Metal working – Method of mechanical manufacture – Electrical device making
Reexamination Certificate
2003-06-18
2004-11-23
Arbes, Carl J. (Department: 3729)
Metal working
Method of mechanical manufacture
Electrical device making
C029S612000, C029S613000, C029S620000, C219S121690, C219S121850, C439S620040, C439S907000
Reexamination Certificate
active
06820324
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a resistor connector employed to restrict the current value of a control circuit, or to detect the resistance value to conduct identification of electrical components. Furthermore, the present invention relates to a manufacturing method of such a resistor connector.
BACKGROUND ART
An example of the above resistor connector is shown in FIG.
21
. This resistor connector C has a resistor
10
fixed in a manner bridging across a pair of parallel lead frames
1
,
1
. Said resistor
10
is covered with a mold resin
2
in a state where the terminal portion of each lead frame
1
projects. In general, resistor
10
has a resistor unit
12
provided on a substrate
11
. Resistor unit
12
is covered with a glass protection film
13
, and each of electrodes
14
,
14
is partially lead out from protection film
13
. The portion of each electrode
14
leading out from protection film
13
is electrically connected to each lead frame
1
by solder
15
. Solder
15
also serves to fasten resistor
10
to lead frame
1
.
The site where this resistor connector C is installed is often in a severe environment such as in the neighborhood of the engine compartment of an automobile. Variation in temperature is significant in such an environment. Although resistor connector C exhibits variation in the resistance value depending upon the change in temperature, the variation in the resistance value must be within a tolerable range. The varying range of the resistance value is preferably as small as possible.
In this type of resistor connector C, occurrence of a crack in resistor unit
12
causes change in the resistance value. It is therefore desirable to suppress generation of a crack in resistor unit
12
. However, many conventional resistor connectors already have cracks in glass protection film
13
. This is considered to be caused by the molding pressure during the mold cover process and the residual strain after the molding process. If such a resistor connector C is exposed to severe change in temperature, thermal stress (thermal shock) occurs due to the difference in the coefficient of thermal expansion between mold resin
2
and resistor
10
. This thermal stress causes the crack in protection film
13
to grow to result in a crack in resistor unit
12
, as well as increasing the crack in resistor unit
12
, when already present. Not only generation of a crack, but the growth of a crack induces a great change in the resistance value. In view of the foregoing, it is required to prevent generation of a crack in protection film
13
as well as in resistor unit
12
during the mold covering process. It is also important to prevent generation of cracks in such regions during the temperature cycle, i.e., during usage.
In view of the above requirements, the present applicant developed the approach to provide a buffer layer between resistor
10
and mold resin
2
(refer to
FIG. 2
in the first embodiment of the present invention; wherein silicon resin
20
in
FIG. 2
corresponds to this buffer layer), as disclosed in Japanese Patent Laying-Open No. 2000-173803. By virtue of this buffer layer, generation of a crack in resistor
10
during a mold covering process is suppressed to a minimum level. Also, even in the case where there is a severe change in temperature to cause thermal stress in resistor
10
due to the difference in the coefficient of thermal expansion between mold resin
2
and resistor
10
, the thermal stress can be absorbed to suppress generation of a crack in resistor
10
during the temperature change to a minimum level.
This resistor connector C has an extremely small variation width of the resistance value during temperature change, and is highly reliable. It was considered that the scattering of the flux volatile components from the solder can be prevented by entirely covering the resistor including the solder by that buffer layer (refer to
FIG. 11
of the second embodiment in the present invention).
However, it is to be noted that, at the interface between, for example, the silicon resin forming the buffer layer and the metal lead frame, secure adhesion is obtained only partially. That strength could not be achieved at the entire interface. The volatile component of the solder flux flows out from a portion of the interface to adhere to the terminal portion of the lead frame or enter and contaminate the mold resin. Adhesion to the terminal portion induces connection (contact) failure to result in a defective product. Intrusion in the mold resin will result in a defective product from the standpoint of appearance. As a result, the above-described resistor connector had an extremely low yield.
DISCLOSURE OF THE INVENTION
An object of the present invention is to prevent scattering of solder flux volatile components.
To achieve the above object, the present invention regulates the flow of solder to the terminal portion as one approach. Accordingly, the solder will not arrive at the terminal portion. Connection failure caused by adhesion of solder is eliminated.
As another approach, the flux volatile component is forced to volatilize before the mold covering process. By the forced volatilization, the amount of flux volatile component in the solder during the mold covering process is reduced. Accordingly, the amount that adheres to the terminal portion is reduced.
In view of the above object, a resistor connector of the present invention includes a pair of parallel lead frames, a resistor with a pair of electrodes, and a mold resin. Each of the above lead frames includes a terminal portion and an electrode connection portion. The pair of electrodes are electrically connected to respective electrode connection portions of the pair of lead frames. The mold resin covers the resistor so as to expose the terminal portion. The lead frame includes solder flow inhibit means between the electrode connection portion and the terminal portion for inhibiting flow of the solder towards the terminal portion.
If the cover by the mold resin is thin in the above structure, the flux volatile component may break through the thin mold resin cover due to the mold pressure and the like to flow to the surface of the cover during the covering process. To cope with the situation, a wall or trench is preferably formed so as to enclose the entire perimeter of the electrode connection portion (the solder land region). By setting the enclosed region to the least required level, the required amount of solder can be minimized. Accordingly, the absolute scattering amount of the flux volatile component can be reduced. Also, the amount of flow towards the surface of the cover can be reduced in accordance with the lower scattering amount. Furthermore, by selecting that region as the solder position (the place to mount the resistor), the solder will be gathered at the predetermined position in the region by solder fusion even if the solder print position protrudes from that region at the time of reflow. This travel causes the resistor to be shifted to the predetermined position to be attached accurately. In other words, self alignment is effected. This wall or trench is also advantageous in suppressing scattering of the flux volatile component towards the direction along the interface between the resin mold cover and the lead frame. Possible materials for the formation of this wall include resist printing, chromium coating, nickel coating, and the like that have poor wettability with respect to solder.
Preferably in the above invention, a buffer layer is provided at the interface between the resistor and the mold resin. As the material of the buffer layer, silicon resin (rubber), urethane type resin (rubber) and the like can be cited from the standpoint of heat resistance, adherence, hardness, spreadability, and the like. The buffer layer also serves to prevent scattering of the flux volatile component in addition to the role to protect the resistor, as described above. The buffer layer is preferably minimized in amount, as long as there is no problem. For example,
Matsumoto Yoshifumi
Yabutani Hiromi
Arbes Carl J.
Phan Tim
Smith , Gambrell & Russell, LLP
Sumitomo Electric Industries Ltd.
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