What Lies Behind The Sony Battery Recall? Cracked MLCCs Or The Absence Of An NTC Resistor?
Although the major cause of the recent Sony battery recall has not been revealed, passive component makers suspect that cracking of the multi-layer ceramic capacitors (MLCCs) or the inappropriate use of negative temperature coefficient (NTC) resistors caused the batteries to overheat.
Sources at US-based passive component makers commented that overheating may have originated in the electrical insulation of the batteries and that MLCC and other passive components should not be the major cause of the incident.
Some Taiwan-based makers, on the other hand, suspect that the adopted MLCCs had been cracked by printed circuit board (PCB) assembly, and that this may have caused an unstable flow of current, leading eventually to overheating.
Most of the MLCCs that had been found to be cracked had been made using X7R material, and X7R-based MLCCs are widely employed in applications that require a relatively high current.
In order to avoid cracking, some makers introduce a so-called "open mode design," which adjusts the design of the MLCC electrode. The US-based Kemet and Taiwan-based Walsin Technology have both introduced this kind of design.
Some industry players add organic materials to MLCCs, to avoid cracking. They usually term this type of supplementation of organic materials, "soft termination”or "polymer termination." Industry players that include the UK-based Syfer and Avx/Kyocera have introduced this type of solution.
The inappropriate adoption or lack of NTC resistors may also lead to overheating problems, said some Taiwan players. Since NTC resistors play a critical role in terminating the power supply, when overheating is detected, the inappropriate use or lack of NTC resistors may also have the effect of causing overheating.
Source: DigiTimes
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