Evaluation Engineering - 18

SEMICONDUCTOR TEST

COST-REDUCTION AND SIMPLIFICATION
1000A high-current RDSon static parameter
DC testing vs. pulse testing at 300µs
by Christian Degenhart
The need for high-power semiconductors like diodes, MOSFETS, or IGBTs
is increasing rapidly. All areas of renewable energy, e-mobility, or industrial electronic drives have a strongly growing
need for more powerful components.
Testing these components is a big challenge for test engineers, since currents and
voltages have been rising rapidly in the last
few years and will continue as such going forward. To cut excess costs in mass
volume production, these tests have to be
done at different steps in the process, from
front-end wafer level, bare-die, to backend, where the discrete component and
final product is tested. On one hand, this
is mandatory to ensure consistently high
quality and reliability of the devices. On the
other hand, it is also important to detect
failing parts as soon as possible-avoiding
continuous processing of failed parts, and
therefore lower production costs. The best
cost-saving results can be achieved if you
are able to completely cover test specification in every process step. For the most

part, this isn't easy. I'll explain
why-further along in this article-and provide an example
that shows how you can work around
problems by calculating for testing the
R DS(on) static on-resistance parameter of
a MOSFET. Most of that can be adapted
to the measurement of Vf forward voltage
of a diode or VCE,sat saturation voltage
of an IGBT.
MOSFETs with R DS(on) drain-source resistance of less than 1m Ohm are already
available on the market. Maximum voltages and currents, which can be switched
by modern IGBTs like B2/4/6-modules or
MOSFETs (see Figure 1), are increasing.
According to typical test specifications for
R DS(on), the components have to be tested
at the maximum ratings, so test currents
of 1.000A or more are required nowadays.
In this article, we will discuss the advantages and disadvantages of measuring R DS(on) with direct current (DC)-based
instruments, and current pulse sources in
comparison. DC voltage and DC current

System concept

18

EVALUATION ENGINEERING MAY 2019

Figure 1:
An SOT-227 MOSFET.
VX Instruments

sources have slow rise times that settle
to a stable current level and need test
times from 10ms or more. Thus, such
tests are often performed within 100ms.
Since 100ms is far away from any time
constant of thermal elements in a typical
test system setup (e.g. heating of contact
pin/needle), we call that kind of testing
"DC testing." In comparison, we will show
how fast current pulse sources can help
to achieve test requirements.
The decision of which method of testing you choose for your test case has a
dominant influence on all test system
equipment. In one method it has to be DCcapable, and just pulse-capable with the
other method. Simplified, a typical test
setup for measuring the R DS(on) resistance
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