Chip electronic device with a resin housing and manufacturing process thereof

A chip electronic device wherein an electronic element such as an inductor and capacitor, and terminals are covered with a resin housing. Plated lower surfaces and edges of the terminals show on a bottom and sides of a housing respectively. The lower surfaces of the terminals are soldered onto conductive patterns of a printed wiring board, and fillets of solder are formed at the edges of the terminals.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a chip electronic device produced by 
housing a compact electronic element such as an inductor, a capacitor and 
a resistor with resin and a manufacturing process thereof. 
2. Description of Related Art 
When a chip electronic device is mounted on a printed wiring board, in 
general, it is known that whether soldering has been done sufficiently is 
decided by checking visually whether a fillet of solder is formed between 
an external terminal of the chip and a conductive pattern of the printed 
wiring board. To check the soldering condition surely in this way, the 
fillet needs to be formed on a side of the chip electronic device. As for 
a chip wherein external terminals are formed by punching a strip into a 
specified shape, the easiest method of forming a fillet which can be 
checked from outside is forming the fillet on cut surfaces which are made 
when the external terminals are separated from the strip. The terminals 
show on sides of a housing of the electronic element. The external 
terminals, after separated from the strip, are plated in order to improve 
solderability before an electronic element is mounted thereon. However, 
since the cut surfaces are formed after the plating, the cut surfaces are 
not plated and easy to be oxidized by heat generated during cutting or 
during soldering of the electronic element onto the external terminals. 
Thus, the solderability of the cut surfaces are deteriorated, and it 
becomes difficult to form the fillet of solder thereon. 
To solve this problem, the external terminals are bent so that plated sides 
of the terminals show on the sides of the housing, or the cut surfaces are 
plated again separately to avoid oxidation. However, these bending or 
extraplating helps to raise a production cost. 
SUMMARY OF THE INVENTION 
An object of the present invention is to provide a chip electronic device 
which has a fillet of solder surely on a side of a housing, the fillet of 
solder being formed without bending nor extra-plating of terminals after 
molding of the housing and separation of the terminals from a strip. 
Another object is to provide a manufacturing process of the chip electronic 
device. 
In order to attain the objects, a chip electronic device according to the 
preset invention is manufactured by forming and plating terminals and 
exposing their lower surfaces and edges on a bottom and sides of a resin 
housing covering an electronic element. 
The terminals of the chip electronic device are soldered at their bottom 
side onto conductive patterns of a printed wiring board or the like. At 
that time, since the edges of the terminals which show on the sides of the 
housing are plated as the lower surfaces of the terminals are, a fillet 
can be easily formed thereon when soldering. Acceptability of the 
soldering is decided by checking a forming condition of the fillet 
visually. 
In other word, according to the present invention, bending and 
extra-plating of the terminals after separation of the terminals from the 
strip, which have been conventionally carried out in order to facilitate 
checking of the soldering, are no longer necessary, and the production 
cost of the chip electronic device can be reduced.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The description of preferred embodiments according to the present invention 
is given below, referring to the drawings. 
The description below is for the case that the present invention is applied 
to a chip inductor. 
As shown in FIG. 1, pairs of external terminals 2 and in a specified shape 
are formed consecutively by punching a lengthy strip 1 at regular 
intervals. FIG. 1 shows only one pair of the external terminals 2 and 5. 
The external terminals 2 and 5 protrude their center portions outward. The 
center portions of the terminals 2 and 5 are protruded by such lengths 
that the edges 2a and 5a of the terminals 2 and 5 will be exposed flush 
with sides of the housing 16 (shown in FIG. 2). 
After the punching process, surfaces of the external terminals 2 and 5 are 
plated with tin or the like. An about 0.3 mm thickness conductive metal 
plate such as copper, brass and monel is used as the strip 1. The strip 1 
is conveyed by a conveying apparatus (not shown) and adjusted by pilot 
holes 1a which are provided at uniform intervals on an edge of the strip 
1. 
An inductor element 9 is composed of a core 10 and a coil 12 which is wound 
around a body of the core 10. Electrodes 14a and 14b are provided at a 
bottom of the core 10 (shown in FIG. 5), and both ends of the coil 12 are 
connected electrically with the electrodes 14a and 14b. 
The inductor element 9 is mounted on the external terminals 2 and 5 which 
are prepared in the above-mentioned process In other words, the electrodes 
14a and 14b of the inductor element 9 are fixed on and connected 
electrically with the external terminals 2 and 5 respectively via solder 
20 (refer to FIG. 5). Then the inductor element 9 and the external 
terminals 2 and 5 are inserted into a mold for resin molding (not shown). 
Then a resin is injected into the mold and forms a housing 16 therein. In 
this way, as shown in FIG. 2, the inductor element 9 and the external 
terminals 2 and 5 are covered with the housing 16. In this state, the 
edges 2a and 5a and lower surfaces 2c and 5c of the external terminals 2 
and 5 (refer to FIG. 5) are exposed flush with the sides and the bottom of 
the housing 16 respectively. After the molded resin becomes stiff, a flash 
(a part protruded from the housing 16) is cut, and then the chip inductor 
is separated from the strip 1. 
FIGS. 3, 4 and 5 show the chip inductor after separated from the strip 1. 
The lower surfaces 2c and 5c of the external terminals 2 and 5 are exposed 
flush with the bottom 17 of the chip inductor. Also, the edges 2a and 5a 
of the external terminals 2 and 5 are exposed flush with mutually opposite 
sides 18a and 18b of the chip inductor, adjoining to the bottom 17. In the 
same way, edges 2b and 5b of the external terminals 2 and 5 which are cut 
after resin molding show on the other mutually opposite sides 18c and 18d. 
Since the edges 2a and 5a and the lower surfaces 2c and 5c of the external 
terminals 2 and 5 are cut and plated before molding, these are not 
oxidized by the heat generated during the final cutting of the terminals 2 
and 5 or during the soldering of the inductor element 9 onto the external 
terminals 2 and 5. Therefore, the edges 2a and 5a and the lower surfaces 
2c and 5c have good solderability. Especially when the chip inductor is 
soldered onto the conductive patterns of the printed wiring board or the 
like, the fillet of solder is easily and surely formed at the edges 2a and 
5a. The acceptability of the soldering is decided by checking the forming 
condition of the fillet visually. 
On the other hand, since the cut edges 2b and 5b are easily oxidized by the 
heat generated during the final cutting or during the soldering of the 
inductor element 9 onto the external terminals 2 and 5, these are not used 
for soldering the chip inductor onto the printed wiring board. 
FIG. 6 shows another shape of external terminals. External terminals 2' and 
5' are shaped like straight plates and formed by punching a strip 1'. 
Edges 2a' and 5a' of the external terminals 2' and 5' are not protruded 
like the edges 2a and 5a shown in FIG. 1. Therefore, when a chip 
comprising an electronic element and the external terminals 2' and 5' is 
produced, the edges 2a' and 5a' of the external terminals 2' and 5' are 
exposed flush with sides of a housing 16' from one end to the other (refer 
to FIG. 7). 
In FIGS. 6 and 7, parts and portions corresponding to the ones shown in 
FIGS. 1 through 5 are provided with the same numbers and alphabets with 
['] marks. 
Although the present invention has been described in connection with the 
preferred embodiments above, it is to be noted that various changes and 
modifications are apparent to a person skilled in the art. Such changes 
and modifications are to be understood as being within the scope of the 
present invention. 
Especially, detailed shapes of the external terminals and the housing are 
optional.