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41

Chip Scale Review May • June • 2019

[ChipScaleReview.com]

needs to also control TDI and TDO. TDI

is connected to the MOSI of the second

SPI, while TDO is connected to the MISO

of the first SPI. The JTAG interface can

require an additional signal, for example

an asynchronous reset, which is called

JCOM. These kinds of signals can be

controlled using common GPIOs.

Th is is t he mi n imal protocol for

accessing a standard TAP. The protocol

cont r ol s t he s t a t e i n side t he TAP

controller, loads instructions inside the

TAP register, downloads results of TAP

instructions and uses the DUT scan chain.

If the structural test requires additional

signals, the protocol can be enhanced with

further SPI interfaces.

Experimental results

The proposed approach has been

u s e d f o r t e s t i ng a SoC , wh i ch i s

based on a 40nm CMOS technology

microcontroller by STMicroelectronics,

which serves automotive applications.

The DUT is safet y- compliant wit h

t he ISO -26262 [14] up t o ASI L -D

applications. Inside the DUT there is

a microcontroller with embedded non-

volatile memory (i.e., a MCU).

This product undergoes severe test

requirements to reach very low DPPM

f igu res. Especially begi nni ng with

the 40nm node, these devices reached

a r el a t ively h ig h complex it y. The

complexity depends on a combination

of factors, i ncludi ng the relat ively

large number of integ rated IPs and

the possibility of IP reconfiguration

offered by the non-volatile memory.

The widest possible ver if ication of

configurations is a main goal for the

applicative test. To implement this

objective, we def ined an applicative

setup with the minimum possible set of

components, for the obvious objective of

minimizing the board space occupation.

Space occupation is a key parameter

determinant in the cost of test because

it directly influences the test parallelism

for a given board space.

The additional key factors driving test

costs are typically the test duration, the

number of stages (e.g., a stage requires the

DUT to be handled and put in a socket for

the test), the parallelism, the throughput

ratio, and the cost of the equipment. In

our analysis we did not consider other

factors, which are independent from our

project scope, such as the efficiency and

the electrical yield.

Table 1

gives some figures used to

compute the test costs per device without

the proposed methodology, i.e., with a

solution where BI and SLT are applied

independently (BI+SLT).

Traditional burn-in operations, usually

characterized by off-line automation, give

better cost efficiency with relatively longer

durations. In this case, to load devices to

the sockets on the board, an equipment is

shared between multiple burn-in testers,

named automated loader/unloader (ALU).

The board movement from the ALU to

the BI tester may happen either manually

or by robots depending on the level of the

automation. These off-line operations add

an overhead time to the electrical burn-in

time and an extra cost.

Table 2

presents the test costs per

device per minute with the proposed

approach. This methodology will be

referenced as BI&SLT. Our analysis does

P RoHS