Page 42 - PEN eBook May 2023

SEMICONDUCTORS SEMICONDUCTORS

Compared with D2PAK technology, based on wire exponentially more transistors while reducing the
bond, LFPAK offers the following benefits: supply voltage. Because the standard SO-8 transistor
package couldn’t handle it all, power supply designs
▶ Prevents localized current crowding had to become more complex, using larger packages
like DPAK and even D2PAK.
▶ Allows for a more uniform current spread
To replace DPAK or D2PAK, LFPAK56 was developed
▶ Acts as a heatsink to the die to provide greater power from the widespread SO-8
package footprint. Despite having less than half the
The internal structure of an LFPAK MOSFET is footprint size (LFPAK’s 30 mm2, compared with DPAK’s
shown in Figure 1. Cu clips can withstand very 70 mm2), the initial generation of 25-V MOSFETs in
high temperatures, as the melting temperature of LFPAK56 (which owes its name to its size of 5 × 6 mm)
copper is about 900°C. The silicon die, due to the exhibited R DS(on) and maximum drain current equivalent
doping process, can operate up to 250°C without to identical devices in DPAK. Because of its enormous
compromising the switching performance. The plastic cross-sectional area, the Cu-clip attachment, which
mold compound, whose composition is carefully substitutes conventional bond-wire connections
selected to withstand high-temperature specification, between the die and leadframe, significantly improves
can potentially harden and becomes brittle at about electrical and thermal performance.
190°C and above. As a result, the internal components
of the MOSFET are either naturally capable of How LFPAK56, at less than half the size of DPAK,
Cu-Clip Package withstanding temperatures >175°C or specifically could achieve equal thermal performance baffled the
selected to do so.
industry at first. Although the physics of soldering the
clip directly to the source connection on the device
Technology Empowers limited to 175°C due to the reliability standards that eliminated the high-current–density regions that often
The maximum junction temperature of MOSFETs is
exist where bond wires are joined, others questioned
MOSFETs must adhere to. By industry standards,
the clip attachment’s reliability. Consequently, a Cu clip
WBG Devices Nexperia uses a temperature limit of 175°C for MOSFET shields the transistor by preventing the development of
qualification and life testing.
thermal “hotspots” at specific sites.

By Maurizio Di Paolo Emilio, editor-in-chief of Power Electronics News

Strengthened by the innovations introduced with wires. Over 400 devices spanning seven design
copper (Cu)-clip package (CCPAK) technology, Nexperia variants, or about 90% of Nexperia’s product line, are
brings its long-time experience producing high-quality LFPAK-based and contribute to a design’s overall
and robust SMD packaging to its gallium nitride FET efficiency.
portfolio. Based on proven technology, CCPAK provides
industry-leading performance in a IT ALL STARTED WITH LFPAK
wire-bond–free package optimized for thermal and In automotive and industrial applications, the need
electrical performance, simplifying the design of for high power has increased in modern electronics.
cascode configuration and eliminating the need for Kilowatt power output is a typical requirement for
complicated drivers and controls. applications like motor drives, inverters or on-board
chargers. This means the need to handle greater
Nexperia introduced LFPAK technology in 2002. power is being transferred to the components,
This was a remarkable and radical departure from especially MOSFETs, due to existing space constraints
the designs of the day because of the characteristic in modules.
continuous clip and gull-wing terminal pins. Very low
electrical and thermal resistance at the PCB level, LFPAK technology was designed to address the Figure 1: LFPAK internal structure (Source: Nexperia)
along with a new low level of R DS(on) , has been made challenging requirements coming from power
possible thanks to this technology. electronics applications. Compared with conventional
wire-bond devices, LFPAK offers several advantages, The computing industry requires exceptionally Testing for reliability and thermal performance
Surprisingly, it required some persuading to convince including compact size, higher power density and high current to power the newest generation of demonstrated that LFPAK could deliver on its
the industry that a device just half as big as its reduced parasitic inductance. Based on Cu-clip bond processors and microcontrollers, which is why promises. Moreover, LFPAK56 passed the demanding
predecessor (DPAK) could have the same thermal technology, these packages have played an essential Nexperia created LFPAK technology. The peak 2× AEC-Q101 automotive qualification, exceeding all
performance but better electrical performance and role in allowing silicon-based MOSFETs to achieve current started approaching 200 A and beyond as standards by a wide margin.
that the novel Cu clip was more reliable than bond very high-current capability. each new silicon technology node brought on-chip

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