Electricity: electrical systems and devices – Discharging or preventing accumulation of electric charge
Reexamination Certificate
2000-01-19
2001-09-25
Berhane, Adolf Deneke (Department: 2838)
Electricity: electrical systems and devices
Discharging or preventing accumulation of electric charge
Reexamination Certificate
active
06295193
ABSTRACT:
The invention relates to an arrangement comprising a first insulating material, and an electronic circuit board having a surface on which at least one conducting island is located, said surface being arranged proximate to the first insulating material, said first insulating material having a number of holes corresponding to at least some of the conducting islands and through which the conducting islands can be reached, each of said holes having, at an end thereof facing said surface, an area which is larger than the area of the corresponding conducting island.
Further, the invention relates to an electronic circuit board therefor.
Such circuit boards and arrangements are used for many purposes. One example is safety electronics circuits for Li-Ion (Lithium-Ion) battery packs, Li-Ion batteries are sensitive to a number of factors, including overcharging. Therefore, all battery pack including one or more Li cells require a safety electronics circuit that can protect the Li cell against critical levels of e.g. charging voltage or charging current.
In the worst case the battery can explode if overcharged and therefore the safety electronics is vital for the safety of battery pack users. Consequently, it is often requested by battery cell vendors to test the safety electronics after the complete pack has been mounted in a production line. This is typically done by attaching probes to test points through holes in the battery pack plastics housing. However, these holes expose sensitive parts of the safety electronics that could be damaged by electrostatic discharges (ESD) after the test has been carried out. Normally, the holes will be sealed after the battery pack has been tested in the production line, but this is often done by a label which can be easily damaged if it comes into contact with a sharp object such as a pencil or a pen. Even with better sealing methods cracks will always be present and thus the risk of damage through ESD remains.
If the safety electronics protecting the Li cell is destroyed by an ESD spark after the test, the result is a battery pack without working safety electronics, and, as mentioned above, in the worst case this may cause an explosion or eruption of the battery cell due to e.g. overcharging of the Li cell.
Although this problem has been described in relation to Li-Ion battery packs, the same problem exists for many other applications in which an electronic circuit can be destroyed by ESD through holes in a surrounding housing.
Therefore, it is an object of the invention to provide an arrangement of the above-mentioned type which can withstand electrostatic discharges without the circuitry of the board being damaged.
In accordance with the invention, this object is accomplished in that a conducting area adapted to carry off an electrostatic discharge (ESD) is located on said surface proximate to the conducting islands and within the area of the holes, and that elements made of a second insulating material are provided in said holes.
When an insulating material is provided in the hole, an ESD spark will strike in between this material and the surrounding material and hit the circuit board underneath. By placing a conducting area within the area of the hole so that it more or less surrounds the conducting island, the spark will hit this area instead of hitting the conducting island which forms part of the sensible circuit, and thus the circuit will be protected.
As stated in claim
2
, the arrangement may comprise safety electronics for a battery and the first insulating material may be part of a battery housing. As mentioned above this is one of the typical applications for such a circuit board.
Further, as stated in claim
3
, the conducting islands may expediently be test points that are adapted to be used during a test procedure for the circuit board.
As stated in claim
4
, the second insulating material may expediently be an elastic material. This implies that the material will be flexible enough to fill out the entire hole and thus minimize the crack between the two materials in which an electrostatic discharge could strike in. Further, the elements can be secured in the hole without the use of any adhesive, which also means that they can easily be removed again, thus allowing further or repeated testing of the circuit at a later stage.
According to an embodiment of the invention, which is stated in claim
5
, the conducting area adapted to carry off an electrostatic discharge has the form of a circular ring located around each conducting island. In this way the island is completely surrounded by the conducting area and thus well protected.
According to an alternative embodiment of the invention, which is stated in claim
6
, the conducting area adapted to carry off an electrostatic discharge has the form of a number of discrete areas arranged around each conducting island. This is a more flexible solution which still maintains an acceptable level of protection.
Further, it should be noted that the conducting area adapted to carry off an electrostatic discharge may also have other forms.
According to a preferred embodiment of the invention, which is stated in claim
7
, the conducting area adapted to carry off an electrostatic discharge is connected to a ground plane. A ground plane will often be best suited to carry off the electrostatic discharge, but depending on the supply voltages the conducting area may also be connected to a positive or negative supply rail.
As stated in claim
8
, the conducting area adapted to carry off an electrostatic discharge may have a thickness which is greater than the thickness of said conducting islands. This means partly that the top of the area is closer to the insulating materials, thus improving the probability that an ESD spark will hit this area instead of the island, and partly that the area is able to carry off a higher current in case of a strike.
As stated in claim
9
, the probability that an ESD spark will hit the conducting area adapted to carry off an electrostatic discharge instead of the island may be further improved when this area is provided with raised or pointed means. This is due to the fact that electrostatic discharges are attracted to such raised means.
As mentioned, the invention further relates to an electronic circuit board having a surface on which at least one conducting island is located, said surface adapted to be arranged proximate to a first insulating material having a number of holes which correspond to at least some of the conducting islands and through which the conducting islands may be reached, each of said holes having, at an end thereof facing said surface, an area which is larger than the area of the corresponding conducting island, wherein a conducting area adapted to carry off an electrostatic discharge (ESD) is located on said surface proximate to the conducting islands and within the area of the holes.
By placing a conducting area within the area of the hole so that it more or less surrounds the conducting island, the spark will hit this area instead of hitting the conducting island which forms part of the sensible circuit, and thus the circuit will be protected.
As stated in claim
11
, the electronic circuit board may comprise safety electronics for a battery and the first insulating material may be part of a battery housing. As mentioned above this is one of the typical applications for such a circuit board.
Further, as stated in claim
12
, the conducting islands may expediently be test points that are adapted to be used during a test procedure for the circuit board.
According to an embodiment of the invention, which is stated in claim
13
, the conducting area adapted to carry off an electrostatic discharge has the form of a circular ring located around each conducting island. In this way the island is completely surrounded by the conducting area and thus well protected.
According to an alternative embodiment of the invention, which is stated in claim
14
, the conducting area adapted to carry off an electrostatic discharge has the form of a number of discr
Bengtsson Jonas
Hellström Stefan
Kellerman Michael
Mercke Johan Ulf
Berhane Adolf Deneke
Nixon & Vanderhye P.C.
Telefonaktiebologate LM Ericsson (publ)
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