Power MOSFETs for improved robustness and superior thermal performance
Introducing the new members of the TOLx package family
by Francesca Pastorelli, Product Marketing Manager, Infineon Technologies and, Peter Green, Product and System Applications Engineering Manager, Infineon Technologies
High current rating, ruggedness, and extended lifetime are essential for e-scooters, light electric vehicles, forklifts, power tools, and battery management systems. Choosing the right power MOSFET technology is the key to achieving the highest efficiency and power-density in products that meet these requirements. To enable designers to build reliable, high-power applications in a small package, Infineon’s OptiMOS™ power MOSFET family has recently extended its high-performance package offerings. The TOLx family (Figure 1) now includes two new packages that complement Infineon’s innovative TO-Leadless (TOLL) package. These are:
Achieving better thermal cycling on board robustness with TOLG
The coefficient of thermal expansion (CTE) is a material property that indicates how the material is expanding, depending on the heating applied. Copper MOSFET leads have a different thermal expansion coefficient than board materials such as FR4 and Al-IMS. Repetitive mechanical stress causes fatiguing of the solder joint during thermal cycling, leading to cracking and eventual failure of the connection between the lead and the pad (Figure 2). Unlike QFN and TOLL packages, the gullwing leads of TOLG are designed to flex and thereby alleviate the mechanical stress from the solder joint. Temperature cycling on board (TCoB) is a second-level reliability test in which the solder joint between the package and the PCB is tested. Thanks to the flexibility of the gullwing leads, TOLG shows excellent solder joint reliability and achieves 2x higher TCoB compared to the standard requirements (IPC-9701A).
Figure 2 Warpage in FR4 and IMS board correlated to CTE mismatch
Superior thermal performance with TOLT
The TOLT package is constructed with its lead-frame flipped (Figure 3). This arrangement provides an exposed metal on the top side, which enables top-side cooling. In addition, TOLT includes multiple gullwing leads on each side for high current carrying drain and source connections, which offer reduced package resistance.
With bottom-side cooling (Figure 3), the heat must pass through the PCB to reach the heatsink. Apart from the additional thermal resistance introduced by the PCB material, many thermal vias must be added, increasing PCB cost. In addition to that, components cannot be mounted under the MOSFETs.
The TOLT package overcomes all of these limitations, with nearly all of the heat passing through the exposed metal top side and the insulating material (TIM) directly to the heatsink. As a result, the overall thermal resistance is significantly reduced. At the same time, mounting components on the bottom side underneath the MOSFETs is now possible, enabling significant board area reduction. The unique features of the TOLT package offer the possibility to reduce PCB and heatsink size or increase current handling capability in applications such as motor drive inverters.
Figure 3 Bottom-side cooling (TOLL, TOLG) vs. top-side cooling (TOLT)
The TOLG package is available in a broad portfolio, including best-in-class and price-performance optimized products in five voltage classes (60/80/100/200/250 V) and the TOLT package in two voltage classes (80/100 V) (Figure 4).
Figure 4 TOLG and TOLT product portfolio
Infineon – your trusted partner in power and sensor systems.
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