Energy efficiency is very important. In fact, energy efficiency is one of the main assessment indicators for the design of many new automotive power electronic systems. The wasted electricity per watt can be converted to a drop of gasoline that should be left in the tank, or an extra gram of carbon dioxide emitted from the exhaust pipe. Today, both fuel consumption and carbon emissions are facing increasing taxes. How can automotive semiconductor suppliers help customers achieve higher energy efficiency? In the college graduation design, I chose 8mΩ 30V Dpak to drive an H-bridge – which was considered a “tip†device at the time, but today such a device is quite common. Much of this advancement can be attributed to the tremendous advances in semiconductor technology, but how is the packaging technology developing?
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It should be borne in mind that a semiconductor package combines a series of components in a circuit, current must flow through the package without restriction, and heat must be directed into the cooling system. Therefore, the robustness of the system depends on the weakest link in the entire chain. If the on-resistance RDS(ON) of a typical MOSFET is about 8 milliohms, then a package resistance of about 1 milliohm above this value is acceptable. However, when the resistance of the chip is lower than the package resistance, it is obviously necessary to improve the package. Surface mount device packages have solved this problem well: the on-resistance of a typical D2Pak package is only about 0.5 milliohms higher than the chip, while the package technology such as DirectFET contributes only 150 microohms to the on-resistance. But what is the on-resistance of the via package? This is a problem that has received less attention so far and is also an area of ​​insufficient innovation.
One of the packaging technologies commonly used in automotive applications is the TO-262, a long lead variant of the D2Pak. High-power devices often choose this packaging technology. In these applications, in order to achieve good cooling, the power components are placed on a separate substrate from which heat can be more easily extracted. Ironically, although widely used in high-power systems, the performance of TO-262 is not satisfactory in terms of package resistance. The main limitation is not the wire bonding but the wire itself. In general, the total resistance of only the source and drain leads is as high as 1 microohm!
Now, let's consider the 40V TO-262 MOSFET with a 2 milliohm on-resistance as described on the data sheet. The on-resistance value on the data sheet is the sum of the resistance of the MOSFET chip and the package, but does not include the resistance of the lead itself. Therefore, in the worst case of using full-length leads in the system, the total resistance of the leads from head to tail can actually reach 3 milliohms. In practice, this produces several results, one of which is that higher lead resistance causes the leads to self-heat, which in turn "heats" the other components of the MOSFET, resulting in increased cooling costs. Higher package resistance also results in higher conduction losses and lower energy efficiency.
To this end, the industry has made a simple improvement to the standard TO-262, resulting in the WideLead TO-262 (see Figure 2).
Comparing Fig. 1 and Fig. 2, it is found that the lead width of the WideLead TO-262 is significantly increased. As a result, the resistance of the leads is reduced by approximately 50% compared to the standard TO-262 package. The industry also took the opportunity to improve the internal technology of this package. As a result, the on-resistance of WideLead TO-262 is 20% lower than that of TO-262 even without considering the reduction of lead resistance. The lower lead resistance, combined with the improved internal technology of the package, increases the maximum current rating of the device in the WideLead TO-262 package to 240A, which is much higher than the 195A in the leading TO-262 package available on the market. The WideLead TO-262 has the same shape as the "body" and the traditional TO-262, so the conversion from TO-262 to the WideLead package does not require a major change in the mechanical design.
Figure 1: Traditional TO-262 package
Figure 2: The new WideLead TO-262 package.
The system-level advantages of the WideLead TO-262 package can be seen in Figure 3. This figure compares the temperature of the standard TO-262 and WideLead TO-262 package leads as a function of DC current (the chips inside the two packages are the same). At 60A, the temperature of the WideLead package is 39% lower than the standard TO-262 package. This can lead to multiple system-level benefits, including reduced heat and improved device reliability. Since the amount of heat generated is relatively small, the amount of heat that needs to be dissipated is correspondingly reduced, and as a result, the size of the cooling device may be reduced, and it may be possible to use a lower-grade printed circuit board (PCB material) - that is, the rated operating temperature is further Low material.
Figure 3: Lead temperature differences between standard TO-262 packages and the new WideLead TO-262 package at different currents.
At a given operating temperature, the device current can be increased by up to 30%—that is, the same chip can be used to achieve higher currents. Due to the weakening of the packaging performance on the internal chip, either way, the cost of the device can be improved by colleagues who reduce costs.
Energy has been a rich resource for decades, but its supply is now increasingly strained. What is not lacking now is carbon dioxide. In fact, the number is too large, and even governments have introduced corresponding regulations to impose heavy taxes on carbon dioxide emissions in order to achieve emission reduction. This challenge has driven the development of automotive engineering, which must also address this challenge in both chip and package. At present, through-hole packaging is catching up with this wave of development, but with the advent of innovations such as WideLead, the performance difference between package and chip is shrinking.
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