KR102054742B1 - Method for manufacturing Integral type Transfomer coil printed circuit board having Input side Primary coil and Output side Secondary coil - Google Patents

Abstract

The present invention relates to a method for manufacturing a transformer coil printed circuit board having an input primary coil and an output secondary coil. The manufacturing method includes a first drilling step of processing first, second and third through holes in a laminated substrate including a first and second coil side substrate laminates; A copper plating step of plating copper in the first, second and third through holes; A second step drilling step of disconnecting the copper plating layer in the third through hole from the primary coil layer; A resin plugging step of filling resin in the first through hole and the second step through hole; And a solder resist forming step of forming a solder resist layer on the surface of the laminated substrate after the resin plugging step and the resin hardening step. According to the present invention as described above, the primary coil side substrate laminate is completed after the primary coil side substrate laminate and the secondary coil side substrate laminate are laminated and trimmed without processing the inner via hole of the secondary side substrate laminate in advance. When processing the via hole of the sieve, the secondary coil side via hole is processed at the same time, the primary coil side via hole and the secondary coil side via hole are simultaneously plated, and the primary coil side via hole and the secondary coil side via hole are simultaneously filled with resin, so the production efficiency is good. The manufacturing cost can be greatly reduced, and the resin is filled into the via hole and the inner via hole through the resin plugging step before the solder resist layer is applied, so that the applied solder resist does not flow into the via hole or the inner via hole, and thus the thickness of the solder resist layer Because of the uniformity and no generation of pores or cracks, excellent withstand voltage characteristics can be achieved.

Description

Method for manufacturing Integral type Transfomer coil printed circuit board having Input side Primary coil and Output side Secondary coil}

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a transformer coil printed circuit board in which an input side primary coil and an output side secondary coil are integrally formed for a transformer in which a primary side coil and a secondary side coil are laminated in one printed circuit board. Specifically, the primary coil and secondary coil, and the primary and secondary coils and ferrite cores with the guaranteed withstand voltage characteristics and low manufacturing cost, and the input primary coil (primary coil) manufactured by the method and The present invention relates to a method of manufacturing a transformer coil printed circuit board having an output side secondary coil.

With the development of technology, various electric and electronic parts have been made slimmer, and transformers (transformers, transformers) are also being miniaturized, lighter, lighter, and mass. Slimming of the transformer is performed by stacking a thin unit substrate on which a circuit is formed to implement windings of the device.

For reference, a printed circuit board coil transformer may be classified into a coil integrated type and a coil separated type. In the coil integrated type, a primary coil to which power is input and a secondary coil to which power is output are printed. The method is implemented in a circuit board, and the coil separation type is a method in which a printed circuit board of a primary coil and a secondary coil is separately manufactured and then assembled.

The printed circuit board coil transformer may include a coil printed circuit board and a core surrounding the coil printed circuit board. The coil printed circuit board has a configuration in which a plurality of unit substrates in which coils are formed are laminated and molded, and the coils formed in each unit substrate are electrically connected through via holes. The coils of each substrate are electrically connected to each other through plated via holes to form a current path that replaces the wire wound coils of a typical transformer. Of course, the number of stacked layers of the coil printed circuit board multilayer molded article may vary depending on the capacity of the transformer.

1 illustrates an example of a conventional input / output coil integrated coil printed circuit board 10.

Referring to FIG. 1, a conventional coil integrated printed circuit board 10 for transformers includes two sets of primary coil printed circuit boards 20 formed by stacking a plurality of unit substrates 21 and the primary coil printed circuits. It can be seen that the secondary side coil printed circuit board 30 interposed between the circuit board 20, the solder resist layer 16 and the marking layer 18.

Each unit substrate 21 constituting the primary coil printed circuit board 20 includes an insulating layer 21a and a primary coil layer 21b, and each primary coil layer 21b is a via hole 11. Are interconnected up and down through. That is, the primary coil layer 21b of each unit substrate 21 is connected through the via hole 11 to form a three-dimensional structure as a whole. The via hole 11 is a hole in which a copper plating layer 12 is formed.

The primary coil layer 21b should be spaced apart from the secondary coil layer 31b of the secondary coil printed circuit board 30 so as to maintain a predetermined withstand voltage, and an insulating layer 15 having a predetermined thickness or more may be provided to maintain the withstand voltage. It is interposed. The thickness of the insulating layer 15 is at least 0.2 mm.

The secondary coil printed circuit board 30 includes a plurality of unit substrates 31, and each unit substrate 31 has its own insulating layer 31a and secondary coil layer 31b. In addition, the secondary coil layer 31b included in the secondary coil printed circuit board 30 is electrically connected through the inner via hole 13. The inner via hole 13 is a hole in which a copper plating layer 14 is formed on an inner circumferential surface thereof, and electrically connects the upper and lower secondary coil layers 31b.

In the conventional method of manufacturing a coil printed circuit board 10 having the above-described configuration, after manufacturing two sets of primary coil printed circuit boards 20 and one secondary coil printed circuit board 30 separately, they are stacked and stacked. The via hole 11 and the terminal pin hole 17 are formed in the molded state, and the solder resist layer 16 and the marking layer 18 are formed.

However, such a manufacturing method has a problem that the manufacturing process is not only cumbersome but also takes a lot of time and cost. This is because the secondary coil printed circuit board 30 must be manufactured separately. Inner via hole 13 should be formed in secondary coil printed circuit board 30. Since inner via hole 13 should be buried in coil printed circuit board 10, as shown in FIG. When the circuit board 30 is manufactured, it was inevitably formed separately. That is, in the manufacture of the secondary coil printed circuit board 30, the holes penetrating through the laminated molded unit substrate 31 must be drilled separately and copper plating is separately applied to the inside of the holes, which increases additional manufacturing costs. Cause.

In other words, the secondary coil printed circuit board 30 is manufactured separately through a separate process, and the manufactured secondary coil printed circuit board 30 is interposed between the primary coil printed circuit board 20. Drilling and plating again.

In view of the manufacturing process as a whole, a state of drilling and plating once during the fabrication of the secondary coil printed circuit board 30, and the primary coil printed circuit board 20 and the secondary coil printed circuit board 30 are coupled to each other. Drilling and plating are done again. Drilling and plating are carried out twice.

Another problem of the conventional manufacturing method described above occurs when the solder resist layer 16 is formed. The solder resist layer 16 is a layer formed by applying a flowable solder resist to the outer front and rear surfaces of the primary coil printed circuit board 20, and has a constant withstand voltage between the conductor of the via hole 11 and the core to be placed thereon. In order to seal the via hole 11 with a solder thickness of a predetermined thickness, a portion of the applied solder resist flows into the via hole 11, and a portion of the solder resist covering the edge of the conductor of the via hole 11 (part A). ) Is thinner than other parts, or fine perforations or cracks may be generated due to the increase in pressure inside the via hole 11. The coiled printed circuit board 10 having a non-uniform thickness of the solder resist layer 16 or a fine hole or a crack is structurally weak and has a very poor withstand voltage performance, and thus must be discarded.

Korean Registered Patent Publication No. 10-1133397 (Planar transformer and its manufacturing method) Domestic Publication No. 10-2018-0007177 (Dual Core Planar Transformer)

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and it is not necessary to pre-inner via hole processing and copper plating of the secondary coil printed circuit board laminate, and to drill and copper plate the via hole 11 of the primary coil printed circuit board laminate. It is an object of the present invention to provide a method of manufacturing a transformer coil printed circuit board in which an input primary coil and an output secondary coil are integrally manufactured, thereby improving production efficiency and greatly reducing manufacturing costs.

In addition, the present invention, since the applied solder resist does not flow into the via hole, the thickness of the solder resist layer is uniform and there are no pores or cracks, so that the input primary coil and the output secondary coil can realize excellent withstand voltage characteristics. It is another object to provide a method for fabricating an integrated transformer coil printed circuit board.

A method for manufacturing an integrated transformer coil printed circuit board of the present invention for achieving the above object includes a primary side coil printed circuit board on which a plurality of primary coil layers are formed, and a secondary side on which a plurality of secondary coil layers are formed. A multilayer substrate preparation step of preparing an integrated substrate on which coil printed circuit boards are stacked; Primary drilling for processing the first through hole for forming the primary side via hole, the second through hole for forming the primary and secondary terminal pin holes, and the third through hole for forming the secondary side inner via hole in the prepared integrated substrate. Steps; A copper plating step of plating copper on the inner circumferential surface of the first, second, and third through holes; A second drilling step of cutting a portion of the inner diameter of the third through hole to remove a part of the copper plated layer, thereby disconnecting the copper plated layer in the third through hole from the primary coil layer; A resin plugging step of filling a resin in the first through hole and the third through hole after completion of the first and second drilling steps; And a solder resist forming step of forming a solder resist layer on the surface of the integrated substrate on which the resin plugging step is completed.

In addition, through the second drilling step, a step hole having an inner diameter of at least 0.1 mm larger than the outer diameter of the remaining copper plating layer is formed in the third through hole, and the depth of the step hole is at least 0.2 from the surface of the integrated substrate. It may be at least mm.

In addition, the resin used during the plugging step of the resin, epoxy resin (EPOXY RESIN), BTI resin (BISMALEIMIDE TRIAZINE RESIN), polyamide resin (POLYMID RESIN), aramid resin (ARAMID RESIN), acrylic resin (ACRYLIC RESIN), bis Malemade-triazine resin, polyphenylene ether resin, or polyethylene resin.

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In addition, after the resin plugging step is performed, a curing step of curing the plugging resin inside the first and second through holes is further included.

In the method of manufacturing the integrated transformer coil printed circuit board of the present invention as described above, after stacking and trimming the primary coil printed circuit board and the secondary coil printed circuit board without processing the inner via hole of the secondary printed circuit board in advance. In addition, since the primary coil via hole and the secondary coil via hole are simultaneously processed and copper plated, the production efficiency is good and manufacturing cost can be greatly reduced.

In addition, since the resin is simultaneously filled into the primary coil via hole and the secondary coil inner via hole through the plugging step before applying the solder resist layer, the applied solder resist does not flow into the primary coil via hole or the secondary coil inner via hole. Since the thickness of the solder resist layer is uniform and there are no pores, an input primary coil and an output secondary coil integrated transformer coil printed circuit board having excellent breakdown voltage characteristics can be realized.

1 is a cross-sectional view illustrating a problem of a conventional transformer coil printed circuit board having an input primary coil and an output secondary coil.
2 is a perspective view of an integrated transformer to which an input primary coil and an output secondary coil integrated transformer coil printed circuit board are applied according to an embodiment of the present invention.
3 is a block diagram illustrating a method of manufacturing a transformer coil printed circuit board having an input primary coil and an output secondary coil according to an embodiment of the present invention.
4 to 12 are schematic views illustrating a method of manufacturing an input side primary coil and an output side secondary coil integrated transformer coil printed circuit board according to an exemplary embodiment of the present invention.

Hereinafter, one embodiment according to the present invention will be described in detail with reference to the accompanying drawings.

Basically, in the method of manufacturing the transformer coil printed circuit board of the input side primary coil and the output side secondary coil of the present invention, which will be described later, the via and inner via holes are formed after stacking the primary and secondary coil printed circuit boards before drilling. Has characteristics. The manufacturing method of this process is a method that can lower the manufacturing cost, increase the production speed, and greatly improve the withstand voltage characteristics.

The printed circuit board manufacturing method according to the present embodiment is largely divided into a substrate preparation step, a primary drilling step, a copper plating step, a secondary drilling step, an impurity removal step, a resin plugging step, a curing step, a solar It comprises a resist forming step, marking step, appearance processing and surface treatment step, inspection step. Each step will be described in detail with reference to FIG. 3.

2 is a perspective view of a primary and secondary coil integrated transformer 40 to which an input side primary coil and an output side secondary coil integrated transformer coil printed circuit board 50 are applied, according to an exemplary embodiment.

Referring to the drawings, it can be seen that the integrated transformer coil printed circuit board 50 manufactured by the method according to the present embodiment is wrapped in the ferrite core 60. The ferrite core 60 is to work with the printed circuit board 50, the function is the same as a general ferrite core.

In addition, four primary side terminal pin holes 50a are disposed at one end of the printed circuit board 50, and two secondary terminal pin holes 50b are disposed at the other side. The primary terminal pin hole 50a is connected to an external power source and is connected to the primary coil layer 21b to be described later as a part to receive power. The secondary terminal pin hole 50b is a portion for outputting the transformed power to the outside and is connected to the internal secondary coil layer 31b. The number and positions of the primary side terminal pin holes 50a and the secondary side terminal pin holes 50b naturally vary depending on the type of transformer.

Hereinafter, a method of manufacturing the transformer coil printed circuit board 50 of the input side primary coil and the output side secondary coil according to the present embodiment will be described with reference to FIGS. 3 to 12.

3 is a block diagram illustrating a method of manufacturing a transformer coil printed circuit board having an input side primary coil and an output side secondary coil integrated transformer for a primary and secondary coil integrated transformer according to an embodiment of the present invention, and FIGS. It is a figure which shows the manufacturing method graphically. The same reference numerals as the above-mentioned reference numerals indicate the same members having the same function.

As shown, the method of manufacturing the transformer coil printed circuit board integrated with the input side primary coil and the output side secondary coil according to the present embodiment includes a laminate substrate preparation step 103, a primary drilling step 105, and a copper plating step 107. ), Secondary drilling step 109, impurities removal step 111, resin plugging step 113, curing step 115, solder resist forming step 117, marking step 119, appearance processing and surface treatment Step 111, and inspection step 123.

First, the multilayer substrate preparation step 103 is a process of preparing the integrated substrate 49 shown in FIGS. 4 and 5. The integrated substrate 49 is a structure in which the primary coil layer 21b and the secondary coil layer 31b are embedded therein, and the inner via hole is not formed. The inner via hole is formed through the first and second drilling steps 105 and 109 to be described later.

The detailed structure of the integrated substrate 49 is variously implemented as necessary. For example, the number of layers of the stacked unit substrates, the order of arrangement of the primary coil printed circuit board 20 and the secondary coil printed circuit board 30, and the like, of course, vary depending on the model of the product.

The primary coil printed circuit board 20 is composed of a plurality of unit substrates 21. The unit substrate 21 includes an insulating layer 21a having a predetermined thickness and a primary coil layer 21b formed on the insulating layer 21a.

The insulating layer 21a is a layer obtained by cutting an insulating material having insulation according to a design. As an insulating material, epoxy resin, epoxy resin, polyamide resin, aramid resin, etc. (ARAMID RESIN), ACRYLIC RESIN, bismalemade-triazine resin, polyphenylene ether resin, polyethylene resin. The insulating layer 31a applied to the secondary coil printed circuit board 30, which will be described later, is also made of the same material.

The primary coil layer 21b is manufactured by a conventional printed circuit board manufacturing method. For example, it is formed through a series of processes such as exposure, development, etching, photoresist stripping, and inspection. The circuit pattern of the primary coil layer 21b is different for each unit substrate 21, and is interconnected through a copper plating layer (58 of FIG. 12) in a via hole, which will be described later, as well as the primary terminal pin hole 50a shown in FIG. It is also connected to.

The secondary coil printed circuit board 30 also includes a unit board 31. The number of applications of the unit substrate may naturally vary. The unit substrate 31 is composed of an insulating layer 31a and a secondary coil layer 31b. The insulating layer 31a has the same material as the insulating layer 21a used for the primary coil printed circuit board 20. In addition, like the primary coil layer 21b, the secondary coil layer 31b is manufactured by a general printed circuit board manufacturing method. The secondary coil layer 31b is interconnected through the copper plating layer 58 as shown in FIG. 12, and is connected to an external circuit through the secondary terminal pin holes 50b of FIG. 2.

If the integrated substrate 49 is provided through the laminated substrate preparation step 103, the first drilling step 105 is performed. The primary drilling step 105 is a process of processing the through hole drilled in the thickness direction of the integrated substrate 49. That is, as shown in FIG. 7, the first through holes 53, the second through holes 54a and 54b, and the third through holes 55 are drilled. The position or number of the first, second, and third through holes depends on the shape of the primary and secondary coil layers 21b and 31b.

As shown in FIG. 8, the first through hole 53 is a hole for forming the via hole 57, and the second through holes 54a and 54b are holes for forming the terminal pin hole. Further, the third through hole 55 is a hole for forming the inner via hole 59 and the step hole 56 (through the secondary drilling). The via hole 57 serves to connect the primary coil layer 21b, and the inner via hole 59 functions to connect the secondary coil layer 21b. In addition, the step hole 56 is a groove-shaped hole formed through the secondary drilling step 109, which will be described later.

If the first through-hole 53, the second through-hole 54, the third through-hole 55 is formed through the first drilling step 105, the copper plating step 107 is continued. The copper plating step 107 is a process of plating a copper layer on the inner circumferential surface of the first through hole 53, the second through hole 54, and the third through hole 55.

The copper plating layer (58 in FIG. 7) formed in the first through hole 53 and the second through hole 54a connects the primary coil layer 21b of each unit substrate 21. In addition, the plating layer 57b formed in the third through hole 55 and the second through hole 54b serves to connect the secondary coil layer 31b. This internal circuit connection method itself is common.

If the copper plating layer 58 is formed through the plating step 107, the secondary drilling step 109 is performed. The secondary drilling step 109 is a process of removing a part of the copper plating of the third through hole 55 in which the copper plating layer 58 is formed. That is, by using a drill having a diameter of at least 0.1 mm larger than the drill used in the first drilling step 105, a part of the interior of the third through hole 55 is further processed to form a step hole (56 in FIG. 8). will be.

The secondary drilling step 109 includes an upper stepping step 109a and a lower stepping step 109b. The upper step drilling step 109a is, for example, a step of forming a step hole 56 extending downward from the upper surface of the integrated substrate 49 laid horizontally, and the lower drilling step 109b extends from the bottom to the upper part. This is a process of forming the step hole 56. The diameter of the upper and lower step holes 56 may be the same or different from each other depending on the structure of the third through hole 55.

In particular, the inner diameter (D2 of FIG. 8) of the step hole 56 is at least 0.1 mm larger than the inner diameter D1 of the inner via hole 59, and the depth A is at least 0.2 mm from the surface of the integrated substrate 49. to be. If it does not have the size mentioned above, it does not satisfy the withstand voltage performance specified in international safety regulations.

As the step hole 56 is formed, the plating layer 57b corresponding to the depth of the step hole is completely removed. The plating layer 57b remaining after finishing the second drilling step 109 is disconnected from the primary coil layer 21b to become an inner via hole (IVH) 59. That is, as shown in Fig. 8, the plating layer 57b remaining inside the third through hole 55 connects only the secondary coil layer 31b.

After the secondary drilling step 109 is completed, the impurity removal step 111 is performed. The impurity removal step 111 is a process in which the inside of the step hole 56 is pickled and washed with high pressure and then dried. Of course, even if impurities remain in the step hole 56, the breakdown voltage characteristic is reduced.

Subsequently, the resin plugging step 113 is performed. The resin plugging step 113 is a process of filling an insulating material into the input coil via hole 57 and the output side step hole 56. The insulating material is an insulating resin series. Resin that can be used is epoxy resin (EPOXY RESIN), BTI resin (BISMALEIMIDE TRIAZINE RESIN), polyamide resin (POLYMID RESIN), aramid resin (ARAMID RESIN), acrylic resin (ACRYLIC RESIN), bismalemade triazine resin , Polyphenylene ether resin, polyethylene resin. The resin plugging step 113 may be performed in various ways including a silk screen method or a roll method.

As shown in FIG. 10, the resin 61 is cured through a subsequent curing step 115 while being filled in the input side coil via hole 57 and the output side step hole 56. The curing method of the resin depends on the resin characteristics and types, for example, UV curing, infrared curing, and thermal curing can be applied.

In particular, in the resin 61, the resin plugged into each step hole 56 has an insulating property between the primary coil layer 21b, the secondary coil layer 31b, and the ferrite core (60 in FIG. 2). Secure (withstand voltage). By filling the resin 61, the primary coil layer 21b, the secondary coil layer 31b, and the ferrite core 60 are completely insulated, thereby ensuring the withstand voltage characteristic.

The process after completing the curing step 115 follows the conventional manner. For example, after the outer circuit pattern is formed on the outer surface of the integrated substrate 49, the solar resist layer (16 in FIG. 11) is implemented through the solder resist forming step 117, and the marking layer (through the marking step 119) 18) to form. The solder resist layer 16 is formed by a conventional solder masking method. In addition, the marking step 121 is the same as the conventional method for marking a printed circuit board.

In addition, after the marking step 119 is finished, the surface treatment and appearance processing step 111 is performed. Surface treatment and appearance processing step 111 may follow a known method.

In addition, the external processing is a process of cutting and punching the resulting product to a certain size and shape using a laser or a water jet.

If the marking step 121 is completed, the inspection step 123 is performed. The inspection step 123 is a standard and method for determining the specifications and required quality of the finished product, that is, the transformer coil printed circuit board (50 in FIG. 12) of an input primary coil and an output secondary coil. Based on the process of inspection.

Through all the above processes, the transformer coil printed circuit board 50 having an input primary coil and an output secondary coil integrally illustrated in FIG. 12 are completed.

12 is a cross-sectional view of the transformer coil printed circuit board 50 of the input side primary coil and the output side secondary coil integrated manufactured by the manufacturing method.

As shown in the drawing, the resin 61 is filled in the via hole 57 and the step hole 56 so that the primary coil via hole 57 and the secondary coil inner via hole 59 are completely blocked and sealed. Withstand voltage reliability guarantee between secondary coil and ferrite core.

In addition, since there is no empty space due to the filling of the primary coil via hole 57 or the secondary coil inner via hole 59, the solder resist layer 16 applied to the outside of the integrated substrate 49 may have a marking layer 18. In addition, a certain thickness is achieved. As shown in FIG. 1, the conventional products have a portion of the solder resist layer introduced into the via hole, so that the thickness of the solder resist layer is uneven and the breakdown voltage characteristics are poor due to the puncture cracking, but the product manufactured by the manufacturing method of the present invention The thickness of the solder resist layer is uniform and there is no fine bubble, and the voltage resistance performance is good. In addition, since the secondary coil layer 31b is completely embedded by the plugged resin 61, insulation with the ferrite core 60 is ensured. Therefore, it has excellent withstand voltage performance.

As mentioned above, although this invention was demonstrated in detail through the specific Example, this invention is not limited to the said Example, A various deformation | transformation is possible for a person with ordinary knowledge within the scope of the technical idea of this invention.

10: coil printed circuit board 11: via hole 12: copper plated layer
13: Inner via hole 15: Insulation layer 16: Solder resist layer
17: Terminal pin hole 18: Marking layer 20: Primary coil printed circuit board
21: unit substrate 21a: insulating layer 21b: primary coil layer
30: secondary coil printed circuit board 31: unit board 31a: insulating layer
31b: Secondary coil layer 40: Integrated transformer 49: Integrated board
50: integrated transformer coil printed circuit board 50a: primary terminal pin hole
50b: Secondary terminal pin hole 53: First through hole 54a, 54b: Second through hole
55: third through hole 56: step hole 57: via hole
58: copper plating layer 59: Inner via hole 61: resin

Claims (5)

A multilayer substrate preparation step of preparing an integrated substrate on which a primary coil printed circuit board on which a plurality of primary coil layers are formed, and a secondary coil printed circuit board on which a plurality of secondary coil layers are formed;
Primary drilling for processing the first through hole for forming the primary side via hole, the second through hole for forming the primary and secondary terminal pin holes, and the third through hole for forming the secondary side inner via hole in the prepared integrated substrate. Steps;
A copper plating step of plating copper on the inner circumferential surface of the first, second, and third through holes;
A second drilling step of cutting a portion of the inner diameter of the third through hole to remove a part of the copper plated layer, thereby disconnecting the copper plated layer in the third through hole from the primary coil layer;
A resin plugging step of filling a resin in the first through hole and the third through hole after completion of the first and second drilling steps;
A method of manufacturing a transformer coil printed circuit board having an input primary coil and an output secondary coil, the method comprising: forming a solder resist layer on a surface of an integrated substrate on which the resin plugging step is completed. The method of claim 1,
Through the second drilling step, a step hole having an inner diameter of at least 0.1 mm larger than the outer diameter of the remaining copper plating layer is formed in the third through hole,
A method for manufacturing a transformer coil printed circuit board having an input primary coil and an output secondary coil having a depth of at least 0.2 mm from a surface of an integrated substrate. The method of claim 1,
The resin used in the resin plugging step is epoxy resin, bismale resin triazine resin, polyimide resin, aramid resin, acrylic resin, bismale maid A method for manufacturing a transformer coil printed circuit board having an input primary coil and an output secondary coil, which are any one of triazine resin, polyphenylene ether resin, and polyethylene resin. The method of claim 2,
After the secondary drilling step is completed, the input side primary coil and output side secondary coil integrated transformer coil printed circuit board manufacturing method further comprises an impurity removing step of removing impurities inside the step hole. delete

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