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Five Engineers Talk About New Medium-Power Device Products

Part 5
The DFN2020WF Package, Developed for External MOSFETs for Automotive Primary Power Supply ICs

My name is Yaginuma, and I'm in charge of development of new MOSFET products for automotive use. We have recently developed a compact DFN2020WF package (2020 size) that is optimized for external MOSFETs used with power supply ICs for ADAS (Advanced Driver Assistance Systems). And, we will release new products that employ this novel package with N-channel MOSFET chips employing ROHM's fourth-generation fine process technology.

In the automotive industry in recent years, technical fields relating to automated driving, of which ADAS is representative, have been undergoing dazzling progress. Within the field of ADAS as well, great expectations are being placed on sensing units such as millimeter-wave radar and Lidar, serving as the "eyes" of next-generation automobiles, and further engineering progress is anticipated. Greater sophistication of sensing functions tends to lead to increased circuit scales, and for this reason there has been a marked trend toward greater current supply capabilities required of primary power supply ICs.

In general, the current supply capability of power supply ICs incorporating power transistors is at most several amperes or so; when currents greater than this are needed, power supply ICs with external power transistors must be used to configure power supplies.

It was with this background that optimal MOSFETs for such applications were proposed, and so MOSFETs that were compact yet had large current capacities of 10 A or higher were developed. The package was designed with the following features, emphasizing use automotive applications, especially for external MOSFETs in primary power supply ICs for ADAS.

The first feature was a WF (Wettable Flank) structure, achieved by plating treatment of terminal side faces.

A WF structure refers to a structure in which solder fillets are formed on the terminal side surfaces at the time of PCB mounting (see Fig. 1). By forming solder fillets on side surfaces, the soldered state can easily be visually inspected.

Automotive equipment is held to require solder mounting pass/fail tests performed by AOI (automated optical inspection). By using WF structure components, it is possible to reliably execute AOI of the soldered state.

In these new products, through the adoption of ROHM proprietary manufacturing methods, a plated terminal side surface height of 100 μm or higher can be secured. The higher the plated terminal side surfaces, the higher are the fillets at solder mounting, thus improving visibility of the soldered state. Hence AOI inspections can be performed more reliably.

A second feature is the provision of a terminal layout pattern (DFN2020WF-L7) unique to ROHM, in addition to a general terminal layout pattern (DFN2020WF-L8).

In general terminal layouts, the drain and source are positioned adjacently on a side surface of the package, but in ROHM's proprietary terminal layout, the source terminal is positioned on the opposite side from the drain.

By using a structure in which the drain terminal and the source terminal are not adjacent, the risk of drain-source shorting due to solder bridges, foreign matter, etc. can be eliminated.

When a MOSFET drain-source short mode affects an entire later-stage circuit block, as in the case of an external MOSFET of a primary power supply IC, this can be said to be a pattern that can physically reduce risks.

Using a newly developed package having these features, we will first release a new N-channel 40 V product (ID = 12 A, Ron_typ = 21 mΩ, Qg_typ = 9.1 nC, Cisss_typ = 520 pF). Hereafter there are plans to expand the lineup to -30 V/-40 V products using P-channel fifth-generation microfine processes.

Finally, a few words about future plans for new products for the automotive market.

To begin with, there will be continuing expansion of the 40 V series based on N-channel fourth-generation fine process technology. Packages to be used, in addition to the DFN2020WF of this new device, will be the TO252, HPLF5060 (5060 size), and HSMT8AG (3333 size). The HPLF5060 products use clip connections rather than wire connections, and so can be provided in a compact 5.0x6.0 mm size with large current capacities of up to 120 A. The HSMT8AG products, by using ROHM's own terminal layout pattern, offer improved mounting reliability in thermal cycle tests. We also have plans to similarly extend the -30 V/-40 V series of P-channel fifth-generation fine process products using these packages.

Hereafter we will be continuing development of products for automotive applications featuring ease of use.

This fifth column is the last of this series. Thank you very much for your kind attention.

Power Supply Design Technical Materials Free Download

Power Supply Design Technical Materials Free Download

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