Over-current protection device and battery protection circuit assembly containing the same

An over-current protection device is disposed on a circuit board and configured to protect a battery. The over-current protection device includes a resistive device, at least one insulation layer and a weld electrode layer. The resistive device exhibits positive temperature coefficient behavior. The insulation layer has a thickness of at least 0.03 mm. The weld electrode layer is configured to weld a strip interconnect member to electrically coupled to the battery, and has a thickness of at least 0.03 mm. The insulation layer and the resistive device are disposed between the weld electrode layer and the circuit board. The circuit board, the resistive device and the weld electrode layer are electrically coupled in series. The association of the resistive device and the weld electrode layer has a thermal mass capable of withstanding welding the strip interconnect member without significant damage to the over-current protection device.

CROSS-REFERENCE TO RELATED APPLICATIONS

Not applicable.

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NAMES OF THE PARTIES TO A JOINT RESEARCH AGREEMENT

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BACKGROUND OF THE INVENTION

1. Field of the Invention

The present application relates to an over-current protection device and a battery protection circuit assembly containing the same.

Because the resistance of conductive composite materials having a positive temperature coefficient (PTC) characteristic is very sensitive to temperature variation, it can be used as the material for current sensing devices, and has been widely applied to over-current protection devices or circuit devices. The resistance of the PTC conductive composite material remains extremely low at normal temperature, so that the circuit or cell can operate normally. However, when an over-current or an over-temperature event occurs in the circuit or cell, the resistance instantaneously increases to a high resistance state (e.g. at least 102Ω), so as to suppress over-current and protect the cell or the circuit device.

For battery protection, a known method is to surface-mount an over-current protection device on a circuit board, so as to form a protection circuit module (PCM), which is coupled to positive and negative electrodes of a battery through, for example, strap interconnects to form a protection circuit.

To improve manufacturing efficiency, the over-current protection device is in an attempt to be in connection with the strap interconnects through spot-welding or reflow. However, for spot-welding, the temperature would be somewhere near or above 1500° C., and thus electrical properties of the over-current protection device would be damaged due to high temperature. To prevent damage to the over-current protection device, the impact of high temperature needs to be overcome effectively.

BRIEF SUMMARY OF THE INVENTION

The present application provides an over-current protection device and a battery protection circuit assembly containing the same, with a view to preventing damage to the over-current protection device when it is welded to outer electrodes.

A first aspect of the present application is to disclose an over-current protection device, which is disposed on a circuit board and configured to protect a battery. In an embodiment, the over-current protection device is of a laminated structure, and includes a resistive device, at least one insulation layer and a weld electrode layer. The resistive device exhibits positive temperature coefficient behavior. The insulation layer has a thickness of at least 0.03 mm. The weld electrode layer is configured to weld a strip interconnect member to electrically couple to the battery, and has a thickness of at least 0.03 mm. The insulation layer and the resistive device are disposed between the weld electrode layer and the circuit board. The circuit board, the resistive device and the weld electrode layer are electrically coupled in series. The association of the insulation layer and the weld electrode layer has a thermal mass capable of withstanding welding the strip interconnect member without significant damage to the over-current protection device.

In an embodiment, the resistive device includes a first electrode foil, a second electrode foil and a PTC material layer disposed therebetween. The PTC material layer, the first electrode foil and the second electrode foil extend along a first direction to form a laminated structure. A first insulation layer has a thickness of at least 0.03 mm and is disposed on a surface of the first electrode foil. The weld electrode layer has a thickness of at least 0.03 mm and is disposed on a surface of the first insulation layer. In an embodiment, the over-current protection device further includes a conductive connecting member extends along a second direction substantially perpendicular to the first direction, and electrically connects the weld electrode layer and the first electrode foil. The conductive connecting member is insulated from the second electrode foil. The second electrode foil is configured to electrically coupled to a circuit board, and the first electrode foil is configured to electrically couple to an electrode of a battery by welding the strip interconnect member to the weld electrode layer.

A second aspect of the present application is to disclose a battery protection circuit assembly. In an embodiment, the battery protection circuit assembly includes a circuit board with a plurality of electronic devices disposed thereon. The electronic devices include the aforesaid over-current protection device to avoid over-current in the circuit. The battery protection circuit assembly further includes a battery having a first outer electrode and a second outer electrode. The first outer electrode may include the strip interconnect member that is configured to weld to the weld electrode layer. The strip interconnect member may be of straight shape, crooked shape or L-shape as desired.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1shows a battery protection circuit assembly in accordance with an embodiment of the present application. The battery protection circuit assembly10includes a battery11and a circuit board12. Various electronic devices15are placed on the circuit board12, in which an over-current protection device13is provided to form a protection circuit module (PCM). The over-current protection device13exhibits positive temperature coefficient behavior and has a surface welded to an end of a strip-form outer electrode16. Another end of the outer electrode16is coupled to the battery11. The circuit board12is provided with a bond pad14, which is welded to an end of an outer electrode17, and another end of the outer electrode17is coupled to the battery11. The outer electrodes16and17are coupled to the positive electrode and negative electrode, or negative electrode and positive electrode of the battery11, respectively, so as to form a protection circuit.

FIG. 2AandFIG. 2Bshow the battery protection circuit assemblies of the present application. For simplification,FIG. 2AandFIG. 2Bonly show the essential components of the circuit board12serving as a PCM, and the battery is not shown. InFIG. 2A, the circuit board12is provided with the over-current protection device13, electronic devices15and the bond pad14. In consideration of the need of fabrication, the over-current protection device13may weld a strip interconnect member20, so as to connect to a battery electrode. Specifically, the strip interconnect member20could be equivalent to the outer electrode16. In other words, the outer electrode16extending from the battery11is welded to a surface of the over-current protection device13. Alternatively, the battery11may be provided with an extending connecting member (not shown), and the strip interconnect member20has an end welded to the surface of the over-current protection device13and another end welded to the extending connecting member of the battery11. That is, two electrode members form the outer electrode16shown inFIG. 1. In summary, the outer electrode16includes the strip interconnect member20and may be changed in various forms if needed.

The outer electrode16ofFIG. 1extends from a side of the circuit board12. The strip interconnect member20inFIG. 2Ais straight and extends along the longitudinal direction of the circuit board12. In an embodiment, the strip interconnect member20may be of crooked shape or L-shape as shown inFIG. 2B. For L-shape strip interconnect member20, it includes a horizontal portion22and an uplift portion24. The horizontal portion22is welded to the over-current protection device13, and the uplift portion24and the horizontal portion22have an angle α between 60° and 120° or preferably between 75° and 105°. In another embodiment, the strip interconnect member20may extend from a side of the circuit board12, i.e., the direction projecting out of the figure. The extension direction of the strip interconnect member20is dependent on the requirements of the connection to the battery.

FIG. 3Ashows an over-current protection device13, which is an rectangular surface mountable device and can be disposed on the circuit board12as shown inFIG. 1.FIG. 3Bis an upside-down view of the device shown inFIG. 3A. The over-current protection device13includes a resistive device31, a first insulation layer32, a second insulation layer33, a weld electrode layer34, conductive connecting members35and39and bond pads41and42. The resistive device31includes a first electrode foil36, a second electrode foil37and a PTC material layer38laminated between the first electrode foil36and the second electrode foil37. The PTC material layer38, the first electrode foil36and the second electrode foil37extend along a first direction to form a lamination structure. The first insulation layer32is formed on a surface of the first electrode foil36, and has a thickness of at least 0.03 mm, particularly between 0.05 and 1.0 mm, and preferably between 0.1 and 0.3 mm. The weld electrode layer34is formed on the first insulation layer32, and has a thickness of at least 0.03 mm, particularly between 0.05 and 1.0 mm, and preferably between 0.1 and 0.3 mm. In practice, the thickness of the first insulation layer32or the weld electrode layer34may be 0.06 mm, 0.08 mm, 0.15 mm, 0.2 mm, 0.25 mm. The conductive connecting members35and39are formed on sides of the device13, and extend along a second direction substantially perpendicular to the first direction. In an embodiment, the conductive connecting members35and39may be semi-circular holes plated conductive films or the like. The conductive connecting member35electrically connects the weld electrode layer34and the first electrode foil36, and the conductive connecting member35is insulated from the second electrode foil37. The second electrode foil37is electrically coupled to the circuit board12through the conductive connecting member39and the bond pad42. The weld electrode layer34has a circular notch40near the conductive connecting member39, so that the weld electrode layer34is insulated from the conductive connecting member39. The first electrode foil36can be electrically coupled to an electrode of a battery11by welding the strip interconnect member20to the weld electrode layer34. The bond pad42may be surface mounted by reflow on the circuit board12, and the bond pad41is used for being secured on the circuit board12only and is not connected to the circuit in the circuit board12. Accordingly, the bond pad42and the weld electrode layer34serve as a lower electrode and an upper electrode to be coupled to the circuit board12and the strip interconnect member20, respectively.

Moreover, the first insulation layer32ofFIG. 3Amay be omitted, and the weld electrode layer34contacts the first electrode foil36directly. Alternatively, the second insulation layer33and bond pads41and42may be omitted, and the second electrode foil37is surface-mounted on the circuit board12directly. In summary, at least one of the insulation layers32and33and the resistive device31are laminated between the weld electrode layer34and the circuit board12, and the circuit board12, resistive device31and the weld electrode layer34are connected in series.

Referring toFIG. 4, two ends of the weld electrode layer34may be covered by solder masks43, and the bond pads41and42ofFIGS. 3A and 3Bmay be replaced with the weld electrode layer34with solder masks43as an interface for surface-mounting on the circuit board12. In such case, the weld electrode layer34serving as a surface-mounting interface has to have a notch near the conductive connecting member35for insulation. Accordingly, the upper and lower surfaces of the device13are of symmetrical solder mask design as shown inFIG. 4. Therefore, the orientation of the device13needs not to be considered when the device13is combined with the circuit board12and the strip interconnect member20.

The association of the first insulation layer32and/or the second insulation layer33and the weld electrode layer34has to have a thermal mass capable of withstanding the force, temperature, voltage and energy when welding the strip interconnect member20without significant damage to the device13, or particularly to over-current protection31. Therefore, the thicknesses of the insulation layers32and33and the weld electrode layer34are at least 0.03 mm. Thicker thickness usually provides better resistance, but is not suitable for downsizing requirement. In an embodiment, the device13can withstand a welding voltage of 1V-5V, particularly 1.3V-4V, and preferably 1.6V-3V. The welding may include spot-welding, reflow, resistance welding, or laser welding. The insulation layers32and33may include polypropylene, glass fiber or heat dissipation material. The heat dissipation material includes polymer having thermosetting resin and fiber, and polymer having thermoplastic and thermosetting resin interpenetrating network. One example of the polymer having thermoplastic and thermosetting resin interpenetrating network is described in U.S. Pat. No. 8,003,216, and this disclosure is expressly incorporated herein by reference. In an embodiment, the weld electrode layer34includes copper foil, nickel foil, nickel-plated copper foil, tin-plated copper foil or nickel-plated stainless.

FIG. 5shows the over-current protection device13in accordance with another embodiment of the present application. The device13may be placed on the circuit board12as shown inFIG. 1and is a rectangular surface mountable device. The difference of the devices13inFIG. 5andFIGS. 3A and 3Bis that the conductive connecting member is formed at corners of the rectangular device. The over-current protection device13includes a resistive device51, a first insulation layer52, a second insulation layer53, a weld electrode layer54, conductive connecting members63,64,65and66and bond pads61and62. The resistive device51includes a first electrode foil56, a second electrode foil57and a PTC material layer58laminated between the first electrode foil56and the second electrode foil57. The PTC material layer58, the first electrode foil56and the second electrode foil57extend along a first direction to form a lamination structure. The first insulation layer52is formed on a surface of the first electrode foil56, and has a thickness of at least 0.03 mm, particularly between 0.05 and 1.0 mm, and preferably between 0.1 and 0.3 mm. The weld electrode layer54is formed on the first insulation layer52, and has a thickness of at least 0.03 mm, particularly between 0.05 and 1.0 mm, and preferably between 0.1 and 0.3 mm. The conductive connecting members65and66extend along a second direction substantially perpendicular to the first direction, so as to electrically connect the weld electrode layer54and the first electrode foil56, and the conductive connecting members65and66are insulated from the second electrode foil57. The second electrode foil57is electrically coupled to the circuit board12through the conductive connecting members63and64and the bond pad61. The weld electrode layer54has a circular notch40near the conductive connecting members63and64, so that the weld electrode layer54is insulated from the conductive connecting members63and64. The first electrode foil56can be electrically coupled to an electrode of a battery11by welding the strip interconnect member20to the weld electrode layer54. The bond pad62is provided with a notch50near the conductive connecting member66for insulation between them. Likewise, the bond pad61near the conductive connecting member65forms a notch for insulation. One of the bond pad61or62may be surface mounted to on the circuit board12, and the other one is used for being secured to the circuit board12only and is not connected to the circuit in the circuit board12. In this embodiment, the device is symmetrical; therefore the orientation of the device13needs not to be considered when welding. Accordingly, the bond pad61or62and the weld electrode layer54serve as a lower electrode and an upper electrode to be coupled to the circuit board12and the strip interconnect member20, respectively.

Likewise, the first insulation layer52may be omitted, and the weld electrode layer54is in contact with the electrode foil56. Moreover, the second insulation layer53and bond pads61and62may be omitted, and the electrode foil57is surface-mounted on the circuit board12by, for example, reflow. Moreover, two ends of the weld electrode layer54may be covered with solder masks as mentioned above to provide equivalent function.

The surface mountable over-current protection device13may be of other types as described in U.S. Pat. Nos. 6,377,467 and 7,701,322. The disclosures are expressly incorporated herein by reference.

One presently preferred example of a spot-welding apparatus is a model MSW-412 micro spot welder power supply with a dual tip weld head model VB-S+ZH-32 and pressure monitor model SMC G36-10-01 available from SEIWA Manufacturing Co., Ltd. A weld profile using the spot welding apparatus is a square waveform approximately as follows: 1V for 1 ms, 0V for 1.3 ms, and 1.9V for 1.9 ms. The pressure of the dual tip weld head is 0.3 MPa. In this embodiment, the SMD devices are of 2920 and 1812 types, or 2.3 mm×6 mm. The weld electrode layer is tin-plated copper foil, and the insulation layer uses polypropylene. The resistances before and after welding are shown in Table 1.

As shown in Table 1, the resistances before and after spot-welding do not change obviously, and damage to the devices is not observed. Having thus described preferred embodiments of the present application, it will be understood that thermal mass of the association of the insulation layer and the weld electrode layer is sufficient to withstand welding the strip interconnect member without significant damage to the devices.