The growing need for smaller, lower-resistance fuses
Self Control Protectors (SCPs) are surface mount fuses that interrupt circuits in the event of an overcharge or overcurrent in lithium-ion batteries. Since our fuses launch in 1994 by Dexerials’ antecedent company, lithium-ion batteries have been used in a growing variety of electronic devices. In recent years, as the demand for fast charging smartphones has increased, fuses are now required to be compatible with such devices as well.
The biggest problem with fast charging batteries is that the internal circuitry tends to heat up due to the large amount of current flowing over a short period of time in comparison with conventional products. Therefore, fast charging smartphones must have a battery protection fuse with low-resistance so that it does not generate heat easily. At the same time, there is a growing need for miniaturized fuses that do not take up too much space in the narrow space inside of smartphones.
Newly developed low-resistance fuse elements
Dexerials has always been quick to commercialize products that meet the demands of the times. Among them are products developed in 2016 such as the 22A (small) SFJ-series (model number: SFJ-xx22) and the 12A (small and thin) SFR-series (model number: SFR-xx12). These have significantly increased the current that can flow per volume, from approximately 1.3 A/mm3 to 3.3 A/mm3. From 2013 to 2016, although the size of the SFJ series has been the same, the resistance has been reduced by about one third, from 3.0 mΩ to 0.9 mΩ.
The birth of a new series
In 2021, Dexerials introduced a series of new miniaturized and low-resistance fuse. The features and technologies of this new series are explained below.
As shown in the figure above, both the black cap and white ceramic substrate are approximately 50% thinner in the new series. The 0.2 mm thickness of the ceramic substrate is currently the thinnest amongst Dexerials’ surface mount fuses. The height reduction shortens the distance between the fuse element and the mounting electrode on the back of the ceramic substrate (the opposite side of the element mounting surface). These improvements allow the fuse carrying a current of 4.6 A/mm3 per volume.
Moving the heater to the board mounting surface
A further innovation is the location of the heater that melts the fuse element. In conventional products, the heater is placed inside the cap in order to efficiently transmit heat to the fuse element. In pursuit of a slimmer product, the board with half the thickness of conventional products was developed. This allows sufficient heat to be transmitted to the mounting surface of the board to melt the element. Additionally, by moving the heater to the mounting surface of the board, the cap height was also reduced by half, further reducing the overall thickness. These various innovations have made it possible for the new series to have low resistance while also being compact.
Miniaturization and lower resistance open up possibilities for new devices
The Dexerials fuse (SCP) miniaturization and low-resistance technologies enable both, smaller-sized products with the same current and same-sized products with higher currents, to be produced. In addition, reducing the heat generated by devices allows for new capabilities such as fast charging. Dexerials’ offers a variety of products that are compatible with a wide range of devices that run on lithium-ion batteries, such as drones and power tools, as well as electronic devices such as smartphones and tablets.