WO2017000897A1 - 可回流焊的正温度系数电路保护器件 - Google Patents

可回流焊的正温度系数电路保护器件 Download PDF

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Publication number
WO2017000897A1
WO2017000897A1 PCT/CN2016/087865 CN2016087865W WO2017000897A1 WO 2017000897 A1 WO2017000897 A1 WO 2017000897A1 CN 2016087865 W CN2016087865 W CN 2016087865W WO 2017000897 A1 WO2017000897 A1 WO 2017000897A1
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WIPO (PCT)
Prior art keywords
chip
planar profile
temperature coefficient
positive temperature
bonding portion
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Ceased
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PCT/CN2016/087865
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English (en)
French (fr)
Inventor
胡成
苗传荣
陈建华
傅英松
卜建明
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Littelfuse Electronics Shanghai Co Ltd
TE Connectivity Corp
Original Assignee
Raychem Electronics Shanghai Ltd
Tyco Electronics Corp
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Application filed by Raychem Electronics Shanghai Ltd, Tyco Electronics Corp filed Critical Raychem Electronics Shanghai Ltd
Priority to KR1020177037796A priority Critical patent/KR20180021738A/ko
Priority to US15/739,928 priority patent/US20180268969A1/en
Priority to JP2017568438A priority patent/JP2018519670A/ja
Publication of WO2017000897A1 publication Critical patent/WO2017000897A1/zh
Anticipated expiration legal-status Critical
Ceased legal-status Critical Current

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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01C—RESISTORS
    • H01C1/00—Details
    • H01C1/14—Terminals or tapping points specially adapted for resistors; Arrangements of terminals or tapping points on resistors
    • H01C1/144—Terminals or tapping points specially adapted for resistors; Arrangements of terminals or tapping points on resistors the terminals or tapping points being welded or soldered
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01C—RESISTORS
    • H01C1/00—Details
    • H01C1/14—Terminals or tapping points specially adapted for resistors; Arrangements of terminals or tapping points on resistors
    • H01C1/1406—Terminals or electrodes formed on resistive elements having positive temperature coefficient
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01C—RESISTORS
    • H01C7/00—Non-adjustable resistors formed as one or more layers or coatings; Non-adjustable resistors made from powdered conducting material or powdered semi-conducting material with or without insulating material
    • H01C7/02—Non-adjustable resistors formed as one or more layers or coatings; Non-adjustable resistors made from powdered conducting material or powdered semi-conducting material with or without insulating material having positive temperature coefficient
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
    • H02H9/00—Emergency protective circuit arrangements for limiting excess current or voltage without disconnection
    • H02H9/02—Emergency protective circuit arrangements for limiting excess current or voltage without disconnection responsive to excess current
    • H02H9/026—Current limitation using PTC resistors, i.e. resistors with a large positive temperature coefficient

Definitions

  • This application relates to electrical devices, and more particularly to a reflowable positive temperature coefficient device.
  • PTC chips are widely used in circuit protection.
  • the PTC chip has low resistance in normal operation. Once the current in the circuit is too large, the PTC chip will heat up and heat up. When it exceeds a certain temperature, its resistance sharply increases to the state of the insulator, thereby cutting off the circuit.
  • the PTC chip thus functions as a protection circuit.
  • the PTC chip device is constructed in a simple layered structure: a chip-shaped conductive terminal that completely covers it is soldered on both sides of the PTC chip.
  • the PTC chip device is mounted into the circuit by soldering two sheet-shaped conductive terminals into a circuit, such as a circuit board.
  • FIG. 1 shows a schematic diagram of a prior art PTC circuit protection device.
  • the PTC chip 3 is sandwiched between the conductive upper terminal 1 and the lower terminal 2, and is joined to the upper terminal 1 and the lower terminal 2 by solder (not shown) to realize serial connection.
  • the upper terminal 1 has an epitaxial curved joint portion 103, and a circuit joint portion 105. When mounted, the circuit junction 105 of the lower terminal 2 and the upper terminal 1 is reflow soldered into the circuit, such as a circuit board.
  • the upper terminal 1 and the lower terminal 2 completely cover the PTC chip 3.
  • the prior art PTC circuit protection device shown in FIG. 1 is simple in construction, but has the following problems.
  • a protected state ie, a high temperature state
  • the PTC chip is at a high temperature, and thermal expansion will occur.
  • the sheet-like conductive terminals completely covering the PTC chip are firmly soldered to the circuit and are hard to be deformed, thereby greatly limiting the space for thermal expansion of the PTC chip, and thus generating a large internal stress in the device.
  • This stress may cause physical destruction of the PTC chip to burn out, and may also cause soldering loose between the circuit bonding portion 105 and the circuit, thereby affecting the reliability of the circuit, that is, the electronic device.
  • the PTC chip is a polymer positive temperature coefficient (PPTC chip).
  • PPTC chip polymer positive temperature coefficient
  • the chip-shaped conductive terminals are usually soldered to the PTC chip using reflow soldering, and when the fabricated chip device is mounted in the circuit, reflow soldering technology is also generally used. Therefore, under similar reflow conditions (such as hot air), when the PTC circuit protection device shown in FIG.
  • a positive temperature coefficient circuit protection device comprising:
  • the chip-shaped upper terminal being composed of a first chip bonding portion, a first circuit bonding portion and a connection portion therebetween, wherein the first chip bonding portion has a first planar profile;
  • the tab lower terminal including a second chip bond, wherein the second chip bond has a second planar profile
  • the positive temperature coefficient chip has a third planar profile
  • the first planar profile and the second planar profile are internal to the third planar profile, and
  • the third planar profile has portions that are not covered by the first profile and/or the second profile to allow the positive temperature coefficient chip to have a free thermal expansion space.
  • the area of the portion of the third planar profile not covered by the first contour is at least 20% of the area of the third planar contour
  • the area of the portion of the third planar profile that is not covered by the second contour is at least 20% of the area of the third planar profile.
  • An overflow barrier is provided between the edges of the first planar profile and the third planar profile, and/or an overflow barrier is provided between the edges of the second planar profile and the third planar profile.
  • the first chip bond and/or the second chip bond have a through hole.
  • the first chip bond has a plurality of through holes, preferably three or more through holes.
  • FIG. 1 is a schematic diagram of a PTC circuit protection device of the prior art.
  • FIGS. 2A to 2C are external views showing a PTC circuit protection device according to an embodiment of the present application.
  • Fig. 3 is a view showing the relationship between the bonding force between the upper terminal and the PTC chip and the through hole in the upper terminal of the sheet.
  • FIG. 2A to 2C are views showing the appearance of a PTC circuit protection device according to an embodiment of the present application.
  • Fig. 2A is a plan view from above.
  • Fig. 2B is a side view.
  • Fig. 2C is a bottom view from below.
  • the upper and lower terminals are conductive materials such as metal, for example, nickel, copper, tin-plated copper, stainless steel, copper-plated stainless steel.
  • the thickness of the chip terminal is usually from 0.05 mm to 0.5 mm.
  • the PTC chip can be a PPTC chip. Although the appearance shown is substantially rectangular, any shape of terminal and chip material can optionally be used without affecting the effects of the present application.
  • the upper terminal 1 has a circuit bonding portion 105, a portion bonded to the PTC chip (referred to as a first chip bonding portion 101), the first chip bonding portion 101 has a through hole 505, and the circuit bonding portion 105 and the A connection portion 103 between the chip bonding portions 101.
  • the planar profile of the first chip bond 101 (referred to as the first planar profile) is within the profile of the PTC chip (referred to as the third planar profile).
  • the first planar profile is smaller than the third planar profile and has a gap with the edge of the third planar profile.
  • a larger region 501 is not covered by the first planar profile. Since the region 501 is not spatially restricted by the first chip bonding portion 101 of the upper terminal 1, it can be freely expanded at a high temperature, so that excessive internal stress is not generated.
  • the region 501 preferably has a ratio of the third planar profile area of > 20%, more preferably > 25%, and preferably ⁇ 50%. There is no special regulation on the shape of the region 501.
  • the gap 503 Between both sides of the first planar profile, there is a gap 503 between the edges of the third planar profile. Due to the presence of the gap 503, even when soldering the device back into the circuit, the solder in the remelted device is even The overflow will also remain on the PTC chip around the first planar profile without overflowing to the side and flowing down to form a tin bridge.
  • the gap capable of performing the above functions is referred to herein as an "overflow gap.”
  • the first chip bond 101 of the upper terminal 1 may also have any number and shape of vias 505 for receiving spilled solder.
  • the PTC circuit protection device is soldered into the circuit by reflow soldering, if there is a via hole in the upper terminal of the chip, there is a particularly advantageous effect that the bonding force between the upper terminal and the PTC chip is remarkably improved. Without any theory, this may be because the solder between the upper terminal and the PTC chip is remelted under reflow conditions and enters the through hole. When the reflow is completed and the solder is condensed, a solder column is formed in the through hole. .
  • FIG. 3 shows the relationship between the through hole and the bonding force in the upper terminal (90 degree peeling force vs hole size and number).
  • a comparative example without a through hole is shown, and three embodiments each having a through hole having a diameter of 0.35 mm, a through hole of 0.80 mm, and three through holes of 0.35 mm. It can be seen from the figure that as the pore size becomes larger and the number of pores increases, the binding force increases remarkably. Therefore, in the reflowable positive temperature coefficient circuit protection device, the through hole in the upper terminal of the sheet is particularly preferable.
  • a notch 701 is provided at the connecting portion 103.
  • the notches 701 are symmetrically disposed on both sides of the connecting portion.
  • the presence of the recess is such that the terminal is narrowed over the portion of the sheet and has better flexibility than the other portions.
  • the stress generated by the thermal expansion in the upper terminal causes a large elastic deformation of the joint at the notch, thereby alleviating the force applied to the other portions of the upper terminal of the sheet caused by the thermal expansion, and also slowing the PTC from the circuit board via the upper terminal.
  • the reaction force exerted by the chip protects the PTC chip, the upper terminal, and the circuit board.
  • a notch can also be provided when there is no curved connection in the circuit protection device. However, in the case of having a bent portion, it is particularly preferable to provide a notch.
  • the planar profile (referred to as the second planar profile) of the portion of the lower terminal 2 that is bonded to the PTC chip (referred to as the second chip joint 201) is in the outline of the PTC chip (referred to as a third planar profile).
  • a third planar profile Similar to the upper terminal, at one end of the third planar profile, a larger area 601 is not covered by the second planar profile.
  • This region 601 is substantially unaffected by the second chip bonding portion 201 of the lower terminal 2
  • the space is limited, so it can expand freely at high temperatures, so that it does not generate excessive internal stress.
  • the region 601 preferably accounts for 20% of the third planar profile area, more preferably > 25%, and preferably ⁇ 50%. There is no special regulation on the shape of the region 601.
  • the regions 501 and 601 that are not constrained by the upper and lower terminals are staggered so that free expansion spaces can be provided in different portions more efficiently.
  • an overflow prevention gap 603. When the device is reflow soldered into the circuit, even if the solder in the remelted device overflows, it will remain under the PTC chip around the second planar profile without spilling sideways and stacking up to form a tin bridge.
  • the second chip bonding portion 201 of the lower terminal 2 may have any number and shape of through holes 605 for accommodating overflow solder.
  • the above configuration is particularly effective when the PTC chip is a PPTC chip.
  • the PPTC chip comprises a PPTC sheet comprising a conductive powder dispersed in a polymer, the volume ratio of the polymer to the conductive powder being 35:65 to 65:35, wherein
  • the polymer comprises at least one copolymer selected from the group consisting of polyolefins, at least one olefin and at least one non-olefin monomer copolymerizable therewith, and a semi-crystalline polymer of a thermoformable fluoropolymer, said conductive
  • the powder includes at least one of a transition metal carbide, a transition metal carbon silicide, a transition metal aluminide, and a transition metal carbon tin compound, and the size distribution of the conductive powder satisfies: 20>D 100 /D 50 >6 Wherein D 50 represents the particle diameter corresponding to a cumulative particle size distribution percentage of a sample of 50%, and D 100 represents the maximum particle diameter.
  • polyolefins include polypropylene, polyethylene (including high density polyethylene, medium density polyethylene, low density polyethylene, and linear low density polyethylene), or copolymers of ethylene and propylene;
  • the copolymer includes an ethylene-vinyl acetate copolymer, an ethylene-vinyl alcohol copolymer, an ethylene-methyl acrylate copolymer, an ethylene-ethyl acrylate copolymer, an ethylene-acrylic acid copolymer, an ethylene-butyl acrylate copolymer;
  • Thermoformable fluoropolymers include polyvinylidene fluoride, and ethylene/tetrafluoroethylene copolymers and the like.
  • the conductive powder may be, for example, titanium carbide, tungsten carbide, titanium carbonitride, titanium aluminide, titanium tin carbide. Wait. Titanium carbonitride, titanium aluminide, titanium tin carbide, and the like have properties similar to those of tungsten carbide.
  • the above conductive powder has a spherical shape.
  • the term "sphere-like" includes a sphere and a shape similar to a sphere.
  • the conductive powder may have an average particle size of 0.1 to 50 ⁇ m.
  • the size of the conductive powder of the present application satisfies: D 50 ⁇ 5 ⁇ m, D 100 ⁇ 50 ⁇ m.
  • the conductive powder has a wide size distribution.
  • the transition metal since the transition metal generally has a variable valence state, in its carbide, there may be an MxC phase (M represents a transition metal, x is greater than 1), and the presence of such an MxC phase reduces the total carbon content in the carbide.
  • M represents a transition metal, x is greater than 1
  • MxC phase reduces the total carbon content in the carbide.
  • WC tungsten carbide
  • the theoretical total carbon content of pure WC is 6.18%, but the WC phase usually contains W 2 C (W 2 C is metastable phase), and WC contains a small amount of W 2 C. The carbon content will decrease. Under the condition that the particle size distribution is similar, the carbide having a lower carbon content has a lower resistivity.
  • the carbon content in the tungsten carbide is TC ⁇ 6.0% (where TC is 100% by mass ⁇ C/WC), in particular, when the content of TC is about 5.90%, a low electric resistance can be obtained.
  • TC>6.0% the resistivity is high. Therefore, it is preferred that the carbon content in the transition metal carbide is lower than the theoretical total carbon content of the pure transition metal carbide MC (M is a transition metal element) by a certain value.
  • the carbon content in the transition metal carbide is 2% to 5% lower than the theoretical total carbon content of the stoichiometric transition metal carbide MC, where M represents a transition metal element.
  • M represents a transition metal element.
  • the carbon content TC in the WC is 5.90% to 6.00%, wherein TC is 100% by mass/C/WC; or when the conductive powder is titanium carbide (TiC)
  • the carbon content TC in TiC is 19.0% to 19.5%, wherein TC is 100% by mass/C/TiC.
  • the volume ratio of the polymer to the conductive powder may be 35:65 to 65:35, preferably 40:60 to 60:40, more preferably 45:55. To 55:45, that is, mixed in substantially equal volume ratios.
  • the PPTC sheet may contain components other than the above polymer and conductive powder, for example, inorganic filling Materials or other polymeric materials, provided that the low resistance and processability of the PPTC sheet are not compromised.
  • the resistivity of the PPTC sheet when it is not in a protective state is 200 ⁇ cm or less.

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Abstract

提供了一种可回流焊的正温度系数电路保护器件，其包括：导电的片状上端子（1），其由第一芯片结合部（101）、第一电路结合部（105）和它们之间的连接部（103）组成，其中第一芯片结合部（101）具有第一平面轮廓；导电的片状下端子（2），其包括具有第二平面轮廓的第二芯片结合部（201）；夹在片状上端子（1）和片状下端子（2）之间并且通过焊锡分别与第一芯片结合部（101）的下表面及第二芯片结合部（201）的上表面结合的正温度系数芯片，其具有第三平面轮廓，其中：第一平面轮廓和第二平面轮廓在第三平面轮廓的内部，并且第三平面轮廓具有未被第一平面轮廓和/或第二平面轮廓覆盖的部分，以允许所述正温度系数芯片具有自由热膨胀空间。该器件可以减小在保护状态下器件内部导致器件失效的由高温热膨胀引起的应力。

Description

可回流焊的正温度系数电路保护器件 技术领域
本申请涉及电气器件，尤其涉及一种可回流焊的正温度系数器件。
背景技术
正温度系数(Positive Temperature Coefficient，PTC)芯片广泛应用于电路保护。PTC芯片在正常工作状态时具有低电阻。一旦电路中电流过大，PTC芯片将发热并升温。当超过一定温度后，其电阻急剧增加，达到绝缘体状态，从而切断电路。PTC芯片由此起到保护电路的作用。
常见地，PTC芯片器件的构造为简单的层状结构：在PTC芯片的两侧焊接有完全覆盖它的片状导电端子。在使用中，通过在将两个片状导电端子焊接至电路中(例如电路板上)，来将PTC芯片器件安装至电路中。
图1显示了现有技术的一种PTC电路保护器件的示意图。如图1所示，PTC芯片3被夹在导电的上端子1和下端子2之间，通过焊锡(未示出)与上端子1及下端子2结合，实现串行连接。上端子1具有外延的弯曲的结合部103，以及电路结合部105。当安装时，下端子2和上端子1的电路结合部105回流焊至电路中，如电路板上。上端子1和下端子2将PTC芯片3完全覆盖。
图1所示的现有技术的PTC电路保护器件虽然构造简单易行，但存在如下问题。首先，当处于保护状态(即高温状态)时，PTC芯片处于高温，并且将发生热膨胀。但是，完全覆盖PTC芯片的片状导电端子牢固焊接在电路上，难以变形，因此大大限制了PTC芯片热膨胀的空间，并且因此在器件内产生很大的内应力。该应力可能导致PTC芯片发生物理破坏从而烧毁，也可能导致电路结合部105与电路之间的焊接松脱等，从而对电路即电子装置的可靠性产生影响。这在PTC芯片是聚合物正温度系数(Polymeric Positive Temperature Coefficient，PPTC芯片的情况下尤其严重。总之，在存在热膨胀的情况下，如 果使用常规的PTC芯片器件的构造，产生的大应力使得产品可靠性大受影响。其次，在PTC芯片器件的制造中，通常使用回流焊将片状导电端子焊接至PTC芯片，而当将制成的芯片器件安装至电路中时，也通常使用回流焊技术。因此，在类似的回流焊条件(如热风)下，当将图1所示的PTC电路保护器件通过回流焊焊接到电路如电路板上以完成安装时，在上下端子与PTC芯片之间的焊锡会产生再熔融，从而存在锡珠的溢出。由于片状导电端子完全覆盖PTC芯片，溢出的锡珠将向电阻器件的侧面流淌，可能导致两个导电端子之间形成“锡桥”，从而在冷凝后造成端子间短路，影响电路的性能，甚至使PTC芯片器件失效。此外，覆盖PTC芯片的片状上端子与PTC芯片之间的结合力有时不够充分，容易产生剥离。
因此，需要一种改进的正温度系数电路保护器件结构，其能够减轻PTC芯片的热膨胀对器件可靠性的不利影响，同时还可以防止在安装该器件的回流焊期间产生“锡桥”。
发明内容
为了解决以上问题，本申请提供了以下技术方案。
[1]一种正温度系数电路保护器件，所述正温度系数电路保护器件包括：
导电的片状上端子，所述片状上端子由第一芯片结合部、第一电路结合部和它们之间的连接部组成，其中所述第一芯片结合部具有第一平面轮廓；
导电的片状下端子，所述片状下端子包括第二芯片结合部，其中所述第二芯片结合部具有第二平面轮廓；
夹在所述片状上端子和片状下端子之间并且通过焊锡分别与所述第一芯片结合部的下表面及所述第二芯片结合部的上表面结合的正温度系数芯片，所述正温度系数芯片具有第三平面轮廓，
其中：
所述第一平面轮廓和第二平面轮廓在所述第三平面轮廓的内部，并且所述 第三平面轮廓具有未被所述第一轮廓和/或第二轮廓覆盖的部分，以允许所述正温度系数芯片具有自由热膨胀空间。
[2]根据[1]所述的正温度系数电路保护器件，其中
所述第三平面轮廓未被所述第一轮廓覆盖的部分的面积至少为所述第三平面轮廓面积的20％，
和/或
所述第三平面轮廓未被所述第二轮廓覆盖的部分的面积至少为所述第三平面轮廓面积的20％。
[3]根据[1]所述的正温度系数电路保护器件，其中所述第三平面轮廓未被所述第一轮廓覆盖的部分和未被所述第二轮廓覆盖的部分是错开的。
[4]根据[1]所述的正温度系数电路保护器件，其中
在所述第一平面轮廓和第三平面轮廓的边缘之间具有防溢间隙，和/或，在所述第二平面轮廓和第三平面轮廓的边缘之间具有防溢间隙。
[5]根据[1]所述的正温度系数电路保护器件，其中
所述第一芯片结合部和/或第二芯片结合部具有通孔。
[6]根据[5]所述的正温度系数电路保护器件，其中
第一芯片结合部具有多个通孔，优选三个以上通孔。
[7]根据[1]所述的正温度系数电路保护器件，其中所述连接部的两侧边缘具有凹口。
[8]根据[1]所述的正温度系数电路保护器件，其中所述连接部是弯曲的，使得所述第一电路结合部的下表面与所述第二芯片结合部的下表面基本上处于同一平面内。
[9]根据[1]所述的正温度系数电路保护器件，其中所述片状下端子还包括从所述第二芯片结合部外延的电路结合部。
附图说明
图1是现有技术的一种PTC电路保护器件的示意图。
图2A至图2C是显示根据本申请的一个实施方案的PTC电路保护器件的外观图。
图3是显示了上端子与PTC芯片之间的结合力与片状上端子中的通孔之间的关系的图。
具体实施方式
下面结合附图，详细说明根据本申请的一些实施方案。
图2A至图2C显示根据本申请的一个实施方案的PTC电路保护器件的外观图。图2A是从上方的俯视图。图2B是侧视图。图2C是从下方的仰视图。其中，上下端子为导电材料，如金属，例如，镍、铜、镀锡的铜、不锈钢、镀铜的不锈钢。片状端子的厚度通常为0.05mm-0.5mm。PTC芯片可以是PPTC芯片。尽管所示的外观是基本上矩形的，但在不影响本申请效果的前提下，可以任选地使用任何形状的端子和芯片材。
图2A显示了，上端子1具有电路结合部105、与PTC芯片结合的部分(称为第一芯片结合部101)，第一芯片结合部101上具有通孔505，以及电路结合部105与第一芯片结合部101之间的连接部103。
第一芯片结合部101的平面轮廓(称为第一平面轮廓)在PTC芯片的轮廓(称为第三平面轮廓)之内。或者说，第一平面轮廓小于第三平面轮廓，并与第三平面轮廓的边缘具有空隙。其中，例如在第三平面轮廓的一端，有一块较大的区域501未被第一平面轮廓所覆盖。该区域501由于未受到上端子1的第一芯片结合部101在空间上的限制，因此在高温时可以自由膨胀，从而不会产生过高的内应力。为了达到较佳的降低应力的效果，区域501优选占第三平面轮廓面积的比例＞20％，更优选＞25％，并且优选＜50％。对区域501的形状，没有特别的规定。
在第一平面轮廓的两侧，与第三平面轮廓的边缘之间存在着间隙503。由于间隙503的存在，当将器件回流焊到电路中时，再融化的器件内的焊锡即使 溢出，也将保持在第一平面轮廓周围的PTC芯片上，而不会向侧面溢出进而向下流淌而形成锡桥。能够起到上述作用的间隙在本文中称为“防溢间隙”。
任选地，上端子1的第一芯片结合部101上还可以有任意数量和形状的通孔505，用于容纳溢出的焊锡。在利用回流焊将PTC电路保护器件焊接至电路中时，如果在片状上端子中存在通孔，将有特别有利的效果：上端子与PTC芯片之间的结合力将明显提高。不拘于任何理论，这可能是由于，在上端子与PTC芯片之间的焊锡在回流焊条件下再熔融并进入通孔中，当回流焊结束且焊锡冷凝后，在通孔中形成了焊锡柱。这些焊锡柱一方面增大了焊锡与上端子的粘合面积，一方面起到限制其周围通孔移动的作用，从而总体上提高了上端子与PTC芯片之间的结合力。图3显示了上端子中通孔与结合力之间的关系(90度剥离力vs孔尺寸和数量)。在图中，显示了没有通孔的对照例，以及三个实施例，分别具有一个直径为0.35mm的通孔、一个0.80mm的通孔以及三个0.35mm的通孔。从图中可见，当孔径变大、孔数变多时，结合力明显增大。因此，在可回流焊的正温度系数电路保护器件中，片状上端子中的通孔是特别优选的。
此外，在连接部103处，设置了凹口701。优选地，在连接部两侧对称地设置凹口701。凹口的存在使得在该部分片状上端子变窄，具有较其他部分为佳的挠性。上端子内由于热膨胀产生的应力使凹口处的连接部发生较大的弹性变形，从而减缓了热膨胀引起的片状上端子的其他部分的受力，也减缓了从电路板经由上端子向PTC芯片施加的反作用力，从而保护了PTC芯片、上端子以及电路板。当电路保护器件中没有弯曲的连接部时，也可以设置凹口。但在具有弯曲部的情况下，设置凹口是特别优选的。
图2C显示了，下端子2的与PTC芯片结合的部分(称为第二芯片结合部201)的平面轮廓(称为第二平面轮廓)在PTC芯片的轮廓(称为第三平面轮廓)之内。与上端子类似地，在第三平面轮廓的一端，有一块较大的区域601未被第二平面轮廓所覆盖。该区域601由于基本未受到下端子2的第二芯片结合部201 在空间上的限制，因此在高温时可以自由膨胀，从而不会产生过高的内应力。为了达到较佳的降低应力的效果，区域601优选占第三平面轮廓面积的20％，更优选＞25％，并且优选＜50％。对区域601的形状，没有特别的规定。
优选地，不受上下端子限制的区域501和区域601是错开的，从而可以更高效地在不同的部分提供自由膨胀空间。
同样，在第二平面轮廓的两侧，存在着防溢间隙603。当将器件回流焊到电路中时，再融化的器件内的焊锡即使溢出，也将保留在第二平面轮廓周围的PTC芯片下方，而不会向侧面溢出进而向上堆积而形成锡桥。
与上端子1类似地，下端子2的第二芯片结合部201上还可以有任意数量和形状的通孔605，用于容纳溢出的焊锡。
上述构造在PTC芯片是PPTC芯片时尤其有效。
在本申请的一个实施例中，PPTC芯片包含PPTC片材，所述PPTC片材包含分散在聚合物中的导电粉末，聚合物和导电粉末的体积比为35∶65至65∶35，其中所述聚合物包括至少一种选自聚烯烃类、至少一种烯烃与至少一种可与其共聚合的非烯烃单体的共聚物和可热成型含氟聚合物的半结晶聚合物，所述导电粉末包括过渡金属碳化物、过渡金属碳硅化物、过渡金属碳铝化物和过渡金属碳锡化物中的至少一种粉末，并且所述导电粉末的尺寸分布满足：20＞D100/D50＞6，其中D50表示一个样品的累计粒度分布百分比达到50％时所对应的粒径，D100表示最大粒径。
在半结晶聚合物中，聚烯烃类包括聚丙烯、聚乙烯(包括高密度聚乙烯、中密度聚乙烯、低密度聚乙烯和线型低密度聚乙烯)、或乙烯和丙烯的共聚物；所述共聚物包括乙烯-醋酸乙烯共聚物、乙烯-乙烯醇共聚物、乙烯-丙烯酸甲酯共聚物、乙烯-丙烯酸乙酯共聚物、乙烯-丙烯酸共聚物、乙烯-丙烯酸丁酯共聚物；所述可热成型含氟聚合物包括聚偏氟乙烯，和乙烯/四氟乙烯共聚物等。
导电粉末可以为，例如碳化钛、碳化钨、碳硅化钛、碳铝化钛、碳锡化钛 等。碳硅化钛、碳铝化钛、碳锡化钛等具有与碳化钨类似的性质。
上述导电粉末为类球形形状。此处，术语“类球形”包括球形以及与球形类似的形状。
导电粉末的平均颗粒大小可以为0.1至50μm。在一些实施方案中，本申请导电粉末的尺寸满足：D50＜5μm，D100＜50μm。
优选地，为了获得超低的电阻率(低于200μΩ·cm)，导电粉末具有较宽的尺寸分布。优选地，20＞D100/D50＞6，更优选10＞D100/D50。
通过将两种导电粉末混合以满足D100/D50＞6时，也可以得到类似的结论。
另外，由于过渡金属一般具有可变价态，在其碳化物中，可以存在MxC相(M表示过渡金属，x大于1)，这种MxC相的存在会降低碳化物中的总碳含量。以碳化钨(WC)为例，纯WC的理论总碳含量为6.18％，但WC物相中通常含有W2C(W2C是亚稳态相)，WC中含有少量W2C时总碳含量会降低。而在颗粒尺寸分布类似的条件下，具有较低碳含量的碳化物电阻率偏低。例如，碳化钨中碳含量在T.C.＜6.0％时(其中T.C.是以质量计的100％×C/WC)，特别地，T.C.的含量在5.90％左右时可得到低的电阻。而T.C.＞6.0％时，电阻率偏高。因此，优选过渡金属碳化物中的碳含量比纯过渡金属碳化物MC(M为过渡金属元素)的理论总碳含量低一定数值。
优选地，过渡金属碳化物中的碳含量比化学计量比的过渡金属碳化物MC的理论总碳含量低2％至5％，其中M表示过渡金属元素。其中，当导电粉末是碳化钨(WC)时，WC中碳含量T.C.为5.90％至6.00％，其中T.C.是以质量计的100％×C/WC；或当导电粉末是碳化钛(TiC)时，TiC中碳含量T.C.为19.0％至19.5％，其中T.C.是以质量计的100％×C/TiC。
PPTC片材中，为了使导电粉末可以均匀地分散在聚合物中，聚合物与导电粉末的体积比可以为35∶65至65∶35，优选40∶60至60∶40，更优选45∶55至55∶45，即，以大致相等的体积比混合。
PPTC片材可以包含除上述聚合物和导电粉末之外的组分，例如，无机填 料或其他聚合物材料，前提是不损害PPTC片材的低电阻和加工性能。
在本申请的一个实施例中，PPTC片材在没有处于保护状态(即高温状态)时的电阻率为200μΩ·cm以下。
应当理解，上述实施方案和实施例仅是为了说明本申请，而非限制本申请的范围。本领域技术人员可以在不脱离本申请的精神的前提下进行各种修改和变更。本申请的范围由后附的权利要求书限定。

Claims (9)

  1. 一种正温度系数电路保护器件，所述正温度系数电路保护器件包括：
    导电的片状上端子，所述片状上端子由第一芯片结合部、第一电路结合部和它们之间的连接部组成，其中所述第一芯片结合部具有第一平面轮廓；
    导电的片状下端子，所述片状下端子包括第二芯片结合部，其中所述第二芯片结合部具有第二平面轮廓；
    夹在所述片状上端子和片状下端子之间并且通过焊锡分别与所述第一芯片结合部的下表面及所述第二芯片结合部的上表面结合的正温度系数芯片，所述正温度系数芯片具有第三平面轮廓，
    其中：
    所述第一平面轮廓和第二平面轮廓在所述第三平面轮廓的内部，并且所述第三平面轮廓具有未被所述第一轮廓和/或第二轮廓覆盖的部分，以允许所述正温度系数芯片具有自由热膨胀空间。
  2. 根据权利要求1所述的正温度系数电路保护器件，其中
    所述第三平面轮廓未被所述第一轮廓覆盖的部分的面积至少为所述第三平面轮廓面积的20％，
    和/或
    所述第三平面轮廓未被所述第二轮廓覆盖的部分的面积至少为所述第三平面轮廓面积的20％。
  3. 根据权利要求1所述的正温度系数电路保护器件，其中所述第三平面轮廓未被所述第一轮廓覆盖的部分和未被所述第二轮廓覆盖的部分是错开的。
  4. 根据权利要求1所述的正温度系数电路保护器件，其中
    在所述第一平面轮廓和第三平面轮廓的边缘之间具有防溢间隙，和/或，在所述第二平面轮廓和第三平面轮廓的边缘之间具有防溢间隙。
  5. 根据权利要求1所述的正温度系数电路保护器件，其中
    所述第一芯片结合部和/或第二芯片结合部具有通孔。
  6. 根据权利要求5所述的正温度系数电路保护器件，其中
    第一芯片结合部具有多个通孔。
  7. 根据权利要求1所述的正温度系数电路保护器件，其中所述连接部的两侧边缘具有凹口。
  8. 根据权利要求1所述的正温度系数电路保护器件，其中所述连接部是弯曲的，使得所述第一电路结合部的下表面与所述第二芯片结合部的下表面基本上处于同一平面内。
  9. 根据权利要求1所述的正温度系数电路保护器件，其中所述片状下端子还包括从所述第二芯片结合部外延的电路结合部。
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