Direct FET MOSFETs Double Current Density In High

Direct. FET MOSFETs Double Current Density In High Current DC-DC Converters With Double Sided Cooling © International Rectifier 2002 www. irf. com 1

Increasing Current Requirement In DC-DC Converters § DC-DC converters for next generation Intel and AMD microprocessors § Trending towards >100 A or 25 A per phase § Core processor voltages are stabilizing around 1 V © International Rectifier 2002 www. irf. com 2

The Challenge: How To Remove The Heat § Current requirements PCB size § Less and less area to dissipate the heat § 30% of RDS(on) of best SO-8 is due to package 5. 00 Power Dissipated in a VRM Module 4. 50 Power dissipated/in. sq (W/in 2) 4. 00 3. 50 3. 00 2. 50 2. 00 1. 50 1. 00 0. 50 0. 00 1996 © International Rectifier 2002 1997 1998 1999 2000 2001 2002 www. irf. com 3

Thermal Limitations Of Single-Sided Cooled SO-8 § Top-side cooling is inefficient § PCB is the main path of heat dissipation § New SO-8 derivatives improve Rth(j-b), to make it easier to dissipate heat into PCB and lower junction temperature – Fairchild Bottomless. SO 8™, Siliconix Power. Pak™, leadless SO-8 § PCB thermal conduction is at its limit now SO-8 Rth(j-c): 18°C/W Rth(j-a)top >55°C/W at 400 LFM Actual measurement Rth(j-pcb): 20°C/Wmax + Rth(pcb-a)>40 °C/W Rth(j-a)bottom >60°C/W Þ Standard and derivative SO-8 can only be effectively cooled on 1 side © International Rectifier 2002 www. irf. com 4

What Is Direct. FET Power Packaging? passivated die attach copper ‘drain’ material clip gate connection source copper track connection on board § Large area source and gate contacts are directly soldered onto the PCB board § Copper drain clip facilitates the drain connection and also improves transfer of heat from the top of the device. § Proprietary passivation system for electrical isolation, soldering mask and die protection © International Rectifier 2002 www. irf. com 5

Best Package Resistance In Any SMT Package § Reducing Die-Free Package Resistance by over 90% over SO-8 1. 7 mm Cu-strap SO-8 0. 1 m. Ohm Direct. FET 0. 7 mm © International Rectifier 2002 www. irf. com 6

Enabling Efficient Dual Sided Cooling § Increases the power dissipated out of the package by removing the heat very efficiently through the top of the package. SO-8 Rth(j-a)top >55°C/W at 400 LFM Direct. FET Rth(j-a)top<12°C/W Rth(c-a)gap pad <9°C/W + Rth(j-c): 3°C/W Rth(j-c): 18°C/W Rth(j-b): 20°C/Wmax + Rth(pcb-a)>40 °C/W Rth(j-a)bottom >60°C/W Rth(j-pcb): 1°C/W + Rth(pcb-a) >40 °C/W Rth(j-a)bottom >41°C/W Gap pad cannot justify cost with SO-8 Gap filling thermal pad to metallic chassis © International Rectifier 2002 www. irf. com 7

Top side cooling benefits § Increases the power dissipated out of the top of the package by 50% compared to standard SO-8 – And by 100% when compared to Bottomless SO-8 105°C PCB Temperature and 70 °C Ambient Minimum footprint. Gap filler. © International Rectifier 2002 www. irf. com 8

Specifications And Availability § 20 VN for servers and very high end desk-tops. § 30 VN devices for notebooks and designers who require a higher safety margin. § Sample available immediately, volume production 3 rd quarter 2002 § Extensive reliability testing completed. © International Rectifier 2002 www. irf. com 9

50 o. C Cooler In Still Air! § Measured results at max standard SO-8 current in still air © International Rectifier 2002 www. irf. com 10

35 A/Phase Using 2 Direct. FET MOSFETs! § 3 applications for Direct. FET MOSFETs: – 35 A/phase with a single pair of Direct. FET MOSFETs using top side cooling – 33% more current in still air – 50°C cooler and up to 3% higher efficiency at same current level Direct. FET 30 VN Vs 30 VN SO-8 using same silicon technology 12 VIN, 1. 3 VOUT, buck Converter @300 k. Hz, 105°C max PCB temperature 75 o. C Tj 3% 17 A more! 125 o. C Tj 33% more © International Rectifier 2002 105 o. C Tj www. irf. com 11

100 A at 85% Efficiency © International Rectifier 2002 www. irf. com 12

Double Current Density for 30 A/phase! § 50% smaller solution footprint § 100% improvement in Current Density! § In real circuit, can cut part count by up to 60% compared to best SO-8 (2 Direct. FETs replace 5 SO-8) § And lower system cost © International Rectifier 2002 www. irf. com 13

Lower Total System Cost § Cost of heat removal using SO-8 – Additional 1 oz. Cu for the whole PCB area • @ >$0. 25/sq. in (>$3. 50/system) – Additional fan ($2 to $3/system) – Using heat pipe and additional fan ($4 to $10/system) § Direct. FET MOSFETs – Can use chassis for heat removal with no additional fan – Can use minimum PCB footprint and fewer devices § Direct. FET MOSFETs cut the cost of heat removal by at least 50% – Reduce cost of heat removal – Cut the size of PCB © International Rectifier 2002 www. irf. com 14

4 -phase Converter Using Direct. FET MOSFETs Heatsink added to remove heat from top of Direct. FETTM away from board § Single Direct. FET pair/phase for current up to > 25 A/phase in a 3. 8 in x 1. 25 in footprint for a total of 100 A. Existing best 60 A. § Low profile allows the Direct. FET to be mounted on the back of the board with heatsink and still stay within VRM outline specifications. © International Rectifier 2002 www. irf. com 15

Ease of Layout Additional drain contact and/or further mechanical stability gate rail Source rail solder mask defined pads drain rail § Easier board layout § Easier to parallel © International Rectifier 2002 www. irf. com 16

Direct. FET can replace SO-8 with minimal rework Drain = Pin 5 - 8 Source = Pin 1 - 3 Direct. FET outline Vs SO-8 Outline © International Rectifier 2002 Gate = Pin 4 A board can be reworked with a few simple changes www. irf. com 17

Alternatives to dissipate heat through the top of the package Forced air cooling + finned sink © International Rectifier 2002 www. irf. com Gap filling thermal pad to metallic chassis 18

Bend Strength Measurement § Direct. FET far outlasted the ceramic capacitors on the board in this measurement § Reliability testing demonstrate reliability similar to SO-8 © International Rectifier 2002 www. irf. com 19

Direct. FET Package in Summary Improve thermal characteristics § Enables dual sided cooling in SMT § Remove the heat from the device faster and away from PCB Reduce stray inductance § To enable faster switching frequencies and better response to current transients Environmentally friendly § Lead and bromide free © International Rectifier 2002 Direct. FET power packaging Reduce package resistance § Increase efficiency § With MOSFET in sub-10 m. Ohm RDS(ON), the package becomes an important contributor to the resistance. Compatible with high volume manufacturing processes § Easy to design, easy to parallel Low profile § 0. 7 mm high Double current density Cut PCB by 50% Cut part count by up to 60% Lowerwww. irf. com total system cost 20