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Chip Scale Review May • June • 2019

[ChipScaleReview.com]

not account for the utilization efficiency, which we considered the

same for each equipment. Our work aims at enabling the technical

conditions to maintain the best possible cost effectiveness of

the test flow during its entire lifecycle. In the early phases, with

relatively high defectivity and consequent long time for the

screening of early-life fails, the adoption of a flow with both

BI&SLT is economically affordable. In these phases, you should

also expect relatively low manufacturing volumes.

Figure 6

shows that a cost tradeoff exists between the BI&SLT and BI+SLT

approaches depending on the BI time. It is possible to combine

BI and SLT duration such that the possibility of combining them

together becomes economically convenient.

In

Figure 6

the time axis represents the effective burn-in time

without the additional time for load/unload operations. Conversely,

the time for the BI+SLT approach accounts also for the extra time

for the load/unload operations, because it is required intrinsically

by the approach, while the time for the BI&SLT methodology is

only the BI time.

The proposed strategy becomes even more convenient when

exploiting the high-voltage stress for exponentially reducing the

BI time, as described in [1]. Using high voltages in BI reduces

dramatically the DPPM even with a short BI time duration.

The proposed flow has its maximum saving when the BI time is

lower than 10-12min. In addition, it is also important to remark on

the existence of mechanical effects at each stage. Each time parts are

handled, there is the probability of a mechanical damage to leads/balls

and/or to the package body. The reduction in the number of stages,

Table 1:

Test costs per device without the proposed methodology.

Table 2:

Test costs per device with the proposed methodology. For footnote a, refer

to Table 1.