Chip resistor and method for manufacturing the same

A chip resistor includes a resistive element, first and second electrodes disposed on a lower surface the resistive element, a protective film disposed on the lower surface of the resistive element and between the first and second electrodes. The resistive element has first and second recesses therein. The first recess extends from the lower surface along a first edge surface and does not reach an upper surface of the resistive element. The second recess extends from the lower surface along a second edge surface and does not reach the upper surface of the resistive element. The first and second electrodes are disposed between the first and second recesses. The protective film is disposed between the first and second electrodes. A first plating layer disposed on the first electrode and an inner surface of the first recess. A second plating layer is disposed on the second electrode and an inner surface of the second recess. This chip resistor avoids mounting failures.

This application is a U.S. national stage application of the PCT international application No. PCT/JP2017/016518 filed on Apr. 26, 2017, which claims the benefit of foreign priority of Japanese patent application No. 2016-089333 filed on Apr. 27, 2016, the contents all of which are incorporated herein by reference.

TECHNICAL FIELD

The present invention relates to a chip resistor including a resistive element made of a metal plate, and a method for fabricating the chip resistor.

BACKGROUND ART

FIG. 9is a cross-sectional view of conventional chip resistor500. Chip resistor500includes resistive element1made of a metal having a plate shape, electrodes2aand2bdisposed on both ends of a lower surface of resistive element1, protective film3formed between electrodes2aand2bon the lower surface of resistive element1, and plating layer4formed on electrodes2aand2b. While mounting chip resistor500is mounted onto mounting board6, solder layer5formed on mounting board6by plating is formed on plating layer4.

A conventional resistor similar to chip resistor500is disclosed in, e.g. PTL 1.

CITATION LIST

Patent Literature

SUMMARY

A chip resistor includes a resistive element, first and second electrodes disposed on a lower surface of the resistive element, a protective film disposed on the lower surface of the resistive element and between the first and second electrodes. The resistive element has first and second recesses therein. The first recess extends from the lower surface along a first edge surface and does not reach an upper surface of the resistive element. The second recess extends from the lower surface along a second edge surface and does not reach the upper surface of the resistive element. The first and second electrodes are disposed between the first and second recesses. The protective film is disposed between the first and second electrodes. A first plating layer disposed on the first electrode and an inner surface of the first recess. A second plating layer is disposed on the second electrode and an inner surface of the second recess.

This chip resistor avoids mounting failures.

DETAIL DESCRIPTION OF EMBODIMENTS

FIG. 1Ais a cross-sectional view of chip resistor1000according to Exemplary Embodiment 1. Chip resistor1000includes resistive element11having a plate shape, a pair of recesses112and212that are formed at both ends of lower surface11aof resistive element11and do not pass through resistive element11, a pair of electrodes113and213formed on lower surface11aof resistive element11and between recesses112and212, and protective film14formed on lower surface11aof resistive element11and between electrodes113and213.

Resistive element11has a plate shape having upper surface11b, lower surface11a, edge surface111c, and edge surface211c. Edge surface111cis connected to upper surface11band lower surface11a. Edge surface211cis connected to upper surface11band lower surface11a, and is opposite to edge surface111c. Resistive element11has recesses112and212provided therein.

Electrode113has upper surface113b, lower surface113a, edge surface113d, and edge surface113c. Upper surface113bis disposed on lower surface11aof resistive element11. Edge surface113dis connected to upper surface113band lower surface113a. Edge surface113cis connected to upper surface113band lower surface113a, and is opposite to edge surface113d. Electrode213has upper surface213b, lower surface213a, edge surface213d, and edge surface213c. Upper surface213bis disposed on lower surface11aof resistive element11. Edge surface213dis connected to upper surface213band lower surface213a. Edge surface213cis connected to upper surface213band lower surface213a, and is opposite to edge surface213d.

Plating layer115is formed on inner surface112aof recess112, edge surface113cof electrode113, and lower surface113aof electrode113which are exposed from protective film14. Plating layer215is formed on inner surface212aof recess212, edge surface213cof electrode213, and lower surface213aof electrode213which are exposed from protective film14.

Resistive element11is made of metal, such as NiCr, CuNi, or CuMn. Upper surface11band lower surface11aof resistive element11are arranged in thickness direction DT with a distance between surfaces11aand11b. Edge surfaces111cand211care arranged in longitudinal direction DL with a distance between edge surfaces111cand211c. Resistive element11may have a slit therein to adjust a resistance value of resistive element11. This slit does not necessarily pass through resistive element11.

Recesses112and212are disposed in lower surface11aof resistive element11at both ends of lower surface11aof resistive element11in longitudinal direction DL, and do not reach upper surface11bof resistive element11. That is, recess112extends from lower surface11aalong edge surface111cand does not reach upper surface11b. Recess212extends from lower surface11aalong edge surface211cand does not reach upper surface11b. Recess112has inner side surface112cand bottom surface112bconnected to inner side surface112cand edge surface111cof resistive element11. Inner side surface112cand bottom surface112bconstitute inner surface112aof recess112. Recess212has inner side surface212cand bottom surface212bconnected to inner side surface212cand edge surface211cof resistive element11. Inner side surface212cand bottom surface212bconstitute inner surface212aof recess212. In accordance with Embodiment 1, bottom surfaces112band212bof recesses112and212are substantially parallel to lower surface11aof resistive element11, while inner side surfaces112cand212care substantially perpendicular to lower surface11aof resistive element11. A length of each of recesses112and212in thickness direction DT, which is the depth of each of recesses112and212, ranges from about ⅓ to ⅔ the length of resistive element11in thickness direction DT.

Electrodes113and213are formed by plating or printing copper on lower surface11aof resistive element11, and are spaced from each other on lower surface11aof resistive element11with a predetermined interval. In accordance with Embodiment 1, edge surfaces113cand213cof electrodes113and213are substantially flush with inner side surfaces112cand212cof recesses112and212, respectively.

Protective film14is made of an insulating material, such as an epoxy resin, and is formed between electrodes113and213and on lower surface11aof resistive element11. Protective film14has upper surface14bdisposed on lower surface11aof resistive element11and lower surface14a. Lower surface14aof protective film14is substantially flush with lower surfaces113aand213aof electrodes113and213. Protective film14contacts edge surfaces113dand213dof electrodes113and213so as to entirely cover a portion of lower surface11aof resistive element11extending from electrode113to electrode213.

FIG. 1Bis an enlarged cross-sectional view of chip resistor1000, and mainly illustrates plating layers115and215. Plating layer115includes Ni plating layer1115made of Ni and Sn plating layer2115made of Sn. Ni plating layer1115is disposed on inner surface112aof recess112and edge surface113cand lower surface113aof electrode113. Sn plating layer2115is disposed on Ni plating layer1115. Ni plating layer1115and Sn plating layer2115are formed in this order. Similarly, plating layer215includes Ni plating layer1215made of Ni and Sn plating layers2215made of Sn. Ni plating layer1215is disposed on inner surface212aof recess212and edge surface213cand lower surface213aof electrode213. Sn plating layers2215is disposed on Ni plating layer1215. Ni plating layer1215and Sn plating layer2215are formed in this order. That is, plating layers115and215are formed on portions of chip resistor1000exposed downward from protective film14.

FIG. 1Cis an enlarged cross-sectional view of another chip resistor1000, and mainly illustrates plating layers115and215. InFIG. 1C, components identical to those of plating layers115and215illustrated inFIG. 1Bare denoted by the same reference numerals. Plating layer115illustrated inFIG. 1Cincludes Cu plating layer3115made of Cu, Ni plating layer1115made of Ni, and Sn plating layer2115made of Sn. Cu plating layer3115is disposed on inner surface112aof recess112and edge surface113cand lower surface113aof electrode113. Ni plating layer1115is disposed on Cu plating layer3115. Sn plating layer2115is disposed on Ni plating layer1115. Cu plating layer3115, Ni plating layer1115, and Sn plating layer2115are formed in this order. Similarly, plating layer215illustrated inFIG. 1Cincludes Cu plating layer3215made of Cu, Ni plating layer1215made of Ni, and Sn plating layers2215made of Sn. Cu plating layer3215is disposed on inner surface212aof recess212and edge surface213cand lower surface213aof electrode213. Ni plating layer1215is disposed on Cu plating layer3215. Sn plating layers2215is disposed on Ni plating layer1215. Cu plating layer3215, Ni plating layer1215, and Sn plating layers2215are formed in this order.

FIG. 2is a cross-sectional view of chip resistor1000mounted onto mounting board16. Chip resistor1000is mounted onto mounting board16while lands of mounting board16are connected to plating layers115and215via mounting solder layers117and217, respectively.

Solder layer117is formed both on a portion of plating layer115parallel to lower surface11aof resistive element11and on a portion of plating layer115perpendicular to lower surface11a. Similarly, solder layer217is formed both on a portion of plating layer215parallel to lower surface11aof resistive element11and on a portion of plating layer215perpendicular to lower surface11a.

A method for manufacturing chip resistor1000will be described below with reference to drawings.FIG. 3Ais a plan view of the chip resistor according to Embodiment 1 for illustrating the method for manufacturing the chip resistor.FIG. 3Bis a cross-sectional view of the chip resistor along line3B-3B shown inFIG. 3A.FIG. 4Ais a plan view of the chip resistor according to Embodiment 1 for illustrating the method for manufacturing the chip resistor.FIG. 4Bis a cross-sectional view of the chip resistor along line4B-4B shown inFIG. 4A.FIG. 4Cis a plan view of the chip resistor according to Embodiment 1 for illustrating the method for manufacturing the chip resistor.FIG. 4Dis a cross-sectional view of the chip resistor along line4D-4D shown inFIG. 4C.FIG. 5Ais a plan view of the chip resistor according to Embodiment 1 for illustrating the method for manufacturing the chip resistor.FIG. 5Bis a cross-sectional view of the chip resistor along line5B-5B shown inFIG. 5A.FIG. 5Cis a plan view of the chip resistor according to Embodiment 1 for illustrating the method for manufacturing the chip resistor.FIG. 5Dis a cross-sectional view of the chip resistor along line5D-5D shown inFIG. 5C.

First, as illustrated inFIGS. 3A and 3B, resistive sheet21made of a metal, such as NiCr, CuNi, or CuMn, having a plate shape is prepared. Resistive sheet21has surface21a, surface21bopposite to surface21a, edge surface121c, and edge surface221c. Edge surface121cis connected to surfaces21aand21b. Edge surface221cis connected to surfaces21aand21b, and is opposite to edge surface121c. Surface21bof resistive sheet21constitutes upper surface11bof resistive element11, while surface21aconstitutes lower surface11aof resistive element11. Paste mainly containing Cu is printed or plated on surface21aof resistive sheet21in strip shapes at predetermined intervals, thereby forming strip electrode layers22on surface21aof resistive sheet21. Center line22cof each of strip electrode layers22corresponds to an edge surface of s single piece of chip resistor1000. Resistive sheet21is divided into pieces constituting resistive elements11, while strip electrode layers22constitute pairs of electrodes113and213.

Next, as illustrated inFIGS. 4A and 4B, an insulating material, such as an epoxy resin, is applied onto portions of surface21aof resistive sheet21between strip electrode layers22and is dried, thereby forming protective film34constituting protective film14. The surface of protective film34and the surfaces of electrode layers22are substantially flush with each other. Resistive sheet21having surfaces21aand21b, electrode layers22separated from each other on surface21aof resistive sheet21, and protective film34provided on surface21aof resistive sheet21between electrode layers22constitute layered body1000A.

Then, as illustrated inFIGS. 4C and 4D, grooves23having straight shapes are formed by dicing along center lines22cof strip electrode layers22. Grooves23completely pass through strip electrode layers22but do not completely pass through resistive sheet21to extend halfway in thickness direction DT. That is, grooves23enter into surface21aof resistive sheet21but do not reach surface21b. Grooves23constitute recesses112and212.

Subsequently, as illustrated inFIGS. 5A and 5B, an Ni plating layer and an Sn plating layer are formed in this order on surfaces of strip electrode layers22, that is, a portion of strip electrode layers22exposed from protective film14and inner surfaces of grooves23, thereby providing plating layer315. Plating layer315is thus formed continuously on inner surfaces112aand212aof recesses112and212, edge surfaces113cand213cof electrodes113and213, and lower surfaces113aand213aof electrodes113and213.

Then, as illustrated inFIGS. 5C and 5D, dicing or laser application is performed from grooves23or on surface21aof resistive sheet21, thereby forming grooves24in surface21bof resistive sheet21. Grooves24are narrower than grooves23, and overlap grooves23in a plan view. Since grooves23are formed before forming grooves24, grooves24can be easily positioned.

Even if grooves24are deviated a little, as long as respective distances between pairs of grooves24adjacent to each other are identical to one another, resistive elements11obtained by dividing resistive sheet21have the same length, thus reducing variations in resistance values of the resistive elements. Since grooves24are narrower than grooves23, plating layers115and215can remain on bottom surfaces112band212bof recesses112and212, as illustrated inFIG. 1A.

Resistive sheet21, electrode layers22, protective film34, and plating layer315are divided at grooves24and division grooves25perpendicular to grooves24so that resistive sheet21can be divided into pieces each constituting chip resistor1000illustrated inFIG. 1A. Then, the resistance value of chip resistor1000may be adjusted with the slits described above.

To simplify the description, inFIGS. 3A to 5D, chip resistors1000as individual pieces are arranged in a matrix constituted by two columns and two rows.

In conventional chip resistor500illustrated inFIG. 9, when mounting board6warps, a stress in upward and downward directions is concentrated on end portions of solder layer5and may produce cracks in solder layer5, thus raising a failure in mounting.

In chip resistor1000according to Embodiment 1, recesses112and212which do not pass through provided at both ends of lower surface11aof resistive element11have inner side surfaces112cand212cperpendicular to lower surface11aof resistive element11. When mounting board16warps, a stress in thickness direction DT is applied to solder layers117and217. Since solder layers117and217are formed on inner side surfaces112cand212c, the direction of the stress applied to solder layers117and217is parallel to inner side surfaces112cand212cperpendicular to lower surface11aof resistive element11. Thus, the stress on solder layers117and217can be reduced so that cracking in solder layers117and217can be reduced, thereby reducing occurrence of mounting failures. As a result, the resistance value of chip resistor1000can be stabilized.

Recesses112and212serve as spaces in mounting chip resistor1000, and increase contact areas between mounting solder layers117and217and plating layers115and215, accordingly increasing a mounting strength.

FIG. 6is a cross-sectional view of another chip resistor1001according to Embodiment 1. InFIG. 6, components identical to those of chip resistor1000illustrated inFIG. 1Aare denoted by the same reference numerals. Chip resistor1001illustrated inFIG. 6includes metal layer91made of CuNi and disposed on lower surface11aof resistive element11. Metal layer91contacts electrodes113and213and protective film14. Metal layer91reduces a temperature coefficient of resistance (TCR) of chip resistor1001.

FIG. 7is a cross-sectional view of chip resistor1002according to Exemplary Embodiment 2. InFIG. 7, components identical to those of chip resistor1000according to Embodiment 1 illustrated inFIGS. 1A to 5Dare denoted by the same reference numerals.

In chip resistor1002according to Embodiment 2, cross sections of inner surfaces112aand212aof recesses112and212have arcuately concave portions, unlike resistor1000(1001) according to Embodiment 1.

The cross sections of inner surfaces112aand212amay be entirely arcuate or may be partially arcuate, or the cross sections of inner surfaces112aand212amay be linear. Portions of inner surfaces112aand212aconnected to edge surfaces111cand211cof resistive element11, that is, bottom surfaces112band212b, preferably have arcuate cross sections. In this case, end portions of plating layers115and215connected to edge surfaces111cand211cof resistive element11may be arcuate.

This configuration can disperse a stress applied to end portions of plating layers115and215contacting edge surfaces111cand211cof resistive element11, thereby increasing mounting strength.

FIG. 8is a cross-sectional view of chip resistor1003according to Exemplary Embodiment 3. InFIG. 8, components identical to those of chip resistor1000according to Embodiment 1 illustrated inFIGS. 1A to 5Dare denoted by the same reference numerals.

Chip resistor1003according to Embodiment 3 further includes fluorine-based coating layer18disposed on an exposed surface of resistive element11of chip resistor1000according to Embodiment 1. In accordance with Embodiment 3, fluorine-based coating layer18is formed on upper surface11band edge surfaces111cand211cof resistive element11.

Fluorine-based coating layer18is made of an anti-flux agent mainly containing fluorine, and repels flux contained in solder layers117and217due to a repelling effect of fluorine. Thus, solder layers117and217are not formed on portions where fluorine-based coating layer18is formed.

A portion of the chip resistor between solder layer117and edge surface111cand a portion of the chip resistor between solder layer217and edge surface211care vulnerable to a stress in thickness direction DT applied to solder layers117and217due to the warpage of mounting board16. In the case that solder layers117and217extend to edge surfaces111cand211c, a failure in mounting the chip resistor might occur. In chip resistor1003according to Embodiment 3, fluorine-based coating layer18prevents solder layers117and217from extending to edge surfaces111cand211cof resistive element11, thus preventing mounting failures.

In the case that solder layers117and217extend to upper surface11b, solder layers117and217increases the height of a product including the chip resistor according to the thickness of the extending portions of solder layers117and217. Fluorine-based coating layer18formed on upper surface11bof resistive element11prevents solder layers117and217from extending to upper surface11bof resistive element11, hence reducing that the height of a product including chip resistor1003.

In Embodiments 1 to 3, terms, such as “upper surface” and “lower surface”, indicating directions indicate relative directions depending only on relative positional relationships among components, such as resistive element11and electrodes113and213, of the chip resistor, and do not indicate absolute directions, such as a vertical direction.

REFERENCE MARKS IN THE DRAWINGS