A surface mountable resistor

Abstract: The present invention is to offer a resistor which can be mounted exactly on the terminals disposed on a circuit board regardless the sides of the resistor, and to offer its manufacturing method by forming the surface of the side-electrode layer at a height higher than the surface of protection layer, or by forming the surface of the second surface electrode layer at a height higher than the surface of protection layer. By these, the resistor can be mounted exactly on the terminal of circuit board at a high yield. Furthermore, since the first surface electrode layer and the second upper electrode layer are electrically connected together through a window provided on the protection layer, a higher connection reliability can be obtained.

Description: FIELD OF THE INVENTION This invention relates to a resistor according to the preamble of claim 1, employed to manufacture a high-density circuit-board. BACKGROUND OF THE INVENTION Whereas the conventional resistor such as the one disclosed by the laid-open patent Hei 4-102302 had been known, the conventional resistor and its manufacturing method are reviewed by referring attached drawing Fig. 23 showing a cross-section of the conventional resistor. In Fig. 23, 1 is an insulation substrate, 2 is a first surface electrode layer disposed on the left and right ends of insulation substrate 1, and 3 is a resistor layer disposed on first surface electrode layer 2 partly overlapping with first surface resistor layer 2, 4 is a first protection layer disposed to cover the entire surface of resistor layer 3, and 5s are trimming grooves disposed on resistor layer 3 and first protection layer 4, and said trimming grooves are cut when the resistance of resistor 3 has to be trimmed. 6 is a second protection layer disposed only on the surface of first protection layer 4, and 7 is a second surface electrode layer extended over the entire width of insulation substrate 1 on the surface of first surface electrode layer 2. 8s are side-electrode layers disposed on the both sides of insulation substrate 1, 9 and 10 are nickel-plated and solder-plated layers respectively disposed on second surface electrode layer 7 and side-electrode layer 8. At this time, solder-plated layer 10 is disposed at a height lower than the height of said second protection layer 6. That is, second protection layer 6 is disposed at a highest height on the conventional resistor. The manufacturing processes of conventional resistor having the above-shown construction are now explained below by referring the attached drawings. Figs. 24 and 25 show manufacturing processes of the conven-tional resistor. As shown in Fig. 24(a), first surface electrode layer 2 is formed by applying a coating on the left and right ends of insulation substrate 1. Then, as shown in Fig. 24(b), resistor layer 3 is formed by applying a coating on the both ends of insulation substrate 1 overlapping partly with resistor layer 3. Then, in next, as shown in Fig. 24(c), after coating first protection layer 4 covering the entire surface of resistor layer 3, trimming grooves 5 are formed on resistor layer 3 and first protection layer 4 by applying a laser-trimming method in order to set the resistance of resistor layer 3 within a predetermined range. Then, as shown in Fig. 25(a), a second protection layer 6 is disposed on the surface of first protection layer 4, and as shown in Fig. 25(b), second surface electrode layer 7 is disposed on first surface electrode layer 2 extending over the entire width of insulation substrate 1. Then, as shown in Fig. 25(c), side-electrode layers 8 electrically connecting first surface electrode layer 2 to second surface electrode layer 7 are disposed on the both sides of insulating substrate 1. After applying a nickel-plating and a solder plating on the surfaces of second surface electrode layer 7 and side-electrode layer 8 as shown by a cross-section shown in Fig. 23, the resistor of conventional construction provided with nickel plated layer 9 and solder plated layer 10 are obtained. However, with the resistor of conventional construction and manufacturing processes, since second protection layer 6 is deposited at a height higher than solder-plated layer 10. the resistor can be mounted on a circuit board (not shown) by utlizing only the back surface of insulation substrate 1. Therefore, there should be a definite disadvantage excluding the automatic resistor mounting machine from the mounting work of circuit boards because of the lack of ability discriminating the top or the bottom of resistors. A resistor having the features of the preamble of claim 1 is known from document DE 3 122 612 A1. The Patent Abstract of JP 08031603 A discloses a thin film chip resistor, wherein a thin film edge face electrode layer is formed on the edge face on both sides of a substrate, said layer electrically connecting a first thin film upper surface electrode layer formed on the substrate, a second conductor resin upper surface electrode layer formed on a resistor layer which is disposed on said first thin film upper surface electrode layer and a thin film back side electrode layer formed on the back side of the substrate. EP 0 229 286 A1 discloses an electrical component, e.g., a ceramic resistor. Such an electrical component consists of a body of electrically effective material which is completely covered on two opposite sides with two metallic layers. These metallic layers are completely covered with an insulating protection layer which has a window on each side of said metallic layers, and wherein the sides of the electrical body are covered with contact element layers. The Patent Abstract of JP 08 236325 A is a post-published document which is only relevant concerning the question of novelty and discloses a chip resistor, wherein a first metal glaze type electrode is printed on the surface of an insulative ceramic board. On the back side of the board a second metal glaze type electrode is printed on the opposite position to the electrode. A resistance directly connected to the electrode is printed and covered with a glass coat. The board with printed electrodes and and resistance is scribed such that these electrodes and resistance are located on end parts of its front and back sides. A silver paint is coated in a C-shaped pattern on the side end of each scribed board to form a third electrode. However, there is a need and it is the object of the present invention to provide improved resistors mountable on circuit boards without discriminating the surface and back of the resistors and with a minimum number of unacceptable connections. This object is solved by the resistor having the features of claim 1. Fig, 1 show a cross-section of the resistor which is a first example for better understanding the invention. Fig. 2 shows manufacturing processes of the resistor which is the same example. Fig. 3 shows manufacturing processes of the resistor which is the same example. Fig. 4 is a drawing illustrating a mounting failure found at the mounting of the resistor on a circuit board. Fig. 5 is a cross-section of the resistor which is a second example for better understanding the invention. Fig. 6 is manufacturing processes of the resistor which is the same example. Fig. 7 shows manufacturing processes of the same resistor. Fig. 8 shows a cross-section of the resistor which is a first embodiment of the invention. Fig. 9 shows manufacturing processes of the resistor which is the same embodiment of the invention. Fig. 10 shows manufacturing processes of the same. Fig, 11 show a cross-section of the resistor which is a second embodiment of the invention. Fig. 12 shows manufacturing processes of the same resistor Fig. 13 shows manufacturing processes of the same. Fig. 14 shows a perspective view of the resistor which is a third embodiment of the invention. Fig. 15 shows a perspective view of the resistor which is a third example for better understanding the invention. Fig. 16 shows a cross-section of the same resistor. Fig. 17 shows manufacturing processes of the same resistor. Fig. 18 shows manufacturing processes of the same resistor. Fig. 19 shows a perspective view of the resistor which is a fourth example for better understanding the invention. Fig. 20 shows a cross-section of the same resistor. Fig. 21 shows manufacturing processes of the same. Fig. 22 shows manufacturing processes of the same. Fig. 23 shows a cross-section of the conventional resistor. Fig. 24 shows manufacturing processes of the same resistor. Fig. 25 shows manufacturing processes of the same. DESCRIPTION OF PREFERRED EMBODIMENTS A first example is now explained below by referring the attached drawings. In Fig. 1, 11 is a substrate made of alumina or such, 12s are a pair of surface electrode layers made of a mixed material consisted of silver and glass disposed on the both ends of substrate 11, and this should preferably be disposed to the side ends of substrate 11. 13 is a resistor layer made of a mixed material consisted of ruthenium oxide and glass disposed on the substrate 11 and on the both ends of surface electrode layers 12 making electrical connections thereto also. 14 is a protection layer made of boro-silicate lead glass disposed to cover at least the surface of resistor layers 13. 15s are side electrodes made of a mixed material consisted of silver and glass disposed on the both sides of substrate 11 and both ends of surface electrode layer 12, and a part of surface electrode layers 12 producing an electrically superposed region at a height higher than the surface of protection layer 14, producing also rounded edges of side-electrode layers 15. 16 is an electro-plated layer made of a metal such as nickel to cover side-electrode layers 15s when it is necessary. 17s are solder layers disposed to cover said nickel-plated layers 16 when necessary, and these should preferably be provided with rounded edges of solder layers 17. The manufacturing processes of resistor of the above-shown construction are now explained below be referring the attached drawings Figs. 2 and 3 showing a manufacturing method of resistor which is a first example. As shown in Fig. 2(a), after a mixed paste material consist-ed of silver and glass is screen-printed on sheet-formed subst-rate 22 made of alumina crossing over vertical and horizontal dividing grooves 21 disposed on said substrate 22, and are dried and sintered in a belt-system continuous furnace at a temperature of about 850°C kept for a period of about 45 minutes. Surface electrode layer 23 is formed by this. Then, as shown in Fig. 2(b), after a mixed paste material consisted of ruthenium oxide and glass is screen-printed on the surface of sheet-shaped substrate 22 superposing on each end of surface electrode layers 23 in order to electrically combine surface electrode layers 23, these are dried and sintered in a belt-system continuous furnace at a temperature of about 850°C for a period of about 45 minutes. Resistor layers 24 are formed by this. In next, as shown in Fig. 2(c), the resistance of resistor layer 24 is trimmed by using a laser trimmer, forming trimming grooves 25. At this time, trimming grooves may be formed by cutting resistor layer 24 and the coating layer altogether after at least the surface of resistor layer 24 are covered by a coating layer (not shown) made of glass or others. As shown in Fig. 2(d) in next, after a boro-silicate lead glass paste is screen-printed in order to completely cover surface resistor layer 24, the paste is dried and sintered in a belt-system continuous furnace at a temperature of about 850°C for a period of about 45 minutes, and by this, protection layers 26 is formed. Then, as shown in Fig. 3(a), sheet-shaped substrate 22 is divided along dividing grooves 21, exposing surface electrode layers 23 from the sides of substrate, and forming rectangular-shaped substrates 27. In next, as shown in Fig. 3(b), after a mixed paste prepared by mixing silver and glass is transfer-printed by a roller on the side of rectangular-shaped substrate 27 forming an overlapped part on surface electrode layer 23 which is made higher than the surface of protection layer 26, the paste is dried and sintered in a belt-system continuous furnace at a temperature of about 600°C for a period of about 45 minutes forming side-electrode layers 28. As shown in Fig. 3(c), rectangular-shaped substrates 27 are then divided into individual substrates producing individual pieces of resistors 20 at the last stage. Then, at the last stage, according the a necessity, a metal plated layer such as a nickel plated layer covering the exposed parts of surface electrode layer 23 and side-electrode layer 28 is formed, and at the same time, a solder plated layer (not shown) made of an alloy of tin and lead is disposed over the metal plated layer, and by this, the resistors are produced. Although a case where a protection layer is made of a boro-silicate lead glass material has been explained for far, nearly the same effects could be obtained by using an epoxy resin material. In addition to this, although a mixed paste material obtained by mixing silver and glass is used as a side-electrode material has been explained in this embodiment of the invention, the same effects could be obtained even when a mixed material consisted of nickel and phenol resin were used. Results experimenting the resistors of above-construction and obtained with the conventional resistors mounting on circuit boards are now explained in below. (Experimental Method) Using an automatic electronic component placement machine (made by Matsushita Elec. Ind. Co. Ltd., Panasert MV2), a bulk one by one cassette mounting is performed, then a re-flow soldering is fulfilled at 200-250ºC for 10-30 seconds thus resistors are mounted on a circuit board. In this situation, about half of the resistors are soldered to the terminals of the circuit board facing downwardly. (Judgments of The Results) As for the resistor chips of which a side is not bonded as shown in Fig. 4(a), the cases where one sides of solder lands are found unsoldered are judged unacceptable. As for the miss-registration of mounting angle to the soldering land on the circuit board, the cases where the resistors on the soldering lands are found rotated for more than an angle of 0.2 degree are judged unacceptable. Table 1 shows relationships between the heights of side-electrode layer above the surface of protection layers and the unacceptable mountings for the experimented resistors having a construction of the first example and for the conventional resistors. Conventional Example-1 Conventional Example-2 Experimented Example-1 Experimented Example-2 Height differences, protection layer/side-electrode (µm) -5 0 5 10 Exp. Unacceptable 25 4 0 0 Results connections Off-angle Mountings 100 16 2 0 As shown in Table 1, since the invented resistors are provided with side-electrode layers disposed at a height higher than the surface of protection layer by more than 5 microns, the numbers of unacceptable connections are far less than the cases of conventional resistors. The cases of a second example are now explained below. Fig. 5 shows a cross-section of the resistor which is a second example. In Fig. 5, 31 is a substrate made of a material such as alumina. 32s are a pair of surface electrode layers made of a mixed material consisted of silver and glass which is preferred to be disposed up to the ends of substrate 31. 33 is a pair of back electrode layers made of a mixture of silver and glass, and it is preferable to dispose them to the side ends of the substrate 31. 34 is a resistor layer made mainly of a mixed material obtained by mixing ruthenium oxide and glass disposed on the surface of substrate 31 and superposed on the both ends of upper electrode layers 32 also in order to establish electrical connections thereto. 35 is a protection layer made mainly of a boro-silicate lead glass disposed to cover at least the surface of resistor layers 34. 36 is a side-electrode layer made mainly of a mixed material obtained by mixing silver and glass, and is disposed on the sides of substrate 31, superposed both ends of surface electrode layers 32, and on a part of the surface of surface electrode layers 32, establishing electrical connections thereto, making the supperposed part is higher than the surface of protection layer 35, and the edges of side-electrode layers 36 rounded. 37 is an electro-plated layer such as a nickel plated layer covering the side-electrode layers 36 if necessary. 38 is a solder layer covering plated layer 37 if necessary, and said solder layer should preferably be provided with rounded edges. As for the resistors of above-explained construction, its manufacturing method is now explained by referring the attached drawings Figs. 6 and 7 which show manufacturing processes of resistor which is a second example. As shown in Fig. 6(a), after a mixed paste material consisted of silver and glass is screen-printed on a sheet-shaped substrate 42 provided with vertical and horizontal dividing grooves 41 on its both surfaces, the paste is dried. Then, after the sheet-shaped substrate 42 is reversed and the same paste material is screen-printed again over the dividing grooves (not shown) and is dried. After this, substrate 42 is sintered in a belt-type continuous furnace at a temperature of about 850°C for a period of about 45 minutes forming surface electrode layer 43 and back electrode layer 44. Then, as shown in Fig. 6(b), after a mixed paste material consisted of ruthenium oxide and glass is screen-printed on the surface of sheet-shaped substrate 42 crossing over the respective edges of surface electrode layer 43 and connecting these electrically, a printed mixed paste material is dried and placed in a belt-type continuous furnace and is sintered at a temperature of about 850°C for a period of about 45 minutes forming resistor layers 45. As shown in Fig. 6(c), by using a laser trimmer or such, a trimming process to trim the resistance of resistor layer 45 and to form trimming grooves 46. At this time, after the surface of resistor layer 45 (not shown) is coated with a material such as glass, both the coating layer and the resistor layer may be trimmed at once by using a laser trimmer through the coating layer, and by this, trimming grooves 46 are formed. Then, as shown in Fig. 6(d), after a mixed paste material made of boro-silicate lead glass is screen-printed on the surface of resistor layer 45 covering completely the surface of resistor 45, the paste is dried and is sintered in a belt-type continuous furnace at a temperature of about 850°C for a period of about 45 minutes forming protection layer 47. Then, as shown in Fig. 7(b), sheet-shaped substrate 42 is divided along dividing grooves 41 exposing surface electrode layers 43 from the side of substrate, and rectangular-shaped substrates 48 are obtained. In next, as shown in Fig. 7(b), after a mixed paste material consisted of silver and glass is transfer printed by using a roller on the both sides of rectangular substrates 48 superposing on a part of surface electrode layers 43, making the superposed area is higher than the surface of protection layer 47 at the same time, the paste is dried and is sintered in a belt-type continuous furnace at a temperature of about 600°C for a period of about 45 minutes, and by this, side electrode layers 47 are formed. As shown in Fig. 7(c), then, rectangular substrate 48 is divided into individual resistors 50. Then, at the last, by forming a plated layer (not shown) of such as a nickel plated layer covering the exposed parts of sur-face electrode layer 43 and side-electrode layer 49 if needed, and by forming a solder layer (not shown) made of an alloy of tin and lead covering said plated layer, the resistors can be obtained. Although cases using a boro-silicate lead glass as a material of the protection layer have been explained, the same effects can be obtained by using an epoxy resin system material. Although cases using a mixed material consisted of silver and glass as a material of side electrode have been explained in this embodiment of the invention, the same effects can be obtained by using a mixed material consisted of nickel and phenol resin. The experimental results obtained by mounting the resistors of a above-explained construction and the conventional resistors are now explained in the followings. The experimental method and the judgment of the results employed in these experiments are identical with those shown in a first example. Table 2 shows relationships between the heights of side-electrode layers above the surface of protection layers and the unacceptable connections for the experimental resistors having a second construction and the conventional resistors. Conventional Example-1 Conventional Example-2 Experimented Example-1 Experimented Example-2 Height differences, protection layer/side-electrode (µm) -5 0 5 10 Exp. Unacceptable 32 2 0 0 Results Connections Off-angle Mountings 83 9 0 0 As shown in Table 2, since the invented resistors are provided with side-electrode layers disposed at a height higher than the surface of protection layer by more than 5 microns, the number of unacceptable connections are far less than the ones in the cases of conventional resistors. A first embodiment of the invention is now explained by referring Fig. 8 showing a cross-section of resistor which is a first embodiment of the invention. In Fig. 8, 51 is a substrate made of a material such as alumina. 52 are a pair of the first surface electrode layers made of a mixed material consisted of silver and glass, and this would be preferred to dispose up to the side ends of substrate 51. 53 is a resistor layer made mainly of a mixed material consisted of ruthenium oxide and glass disposed on the surface of substrate 51 and on the both ends of the first surface electrode layer 52 making electrical connections thereto. 54 is a protection layer made mainly of a boro-silicate lead glass or epoxy resin disposed to on first surface electrode layer 52 and resistor layers 53, and preferably to the side ends of substrate 51. 55 are a pair of second surface electrode layers made mainly of a mixed material consisted of silver and glass or made of phenol resin disposed preferably to the side ends of substrate 51. 56 are side electrode layers made mainly of a mixed material consisted of silver and glass electrically connecting the side of the substrate 51, the first surface electrode layer 52 and the second surface electrode layer 55, and these are provided with rounded edges. 57 is a nickel plated layer covering side-electrode layer 56. 58 is a solder layer disposed to cover plated layer 57 if necessary, having rounded edges preferably. As for the resistor layer of above-explained construction, its manufacturing method is now explained below by referring the attached drawings Figs. 9 and 10 showing its manufacturing processes. As shown in Fig. 9(a), after a mixed paste material made of silver and glass is screen-printed on horizontal dividing grooves 61 disposed on sheet-shaped substrate 62 made of alumina or others provided with both the horizontal and vertical dividing grooves, the paste is dried, and is sintered in a belt-type continuous furnace at a temperature of about 850°C for a period of about 45 minutes forming first surface electrode layers 63. As shown in Fig. 9(b), then, after a mixed paste material made of ruthenium oxide and glass is screen-printed on the surface of sheet-shaped substrate 62 in order to establish electrical connections betwen first surface electrode layers 63, this is placed in a belt-type continuous furnace to dry and is sintered at a temperature of about 850°C for a period of about 45 minutes, forming resistor layers 64. As shown in Fig. 9(c) in next, by using a laser trimming device or such, a process to trim the resistance of resistor layer 64 is performed, and by this, trimming grooves 65 are formed. At this time, after the surface of resistor layer 45 is coated (not shown) by a material such as glass, both the coating layer and the resistor layer 64 may be trimmed through the coating layer, and by this, trimming grooves 65 are formed. In next, as shown in Fig. 9(d), after a boro-silicate lead glass paste is screen-printed on the entire surfaces of first surface electrode layer 63 and resistor layer 64, the paste is dried and is sintered in a belt-type continuous furnace at a temperature of about 600°C for a period of about 45 minutes, forming protection layer 66. At this time, protection layer 66 has to be deposited to cover at least first surface electrode layer and resistor layer 64. Then, as shown in Fig. 10(a), a paste material consisted of silver and glass is screen-printed on the surface of protection layer 66 and dried. This is then placed in a belt-type continuous furnace and is sintered at a temperature of about 600°C for a period of about 45 minutes forming the second surface electrode layer 67. Then, in next, as shown in Fig. 10(b), sheet-shaped substrate 62 is divided along dividing grooves 61 exposing the first and the second surface electrode layers from the sides of substrate, and rectangular substrates 68 are formed by this. Then, as shown in Fig. 10(c), a mixed paste material consisted of silver and glass is transfer-printed by a roller on the sides of rectangular substrate 68 in order to electrically connect first surface electrode layer 63 to second surface electrode layer 67 and dried. This is then placed in a belt-type continuous furnace and is sintered at a temperature of about 600°C for a period of about 45 minutes forming side-electrode layers 69. As shown in Fig. 3(d), rectangular substrate 68 is divided into individual substrates producing individual resistor chips 70. Then, at the last, according to a neccessity, an electro-plated layer (not shown) such as a nickel plated layer is formed to cover side-electrode layer 69, and at the same time, a solder layer (not shown) such as a layer on which an alloy of tin and lead is plated is deposited, and by this, the resistors are produced. The experimental results obtained by mounting the resistors of above-explained construction and the conventional resistors on circuit boards are now explained below. The experimental methods and the judgments of the results employed in these experiments are identical with those shown in the first example. Table 3 shows relationships between the heights of second surface electrode layers above the surface of protection layers and the unacceptable mountings for the experimental resistors of a second construction and the conventional resistors. Conventional Example-1 Conventional Example-2 Experimented Example-1 Experimented Example-2 Height differences protection layer/ second surface electrode (µm) -5 0 5 10 Exp. Unacceptable 25 2 0 0 Results Connections Off-angle Mountings 105 13 2 0 As shown in Table 3, since the inventive resistors are provided with second surface electrode layers disposed at a height higher than the surface of protection layer by more than 5 microns, the number of unacceptable connections are far less than the cases obtained with conventional resistors. Likewise, Table 4 shows relationships between the heights of side electrode layers above the surface of protection layers and the unacceptable connections. Conventional Example-1 Conventional Example-2 Experimented Example-1 Experimented Example-2 Height ratios protection layer/side-electrode (µm) -10 0 10 20 Exp. Unacceptable 20 1 0 0 Results Connections Mounting Off-Angle 100 14 0 0 As shown in Table 4, since the invented resistors are provided with the side electrode layers disposed at a height higher than the surface of protection layer by more than 10 microns, the number of unacceptable connections are far less than the cases of conventional resistors. The resistors and its manufacturing method of a second embodiment of the invention are now explained by referring the attached drawings. Fig. 11 shows a cross-section of the resistor which is a second embodiment of the invention. In Fig. 11, 71 is a substrate made of alumina or others, 72 are a pair of first surface electrode layers made of a mixed material consisted of silver and glass disposed on both end surfaces of substrate 71, and are preferably disposed up to the ends of side of substrate 71. 73 are a pair of back electrode layers made of a mixed material consisted of silver and glass disposed on the both ends of the back surface of substrate 71, which are preferably disposed up to the side ends of substrate 71. 74 is a resistor layer made of a mixed material consisted of ruthenium oxide and glass disposed on the surface of substrate 71 and superposed on to the both ends of first surface electrode layers 72 making electrical connections thereto. 75 is a protection layer made of boro-silicate lead glass disposed to cover at least first surface electrode layer 72 and resistor layer 74, and is preferably extended to the side end of substrate 71. 76 are a pair of second surface electrode layers made of a mixed material consisted of silver and glass disposed on the both ends of protection layer 75, and is preferably disposed up to the side-end of substrate 71 having a shape same as the one of back electrode layer 73. 77 is a side electrode layer made of a mixed material consisted of silver and glass disposed to electrically combine the sides of substrate 71, first surface electrode layer 72, and the both ends of second surface electrode layer 76, where said side-electrode layers are preferably provided with rounded edges. 78 is an electro-plated layer such as a nickel plated layer disposed to cover side-electrode layer 77 if necessary. 79 is a solder layer disposed preferably to cover nickel-plated layer 78, where the edges of solder layer 79 are preferably provided with rounded edges. For the resistors of above-explained construction, its manufacturing method is now explained below by referring the attached drawings Figs. 12 and 13 showing manufacturing processes of the resistor which is a second embodiment of the invention. As shown in Fig. 12(a), a mixed paste material made of silver and glass is screen-printed on sheet-shaped substrate 82 made of alumina provided with horizontal and vertical dividing grooves 81 in order to cross the horizontal dividing groove 81, and the paste is dried. Next, a mixed paste material made of silver and glass is screen-printed on the back surface of sheet-shaped substrate 82 provided with horizontal and vertical dividing grooves (not shown). Then, placed in a belt-type continuous furnace, the paste is sintered at a temperature of about 850°C for a period of about 45 minutes, forming first surface electrode layer 83 and back electrode layer 84. As shown in Fig. 12(b), then, after a mixed paste material made of ruthenium oxide and glass is screen-printed on the edges of first surface electrode layers disposed on sheet-shaped substrate 82 establishing superposed areas and electrical connections there between on the both ends of first suface electrode layers, the paste is dried and sintered in a belt-type continuous furnace at a temperature of about 850°C for a period of about 45 minutes, forming resistor layers 85. As shown in Fig. 12(c), by means of a laser trimmer, the resistance of resistor layer is trimmed and trimming grooves 86 are formed. However, said trimming grooves 86 may be formed by applying said laser trimmer through a coating layer (not shown), trimming both said coating layer and the resistor layer 85 which are deposited in advance. Then, as shown in Fig. 12(d), after a paste made of boro-silicate lead glass is screen-printed on first surface electrode layer 83 and resistor layer 85 covering of these surfaces, the paste is dried and is sintered in a belt-type continuous furnace and at a temperature of about 600°C for a period of about 45 minutes, forming protection layer 87. In this case, protection layer 87 has to be disposed to cover at least the surfaces of first surface electrode layer 83 and resistor layer 85. Then, as shown in Fig. 13(a), after a mixed paste made of silver and glass is screen-printed on the surface of protection layer 87, the paste is dried and sintered in a belt-type continu-ous furnace at a temperature of about 600°C for a period of about 45 minutes forming second surface electrode layer 88. As shown in Fig. 13(b), then, by dividing sheet-shaped sub-strate 82 along dividing grooves 81, first and second surface electrode layers are exposed from the sides of substrate, rectangular substrates 89 are formed. As shown in Fig. 13(c) in next, a mixed paste made of silver and glass is transfer-printed in order to electrically connect first surface electrode layer 83 and second surface electrode layer 88. After this, the paste is dried and is sintered in a belt-system continuous furnace at a temperature of about 600°C for a period of about 45 minutes, and side-electrode layer 90 is formed. Then, individual resistors are formed by dividing rectan-gular substrate 89 into individual resistors as shown in Fig. 13(d). Then, according to the necessity, an electro-plated layer (not shown) made of a nickel plated layer or others, is formed to cover side-electrode layer 90, and at the same time, a solder layer (not shown) made of an alloy of tin and lead covering said plated layer is disposed, and by this, the resistors are produced at the last. The experimental results mounting the resistors having an above-explained construction and the conventional resistors mounted on circuit-boards are explained in below. The experi-mental method and the judgments of the results employed in these case are identical with those shown in a first embodiment of the invention. Table 5 shows experimental results obtained with the resistors of a fourth construction and the relationships between the heights of second surface electrode layers above the surface of protection layers and the number of unacceptable mountings with the conventional resistors. Conventional Example-1 Conventional Example-2 Experimented Example-1 Experimented Example-2 Height differences protection layer/second surface electrode (µm) -5 0 5 10 Exp. Unacceptable 26 3 0 0 Results Connections Off-angle Mountings 98 12 1 0 As shown in Table 5, since the invented resistors are provided with second surface electrode layers disposed at a height higher than the surface of protection layer by more than 5 microns, the numbers of unacceptable connections are far less than the cases obtained with the conventional resistors. Likewise, Table 6 shows relationships between the heights of side-electrode layer above the protection layers and the unacceptable mountings. Conventional Example-1 Conventional Example-2 Experimented Example-1 Experimented Example-2 Height differences protection layer/side-electrode (µm) -10 0 10 20 Exp. Unacceptable 22 3 0 0 Results Connections Off-angle Mountings 101 12 0 0 As shown in Table 6, since the resistors of this embodiment of the invention are provided with the side-electrode layers disposed at a height higher than the surface of protection layer by more than 10 microns, the numbers of unacceptable connections are far less than the cases using the conventional resistors. The resistors of a third embodiment are now explained by referring the attached drawings. Fig. 14 shows a perspective view of the resistor of a third embodiment, and the differences of this from first and second embodiments of the invention are that second surface electrode layer 88 of the resistor divided into individual resistor pieces is provided with a width same as the width of substrate 89 as shown in Fig. 14 and those are provided with notched corners 88a on the corners of mutually facing edges of second surface electrode layer. By providing these notches 88a, the bonding area are enlarged and the bonding strength are increased, and at the same time, the possible peeling of resistor from the circuit board are prevented. The resistors of a third example and its manufacturing method are now explained by referring the attached drawings. Fig. 15(a) shows a perspective view of the resistor of a third example, and Fig. 15(b) is a perspective view from the back of the same, and Fig. 16 shows a cross-section of the same. In Figs. 15 and 16, 91 is a substrate made of alumina or others, 92 are a pair of first surface electrode layers made of a mixed material consisted of silver and glass disposed on both end surfaces of substrate 91, and these are preferably extended to the side ends of substrate 91. 93 is a resistor layer made of a mixed material consisted of ruthenium oxide and glass superposed on the both ends of first surface electrode layer 92 making electrical connections there between. 94 is a protection layer made either of a boro-silicate lead glass or an epoxy system resin disposed to cover first surface electrode layer 92 and resistor layer 92, having window 99 disposed on first surface electrode layer 92, and these are preferably disposed up to the side of substrate 91. 95s are a pair of second surface electrode layers made of a mixed material consisted of silver and glass or a phenol resin system resin disposed on the side of protection layer 94 in order to be electrically connected to first surface electrode layer 92 through window 99 disposed on protection layer 94, and this is preferably disposed up to the side of substrate 61. A pair of angled corners 95a disposed on the mutually facing edges of second surface electrode layer 95 are provided with protrusions respectively as shown in Fig. 15(a). 96s are side-electrode layers made of a mixed material consisted of silver and glass disposed on the sides of substrate 91 and on first and second surface electrode layers 92 and 95 to make electric connections, and side-electrode layer 96 are provided with rounded edges. 97 is an electro-plated layer such as a nickel-plated layer disposed to cover side-electrode layer 97 if necessary, 98 is a solder layer disposed to cover said nickel-plated layer 97 if necessary, and preferably solder layer 98 is provided with rounded edges. As for the resistor of abode-shown construction, its manufacturing method is explained in below by referring the attached drawings. Figs. 17 and 18 show manufacturing processes of the resistor which is a third example. As shown in Fig. 17(a), after a mixed paste material consisted of silver and glass is screen-printed on sheet-shaped substrate 102 made of alumina provided with vertical and horizontal divid-ing grooves 101 crossing over horizontal dividing grooves 101, the paste is dried and sintered in a belt-type continuous furnace at a temperature of about 850°C for a period of about 45 minutes, forming first surface electrode layers 103. In next, as shown in Fig. 17(b), a mixed paste material consisted of ruthenium oxide and glass is screen-printed on each end of first surface electrode layers 103 disposed on sheet-shaped substrate 102 making electrical connections between the first surface electrode layers 103. Then, after this, the paste is dried and sintered in a belt-type continuous furnace at a temperature of about 850°C for a period of about 45 minutes, forming resistor layer 104. Then, as shown in Fig. 17(c). a trimming process by using a laser trimmer is performed in order to trim the resistance of resistor layer 104, forming trimming grooves 106. However, said trimming process may be performed after at least the surface of resistor layer 104 is coated by glass and trimming grooves 105 are formed by trimming the coated layer (not shown) and resistor layer 104 simultaneously through the coating layer (not shown) disposed on resistor layer 104. As shown in Fig. 17(d), a paste made of boro-silicate lead glass is screen-printed to cover first surface electrode layer 103 and resistor layer 104, making window 110 disposed on first surface electrode layer 103. After this, the paste is dried and sintered in a belt-type continuous furnace at a temperature of about 600°C for a period of about 45 minutes, forming protection layer 106. At this time, protection layer 106 has to be deposited to cover at least first surface electrode layer 103 and resistor layer 104. Then, as shown in Fig. 18(a), after a mixed paste material consisted of silver and glass is screen-printed establishing electrical connections to the first surface electrode layer through window 110 of protection layer 106, the paste is dried and sintered in a belt-system continuous furnace at a temperature of about 600°C for a period of about 45 minutes, forming second surface electrode layers 107. At this time, corners 107a each having a shape of protrusion 107a are provided on the mutually facing edge surfaces of second surface electrode layer 107 disposed along vertical dividing grooves 101 provided on sheet-shaped substrate 102. Then, as shown in Fig. 18(b) next, sheet-shaped substrate 102 is divided along dividing grooves 101 exposing first and second surface electrode layers from the sides of substrate, forming rectangular substrates 108. As shown in Fig. 18(c) in next, after a mixed paste material consisted of silver and glass is transfer-printed by a roller on the side of rectangular substrate 108 in order to electrically connect first surface electrode layer 103 to second surface electrode layer 107, the paste is dried and sintered in a belt-type continuous furnace at a temperature of about 600°C for a period of about 45 minutes, forming side-electrode layers 109. Then, as shown in Fig. 18(d), rectangular substrate 108 is divided into individual substrates forming individual resistor pieces. At the last, after forming an electro-plated layer (not shown) made of electro-plated nickel covering the side electrode layer 109 if necessary, a solder layer (not shown) of electro-plated alloy made of tin and lead covering said electro-plated layer is disposed if necessary, and the individual resistors are obtained. The experimental results mounting the resistors having above-explained constructions and the conventional resistors on circuit-boards are explained in below. The experimental methods and the method of judgment employed in these experiments are identical with those shown in a first embodiment of the invention. Table 7 shows experimental results obtained with the resistors having a third example and relationships between the heights of second surface electrode layers above the protection layers and the number of unacceptable mountings for the conventional resistors. Conventional Example-1 Conventional Example-2 Experimented Example-1 Experimented Example-2 Height differences protection layer/second surface electrode (µm) -5 0 5 10 Exp. Unacceptable Results Connections 18 3 0 0 Off-angle Mountings 50 7 0 0 As shown in Table 7, since the resistors of this example are provided with the second surface electrode layers disposed at a height higher than the surface of protection layer by more than 5 microns, the number of unacceptable connections are far less than those in the cases of conventional resistors. Likewise, Table 8 shows relationships between the heights of side-electrode layers above the surface of protection layers and the unacceptable connections. Conventional Example-1 Conventional Example-2 Experimented Example-1 Experimented Example-2 Height differences protection layer/side-electrode (µm) -10 0 10 20 Exp. Unacceptable Results Connections 14 1 0 0 Off-angle Mountings 61 6 0 0 As shown in Table 8, since the resistors of this example are provided with side-electrode layers disposed at a height higher than the surface of protection layer by more than 10 microns, the numbers of unacceptable connections are far less than the cases of conventional resistors. The resistor which is a fourth example is now explained by referring the attached drawings. Fig. 19(a) shows a higher perspective view of resistor which is a fourth example, Fig. 19(b) is a perspective view viewed from the back, and Fig. 20 shows a cross-section of the same resistor. In these drawings, 111 is a substrate made of alumina or others, 112s are a pair of first surface electrode layers made of a mixed material consisted of silver and glass disposed on both ends of the surface of substrate 111, and are disposed preferably up to the side ends of substrate 111. 113s are a pair of back surface electrode layers made of a mixed material consisted of silver and glass disposed on both ends of the back of substrate 111, like a case of first surface electrode layer 112, this should preferably be disposed up to the side-ends of substrate 111. Corner parts 113s of back electrode layer 113 are disposed at both mutually facing ends of the edges of a pair of back electrode layers. 114 is a resistor layer made of a mixed material consisted of ruthenium oxide and glass disposed on the surface of substrate 111 and superposed on both ends of first surface electrode layer 112 establishing electrical connections there between. 115 is a protection layer made of boro-silicate lead glass disposed to cover the surfaces of first upper electrode layer 112 and resistor layer 114 having window 120 on first surface electrode layer 112, and this layer should preferably be disposed up to the sides of substrate 111. 116s are a pair of second surface electrode layers made of a mixed material consisted of silver and glass disposed on both ends of the surface of protection layer 115 electrically connecting protection layer 115 to first surface electrode layer 112 through window 120 disposed on protection layer 115, and this should preferably be disposed up to the sides of substrate 111, and should also have a shape same as the back electrode 113. The corner parts 116a of second surface electrode layer 116 are disposed on both sides of a pair of the mutually facing edges of second surface electrode layer 116. 117s are side-electrode layers made of a mixed material consisted of silver and glass disposed to electrically connect first and second surface electrode layers 112 and 116, and side-electrode layers 117 which are provided with rounded edges. 118 is an electro-plated layer such as a nickel-plated layer disposed to cover side-electrode layers 117 if necessary, and 119 is a solder layer disposed to cover nickel-plated layer 118 and solder layer 119 is preferably provided with rounded edges. With the resistors of a construction of above, its manufacturing method is now explained in below by referring the attached drawings. Figs. 21 and 22 show manufacturing processes of a resistor which is a fourth example. As shown in Fig. 21(a), a mixed paste material consisted of silver and glass is screen-printed on sheet-shaped substrate 122 made of alumina provided with vertical and horizontal dividing grooves 121 on its surface and back, crossing horizontal dividing grooves 121. After the paste is dried, the same paste made of silver and glass is screen-printed on the back of sheet-shaped substrate 122 crossing the dividing grooves (not shown) and dried. After this, the paste is sintered in a belt-type continuous furnace at a temperature of about 850°C for a period of about 45 minutes, forming first surface electrode layer 123 and back electrode layer 124. At this time, the corners (not shown) of back electrode layer 124 are disposed at the edges where a pair of edges of back electrode layer 124 face each other. As shown in Fig. 21(b) in next, after a mixed paste material consisted of ruthenium oxide and glass is screen-printed on sheet-shaped substrate 122 in order to operlap the both ends of first surface electrode layers 123 and to electrically combine first surface electrode layers 123, the paste is dried and sintered in a belt-system continuous furnace at a temperature of about 850°C for a period of about 45 minutes, and resistor layers 125 are formed by this. Then, as shown in Fig. 21(c). a trimming process is perform-ed in order to trim the resistance of resistor layer 125, forming trimming grooves 126. However, said trimming processes 126 may be formed after at least the surface of resistor layer 125 (not shown) is coated by glass, and by trimming the glass-coated layer and resistor layer 125 together through the coated layer by using a laser trimmer. As shown in Fig. 21(d), a paste made of boro-silicate lead glass is screen-printed in order to cover first surface electrode layer 123 and resistor layer 125, where window 131 disposed on first upper electrode layer 123. After this, the paste is dried and sintered in a belt-system continuous furnace at a temperature of about 600°C for a period of about 45 minutes, forming protection layer 127. Then, as shown in Fig. 22(a), after a mixed paste material consisted of silver and glass is screen-printed on first surface electrode layer in order to establish an electrical connection thereto through window 131 of protection layer 127, the paste is dried and sintered in a belt-type continuous furnace at a temperature of about 600°C for a period of about 45 minutes, forming second surface electrode layers 128. At this time, corner parts 128s each having a shape of protrusion are disposed on the mutually facing edges of second surface electrode layer 128 disposed along vertical dividing grooves 121 provided on sheet-shaped substrate 122. Then in next, as shown in Fig. 22(b). sheet-shaped substrate 122 is divided along dividing grooves 121 exposing first and second surface electrode layers from the side of substrate, forming rectangular substrates 129. As shown in Fig. 22(c), after a mixed paste material consisted of silver and glass is then transfer-printed by a roller in order to establish electrical connections between first surface electrode layer 123 and second surface electrode layer, the paste is dried and sintered in a belt-system continuous furnace at a temperature of about 600°C for a period of about 45 minutes, forming a pair of side-electrode layers 130. Then, as shown in Fig. 22(d), rectangular-shaped substrate 129 is divided in individual substrates forming individual resistor pieces. At the last, as forming an electro-plated layer (not shown) such as a nickel-plated layer covering the side-electrode layer 130 according to the necessity, a solder layer (not shown) made of a layer of alloy consisted of tin and lead covering said nickel-plated layer is disposed, and the resistors are obtained. The experimental results mounting the resistors having the above-explained constructions and the conventional resistors on circuit-boards are explained in below. The experimental methods and the method of judgment of the results employed in these experiments are identical with those shown in the first embodiment of the invention. Table 9 shows experimental results obtained with the resistors of the fourth example and relationships between the heights of second surface electrode layers above the surface of protection layers and the unacceptable connections of conventional resistors. Conventional Example-1 Conventional Example-2 Experimented Example-1 Experimented Example-2 Height differences protection layer/second surface electrode (µm) -5 0 5 10 Exp. Unacceptable 17 2 0 0 Results Connections Off-angle Mountings 56 8 0 0 As shown in Table 9, since the resistors of this example are provided with second surface electrode layers disposed at a height higher than the surface of protection layer by more than 5 microns, and corners disposed respectively on the edges of second surface electrode layer and back electrode layer, the numbers of unacceptable connections are far less than the cases employing the conventional resistors. Likewise, Table 10 shows relationships between the heights of side-electrode layer above the surface of protection layers and the unacceptable connections. Conventional Example-1 Conventional Example-2 Experimented Example-1 Experimented Example-2 Height differencesprotection layer/side-electrode (µm) -10 0 10 20 Exp. Unacceptable 16 1 0 0 Results Connections Off-angle Mountings 63 7 0 0 As shown in Table 10, since the resistors of this example are provided with side-electrode layers disposed at a height higher than the surface of protection layer by more than 10 microns, the number of unacceptable connections are far less than the cases of conventional resistors. According to the resistors of this invention, since the side-electrode layer or the second surface electrode layer is disposed at a height higher than the protection layer, the resistors can be mounted on the circuit board regardless the surface or the back of resistors with excellent mounting reliability.

Claims: A resistor comprising; a substrate (51, 71) having an upper surface and a side surface, a pair of surface electrode layers (52, 72), wherein one surface electrode layer (52, 72) of said pair of surface electrode layers (52, 72) is disposed on a lateral part on the upper surface of said substrate (51, 71), and the other surface electrode layer (52, 72) of said pair of surface electrode layers (52, 72) is disposed on an opposing lateral part on said upper surface of said substrate (51, 71), a resistor layer (53, 74) disposed to electrically connect said surface electrode layers (52, 72), a protection layer (54, 75) disposed to cover at least said resistor layer (53, 74), and a side-electrode layer (56, 77) disposed on the side surface of said substrate (51, 71), said side-electrode layer (56, 77) being superposed on at least a part of one of said surface electrode layers (52, 72), and being electrically connected to said surface electrode layer (52, 72), said superposed part of said side-electrode layer (56, 77) protruding from the surface of said protection layer (54, 74), characterized in that said protection layer (54, 74) is disposed to cover the entire surface of said surface electrode layers (52, 72). The resistor of claim 1, wherein said superposed part of said side-electrode layer (56, 77) is formed at a height higher than the surface of said protection layer (52, 72) by more than 5 µm (5 microns). The resistor of claim 1 or 2, further comprising: a pair of back electrode layers (33) disposed respectively on both end surfaces of the back of said substrate (31), wherein said side-electrode layers (30) are disposed on the side of said substrate (31) superposing on a part of said surface electrode layer (32) and on a part of said back electrode layer (33) making electrical connections to said superposed parts of electrode layer (32) and making said superposed parts protruded out of the surface of said protection layer (35). The resistor according to any of claims 1 to 3, wherein said side electrode layer (56, 77) is superposed on a part of said protection layer (54, 74). The resistor according to claim 1, wherein said pair of surface electrode layers is a pair of first surface electrode layers (52) disposed on both end surfaces of said substrate (51), wherein said resistor layer (53) is disposed on said substrate (51) making an electrical connection to said first surface electrode layer (52), said protection layer (54) is disposed to cover at least said first surface electrode layer (52) and the surface of said resistor layer (53), and wherein a pair of second surface electrode layers (55) is disposed on the side surface of said substrate (51), and said side-electrode layer (56) is disposed on the side of said substrate (51) making electrical connections to said first and second surface electrode layers (52,55). The resistor of claim 1, wherein said pair of surface electrode layers is a pair of first surface electrode layers (72) said first surface electrode layers (72) and a pair of back electrode layers (73), respectively, are disposed on the surface and the back of said substrate (71), said resistor layer (74) is disposed on the surface of said substrate (71) making an electrical connection to said first surface electrode layer (72), said protection layer (75) is disposed to cover said first surface electrode layer (72) and said resistor layer (74), and wherein a pair of second surface electrode layers (76) is disposed on the surface of said protection layer (75), and said side electrode layer (77) is disposed at least on the side of said substrate (71) electrically connecting said first and second surface electrode layers (72,76) with said back electrode layer (73). The resistor according to claims 5 or 6, wherein said second surface electrode layer (88) facing to the side of said substrate (89) is provided with a notch (88a). The resistor of claim 1, wherein said pair of surface electrode layers is a pair of first surface electrode layers (92) disposed on both end surfaces of said substrate (91); wherein said resistor layer (93) is disposed on the surface of said substrate (91) making an electrical connection to said first surface electrode layer (92), said protection layer (94) is disposed to cover at least said first surface electrode layer (92) and said resistor layer (93), a pair of second surface electrode layers (95) disposed on both end surfaces of said protection layer (94), and side electrode layers (96) disposed at least on the sides of said substrate (91), electrically combining said first and said second surface electrode layers (92,95), wherein said second surface electrode layer (95) is provided with comers (95a) at the mutually facing ends of said second surface electrode (95). The resistor of claim 1, wherein said pair of surface electrode layers is a pair of first surface electrode layers (112), and wherein said pair of first surface electrode layers (112) and back electrode layers (113) are disposed on the surface and the back of said substrate (111), said resistor layer (114) is disposed on the surface of said substrate (111) electrically connecting to said first surface electrode layer (112), said protection layer (115) is disposed to cover at least the surfaces of said first surface electrode layer (112) and said resistor layer (114), a pair of second electrode layers (116) is disposed at least on both end surfaces of said protection layer (115), and side electrode layers (117) are disposed on the sides of said substrate (111), electrically connecting said first and second surface electrode layers (112,116) and said back electrode layer (113), wherein said second surface electrode layer (116) is provided with corners (116a) at the mutually facing ends of said second surface electrode layer (112,116). The resistor according to either of claims 6, 8, or 9, wherein said back electrode (73) is disposed to the side end of said substrate (71). The resistor according to either of claims 5, 6, 8, or 9, wherein said second surface electrode layer (55) is disposed at a height higher by more than 5µm (five microns) above the surface of said protection layer (54). The resistor according to either of claims 5, 6, 8, or 9, wherein said side electrode layer (36) is covered with a solder layer (37) and is disposed at a height higher by more than 10 µm (ten microns) above said protection layer (35). The resistor according to either of claims 5, 6, 8, or 9, wherein the edges of said side electrode layer (36) or said solder layer (37) are rounded. The resistor according to either of claims 5, 6, 8, or 9, wherein said first surface electrode layer (32) is made of a silver system material. The resistor according to either of claims 5, 6, 8, or 9, wherein said protection layer (35) is made of a glass or a resin material. The resistor according to either of claims 5, 6, 8, or 9, wherein said second surface electrode layer (55) is made of an electro-conductive material containing at least a glass or a resin material. The resistor according to either of claims 5, 6, 8, or 9, wherein said side electrode layer (36) is made of an electro-conductive material containing at least a glass or a resin material. The resistor according to either of claims 5, 6, 8, or 9, wherein said second surface electrode layer (76) and said back electrode layer (73) have a same shape.

Inventors: HASHIMOTO MASATO, MORI SHOJI, NAKAYAMA SHOGO, SHIRAI TAKUMI, TAKASHIMA NAOHIRO, TSUDA SEIJI, HASHIMOTO, MASATO, MORI, SHOJI, NAKAYAMA, SHOGO, SHIRAI, TAKUMI, TAKASHIMA, NAOHIRO, TSUDA, SEIJI
Applicants: MATSUSHITA ELECTRIC IND CO LTD, MATSUSHITA ELECTRIC INDUSTRIAL CO., LTD.
Application year: 1997
Main classification: H01C17
IPC codes: H01C1, H05K3, H01C17