A wirewound balun transformer for planar packaging comprising a flanged core which has end flanges at both ends, at least one center flange, and two or more winding recesses, a flat core held in parallel with the flanged core, and windings coiled around the winding recesses, characterized in that one side face of the center flange is not flush with but is formed behind the plane that connects one side faces on the same side of the end flanges, each of the end flanges of the flanged core has an opposing pair of electrodes formed on both side faces, and the center flange has a single electrode formed on the opposite side face.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to an electronic component and, more particularly, 
to a component (balun transformer) chiefly designed to connect different 
electronic circuits, couple an unbalanced circuit to a balanced, and match 
the impedance between circuits. 
2. Description of the Prior Art 
As components for use in connecting electronic circuits and intended for 
functions such as the coupling of unbalanced and balanced circuits and 
impedance matching between circuits, balun transformers are known which 
comprise a core with flanges that define at least two recesses in between 
on which conductors are wound, and terminal pins set in throughholes 
formed in the flanges. 
In FIG. 1 is shown an embodiment of such a balun transformer described in 
Japanese Patent Application Kokai No. 61-208913. Two conductors are wound 
into coils on two recesses of a flanged ferrite core 2. The flanges of the 
core 2 have a vertically formed throughhole each, and a total of three 
terminal pins 4 are inserted through the holes and fixed securely in 
position. Lead-out conductor ends are suitably bound around upwardly 
projecting ends 3 of the pins and soldered in place for connection so as 
to constitute a circuit similar to the equivalent circuit depicted in FIG. 
11. Each winding 1 comprises, in the equivalent circuit of FIG. 11, 
conductors 8, 9 wound on one recess and conductors 10, 11 on the other 
recess. In the illustrated example the flanged core facilitates the 
winding operation and permits precise control of winding length, thus 
making it possible to avoid the dispersion of characteristic impedance. In 
addition, the pins 4 can be utilized for enhancing the wiring and 
soldering efficiencies. 
FIGS. 2 and 3 illustrate an improved construction of the balun transformer 
of FIG. 1, disclosed in Patent Application Kokai No. 62-90911. A 
bar-shaped ferrite core 5 is located in contact with the flanges of a 
flanged core 2. The protruding ends 3 of the pins 4 are inserted into 
throughholes 6 also formed in the core 5, and lead-out ends of the 
windings are suitably bound around the further protruding ends 3 of the 
pins and soldered in place to provide a circuit like the one shown in FIG. 
11. The cited example has further advantages that its closed magnetic 
circuit structure strengthens the magnetic coupling between the windings 
and keeps off electromagnetic influences from the outside. 
It is common with the prior art devices briefly outlined above that their 
flanges have throughholes in which pins are set securely and the ends of 
windings are bound around the ends of the pins protruding from the holes 
as terminal pins. The structure requires intricate molds to form holes 
through the ferrite core and bar-shaped ferrite core alike. This, in turn, 
increases the part dimensions and defies efforts to decrease the number of 
component parts, thus weakening the competition of the product in the 
market. 
With the spread of electronic equipment and the tendency toward 
miniaturization of the parts, even smaller components for planar packaging 
have become essential for mobile communication. In the art of 
communication the transmission characteristic is an important factor that 
governs the performance of an equipment, since it can have adverse effects 
upon the communication sensitivity. The present state of the components is 
that their characteristic has contradictory aspects. If a better 
characteristic is sought the component size must be larger, and if a 
smaller component is desired its characteristic has to be sacrificed 
accordingly. The balun transformer is no exception to this contradictory 
state. In the fields where equipment size is a major commercial 
consideration, small components are in wide use at the expense of 
characteristic. 
SUMMARY OF THE INVENTION 
The present invention is aimed at providing a balun transformer which 
permits easy mold making, reduction of component size, and a decrease in 
the number of constituent members, without deterioration of the 
characteristic. 
To achieve the aim of the invention, the product of the invention is 
characterized by core configurations suited for high characteristic 
winding, elimination of the usual members for arranging and fixing the 
ends of windings that have hitherto hindered the miniaturization and 
reduction in height of parts, and formation of end joints on side faces of 
a flanged core. 
In brief, the invention provides a wirewound balun transformer for planar 
packaging comprising a flanged core which has end flanges at both ends, at 
least one center flange, and two or more winding recesses, a flat core 
held in parallel with the flanged core, and windings coiled around the 
winding recesses, characterized in that one side face of the center flange 
is not flush with but is formed behind the plane that connects one side 
faces on the same side of the end flanges, each of the end flanges of the 
flanged core has an opposing pair of electrodes formed on both side faces, 
and the center flange has a single electrode formed on the opposite side 
face.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Some embodiments of the wirewound-chip balun transformer for planar 
packaging of the above construction according to the invention will now be 
described. 
One side face of the center flange desirably is flush with the faces on the 
same side of the winding recesses of the flanged core. 
The connection of the ends of the windings desirably is done at the 
positions of the electrodes on the flange side faces substantially 
perpendicular to the surface on which the component is to be mounted. 
In another preferred embodiment, the surfaces of the flanged core and flat 
core to be joined together are rounded off to take in a resin (UV resin) 
coating and keep it from protruding outward. 
The windings desirably are resin coated after they have been secured onto 
the winding recesses. 
Also, preferably the ends of the windings are held in place in contact with 
the winding regions and then soldered to the electrodes. This prevents the 
application of stresses by external forces or the like to the ends of the 
windings. 
Further, all edges of the flanged core are rounded off to protect them 
against chipping by external forces and against unwanted changes in 
characteristic due to such chipping. 
The present invention makes possible the automatization of the winding 
operation, thereby improving the productivity and bringing a cost 
advantage. The ends of the windings are directly connected to the flange 
side faces that are common with external electrodes to be mounted together 
and are perpendicular to the surface on which they are mounted. The 
arrangement can dispense with conventional terminal pins for winding ends 
and reduce the component volume to a minimum that satisfies the 
characteristic requirements. The elimination of members such as terminal 
pins is also beneficial because it saves the production cost. 
One side face of the center flange is not flush with but is formed behind 
the plane that connects one side faces on the same side of the end 
flanges. This facilitates the printing of electrodes only on the desired 
side faces by screen printing or other technique. Also, because the 
individual electrode regions in the finished product are discretely 
defined, the ends of the windings are easily secured in place. 
The invention will be more fully described below with reference to the 
following examples. 
FIGS. 4 and 5 are perspective views of a balun transformer for planar 
packaging according to the present invention, with the windings omitted. 
The transformer comprises a flanged core 12 made of sintered ferrite and a 
flat core 16 also made of sintered ferrite, the two cores being joined 
together. FIG. 4 is a perspective view as seen from one side and FIG. 5, 
as seen from the opposite side. 
Details of the flanged core 12 are shown in FIGS. 6 to 10. FIG. 6 shows the 
core, in perspective, as seen from the same side as FIG. 4. FIG. 7 is a 
plan view, FIG. 8 is a side view as seen from the same side as FIG. 4, 
FIG. 9 is a right end view, and FIG. 10 is an opposite side view as seen 
from the side of FIG. 5. Throughout these figures the flanged core 12 has 
a generally rectangular shape, with the same quadrilateral end flanges 13, 
14 at both ends and a center flange 15 in between. Winding recesses 17, 18 
are defined between the end flanges 13, 14 and the center flange 15. The 
core portions surrounded by the bottoms of the winding recesses 17, 18 are 
the portions on which conductors are to be wound. The side face 19 on the 
side of the center flange 15 shown in FIGS. 4 and 6 is flush with the core 
portions to be wire-wound. The side face 19 is preferably back a short 
distance toward the core portions from the side faces 20, 21 on the same 
side of the end flanges 13, 14, respectively. The side faces 20', 21' on 
the opposite side of the end flanges 13, 14 and the side face 19' on the 
opposite side of the center flange 15 are on the same plane as in FIGS. 5 
and 7. All bottom faces of the end flanges 13, 14 and the center flange 15 
are on the same horizontal plane to ensure stabilized planar packaging. 
Similarly the top faces of the end flanges 13, 14 and the center flange 15 
are on a common horizontal plane so as to be in contact with the 
corresponding surface of the flat core 16 to form a closed magnetic 
circuit. All core edges may be rounded off to prevent the breaking of 
conductors. 
Next, as the electrodes to which the ends of windings are attached and 
which permit connection to external wirings at the time of packaging, 
electrodes 7 are provided on the side faces 20, 20' and opposite side 
faces 21, 21' of the both end flanges 13, 14. At the same time, a single 
electrode 7 is provided on the opposite side face 19' of the center flange 
15. These electrodes are formed flat on the side faces of the flanges, 
preferably from each side face down to the bottom face substantially 
perpendicular to the side face. To reduce the height of the component, it 
is advisable to use positively the electrodes on the vertical plane when 
joining to a printed circuit board or the like by soldering or other 
technique. The electrode portions at the bottom is not so important then 
and they may or may not be utilized. The electrodes are made from a highly 
heat-resisting material which does not hamper packaging. 
Subsequent wiring and connections as desired complete a wirewound-chip 
balun transformer, whose equivalent circuit is shown in FIG. 11. The 
construction of the circuit itself is known in the art. As FIG. 12 
indicates, windings 8, 9 are applied together to the winding recess 17 
shown in FIGS. 7 to 10 and windings 10, 11 to the winding recess 18, and 
then the ends 22 of the windings are soldered to the electrodes on the 
side faces 20, 21, 19', 20', 21' as illustrated in FIG. 11. 
A typical winding procedure is as follows. Two conductors are used to form 
four coils by twice-winding operation. To begin with, the two conductors 
are turned counterclockwise round the winding recess 17 from the side face 
19 of the center flange 15 outward. Next, one of the conductors is 
temporarily fixed at the end to another object. The other conductor is 
then turned back from the side face 19' of the center flange 15 and is 
again arranged in parallel with the former conductor. From that point the 
two conductors are turned together clockwise on the other winding recess 
18. A total of four coils are formed this way. Finally, the ends 22 of the 
windings are separated and soldered securely to the corresponding 
electrodes to constitute the circuit of FIG. 11. The winding structure 
thus obtained and the connections of the winding ends 22 to the electrodes 
7 are shown in FIGS. 18 to 22. 
FIG. 13 exemplifies a state of windings. The winding 8 (represented by 
black circles) and the winding 9 (white circles) coexist on a single 
recess. To strengthen the conductor coupling, the conductors 8, 9 are 
alternately turned close to each other in tight winding. For this purpose 
it is desirable to use a winding method suited for tight winding, such as 
spindle winding or flier winding. FIG. 14 shows another state, in a cross 
section, of windings crossed partly as a result of flier winding, in which 
the core on which the conductors are wound does not rotate but winding 
nozzles not shown revolve around the core. Here again the windings 8, 9 
produce good conductor coupling although they form superposed layers. 
FIG. 15 shows how winding ends 22 and an external electrode 7 are joined 
together. Joints are located on the substantially vertical flange side 
faces 20, 21 and 19', 20', 21'. For the connection of the external 
electrode 7 and winding ends 22, the insulating film that covers the 
winding material is preliminarily torn by the weight and heat applied as 
they are temporarily fixed at the joining points. The insulating film is 
completely removed by heating at a temperature not high enough to 
deteriorate the film. The winding ends 22 and each terminal electrode 7 
are electrically connected by a solder layer 23 formed of fluid solder as 
in FIG. 15. The heating method is desirably such that it generates a 
temperature stable with respect to a preset temperature. 
FIG. 16 shows an impregnating resin coating 24 provided to enhance the 
environmental resistance of the windings 8, 9, 10, 11. The impregnation 
coating desirably is done using a mechanism capable of applying the resin 
at a uniformly controlled rate. The permeability of the impregnating 
material is improved by maintaining either the wirewound flanged core 12 
or the impregnating material at a suitable temperature. It is also 
advisable that the material possesses environmental resistance and good 
workability for production. 
FIG. 17 shows a joint formed between a flat core and a flanged core. An 
adequate amount of adhesive is applied to the surface portions to be 
joined, and the flat core 16 and the flanged core 12 are joined together. 
For the joining purpose a material curable in a short time, such as 
UV-cured resin 25, is used. With the application of a weight, the UV resin 
that has been forced upward along the interface for joining is irradiated 
with ultraviolet rays for preliminary curing. The resin is then 
permanently cured to maintain the joint strength. The materials to be 
joined are desirably chosen in consideration of their physical strength 
and environmental resistance. 
As referred to above, FIGS. 18 to 22 depict the particulars of windings on 
a flanged core. The procedure has already been explained in detail. All 
edges of the flanged core 12 are rounded off to make the core surface 
edgeless. This adds to the durability of the windings against the breaking 
under tension of winding operation and against the tear of the insulating 
film. Rounding the core edges off is suitably done by sandblasting or 
other process that treats small, complex-shaped objects or by removing 
sharp edges from the mold cavity for the core. 
The winding procedure so far described can form four coils by a sequence of 
only two winding cycles, achieving high production efficiency. 
FIG. 22 shows how crossing winding ends are neatly arranged and finished. 
Crossing lead-out conductor portions 26, 27 that continue to the winding 
ends 22 are held in tight contact with the facing coil portions. The 
arrangement eliminates any conductor portion that connects the edges of 
the flanged core 12 in a straight line, removes tensile stresses, and 
makes the lead-out portions continuous to the winding ends 22 more 
resistant to impact and conductor breaking. 
The present invention permits automatization of the winding operation and 
enhances the productivity to an economic advantage. The ends of the 
windings are directly connected to the flange side faces that are common 
with external electrodes to be mounted together and are perpendicular to 
the surface on which they are mounted. The arrangement renders it possible 
to dispense with conventional terminal pins for winding ends and reduce 
the component volume to a minimum that satisfies the characteristic 
requirements. The elimination of members such as terminal pins is 
beneficial from the viewpoint of production cost. The electrodes in the 
planes flush with the vertical flange side faces and bottom faces can be 
easily fabricated by screen printing. They thus lend themselves to 
quantity production at low manufacturing cost. The individual electrode 
regions are discretely defined by the side faces of the flanges, and 
therefore the ends of the windings are easily secured in place. Moreover, 
the coating of the conductors with an impregnating material improves the 
environmental resistance of the component. 
With configurations free from irregularities on the joining faces the 
flanged and flat cores can be joined flush with each other. The 
configurations help mechanize the joining process, with a joint precision 
as high as the designed precision of the machine. When the core 
configurations make use of conventional locating pin holes 6 and arcuate 
recesses 2' as in FIG. 3, the locating accuracy must be set to an 
adequately high level. 
The core shapes illustrated in FIGS. 4 to 10 are superior in high frequency 
characteristics to the currently dominant core shapes. 
The flat core shown in FIGS. 4 and 5 provide the surface against which the 
suction cup of a packaging unit is to be pressed, thus making automatic 
packaging possible. 
The joint position shown in FIG. 15 is the lowest of the positions where 
the ends of windings can be connected to the electrodes on the flanges.