JP4617524B2 - Battery protection device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a battery protection device for protecting a secondary battery such as a lithium ion battery.
[0002]
[Prior art]
A rechargeable battery pack used in a cellular phone device or the like has a lithium ion battery built in an insulating package. This battery pack incorporates a charge protection device for preventing overdischarge and overcharge of the battery. A plurality of circuit components constituting this protection device, specifically, a field effect transistor (FET) 21 as a charging switch means, an FET 22 as a discharging switch means, and a protection IC 23 are printed as shown in FIG. It is mounted on the circuit board 24 having the wiring pattern as a separate package product. As the FET, products manufactured by NEC Corporation, Mitsubishi Electric Corporation, or Hitachi, Ltd. can be used. As the protection IC, a product manufactured by Mitsumi Electric Co., Ltd., the applicant of the present application, can be used.
[0003]
At present, portable devices and the like are being miniaturized, and the battery pack is also required to be miniaturized.
[0004]
[Problems to be solved by the invention]
By the way, in the conventional charge protection device, since the charging FET, the discharging FET, and the protection IC are arranged as separate packages on the circuit board, it is difficult to reduce the weight, reduce the size, and simplify the wiring. Met. It is also difficult to reduce mounting defects.
[0005]
The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a battery protection device that can be reduced in weight, reduced in size, simplified in wiring, and reduced in mounting defects.
[0006]
[Means for Solving the Problems]
In order to solve the above problems, the battery protection device according to the present invention is a battery protection device in one package for preventing overcharge and overdischarge in a secondary battery, and is connected to the secondary battery. a charging FET having a drain on the rear surface, it is connected to the secondary battery, control and discharge FET having a drain on the rear surface, and said discharging FET and the charging FET based on the voltage across the secondary battery And a protection means for preventing overcharge and overdischarge of the secondary battery, and a lead frame including a first die pad and a second die pad, and the protection means is provided on the first die pad of the lead frame. is mounted, said the second die pad of a lead frame, said a charging FET and the discharge FET is mounted, F for the discharge and the back surface of the drain of the charging FET Wherein the the back surface of the drain of T is connected.
[0007]
Here, the die pad for mounting the charging switch means and the discharging switch means and the die pad for mounting the protection means have different potentials.
[0008]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings. This embodiment is a battery protection device for preventing overcharge and overdischarge in a lithium ion battery. As shown in FIG. 1, an FET (charge FET) 1 as a charge control switch, and a discharge control are provided. An FET (discharge FET) 2 as a switch for use and a protection IC 3 are sealed with a resin 4 to form one package.
[0009]
The manufacturing procedure of this battery protection device will be described. A transport hole 7 is formed in the frame 6 of the lead frame 5. On the lead frame 5, a die pad 8 and a die pad 9 having different potentials for a charge amount FET and a discharge FET and for a protection IC are prepared. Inner leads 10 of the lead frame 5 are provided around the two die pads 8 and 9. A tie bar portion 12 is provided between the inner lead 10 and the outer lead 11 following the inner lead 10.
[0010]
The protective IC 3 mounted on one die pad 9 and the charging FET 1 and discharging FET 2 mounted on the other die pad 8 are bonded and connected to each electrode and the inner lead 10 by a wire 13 made of gold Au or the like. Yes. For example, the charging FET 1 has the gate G and the source S bonded to the inner lead 10. The drain D of the FET is the entire back surface of the chip, and the FETs (1 and 2) are connected to each other by silver Ag paste in the die pad portion. Here, the reason why a large number of wires 13 are bonded from the source electrode S of the discharge FET 2 to a part of the lead frame 10 is to prevent the single wire 13 from fusing when a large current of about 5 A flows, for example. It is. One wire melts at about 1A.
[0011]
After the bonding connection with the wire (Au) 13, the protection IC 3, the charge amount FET 1 and the discharge FET 2 are collectively sealed with the resin 4. Thereafter, the frame frame 6 and the tie bar portion 12 are cut out, and the outer leads 11 are made independent to form the battery protection device 14 in one package as shown in FIG. The battery protection device 14 in one package is disposed on a substrate 15 as shown in FIG. On the substrate 15, capacitors, resistors, and the like (not shown) are also arranged. Other components such as capacitors and resistors are not packaged in one package because they often have different constants depending on the user.
[0012]
As described above, the battery protection device 14 can charge the FET 1, the discharge FET 2, and the protection IC 3 in one package and be disposed on the circuit board 15. Therefore, it is possible to reduce the weight, reduce the size, and simplify the wiring. is there.
[0013]
In addition, since the parts such as the FET are integrated into a module, the number of soldering points can be reduced, and as a result, the reliability can be improved and the mounting defects can be reduced.
[0014]
【The invention's effect】
According to the present invention, it is possible to reduce the weight, size, wiring, and mounting defects of the battery protection device.
[Brief description of the drawings]
FIG. 1 is a diagram for explaining a manufacturing procedure of a battery protection device according to an embodiment of the present invention.
FIG. 2 is an external view of the battery protection device.
FIG. 3 is a diagram showing the battery protection device arranged on a circuit board.
FIG. 4 is a diagram showing an arrangement of each part in a conventional battery protection device.
[Explanation of symbols]
1 Charging FET
2 Discharge FET
3 Protection IC
4 Sealing resin 5 Lead frame

Claims (2)

A battery protection device in one package for preventing overcharge and overdischarge in a secondary battery,
A charging FET connected to the secondary battery and having a drain on the back surface ;
A discharging FET connected to the secondary battery and having a drain on the back surface ;
And protection means for preventing overcharge and overdischarge of the secondary battery by controlling the said discharging FET and the charging FET based on the voltage across the secondary battery,
A lead frame including a first die pad and a second die pad;
The protection means is mounted on the first die pad of the lead frame,
The charging FET and the discharging FET are mounted on the second die pad of the lead frame,
Battery protection apparatus characterized by a drain of the rear surface of the back surface of the drain and the discharging FET of the charging FET is connected. 2. The battery protection device according to claim 1, wherein the drain on the back surface of the charging FET and the drain on the back surface of the discharge FET are connected by a silver paste of the second die pad portion.

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