Active solid-state devices (e.g. – transistors – solid-state diode – Integrated circuit structure with electrically isolated... – Passive components in ics
Reexamination Certificate
1999-01-08
2001-03-13
Abraham, Fetsum (Department: 2811)
Active solid-state devices (e.g., transistors, solid-state diode
Integrated circuit structure with electrically isolated...
Passive components in ics
C257S358000, C257S359000, C257S363000, C257S489000
Reexamination Certificate
active
06201290
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to the field of resistors; more particularly, to rectangular chip resistors and their manufacturing method.
BACKGROUND OF THE INVENTION
There is an increasing demand for rectangular chip resistors with highly accurate resistance to eliminate adjustment for circuits, as the size of electronic equipment continues to shrink in recent years. In particular, since the allowance required for the resistance of rectangular chip resistors is ±0.1% to ±0.5%, the demand for rectangular chip resistors made of thin metal film resistance material (hereafter referred to as “thin film rectangular chip resistors”), in which precise resistance can be easily achieved, is overtaking demand for conventional rectangular chip resistors, which are constituted of thick film resistance (hereafter referred to as “thick film rectangular chip resistors”) made in grazed material.
On the other hand, as the use environment of electronic equipment diversifies, the required specification levels for rectangular chip resistors, which are electronic components, is also becoming higher. As the market for thin film rectangular chip resistors expands, reliability equivalent to that of thick film rectangular chip resistors, which have stable moisture resistance characteristics, is required.
A resistor and its manufacturing method of the prior art are explained below with reference to a drawing.
As shown in
FIG. 4
, a resistance layer
2
made of a thin metal film of Ni or Cr systems is disposed on the top face of a substrate
1
made typically of 96% aluminum. A pair of top electrode layers
3
made of a thin metal film such as Cu etc. are disposed on the left and right ends of the top face of the substrate
1
so as to overlap the resistance layer
2
. A pair of bottom electrode layers
4
made of a thin metal film such as Cu etc. are disposed on both ends of the bottom face of the substrate
1
, at positions corresponding to the top electrode layers
3
. A protective layer
5
typically made of polyimide resin is provided on the top face of the resistance layer
2
to cover at least an exposed area of the resistance layer
2
. In addition, a side electrode layer
6
made of a thin metal film such as Ni etc. is disposed on side faces of the substrate
1
so as to connect the top electrode layer
3
and the bottom electrode layer
4
. Lastly, a Ni plating layer
7
is provided to cover the top electrode layer
3
, bottom electrode layer
4
, and side electrode layer
6
. A solder plating layer
8
is provided to cover the Ni layer
7
to form a complete resistor.
A method for manufacturing the resistor as configured above is explained next with reference to a drawing.
FIG. 5
is a process chart showing a method for manufacturing the resistor of the prior art. A substrate
11
is a heat-resisting substrate made typically of 96% aluminum (Process A). A thin film resistance layer, typically of NiCr etc. is provided on the entire face of the substrate
11
by sputtering (Process B). A resistance pattern
12
is formed by photo-etching this thin film resistance layer (Process C).
Next. a thin film top electrode layer such as Ni etc. is sputtered on the entire face of the substrate
11
where the resistance pattern
12
is formed (Process D), and a top electrode pattern
13
is formed by photo-etching this thin-film top electrode layer (Process E). Then, heat treatment at 350° C. to 400° C. is applied in a nitrogen gas ambient to stabilize the films of the resistance pattern
12
and the top electrode pattern
13
(Process F).
Next, laser trimming is applied to adjust the resistance of the resistance pattern
12
to a specified value (Process G). A protective layer
15
made of thermosetting resin such as polyimide resin is provided to protect the resistance
14
after the resistance is adjusted (Process H).
Next, a groove
16
for dividing the substrate
11
is made by scribing with carbon oxide gas laser (Process I), and the substrate
11
is primarily divided to substrate strips
17
(Process J). A side electrode layer
18
is formed on a side face of these substrate strips
17
by means such as sputtering (Process K).
After secondary division of the substrate strips
17
into substrate pieces
19
(Process L), an electrode plating layer
20
is finally formed to secure reliability of soldering (Process M), resulting in manufacture of the resistor of the prior art.
The resistor and its manufacturing method of the prior art, however, use thermosetting resin such as polyimide resin for the protective layer of thin film rectangular chip resistors. This has far greater water vapor permeability, due to its material characteristics, comparing with inorganic materials such as the borosilicate lead glass used as the protective layer for thick film rectangular chip resistors. Accordingly, water molecules are likely to penetrate the resistance layer through the protective layer if the resistor is exposed to a high ambient humidity. This will cause changes in resistance value due to oxidization of the resistance layer. Furthermore, electro-corrosion may cause disconnection if ions with high corrosivity such as Na
+
, K
+
, and Cl
−
are present.
SUMMARY OF THE INVENTION
The present invention reduces the moisture absorbency of the protective layer, improving the resistor's moisture resistance.
The present invention relates to a resistor comprising a substrate, a pair of top electrode layers disposed on both ends of the top face of the substrate, a resistance layer disposed on the top face of the substrate so as to electrically connect with the top electrode layer, a first protective layer made of resin disposed on the top face of the substrate to cover at least the exposed area of the resistance layer, and a second protective layer made of resin disposed to cover at least the first protective layer: and its manufacturing method. More specifically, the moisture absorbency of the protective layer is reduced by covering the resistance layer with two layers: the first and second resin protective layers, which have different characteristics, to improve the reliability, particularly the moisture resistance characteristics, of the resistor.
REFERENCES:
patent: 3971061 (1976-07-01), Matsushita et al.
patent: 4893157 (1990-01-01), Miyazawa et al.
patent: 5554873 (1996-09-01), Erdeljac et al.
Nakatani Mitsunari
Yamada Hiroyuki
Abraham Fetsum
Matsushita Electric - Industrial Co., Ltd.
Ratner & Prestia
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