Page 9 - PEN eBook February 2024

COVER STORY – DESIGN SEMICONDUCTORS

temperature and time to provide the optimum The FOX-XP solution is a versatile test/burn-in
‘stress’ while avoiding inducing failures,” he added. solution that can be customized to accommodate
DiePak Carriers for individual die/module testing.
Moreover, wafer-level burn-in optimizes production A DiePak Loader, which is optional, can be used
yield by reducing the number of defective devices to automate the process of loading and unloading
that proceed through further manufacturing devices into FOX DiePak Carriers. This module test
steps, such as assembly into multi-chip modules, system supports both full wafer and singulated die
heterogeneous integrations and package parts. burn-in and test.
PRECISION AND SCALABILITY MODULAR ARCHITECTURE

Wafer electrical testing attains a superior level of The design of Aehr’s testing systems has followed a
accuracy and expandability by employing numerous modular approach. The FOX-NP system, for instance,
precise, calibrated electrical sources and measuring utilizes identical test hardware as the FOX-XP.
tools for each wafer.
As Rogers explained, Aehr’s “modular architecture”
“At Aehr, we ensure the precision of the instruments used on both the FOX-NP (one- or two-wafer
integrated into our systems using calibration capacity) and the FOX-XP (up to 18-wafer capacity)
procedures that verify and adjust performance ensures consistent test capabilities and an intact
to known industry standards and adhering to transition from a small-lot engineering and NPI
traceability requirements of such standards,” setup to a fully automated, high-volume production Cascode GaN Power
Rogers said. platform.

A perfect correlation between the results obtained Devices in Cu-Clip
from the FOX-NP and FOX-XP systems is ensured by
this modular design.

“The modular architecture used in either the Package for Superior
FOX-NP or FOX-XP systems is assembled and tested
independently of the final system configuration, Power-Conversion
to the same performance and reliability standards
regardless of which platform they are integrated
[into],” Rogers said. Moreover, the software for both Performance
the FOX-NP and FOX-XP is identical, providing a
seamless user experience.
By Sonu Daryanani, contributing writer for Power Electronics News
This correlation is extremely critical, especially in
ensuring a painless transition from the
engineering-oriented FOX-NP, in which product The cascode architecture with power gallium nitride use of a high-threshold–voltage (V ) MOSFET, the
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qualification was completed, to the massively parallel devices uses a depletion-mode (d-mode) HEMT gate drive becomes very robust, allowing for a high
FOX-XP production systems, in which correlation and device and offers many advantages in higher-power– overdrive margin and external gate voltages (V ) of
gs
Figure 2: Aehr’s FOX-XP with Integrated WaferPak Aligner maximum yield are required. The synergy between conversion applications. Improved packaging can help ±20 V. This is in sharp contrast to the low V (<2 V)
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(Source: Aehr Test Systems) the FOX-NP and FOX-XP platforms affords the utilize the benefits of GaN to its fullest extent. This typical in enhancement-mode (e-mode) GaN devices,
manufacturer a wide range of test capabilities for article details Nexperia’s development of the copper where maximum V is typically limited to 6–7 V, which
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various products, such as silicon photonics and GaN (Cu)-clip CCPAK package for its cascode power GaN restricts overdrive. The low V also places greater
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Aehr’s FOX test system platform is architected for and SiC semiconductors. devices, as presented at the December 2023 PowerUP constraints in the gate drive, the gate coupling from
massively parallel testing using a modular system Virtual Expo. drain-switching transitions and added parasitic
design and software that implements real-time inductances from the package and board layout to
monitoring and controls. The company developed ADVANTAGES OF CASCODE GaN minimize noise and oscillation that could cause a
data analysis and reporting tools that identify trends ARCHITECTURE parasitic turn-on.
or anomalies automatically, informing the end user In the cascode architecture, a normally on d-mode
of any potential issue. The FOX-XP with Integrated HEMT is coupled with a normally off low-voltage silicon The use of the d-mode GaN HEMT improves its
WaferPak Aligner, for instance, achieves advanced MOSFET device, as shown in Figure 1. on-state performance with improved carrier mobility,
precision in wafer handling and probe alignment as well as the off state with a much lower gate
using optical alignment with multiple cameras to The silicon device controls the gate drive, hence leakage from the cascode silicon device. The improved
ensure accurate wafer-to-probe alignment and offering flexibility in the use of common gate drivers on-state performance translates to higher-current–
placement in a WaferPak contactor (Figure 2). that are used to drive silicon MOSFETs. With the rated devices. Another key advantage of the cascode

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