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34

Chip Scale Review September • October • 2018

[ChipScaleReview.com]

solution with equal or better performance

than PVD, the operational costs are

significantly less (

Table 2

).

High-viscosity compartmental shielding

paste.

For some package configurations,

where multiple chips of varying frequencies

are housed within the same device, external

EMI protective coatings alone may not

deliver adequate protection as cross talk can

occur between chips inside the package. In

this situation, isolating certain die within the

package may be advantageous and here, too,

new material technology has been developed

to facilitate effective in-package segregation

to minimize the impact of EMI. The solution,

referred to as compartmental shielding,

utilizes highly-conductive, highly-flowable

materials to separate active, RF-emitting

chips from one another.

Processing is simple and effective

(

Figure 5

): Once the target dies are selected,

a narrow channel is routed through the

molded package using precise laser cutting

techniques. The trench is then filled with

the new compartmental material via jet

dispensing. Because the cut channels often

have high aspect ratios (X dimension/Y

dimension) ranging from 5:1 up to 10:1, filling

is challenging and requires simultaneous

air displacement and paste deposition to

optimize EMI shielding performance through

void minimization. Adhesion and shrinkage

Figure 3:

Far-field shielding effectiveness of new

conformal coating metal ink vs. conventional ink at

1.6~2.6GHz.

Figure 4:

Near-field shielding effectiveness of new conformal coating EMI protection materials as compared to

sputtered materials and non-shielded samples at 1GHz and 5GHz.