Structure of joining chip part to bus bars

Details Structure of joining chip part to bus bars Structure of joining chip part to bus bars

2002-10-16

2004-09-07

Reichard, Dean A. (Department: 2831)

Electricity: conductors and insulators

Boxes and housings

Hermetic sealed envelope type

C257S676000, C257S691000

Reexamination Certificate

active

06787700

ABSTRACT:

BACKGROUND OF THE INVENTION
This invention relates to a structure of joining, to bus bars, a chip part connected to an electronic device to be mounted on a circuit board, a J/B (junction box) or the like,.
As shown in
FIG. 5
, when chip parts
21
,
22
and
23
of an electronic device
20
are soldered to bus bars (bar-like metallic conductors)
25
,
26
,
27
and
28
, the chip parts
21
,
22
and
23
are placed on soldering lands
25
a
,
26
a
,
27
a
and
28
a
(indicated in dots-and-dash lines in the drawings) of two or more (four in the illustrated example) bus bars
25
,
26
,
27
and
28
. Then, connecting portions
21
t
,
22
t
and
23
t
of the thus placed chip parts
21
,
22
and
23
are joined by soldering to the corresponding bus bars
25
,
26
,
27
and
28
, respectively.
More specifically, in the soldering operation, when molten solder is dropped and supplied to be coated onto each connecting portion
21
t
,
22
t
,
23
t
of the chip part
21
,
22
,
23
and the associated soldering land
25
a
,
26
a
,
27
a
,
28
a
of the bus bar
25
,
26
,
27
,
28
, the molten solder forms a wide wetting area on the surface of the bus bar, and is solidified. This solder-solidified condition is shown in
FIG. 6
which is a cross-sectional view taken along the line VI—VI of FIG.
5
. In
FIG. 6
, the showing of a board
29
(shown in
FIG. 5
) is omitted.
However, the solder
30
assumes a thin film-like configuration as a whole because of its wide wetting area, and will not form any solder fillet. As a result, there has been encountered a problem that the solder joint strength is insufficient, so that the reliability of the solder joint is lowered.
In order to solve this problem, there has been proposed a method in which spot-plating of metal, having excellent solder wetting properties, is applied to the soldering land
25
a
,
26
a
,
27
a
,
28
a
of each bus bar
25
,
26
,
27
,
28
so that the wetting area of the soldering land
25
a
,
26
a
,
27
a
,
28
a
is limited to a narrow range. However, this method has a problem that the production efficiency is lowered, so that the production cost greatly increases.
SUMMARY OF THE INVENTION
This invention seeks to solve the above problems, and an object of the invention is to provide a structure of joining a chip part to bus bars, in which the sufficient solder joint strength is obtained without increasing the cost, while ensuring the production efficiency, so that the solder joint of high reliability can be achieved.
In order to solve the aforesaid object, the invention is characterized by having the following arrangement.
(1) A joining structure comprising:
two conductive bus bars spaced from each other;
a chip part including connecting portions for an electric circuit, mounted on the two bus bars;
recesses formed in soldering lands of the two bus bars, respectively, so that the connecting portions are spaced apart from inner edges of the recesses; and
a solder fillet formed between at least part of each of the recesses and the corresponding connecting portion.
(2) The joining structure according to (1), wherein the connecting portions has a flat plate-like shape on opposite side surfaces of the chip part, and the connecting portions form a part of a bottom surface of the chip part.
(3) The joining structure according to (1), wherein bottom surfaces of the connecting portions extend inwardly toward each other.
(4) The joining structure according to (1), wherein
each of the recesses includes a flat bottom surface, and
the solder fillets are formed in a state that lower surfaces of the connecting portions are held by the bottom surface.
(5) The joining structure according to (1), wherein
the solder fillets are formed in a state that the connecting portions are spaced from a bottom surfaces of the recesses, so that a solder layer is formed between the bottom surfaces and a lower surface of the connecting portion.
(6) The joining structure according to (1), wherein
each of the recesses includes a projection platform having a height lower than an upper surface of the bus bars, and
the solder fillets are formed in a state that lower surfaces of the connecting portions are held by the projection platforms, respectively.
(7) The joining structure according to (1), wherein the soldering lands correspond to a predetermined solder wetting area.


REFERENCES:
patent: 3429040 (1969-02-01), Miller
patent: 5196726 (1993-03-01), Nishiguchi et al.
patent: 5311405 (1994-05-01), Tribbey et al.
patent: 6200143 (2001-03-01), Haba et al.
patent: 2001053432 (2001-02-01), None

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