturing environment and its relationship to the overall package’s

performance and reliability.

Table S-2

shows how much effect each ingredient in

a molding compound has on its manufacturing performance and reliability.

Die attach adhesives are similar to molding compounds, usually consisting of

a liquid epoxy resin, a filler material, reactive epoxy diluent or solvent, catalyst,

and hardener.

Finally, chip underfill materials are similar to both die attach adhesives and

molding compounds, typically being a liquid epoxy resin filled with fused silica

and additives such as catalysts, hardeners, and coloring agents.