Preventing Quality Problems
Reduction of Battery Voltage and Deterioration of Capacity
(1) Reduction of battery voltage and deterioration of capacity through contact with antistatic conductive materials
Incidents have been reported where terminal-mounted batteries for memory backup or coin-type lithium batteries have come into contact with antistatic conductive materials, thus forming external discharge circuits and leading to voltage drops or capacity deterioration.
In manufacturing plants using ICs, LSI and other semiconductor components, thoroughgoing antistatic measures are taken. Various protective materials are used to prevent static: most of them have special compounds of carbon, aluminum foil and other metals and are therefore conductive. These protective materials are used, for example, in the form of packaging bags, trays, mats, sheets, fi lms, corrugated boards and resin cases. A protective material may have a resistance ranging from 10
3 to 10
6 Ω /cm, for instance. This means that if the (+) and (-) terminals of a battery come into contact with this material, a current ranging from several milliamperes to several microamperes will fl ow and the battery will discharge, causing voltage drop and capacity deterioration.
A terminal-mounted battery was inserted into a conductive mat. The battery charge was exhausted in several days.Conductive mat Exclusive grounding lineA battery was placed directly on a industrial rubber sheet spread over a worktable. The (+) and (-) terminals were in contact with the sheet and the battery charge was exhausted. Conductiverubber sheet +- Conductive rubber sheet Avoiding Hazards and Preventing Quality Problems When batteries are to be used near protective materials, take every possible care to ensure that the (+) and (-) terminals of the batteries or PC boards, etc. on which batteries are mounted do not touch these protective materials directly.
SpacerBattery-mounted PC boards were inadvertently brought into contact with spacers and a conductive rubber sheet. The battery charge was exhausted.Rubber sheet Conductive resin caseA battery-mounted PC board was inadvertently brought into contact with a conductive resin case.The battery charge was exhausted. Chapter 6 Chapter 6- 87