The thick silver process is helping face the challenge of soaring demands in lithium batteries for electric vehicles
and feature high energy density, zero memory effect, low self-discharging, and fast charging and discharging speed.
They have been widely adopted by mobile devices including notebook computers, cellphones, and wearables.
Recently they have also been adopted by electric vehicles and military, space and aviation applications.
Protection Circuit Design To Prevent Lithium Batteries From Explosion
Despite rising popularity, the lithium battery comes with risks of over-heating and explosion caused by over charging and discharging. A protection circuit unit is embedded in every lithium battery to protect it from over-charging, over-discharging, over-loading, and over-heating.
A typical lithium battery's protection circuit is composed of two MOSFETs and one control IC as shown in Figure 1. The control IC is aimed at controlling the gate of two MOSFETs and monitoring battery voltage and current of the entire circuit. This opens and closes the charging and discharging circuits with the two MOSFET switches.
Figure 1: Protection circuit for lithium battery
The Thick Silver (Copper) Process for Lithium Batteries Effectively Cuts Resistance of Rds (on)
In practice, the design and manufacturing of the protection circuit in IC combines two MOSFETs to share the drain as shown in Figure 2, while offering thicker metals, e.g. silver or copper, for greater current and lower resistance.
Figure 2: Illustration of drain shared by two MOSFETs
Tests suggest that temperature may drop to 78°C from 83.4°C when the thickness of Ag is raised from 12um to 15um, and Rds(on) may drop 20% when the thickness of Ag is raised from 10um to 40um on 70um thick Si.
Regarding the wafer backend process, ProPowertek can provide mass production processes for 12um/15um backside metallization and 20um engineering processes with equipment at capacity of 40um thickness as well as thick metal process and cutting. We are one of the few suppliers in Taiwan able to offer this solution.