Patent Application
20170092395
This disclosure relates to a positive temperature coefficient (PTC) circuit protection chip device and a method of making the same, more particularly to a method of making a PTC circuit protection chip device that involves the use of a spacer unit in a hot pressing process.
A positive temperature coefficient (PTC) element exhibits a PTC effect that renders the same to be useful as a circuit protecting device, such as a resettable fuse. The PTC element includes a PTC polymer material and first and second electrodes attached to two opposite surfaces of the PTC polymer material.
The PTC polymer material includes a polymer matrix that contains a crystalline region and a non-crystalline region, and a particulate conductive filler dispersed in the non-crystalline region of the polymer matrix and formed into a continuous conductive path for electrical conduction between the first and second electrodes. The PTC effect is a phenomena that when the temperature of the polymer matrix is raised to its melting point, crystals in the crystalline region start melting, which results in generation of a new non-crystalline region. As the new non-crystalline region is increased to an extent to merge into the original non-crystalline region, the conductive path of the particulate conductive filler will become discontinuous and the resistance of the PTC polymer material will be sharply increased, thereby resulting in an electrical disconnection between the first and second electrodes.
Therefore, an object of the present disclosure is to provide a PTC circuit protection chip device and a method of making the same that can overcome the aforesaid drawback associated with the prior art.
According to one aspect of this disclosure, there is provided a method of making a PTC circuit protection chip device. The method includes: preparing an assembly of a PTC polymer material, a spacer unit, and first and second electrode sheets of a metal-plated copper foil, the PTC polymer material and the spacer unit of the assembly being sandwiched between and cooperating with the first and second electrode sheets to form a stack; subjecting the stack to a hot pressing process, so that the first and second electrode sheets contact and are pressed against the PTC polymer material and the spacer unit and so that the PTC polymer material is bonded to and cooperates with the first and second electrode sheets to form a PTC laminate; and cutting the PTC laminate so as to form the PTC circuit, protection chip device.
According to another aspect of this disclosure, there is provided a PTC protection chip device that includes: a PTC body of a PTC polymer material having opposite first and second surfaces and a peripheral end that is disposed between and interconnects the first and second surfaces; a first single piece of a metal-plated copper foil that has a first electrode portion which is hot-pressedly bonded to the first surface of the PTC body, and a first terminal lead portion that extends from the first electrode portion beyond the peripheral end of the PTC body; and a second single piece of a metal-plated copper foil that has a second electrode portion which is hot-pressedly bonded to the second surface of the PTC body, and a second terminal lead portion that extends from the second electrode portion beyond the peripheral end of the PTC body. The first electrode portion has two opposite punched first side-end-faces that are flush with the peripheral end of the PTC body. The first terminal lead portion has two opposite punched first transverse-end-faces, each of which is transverse to and intersects a respective one of the first side-end-faces so as to define a first corner therebetween. The second electrode portion has two opposite punched second side-end-faces that are flush with the peripheral end of the PTC body. The second terminal lead portion has two opposite punched second transverse-end-faces, each of which is transverse to and intersects a respective one of the second side-end-faces so as to define a second corner therebetween.
In drawing which illustrate an embodiment of the disclosure,
In this embodiment, the first electrode portion 221 has opposite punched first side-end-faces 2210 that are flush with the peripheral end 213 of the PTC body 21. The first terminal lead portion 222 has two opposite punched first transverse-end-faces 2220, each of which is transverse to and intersects a respective one of the first side-end-faces 2210 so as to define a first corner 2215 therebetween. The second electrode portion 231 has two opposite punched second sine-end-faces 2310 that are flush with the peripheral end 213 of the PTC body 21. The second terminal lead portion 232 has two opposite punched second transverse-end-faces 2320, each of which is transverse to and intersects a respective one of the second side-end-faces 2310 so as to define a second corner 2315 therebetween. The first and second side-end-faces 2210, 2310 and the first and second transverse-end-faces 2220, 2320 have structural characteristics indicative of them being formed by punching techniques.
In this embodiment, the cutting of the PTC laminate 6 includes punching the PTC laminate 6 using a puncher (not shown). In certain embodiments, the cutting of the PTC laminate 6 may be conducted by punching the PTC laminate 6, followed by cutting unwanted portions of the punched PTC laminate 6 using a cutter (not shown).
In this embodiment, the metal-plated copper foil 72 is nickel-plated copper foil.
In certain embodiments, each of the first and second electrode sheets 33, 34 or each of the first and second single pieces 22, 23 may have a centerline average surface roughness (Ra) ranging from 0.9 μm to 2.0 μm, while in certain embodiments, each of the first and second electrode sheets 33, 34 or each of the first and second single pieces 22, 23 may have a centerline average surface roughness (Ra) ranging from 1.1 μm to 1.6 μm.
The polymer mixture may contains polyolefin (such as high density polyethylene, HDPE) and optionally a grafted polyolefin (such as grafted HDPE), such as carboxylic acid anhydride grafted polyolefin.
The conductive filler is dispersed in the PTC polymer material 71, and may include conductive non-carbonaceous particles and/or conductive carbon particles (such as carbon black).
Examples of the conductive non-carbonaceous particles may include titanium carbide, zirconium carbide, vanadium carbide, niobium carbide, tantalum carbide, chromium carbide, molybdenum carbide, tungsten carbide, titanium nitride, zirconium nitride, vanadium nitride, niobium nitride, tantalum nitride, chromium nitride, titanium disilicide, zirconium disilicide, niobium disilicide, tungsten disilicide, gold, silver, copper, aluminum, nickel, nickel-metallized glass beads, nickel-metallized graphite, Ti—Ta solid solution, W—Ti—Ta—Cr solid solution, W—Ta solid solution, W—Ti—Ta—Nb solid solution, W—Ti—Ta solid solution, W—Ti solid solution, Ta—Nb solid solution, and combinations thereof.
In certain embodiments, the polymer mixture may be in an amount ranging from 10 wt % to 30 wt % based on the weight of the PTC composition, and the conductive filler may be in an amount ranging from 70 wt % to 90 wt % based on the weight of the PTC composition.
The following examples and comparative examples are provided to illustrate the embodiment of the disclosure, and should not be construed as limiting the scope of the disclosure.
6.75 grams of HDPE (purchased from Formosa plastic Corp catalog no. HDPE9002, having a weight average molecular weight of 150,000 g/mole and a melt flow rate of 45 g/10 min according to AST D-1238 under a temperature of 230° C. and a load of 12.6 Kg), 6.75 grams of carboxylic acid anhydride grafted HDPE (purchased from DuPont, catalog no.: MB100D, having a weight average molecular weight of 80,000 g/mole and a melt flow rate of 75 g/10 min according to AST D-1238 under a temperature of 230° C. and a load of 12.6 Kg), and 136.5 grams of titanium carbide powder (having a particle size D50 ranging from 3.8 μm to 4.585 μm) were compounded in a Brabender mixer. The compounding temperature was 200° C., the stirring rate was 50 rpm, the applied pressure was 5 Kg, and the compounding time was 10 minutes. The compounded mixture was extruded to form pellets of a PTC polymer material. A spacer unit including two parallel stainless steel bars was placed on a first nickel-plated copper foil sheet having a thickness of 105 μm and a centerline average surface roughness (Ra) of 1.10 μm. The pellets were placed on the first nickel-plated copper foil sheet within an accommodating space between the stainless steel bars, such that the pellets slightly overfilled the accommodating space, so that the height of the body of the pellets is higher than that of the spacer unit. A second nickel-plated copper foil sheet (having a thickness of 105 μm and a centerline average surface roughness (Ra) of 1.10 μm) was placed on a top side of the body of the pellets and a top side of the spacer unit so as to cooperate with the body of the pellets, the spacer unit and the first nickel-plated copper foil sheet to form a stack. The stack was hot pressed so as to form a PTC laminate including a PTC polymer material (having a thickness substantially the same as the height of the spacer unit) sandwiched between the first and second nickel-plated copper foil sheets. The hot pressing temperature was 200° C., the hot pressing time was 4 minutes, and the hot pressing pressure was 80 kg/cm2. The spacer unit was removed from the PTC laminate. The PTC laminate was irradiated with Co-60 gamma ray (a total dose of 5 Mrad) for cross-linking of the PTC polymer material, and was subsequently punched using a puncher so as to form a PTC circuit protection chip device. The resistance (R) of the PTC circuit protection chip device was measured to be 0.00133 ohm.
The procedures and conditions in preparing the PTC circuit protection chip devices of Examples 2 to 4 were similar to those of Example 1, except for the centerline average surface roughness (Ra) of the first and second nickel-plated copper foil sheets. The centerline average surface roughness (Ra) of the first nickel-plated copper foil sheets (same for the second nickel-plated copper foil sheets) of Examples 2 to 4 are respectively 1.59 μm, 0.96 μm, and 1.9 μm.
The resistances of the PTC circuit protection chip devices of Examples 2 to 4 were measured to be 0.00132 ohm, 0.00155 ohm, and 0.00149 ohm, respectively.
6.75 grams of HDPE (purchased from Formosa plastic Corp., catalog no.: HDPE9002, having a weight average molecular weight of 150,000 g/mole and a melt flow rate of 45 g/10 min according to AST D-1238 under a temperature of 230° C. and a load of 12.6 Kg), 6.75 grams of carboxylic acid anhydride grafted HDPE (purchased from DuPont, catalog no.: MB100D, having a weight average molecular weight of 80,000 g/mole and a melt flow rate of 75 g/10 min according to AST D-1238 under a temperature of 230° C. and a load of 12.6 Kg), and 136.5 grams of titanium carbide powder (having a particle size D50 ranging from 3.8 μm to 4.585 μm) were compounded in Brabender mixer. The compounding temperature was 200° C., the stirring rate was 50 rpm, the applied pressure was 5 Kg, and the compounding time was 10 minutes. The compounded mixture was extruded to form pellets of a PTC polymer material. The pellets of the PTC polymer material was hot pressed under a temperature of 200° C. in a mold to form a thin sheet. The thin sheet and first and second nickel-plated copper foil sheets (which were respectively disposed on two opposite sides of the thin sheet and which had a centerline average surface roughness (Ra) of 1.10 μm) were hot pressed to for a PTC laminate. The hot pressing temperature was 200° C., the hot pressing time was 4 minutes, and the hot pressing pressure was 80 kg/cm2. The PTC laminate was irradiated with Co-60 gamma ray (a total dose of 5 Mrad) for cross-linking of the PTC polymer material, and was cut into chip-scaled pieces. Each of the chip-scaled pieces was welded to first and second terminal leads (nickel plates) through a lead-free tin solder paste to form a PTC circuit protection chip device. The welding temperature was 260° C., and the welding time was 3 minutes. The resistances of the chip-scaled piece and the PTC circuit protection chip device of Comparative Example 1 were measured to be 0.00122 ohm and 0.00313 ohm, respectively.
The procedures and conditions in preparing the PTC circuit protection chip device of Comparative Example 2 (CE2) were similar to those of Comparative Example 1, except for the centerline average surface roughness (Ra) of the first and second nickel-plated copper foil sheets. The centerline average surface roughness (Ra) of the first and second nickel-plated copper foil, sheets of Comparative Example 2 was 1.59 μm.
The resistances of the chip-scaled piece and the PTC circuit protection chip device of Comparative Example 2 were measured to be 0.00123 ohm and 0.00312 ohm, respectively.
The most hold current test is conducted by stepwisely increasing the current applied to a chip under a fixed DC voltage of 6V to find the maximum current under which the chip can endure for 15 minutes without breakdown.
Ten test samples of the PTC circuit protection chip device of each of E1 to E4 and CE1 to CE2 were subjected to the most hold current test to determine the most hold current of the PTC circuit protection chip device.
Table 1 shows the results of the most hold current test for E1 to E4 and CE1 to CE2, which demonstrate that the PTC circuit protection chip device of each of E1 to E4 has a higher most hold current than those of CE1 and CE2.
The switching cycle test is conducted by switching a chip on for 60 seconds and then off for 60 seconds per cycle under a voltage of 6Vdc and a current of 10 A for 7200 cycles. The initial resistance (Ri) (before the cycle test) and the final resistance (Rf) (after 7200 cycles) of the chip are measured to determine the resistance variation (Rv) of the chip after 7200 cycles, in which Rv=100% ×/Ri.
Ten test samples of the PTC circuit protection chip device of each of E1 to E4 and CE1 to CE2 were subjected to the switching cycle test to determine the resistance variation (Rv) of the PTC circuit protection chip device.
Table 1 also shows the results of the switching cycle test for E1 to E4 and CE1 to CE2, which demonstrate that the PTC circuit protection chip device of each of E1 to E4 has a lower resistance variation than those of CE1 and CE2.
In conclusion, with the use of the spacer unit 32 to form the PTC laminate 6 in the method of making the PTC circuit protection chip device 7 of the disclosure, the aforesaid drawback associated with the prior art can be eliminated.
While the present disclosure has been described in connection with what is considered the exemplary embodiment, it is understood that this disclosure is not limited to the disclosed embodiment but is intended to cover various arrangements included within the spirit and scope of the broadest interpretation and equivalent, arrangements.
