Power Packaging Spins New Automotive Capabilities

Nov 1, 2004 12:00 PM
By David Morrison, Editor, Power Electronics Technology

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A power packaging technology from International Rectifier (IR) improves current handling capabilities and lowers cost versus existing packaging techniques. In doing so, IR's die-on-leadframe (DOL) packaging facilitates development of automotive subsystems such as electro-hydraulic power steering (EHPS) and electric power steering (EPS). To date, limitations in electrical efficiency, the lack of current on the vehicle bus and torque ripple (which adversely affects “steering feel”) have delayed the proliferation of EPS into higher curb-weight vehicles. DOL packaging helps overcome these hurdles to the deployment of EPS.

For medium- to high-power applications, DOL packaging offers better electrical conductivity and increased thermal performance versus alternative packaging methods using insulated metal substrate (IMS), direct-bonded copper (DBC) to a ceramic substrate, thick film substrates or PCB-based modules, which primarily use discrete power devices. A DOL power module includes silicon die directly soldered to a copper leadframe within an injection-molded shell. The internal components are connected directly to outside terminals, eliminating intermediate insulation and conductive layers (see the figure).

When applied in power inverter designs, DOL delivers the lowest package inductance and resistance by minimizing the number of material layers to improve thermal performance while reducing the number of interconnections. Lower thermal resistance, in turn, allows the use of smaller die. Similarly, the lower electrical resistance of the package allows for higher current capabilities with smaller die sizes and lower torque ripple.

Consider a 3-phase inverter power module based on the IRFC2804 MOSFET, a size 4.0 die, and fabricated using either DBC substrate or DOL. When the inverter is constructed with DBC, the average loop resistance from B+ to ground is 5.8 mΩ. However, when the same power module is built using the DOL method, that same parameter is just 3.8 mΩ. Thermal performance also improves with maximum R_θjs (junction-to-substrate) reduced from 1.40°C/W in the DBC module to 1.14°C/W in the DOL module.

The first devices to use DOL technology are IR's power modules for EPS and EHPS applications. The IR11867-E02 is a 120-A module, while the IR11867-E01 is a 160-A module. The current ratings are continuous capability at a maximum junction temperature of 175°C. These modules include built-in temperature-sense feedback and bus-current sensing (see the table).

The DOL modules measure 60 mm × 36 mm × 8 mm. For availability and pricing information, contact International Rectifier at 248-347-1830, extension 110 or visit www.irf.com.

Table. Specifications for IR's DOL automotive power modules.

IR Module Number	IR Die Part Number	VDS (V)*	MOSFETs RDS(on) @25°C (mΩ)	IRMS Max** (A)	Rθjs (°C/W)	Module Loop Resistance (mΩ)***	Package Resistance (mΩ)	Package Inductance (nH)
11867-E01	IRFC2804	40	~0.85	160	~0.40	~3.8	~1.95	~25
11867-E02	IRFC1404Z	40	~1.65	120	~0.60	~5.6	~2.15	~30
*Parameter depends on the MOSFET chosen and can be changed to meet application requirements.
**Values correspond to base-plate temperature of 100°C and Rθjs = 0.8°C/W with IRFC2804 or Rθjs = 1.1°C/W with IRFC2804.
***Values include a 0.3-mΩ current sense resistor, which can be changed to meet application requirements. Loop resistance is the electrical resistance between battery plus and a battery minus terminal when phase terminals are shorted.