IXAN0022 Capitalizing on the Advantages of ISOPLUS Products Introduction IXYS Corporation offers unique power packages with internal isolation, and performance and reliability advantages. The IXYS isolated packages include ISOPLUS220TM, ISOPLUS247TM, ISOPLUS i4-PAC TM, ISOPLUS264 TM as well as the new ISOPLUS-DIL TM modules. The ISOPLUS advantages relative to the standard power packages include: • Better electrical isolation • Larger and multiple die • Multiple circuit configurations • Lower thermal resistance • Higher reliability • UL recognition has been granted to the ISOPLUS220, ISOLPUS247 and ISOPLUS i4-PAC • Higher component density • Easy clip assembly This article will describe and quantify the ISOPLUS advantages and focus on mounting techniques and materials that optimize the ISOPLUS performance and capitalize on their inherent advantages. The focus will be on the ISOPLUS220 and ISOPLUS247 examples, but quantitative tools will be provided for the designer to apply the approach to all ISOPLUS packages. Electrical Isolation Electrical isolation between the power die and heatsink is provided by Direct-Copper-Bonded (DCB) ceramic substrates, which are integrated into the ISOPLUS packages as shown in Figure 1. The ceramic substrate provides superior isolation to most interface materials with isolation greater than 6,000 Vrms, which is higher than the isolation voltage to the leads based on creepage paths. The rated isolation for all products to date is 2,500V. The electrical isolation from leads to backside tab and leads to top of the plastic package where the clips apply force is 100% tested at 3,000 V for 10 seconds. 1 The ceramic in the DCB is alumina for standard products, but aluminum nitride can be substituted where extremely low thermal resistance is required and economically justified. The integrated and molded DCB eliminates exposed electrically active cases, pads and tabs, which may need to be isolated from adjacent traces, components or mounting screws and hardware. The DCB ceramic is immune to dielectric puncture and partial discharge, which can be troublesome with many external interface materials. This immunity to damage and AC wear-out further enhances the reliability of the ISOPLUS packages. Mold Fig. 1. Cross sectional view for the discrete ISOPLUS packages. Larger and Multiple Dice The ISOPLUS packages use the full package body for die attach area by extending the DCB substrate into the areas used for tabs and holes in the standard power packages. This allows larger and higher power die with a direct heat path to the bottom of the package. For example, the die in the ISOPLUS220 IXFC30N60P requires a larger TO-247 standard package to accommodate it and likewise, the die in the ISOPLUS247 must go into a TO-264 standard package. However, it should be noted that ‘hole-less’ non-isolated versions of the TO-220 and TO-247 packages, the PLUS220TM and PLUS247TM, are also offered for very large die product. The use of smaller packages can increase board density and reduce board size and cost. © 2006 IXYS All rights reserved IXYS Corporation - www.ixys.com 3540 Bassett Street; Santa Clara, CA 95054; Ter: (408) 982-0700; Fax: (408) 496-0670 IXAN0022 The ISOPLUS packages provide more internal space for multiple die and the DCB provides a natural technique for isolated metallization for multiple die attach pads and interconnecting traces. The multichip discrete power packages like the ISOPLUS220 and ISOPLUS247 led to the larger 4-lead and 5-lead ISOPLUS264 and ISOPLUS i4-PAC as well as the ISOPLUS DIL modules, shown in the illustration with 5 power leads and 12 signal leads. Additional circuit configurations are now available in ISOPLUS package options. Examples include AC switches, buck and boost configurations with either MOSFETs or IGBTs, common anode or series connected diodes, halfbridge and new 3-phase, Trench MOSFET bridges in the ISOPLUS-DIL package. Clip Assembly The ISOPLUS packages eliminate the mounting hole to allow a large DCB substrate, which improves isolation, reduces thermal resistance and allows a larger internal die area. The elimination of the mounting hole has become another advantage of the ISOPLUS package, because it allows the use of 30 25 Force - Pounds KU4-499 20 15 KU4-498 10 5 0 0 20 40 60 80 100 120 140 160 180 Displacement - mils Fig. 2: Clamping force for the Kunze clips KU4-498 and KU4-499. component clips without special tab or hole isolation, and excessive isolation spacing. Component clips can simplify assembly by eliminating mounting screws with their associated hardware like screws, threaded holes, washers and insulators. Furthermore, clips do not require controlled torque and clamping force as clips are predesigned for a given clamping force for a given package thickness.. Interface materials like silicone grease and thermal pads are often use with lower force clamps, and such materials and clamps can be used with the ISOPLUS packages. New high performance phase change materials often require much higher clamping forces to achieve the lowest possible thermal resistance. Kunze Folien offers a number of high force clamps for power packages. • The Power Clip KU4-498 is an excellent clip for the ISOPLUS220 or ISOPLUS247 providing clamping force of 23 lbs, or 90 lbs per square inch for these two packages. • The Power Clip KU4-499 is an excellent clip for the ISOPLUS247, ISOPLUS264 and ISOPLUS i4-PAC providing for providing a mounting force of 29 lbs.for these packages. • The KU4-495 is a dual clip for mounting either two ISOPLUS220 or ISOPLUS packages sideby-side. The clamping force for the KU4-498 and KU4499 power clips is shown in Figure 2 and is a function of clip displacement.. These clips are available in Multi Transistor Clip configurations, which can further simplify assembly, and multi transistor clips are easier to use with the ISOPLUS packages where all isolation is internal. Table 2 provides a Cross Reference between Kunze Power Clips and Power Semiconductor packages, both ISOPLUS and standard packages. Thermal Resistance The primary advantage of the ISOPLUS packages is that their exceptionally low thermal resistance © 2006 IXYS All rights reserved IXYS Corporation - www.ixys.com 3540 Bassett Street; Santa Clara, CA 95054; Tel: (408) 982-0700; Fax: (408) 496-0670 2 IXAN0022 Table 1: Thermal Resistance Junction-to-Case Comparison of ISOPLUS Package Types to Standard Package Types Package Type ISOPLUS220 PLUS220* ISOPLUS247 PLUS247* Part Number Die Size (mm) IXFC30N60P 8.9X7.4 IXFV30N60P 8.9X7.4 IFR64N60P 14.2x10.6 IXFX64N60P 14.2x10.6 Clip Type Interface-Conductive KU4-498 KU-ALF 5 KU4-498 (NA) KU4-499 KU-ALF 5 KU4-499 (NA) Interface-Isolated R(th)JC (max) (NA) 0.75 K/W KU-KG 2.5 0.25 K/W (NA) 0.35 K/W KU-KG 2.5 0.12 K/W R(th)CS(max) 0.07 K/W 1.74 K/W 0.05 K/W 0.93 K/W R(th)JS (max) 0.82 K/W 1.99 K/W 0.40 K/W 1.05 K/W * ‘Hole-less’ versions of the ISOPLUS220 and ISOPLUS247 packages respectively. material, like the KU-ALF 5. Its thermal resistance is plotted versus applied pressure in Figure 3. Kunze Folien also provides state-of-the-art isolated, phase change materials, like KU-KG 2.5 for standard power packages. However, their thermal resistance per area can be more than ten times greater as evidenced in Figure 4. The product examples shown in Table 1 are The ISOPLUS packages are already isolated allowing direct mounting to heatsinks. However, the representative of the improvements that can be use of silicone grease, thermal pads, or one of the achieved with in the ISOPLUS220 and ISOPLUS247 high performance conductive phase-change materials packages with larger die products and with the be used to reduce contact resistance. Kunze Folien recommended interface materials shown above. offers state-of-the-art conductive phase change (R(th)js) from device junction to case, for power devices requiring isolation from the heatsink. The ISOPLUS packages can provide 10 to 50 percent lower R(th)js than standard packages with the same die and external isolation. The greatest thermal advantages occur with larger die products, which are the focus of the ISOPLUS products. 0.14 Thermal Resistance - K/W Thermal Resistance - K/W 0.025 0.020 0.015 0.010 0.005 0.12 0.11 0.10 0.09 0.08 0.000 0 10 20 30 40 50 60 70 80 Clamp Pressure - PSI Fig. 3: KU-ALF 5 Thermal Resistance per Square Inch vs. Clamp Pressure. 3 0.13 90 0 10 20 30 40 50 60 70 80 90 Clamp Pressure - PSI Fig. 4: KU-KG 2.5 Thermal Resistance per Square Inch vs. Clamp Pressure. © 2006 IXYS All rights reserved IXYS Corporation - www.ixys.com 3540 Bassett Street; Santa Clara, CA 95054; Ter: (408) 982-0700; Fax: (408) 496-0670 IXAN0022 The above comparisons are based on ISOPLUS products with DCB alumina substrates. If the DCB alumina is replaced by DCB aluminum nitride, the thermal resistance can be reduced significantly because the thermal conductivity of aluminum nitride is 7 times higher than alumina. Reliability Power Semiconductor products are always limited by the Coefficient of Thermal Expansion (CTE) mismatch between the die and copper case. The CTE mismatch limits both die size, load cycle capability and temperature cycling reliability. In the ISOPLUS package, the die is attached to the DCB ceramic substrate, and CTE mismatch between the die and substrate is much less than between die and copper. This increases the ISOPLUS package reliability in temperature cycling, and allows the package to withstand larger temperature excursions and number of cycles without damage. The DCB substrate also allows the use of larger power die than can be used directly on copper. Higher Component Density A secondary advantage of the ISOPLUS packages is that they provide higher board densities. The ISOPLUS packages accommodates larger die in a smaller package outline, and the isolated packages can be placed closer together. In some cases, groups of multiple isolated packages can clamped by single multiple fingered clips. Semicustom, cost effective configurations can be developd for qualified opportunites. Table 2: Package Cross Reference for Kunze Power Clips Package Type Kunze Clip Model* TO-3P KU3-392, 3-396/24, 3-397, 3-399, 4-440/3.1, 4-440/4.0, 4-441, 4-443, 4-450, 4-453, 4-490 TO-3P Double KU4-445 TO-220 KU3-381, 3-386, 3-387, 3-388, 3-389, 3-399, 4-440/3.1, 4-440/4.0, 4-441, 4-443, 4-450, 4-453, 4-490 TO-220 Double KU4-430, 4-445, 4-495 Gull Wing Clip TO-220 Multiple Transistors KU4-498/X (X = number of transistors) ISOPLUS220 KU4-498/X (X = number of transistors) TO-247 KU3-392, 3-396, 3-397 TO-247 Double KU4-495 Gull Wing Clip TO-247 Multiple Transistors KU4-499/X (X = number of transistors) ISOPLUS247 KU4-499/X (X = number of transistors) TO-247AD KU3-393 ISOPLUS DIL KU4-501 ISOPLUS i4-PAC KU3-393, 3-395 TO-264 Multiple Transistor KU4-499/X (X = number of transistors) ISOPLUS264 KU4-499/X (X = number of transistors) * Go to <www.heatmanagement.com> for clip and interface material data sheets. © 2006 IXYS All rights reserved IXYS Corporation - www.ixys.com 3540 Bassett Street; Santa Clara, CA 95054; Tel: (408) 982-0700; Fax: (408) 496-0670 4