ROHM Launches New Low-Resistance Resistor Products

<The main uses of low resistance products in the automotive market>

? Various motor drive circuits? The output part of the DC/DC converter? Battery charging and discharging monitoring circuits, power detection, etc. have been widely used in the automotive market, industrial equipment market, computer market, etc., especially in the automotive market in recent years, driven by the development of electric vehicles, hybrid vehicles, in the entire The market's application of high-performance and electronic technology is developing rapidly.

Accompanied by the automotive market, "small low-value products that support higher power," "ultra-low resistance products that can suppress circuit power consumption," and "ensure excellent performance under harsh temperature conditions." The demand for high-precision, low-resistance products with a temperature coefficient of resistance has increased. In order to meet the diverse needs of the automotive market for low-resistance products, we have built a rich lineup of low-resistance products.

<Trends of Current-Sense Low-Resistance Products>

Current-sensing low-resistance products are mounted in series with the load, and the current detection is achieved by measuring the potential difference between the two pins with an IC. When you want to increase the current detection accuracy of an IC, you can achieve this by setting the resistance values ​​of the high and low resistance products. However, the disadvantage of this method is that the product heat (loss) increases when current flows. It can be seen that there is a contradiction between measurement accuracy and heat generation. The selection of low-resistance products requires balancing the balance between detection accuracy and heat generation. However, in recent years, with the improvement of the performance of the LSI, it is possible to perform a highly accurate current detection with a smaller potential difference than before. That is, by using a low-resistance low-resistance product, it is already possible to detect a larger current with less power consumption than before, and the demand for low-resistance products is increasing. Against this backdrop, ROHM successfully developed and launched in March 2014 products that can support high currents of up to 150A (PSR series).

<Overview of Low-Resistance Technology>

Patch low-resistance products are roughly classified into two categories based on their materials and structures. One is a product based on a universal thick film chip resistor technology called a low-resistance thick film, and the other is a metal low-resistance product using a metal material. These products are differentiated according to the required performance. In general, they are generally several tens of mΩ to a thick film low resistance value resistor product, and several mΩ to a metal low resistance value resistance product. The characteristics of a metal low resistance resistor are guaranteed. Higher rated power.

The shape of the patch is divided into two types depending on the electrode structure connected to the mounting board, that is, the general shape of the electrode is formed on the short side of the patch and the long side electrode type is formed on the long side of the patch. In general, the long-edge electrode product has better bonding reliability and temperature cycling characteristics after PCB board mounting. Moreover, compared with the short-edge electrode type product, it also has the characteristics of better heat dissipation and higher rated power of the mounting board.

Nickel plating and tin plating are typically used for electrode plating. However, copper plating is sometimes performed in a low-resistance product in view of low resistance, improved temperature characteristics, resistance measurement stability, and the like.

<Low-resistance products using thick film technology>

? The main process for forming the resistor body of a thick film chip resistor is screen printing pattern molding. By using a screen printing method, a resistor body, an electrode, etc. are formed on an alumina PCB board. The resistance of the low-resistance product uses a material with a lower resistance value. Compared with a material with a common resistance value, the temperature coefficient and the temperature cycle characteristics are easily affected by the composition of the electrode material, the thickness of the resistor and the electrode, and therefore The design needs to take into account its best conditions.

ROHM is the world's first pioneer of thick-film chip resistors for the development of thick-film chip resistors. Utilizing the technical advantages accumulated over the years, ROHM is continuously improving the thick-film low-resistance series with a strong lineup.

? As a product that satisfies the high bonding reliability and rated power requirements of the automotive market, ROHM is expanding its long-edge electrode type low resistance LTR series. By arranging the electrodes on the long side of the patch, high bonding reliability and temperature cycling characteristics are achieved. In addition, the use of long-edge electrode type high heat dissipation can support higher rated power than ordinary thick-film low-resistance products (example: 1W for 3216mm size products).

? As a basic product, it covers a wider range of resistance values ​​(11mΩ~) than conventional general-purpose thick film chip resistors MCR/low resistance series (47mΩ~) and MCR/low resistance series, and by expanding the size of the electrodes / Changed the resistor material to add a UCR series with a high power rating and excellent temperature characteristics. This UCR series not only has advantages in terms of rated power/temperature characteristics, but also adopts a back surface mounting structure in consideration of reducing the resistance value during mounting. (Fig. 5) In addition, the UCR Series lineup has added the ultra-compact 0603mm size (UCR006 series) products that are increasingly active in the automotive market and guarantee a temperature range of -55°C to +155°C.

? These thick-film low-value resistors (LTR series/UCR series), due to their higher power ratings, make it possible to replace the previous product (MCR/low-resistance series) with a smaller package, which helps the PCB board to be small Products.

<Low-resistance products using metal resistor materials>

? The structure of a low-resistance product using a metal resistor is completely different from that of a thick-film low-resistance product. The resistor body uses a resistor metal material having a thickness of several tens of micrometers to several millimeters. The resistor body material is formed by various processing techniques such as etching and machining to achieve a target resistance value and characteristics. Metal low-resistance products have features that ensure high power ratings and high-precision temperature coefficients of resistance compared to thick-film low-resistance products of the same size. In addition, in order to use a thicker resistor body metal in a range of extremely low resistance values ​​of about 0.2 mΩ to 10 mΩ, a resistor body itself is generally used as a method of forming a patch.

? In the range of rated power over 4W, ROHM is expanding the PSR series covering a resistance range of 0.2 mΩ to 3.0 mΩ. The PSR series uses ROHM's unique welding technology to bond resistor metal and copper electrodes to achieve a structure with high heat dissipation and heat capacity. (Fig. 6) In addition, a large copper electrode ensures heat dissipation and achieves a high power rating of up to 5W. Its characteristic is that by selecting the best resistor body metal by resistance value, a high-precision temperature coefficient of resistance is achieved.

? ROHM is expanding the PMR series with a resistance range of 1 mΩ to 10 mΩ below the rated power of 2W. The PMR series has a different structure from the PSR series, but it is the same as the PSR series in that it is made of a resistor metal. In addition, the PMR series adopts ROHM's unique design, which does not require trimming to adjust the resistance value. Its feature is that its structure can reduce the problem of multiple resistor body heating during use.

To expand the size of the PMR series, ROHM has developed the world's smallest class of products and will continue to strive for further miniaturization in the future. In addition, the product lineup of the PML series, which changes the PMR series to a long-edge electrode structure and improves bonding reliability and heat dissipation, is gradually expanding.

<About the future development>

In the area of ​​1 W or more, if a metal material is used to support a low resistance range of several tens of mΩ or more, the thickness of the metal resistor will reach about 100 μm. Therefore, it has been difficult to realize patch molding in a structure in which the resistor itself is the main body. This problem can be solved by fixing the resistor material on the base material of the body, but ROHM in the past has not expanded the lineup of related products. In this field, many users use lead resistors and thick-film low-resistance resistors to form circuits. However, in recent years, as the detection accuracy has increased/the size of PCBs has been reduced/the number of lead components has been reduced, various demands have increased. The demand for low resistance metal resistors is increasing. In view of these demands, ROHM positioned the field as "an important lineup of metal low resistance resistors in the future" and is developing New Products with the concept of "small size and high heat dissipation."

As stated at the beginning of this article, it is expected that the demand for low-resistance products in the future automobile market will become higher and higher. ROHM will use keywords such as high power rating, high heat dissipation, and miniaturization to improve the lower resistance products. The lineup is the goal and we continue to work hard to promote development.