Electrical resistors – With base extending along resistance element – Resistance element coated on base
Patent
1999-04-08
2000-12-26
Lam, Cathy
Electrical resistors
With base extending along resistance element
Resistance element coated on base
338308, 338311, 338323, 338332, H01C 1012
Patent
active
061666203
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to the field of resistance wiring boards used for a wide range of types of electronic components, particularly for chip resistors, and their manufacturing methods.
BACKGROUND OF THE INVENTION
Conventionally, a resistance 6 is formed in a resistance wiring board as described in the following steps shown in FIGS. 8A to 8E. An insulated substrate 4 typically containing alumina (aluminum oxide, Al.sub.2 O.sub.3) is fired at around 1,600.degree. C., and electrode paste such as Ag is printed on the fired insulated substrate 4. It is then fired at around 850.degree. C. to form an electrode 5. Resistance paste made typically of RuO.sub.2 and glass paste to create an insulated protective film are then printed and fired at around 650.degree. C. to complete the resistance 6.
When a resistance wiring board is used as a laminated substrate, electrode paste and resistance paste are patterned on a green sheet of low-temperature firing substrate made typically of glass-aluminum by means of such as printing, and then fired at around 900.degree. C.
The accuracy of the resistance value depends chiefly on the accuracy of the pattern position and shape. One known method is disclosed in Japanese Laid-open Patent No. H1-22379. A circumferential wall is formed using solder resist after forming an electrode in an insulated substrate to prevent the pattern from smearing, and then the resistance is provided in that cavity so as to improve the accuracy of the resistance value.
However, in conventional methods, including the above method, to form the resistance in a cavity for resistance after forming the electrode, a contact face of the electrode and resistance configuring the resistance wiring board is located higher than the level of the surface of the insulated substrate. Accordingly, the electrode surface or resistance surface protrudes from the surface of the insulated substrate, preventing attempts to reduce the height of the resistance wiring board.
When the resistance wiring board is used as a chip resistance, a face-down system involving mounting the resistance wiring board with the electrode side facing down onto the printed wiring board assists increased component mounting density. However, since the resistance surface is higher than the electrode surface in the conventional method as described above, face-down mounting involves practical difficulties.
Furthermore, variations in the thickness of the resistances or variations in resistance values due to difficulties in ensuring that the resistance thoroughly fills to the edges of the cavity may occur as a result of simply providing a resistance in the cavity.
When a low-temperature firing substrate made typically of glass-aluminum and electrode are integrally fired to reduce the height of the resistance wiring substrate, the heat conductivity of the insulated substrate may deteriorate, resulting in overload due to buildup of heat in the resistance.
SUMMARY OF THE INVENTION
The present invention solves the above disadvantages. In the present invention, the electrode surface and the resistance surface are on the same or at a lower level than the surface of the resistance wiring board. One object of the present invention is to achieve a resistance wiring board with high resistance accuracy and good overload characteristics, and which is suitable for face-down mounting.
To achieve this object, a Pd--Ag electrode contains Pd at 60 wt % or more in a resistance wiring board of the present invention on which the resistance is formed between the electrodes. An insulated substrate is made of an aluminum substrate containing 1.5 to 2.5 wt % TiO.sub.2, 1.5 to 2.5 wt % MnO, and 1.5 to 4.5 wt % SiO.sub.2. A boundary phase containing, also called herein a reaction phase, a higher quantity of Mn than inside the aluminum substrate is provided on the boundary between the aluminum substrate and the electrode. This structure realizes an electrode integrated substrate with good heat conductivity, resulting in a resistance wiring board
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Search Report corresponding to application No. PCT/JP98/02602 dated Sep. 16, 1998.
English translation of Form PCT/ISA/210 (No Month/Date).
Furukawa Shigeo
Himori Tsuyoshi
Inuzuka Tsutomu
Kimura Suzushi
Tomioka Satoshi
Lam Cathy
Matsushita Electric - Industrial Co., Ltd.
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