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INSPECTION, MEASUREMENT, AND TEST

INSPECTION, MEASUREMENT, AND TEST 19.13

Guardbanding is a process shown in Fig. 19.6, which adjusts the test limits to take the setup and
*
measurement uncertainty into account. The SEMI organization has quantified this in the E35 docu-
ment. The goal is to eliminate the possibility of falsely passing a bad part, but it also has the unde-
sirable effect of potentially failing a good part. High accuracy and low uncertainty are desirable so
that the guardband can be reduced as much as possible thereby maximizing yield.
Defining the Project. Developing a test program can be a complicated process and must be treated
as a project. Formal project management rules should be used including developing a project defin-
ition with a timeline.
1. Defining the application development phases:
a. The proposal phase defines the deliverables such as the hardware delivered, the test parameter list,
software coding and debugging, production integration (wafer prober or IC handler integration,
special operator interface, or data log needs), solution diagnostics, and project wrap up definition
(items 2 to 6 in this section). The proposal phase requires an agreement from the IC design group.
b. The design phase defines the test strategy and the design of the DUT board hardware.
c. The implementation phase executes the design phase plans.
d. The release phase is when the project is completed and released.
2. Acceptance criteria. The acceptance criteria defines how the list of deliverables will be demon-
strated to be complete and within the specifications of the agreement. The mean, sigma, and corre-
lation limits of the data need to be defined as well as the conditions under which they are taken.
3. Documentation of the project deliverables. A written explanation of the test including schemat-
ics of the circuit used on the DUT board for each test including test data, limits, and the statisti-
cal variations. This documentation will be used for future modifications and maintenance, and for
new engineers to learn the test solution.
4. Training for the deliverables of the project. The training on how to run the program and cor-
rectly set up the hardware. The training could vary depending on the job function of the person
operating the program.
5. Roles and responsibilities of the different parties. A roles and responsibilities definition makes
it clear who is responsible for which deliverables and what specific knowledge is required.
6. Change management definition to this proposal. Since changes will inevitably happen, it is
important to define up front how these changes will be handled.
Each of the project deliverables should be put on a timeline with dependencies to the previous items
noted.
This plan incorporates the common elements of developing a test program—defining the DUT
pins, configuring what test system resources are needed based on the DUT functionality, designing
a DUT interface from the DUT to the tester resources, transferring and translating any EDA data that
are applicable, writing and debugging the test program, data logging the results, further analyzing
the data to look at the mean, sigma, and correlation to known good devices, developing a binning
strategy, developing a diagnostic for the test solution, and documenting the project including train-
ing on the use of the solution.
Common Test Parameters. Usually test parameters are as diverse as the end applications for which
parts are designed. However there are some types of test parameters that are common to all devices.
Continuity: Device pins are ESD-protected by a diode to ground and/or power. A current sink (−)
is placed on the DUT pin while the ground or V substrate is grounded. The resulting current
cc
turns the diode on and a diode drop voltage is measured on the DUT pin. A short circuit would
read as 0 V and an open would go above the preprogrammed voltage clamp value placed on the
DUT pin current force function.

* SEMI E35-0701, Cost of Ownership.

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