JP6629909B2 - Flexible printed circuit board - Google Patents

Description

  The present invention relates to a flexible printed circuit board that ensures reliable electrical connection with a counterpart electrode.

  For example, a strain gauge that measures the strain of a structure is formed on a very thin flexible printed circuit board, and is used for signal transmission that is electrically connected to the electrodes on this board in order to extract the output from the strain gauge. Flexible printed circuit boards are soldered.

  Techniques for performing solder bonding between the electrodes of the former flexible printed circuit board and the mating electrodes provided on the latter flexible printed circuit board are generally known (for example, see Patent Documents 1 and 2). .

JP 2006-303354 A Japanese Utility Model Publication No. 5-29178

  The lands of the solder joints of the flexible printed circuit boards described in Patent Documents 1 and 2 described above do not have a special structure that allows air to escape to the outside during thermocompression bonding. May remain and the solder joint may be peeled off. Specifically, when the preliminary solder is melted and filled in the through-hole, there is no escape space for air in the through-hole, and an air layer is formed between the copper foil and the solder. It causes peeling.

  SUMMARY OF THE INVENTION An object of the present invention is to provide a flexible printed circuit board having an electrode which has excellent solder bonding strength of a solder connection portion with a counterpart electrode and which ensures sufficient conductivity for a long period of time.

According to a first aspect of the present invention,
A flexible printed circuit board,
An insulating layer having a first surface and a second surface and having a through hole extending between the first surface and the second surface;
A first metal land provided around an opening defined on the first surface by the through hole on the first surface; and a second metal surface defined by the through hole on the second surface. A second metal land provided around the opening;
A metal connecting portion provided inside the through hole and connecting the first metal land portion and the second metal land portion;
In the first metal land portion, a passage is formed at a position lower than the top of the first metal land portion to fluidly connect the through hole and the outside of the first metal land portion to each other,
A flexible printed circuit board is provided in which the second metal land surrounds the opening defined on the second surface by the through hole on the second surface.

  In the flexible printed board according to the first aspect, the metal connection portion may be provided on an inner peripheral surface of the through hole.

  In the flexible printed circuit board according to the first aspect, the metal connection portion may be provided on the entire inner peripheral surface of the through hole.

  In the flexible printed circuit board according to the first aspect, the metal connection portion may cover a side surface of the insulating layer that defines the through hole.

  In the flexible printed circuit board according to the first aspect, the first metal land portion may be a disk-shaped member that covers the through hole, and the passage extends in a radial direction of the disk-shaped member, and It may be a slit that divides the shaped member into two parts.

  The flexible printed circuit board of the first aspect may be a flexible printed circuit board which is soldered to a counter electrode using a heater, and the top of the first metal land portion is brought into contact with the heating surface of the heater. When the heating surface of the heater is brought into contact with the contact surface of the first metal land portion, the air in the through-hole passes through the passage and the first metal land. It may be released outside the part.

  In the flexible printed circuit board according to the first aspect, the passage may be a groove.

  In the flexible printed circuit board according to the first aspect, a solder escape portion may be provided on the wiring connected to the second metal land.

  In the flexible printed circuit board according to the first aspect, the first metal land portion where the passage is formed may include a plurality of land portions arranged in a staggered manner.

  In the flexible printed circuit board according to the first aspect, each passage of the plurality of lands may be a groove, and may be formed in a longitudinal direction of a groove of one of two adjacent lands among the plurality of lands. The extended line along the longitudinal direction of the groove included in the other groove may not coincide with the extended line along the longitudinal direction of the groove.

  In the flexible printed circuit board according to the first aspect, the second metal land may have an annular shape.

  In the flexible printed circuit board according to the first aspect, the through hole may be defined by being surrounded by a side surface of the insulating layer extending between a first surface and a second surface, and the through hole may be defined. The metal connecting portion may be provided on the entire side surface of the insulating layer to be formed.

  ADVANTAGE OF THE INVENTION According to this invention, the flexible printed circuit board which has the electrode which is excellent in the solder joint strength of the solder connection part with the other party electrode and ensures sufficient electrical conductivity for a long period of time can be provided.

FIG. 2 is a perspective view of a flexible printed circuit board according to one embodiment of the present invention as viewed from one of the land portions of its electrodes. FIG. 2 is a perspective view showing a mating electrode soldered to the flexible printed circuit board shown in FIG. 1. FIG. 3 is an explanatory view of a welding step along a section taken along the line III-III of FIG. 1 at a stage immediately before the electrodes of the flexible printed circuit board shown in FIG. 1 are soldered to the mating electrodes shown in FIG. FIG. 4 is an explanatory view of a welding step showing a state where the flexible printed circuit board is completely pressed against the counterpart electrode by the pulse heater, following FIG. 3. FIG. 2 is a plan view illustrating an example of a flexible printed board including a plurality of lands illustrated in FIG. 1. FIG. 6 is a perspective view showing a land portion shape (FIG. 6B) according to a modification of the embodiment of the present invention in comparison with a land portion shape (FIG. 6A) according to an embodiment of the present invention. is there.

  Hereinafter, a flexible printed board 1 according to an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a perspective view of a flexible printed circuit board 1 according to one embodiment of the present invention as viewed from one land portion side of its electrodes. FIG. 2 is a perspective view showing a mating electrode soldered to the flexible printed circuit board 1 shown in FIG. FIGS. 3 and 4 are explanatory views showing the flexible printed circuit board 1 according to the present embodiment and a part of the flexible printed circuit board having the mating electrode for connecting the same in the order of the thermocompression bonding step.

  It should be noted that the size, thickness, and size of each component in the present embodiment and each modified example thereof, as well as in the drawings related to the related art, are exaggerated from the actual size in order to facilitate understanding of the invention.

  As shown in FIGS. 3 and 4, the flexible printed circuit board 1 according to the present embodiment is formed on a flexible insulating layer 11 made of polyimide (PI) and an upper surface (one surface) of the insulating layer 11. And the conductor pattern 12 formed on the lower surface (the other surface) of the insulating layer 11. The conductor pattern 12 and the heating land portion 130 are electrically connected via the through hole 140. I have. The conductor pattern 12 is made of a rolled copper foil and has a welding-side land portion 120 having an annular shape; a conductive thin wire pattern (wiring) 125 extending from the welding-side land portion 120 along the insulating layer 11; An insulating coating portion 129 covers the entire flexible printed circuit board except for those portions necessary for establishing electrical conduction with the electrodes.

As shown in FIG. 1 and FIG. 6A, the heating-side land portion 130 has two substantially semi-circular disks in plan view (hereinafter, referred to as “semi-circular plates”) opposed to each other with a small space therebetween. The rolled copper foil and the groove 131 sandwiched between the two rolled copper foils combine to form a disk (hereinafter, referred to as a “disk”) in plan view. That is, the groove 131 is formed as one form of the recess of the heating-side land 130. The heating-side land portion 130 is formed on the upper surface of the insulating layer 11 so as to be concentric with the welding-side land portion 120 in plan view of the flexible printed circuit board 1. Further, the heating-side land portion 130 and the welding-side land portion 120 are electrically connected to each other via a rolled copper foil 141 that covers the inner peripheral surface of the through hole 140. That is, the heating side land portion 130, the through hole 140 formed in the flexible printed circuit board 1, and the welding side land portion 120 are electrically and thermally connected via the rolled copper foil 141 in the through hole.

  Next, the structure of the mating electrode 220 to which the above-described flexible printed circuit board 1 is connected will be described. In the present embodiment, the mating electrode 220 shown in FIG. 2 is an electrode provided at an end of the flexible printed circuit board 20 having a strain gauge (not shown here). The end portion of the flexible printed circuit board 20 has a base portion 21, a gauge-side conductor pattern 22 provided on the upper surface of the base portion 21 and made of rolled copper foil, and a slightly raised portion on the wide surface of the end portion of the gauge-side conductor pattern 22. A spare solder 230 provided as described above, and a cover glass 25 that covers the base portion to protect the gauge-side conductive pattern 22 except for the raised portion of the spare solder 230 are provided.

  Next, a procedure for thermocompression bonding the preliminary solder 230 of the gauge-side conductor pattern 22 to the welding-side land 120 of the flexible printed circuit board 1 will be described. FIG. 3 is an explanatory view of a welding step showing a stage immediately before the electrodes of the flexible printed circuit board 1 shown in FIG. 1 are soldered to the mating electrodes shown in FIG. FIG. 4 is a welding process diagram showing a state in which the flexible printed circuit board 1 is completely pressed against the partner electrode by the pulse heater H following FIG.

  In welding the welding-side land portion 120 of the flexible printed circuit board 1 to the mating electrode 220 via solder, first, as shown in FIG. The lower surface opening of the through hole 140 of the flexible printed circuit board 1 is positioned closer to the upper part. Next, the pulse heater H is lowered while being pressed against the upper surface of the heating-side land portion 130 of the flexible printed circuit board 1. By pressing the pulse heater H against the upper surface of the heating-side land portion 130 in this manner, the heat of the pulse heater H is transmitted to the welding-side land portion 120 of the flexible printed circuit board 1 via the rolled copper foil 141 in the through hole. Subsequently, by further lowering the pulse heater H, the lower opening of the through hole 140 of the flexible printed circuit board 1 and the welding land portion 120 around it are pressed against the preliminary solder 230 and pressed. Is transferred to the preliminary solder 230, and the preliminary solder 230 is melted.

  As shown in FIG. 4, a part of the molten solder 230A travels through the through hole and rises as a whole so as to fill the through hole 140 without any gap. At this time, the air in the space formed by the upper surface of the preliminary solder 230, the lower surface of the pulse heater, and the inner peripheral surface of the through hole 140 passes through the groove 131 of the heating land 130 as the molten solder 230A rises. Released to the outside. After the melted solder 230A reaches the upper surface of the pulse heater H, the excess solder 230B flows into the groove 131 of the heating-side land 130 from the upper surface opening of the through hole 140.

  Then, the solder 230A melted by separating the pulse heater H from the heating-side land portion 130 cools down, and the mating electrode 220 of the gauge-side conductor pattern 22 and the welding-side land portion 120 of the flexible printed circuit board 1 and the inner peripheral surface of the through hole, It is firmly fixed to a part or the whole of the groove 131 of the heating-side land portion 130, and the welding-side land portion 120 and the mating electrode 220 of the gauge-side conductor pattern 22 are reliably electrically connected.

  Conventionally, air in a space formed by the upper surface of the preliminary solder, the lower surface of the pulse heater, and the inner peripheral surface of the through hole remains in this space when welding the preliminary solder by heating the pulse heater, and the other electrode of the gauge-side conductor pattern or Although an air layer was formed between the inner peripheral surface of the through hole and the solder, poor welding of the solder and eventually poor conduction between the welding side land portion of the flexible printed circuit board and the counter electrode of the flexible printed circuit board were caused. Since the flexible printed circuit board 1 according to the present embodiment has the above-described configuration, the air in the space does not remain in the solder welding portion, and the above-described conventional problem can be avoided.

  In addition, in addition to the configuration of the above-described embodiment, although not shown in detail here, the welding-side land is partially provided on the conductive thin wire pattern (wiring) 125 connected to the welding-side land portion formed on the other surface. A solder escape portion which is not covered with the resist by a certain length from the portion 120 may be formed. By having such a solder escape portion, in the process of melting the preliminary solder 230 by the pulse heater H, a part of excess solder flows into the groove of the land portion on the flexible printed circuit board side as in the above-described embodiment. At the same time, in addition to this, a part of the remaining excess solder flows into the solder escape portion, so that air accumulation in the solder welding portion can be more reliably prevented.

  FIG. 5 is a plan view showing an example of the flexible printed circuit board 2 provided with a plurality of welding side lands 120 and heating side lands 130 shown in FIG. .. 336 (330) provided on the upper surface of the flexible printed board 2 with grooves are the same as those in the above-described embodiment, but a plurality of heating-side lands are provided. It is characterized in that 330 are arranged in a zigzag pattern in the width direction of the flexible printed circuit board 2. Further, on the lower surface of the flexible printed circuit board 2, welding side lands 321, 322,... 326 (320) having a circular shape in plan view of the conductor pattern are formed at positions corresponding to the plurality of heating lands 330 described above. Have been. That is, the plurality of welding-side lands 320 are also arranged in a staggered manner in the width direction of the flexible printed circuit board 2, similarly to the heating-side lands 330.

As is apparent from FIG. 5, the longitudinal extension of the groove formed in each of the plurality of heating-side lands 331, 332,. The conductor patterns corresponding to the side lands 330 are formed so that the extending directions thereof coincide with each other. In the present invention, it is preferable that among the plurality of heating-side lands arranged in a staggered manner, the extension lines along the longitudinal direction of the grooves of the adjacent heating-side lands do not coincide with each other. The reason for this is that, assuming that the extension lines along the longitudinal direction of the grooves of the adjacent heating-side lands coincide with each other among the plurality of heating-side lands arranged in a staggered manner, the distance between the adjacent heating-side lands is assumed. In this case, the solder flowing out from the outlet of the opposed groove at the time of melting the solder adheres to each other while adhering to each other, and there is a risk that short-circuiting (short-circuit) occurs between the heated lands.

  .. 326a (320a) extend from each welding-side land portion 320 in the direction in which the flexible printed circuit board 2 extends. Since the plurality of welding-side lands 320 are also arranged in a staggered manner, the conductive thin wire patterns 321a, 322a, The reference numeral 323a extends in the vicinity of the adjacent welding land portions 324 arranged on the base end side or between the welding land 324, 325, 326 in an electrically non-contact state. Since the plurality of heating-side land portions 330, the welding-side land portions 320, and the conductive thin wire patterns 320a are arranged in this manner, the mounting density of the flexible printed circuit board 2 is increased, and the width of the flexible printed circuit board itself is reduced to reduce the size. It is possible to make.

  The above advantages will become more apparent by comparison with the following conventional example. As an example of a flexible printed circuit board according to this conventional example, there is a flexible printed circuit board having a structure in which a comb-shaped electrode is formed and soldered to a mating electrode of a strain gauge.

  Each of the comb teeth of the comb-shaped electrode of such a flexible printed board has a thin and elongated projection shape. Therefore, a land portion is formed on each of the plurality of comb-shaped electrodes, and as is apparent from the present invention in which the plurality of land portions are arranged in a staggered manner on the flexible printed circuit board as described above, In the flexible printed circuit board according to the above, the pitch between adjacent electrodes cannot be reduced. As a result, the conventional example still has a problem that the integration degree of the flexible printed circuit board cannot be improved. However, the flexible printed board according to the present invention having the above-described configuration can increase the degree of integration of the board itself, and can achieve downsizing even with the same number of electrodes.

  In addition, since the comb-shaped electrode has a thin and elongated protrusion shape as described above, it is easily bent (is easily deformed), and extra external force is applied to the comb-shaped electrode during soldering. Care must be taken not to add. However, since the flexible printed circuit board according to the present invention does not have such a configuration, handling at the time of solder bonding is much easier than in the conventional example.

  Note that the present invention is not limited to the above-described embodiment, and can exert its effects even in the following forms. Specifically, for example, as shown in FIG. 6B, the heating-side land portion 430 forms an annular shape (a donut shape) having a hole 435 communicating with the through hole 140 at the center. The groove (concave portion) 431 formed in the portion 430 may be formed to such a depth as to leave a part of the heating-side land portion 430. In the case where the depth of the groove portion reaches halfway to the height of the heating-side land portion, a through hole communicating the groove portion and the through hole is provided on the bottom surface of the groove portion.

  In addition, instead of the heating-side land portion of the above-described embodiment including two semi-circles and a groove portion therebetween, the heating-side land portion has only one semi-circle, and when the extra solder melts, the heating-side land portion has a semi-circle. You may make it flow out to the area | region other than. Further, the groove does not need to be formed over the length of the diameter of the disc-like heating land as in the above-described embodiment, and the heating land is heated from the upper opening of the through hole 140. It may be formed by the length of the radius up to the outer periphery of the side land portion. In this case, the depth of the groove may be such that it reaches the bottom surface of the heating-side land portion as in the above-described embodiment, or is such a depth that the heating-side land portion is partially left as in the above-described modification. It does not matter.

  Further, only one protrusion may be provided on the upper surface of the conventional heating side land portion having a complete annular shape and the same height in the circumferential direction, or the protrusions having the same protrusion height may be formed in the circumferential direction of the upper surface. A plurality of locations may be provided.

  Further, the height of the annular heating-side land portion may be periodically changed like a sin curve over the circumferential direction, or a step having the same height may be periodically formed at a plurality of locations over the circumferential direction. good. That is, even if the heating-side land portion is completely annular, the upper surface of the heating-side land portion against which the pulse heater is pressed is not at a constant height as in the conventional heating-side land portion, and is within the scope of the present invention. It can be said that it is included.

  As described above, the recessed portion in the present invention is formed by a groove formed until reaching the height of the land portion bottom surface so as to divide the disk-shaped heating land portion into two semi-disks so as to be slightly separated from each other. When, for example, three columnar projections having the same height are provided around the opening on the upper surface of the hole, this has a wide meaning including a gap between the projections.

  More specifically, the present invention relates to a flexible printed board in which a conductor is formed on upper and lower surfaces of a flexible insulating layer, as is apparent from one embodiment in the above-mentioned specification. In a flexible printed circuit board in which a concave portion (groove portion) is formed in a land formed on one surface of the flexible printed circuit board, a through hole is formed in the flexible printed circuit board. It relates to the flexible printed circuit board which is connected to the land at the formed opening, the through-hole and the recess communicate with each other and communicates with the outer periphery of the recess and the land, but within the scope of the present invention. As can be seen from the description of the modification in the above specification, the recessed portion is a part of the periphery of the opening of the through hole. A form that is provided and excludes a protrusion that forms a part of the land, a form in which the protrusion has a substantially semicircular shape when viewed from the top surface direction of the land, and a form in which the protrusion is an opening of a through hole. It is clear that the present invention also includes a form including a plurality of protrusions having the same height and formed at regular intervals in the circumferential direction.

  Further, in the above-described embodiment, the mating electrode connecting the flexible printed circuit board is an electrode of a strain gauge, but is not necessarily limited to such an electrode, and achieves the object of the present invention. It goes without saying that the electrodes of the flexible printed circuit board according to the present invention can be securely soldered to the mating electrodes as long as the mating electrodes are within the range of the electric and electronic components.

Further, instead of providing the concave portion (groove portion) in the heating-side land portion as described above, the heating-side land portion is formed into an annular shape having a constant upper surface height as in the related art. A concave portion (groove) having a shape corresponding to the concave portion (groove) is provided on the pulse heater side, and molten solder flows through the hole at the center of the annular heating-side land to form a concave portion (groove) on the pulse heater side. ).

Reference numerals 1 and 2 Flexible printed circuit board 11 Insulating layer 12 Conductive pattern 21 Base part 22 Gauge side conductive pattern 25 Cover glass 120 Welding side land part 125 Conducting thin wire pattern 129 Insulating coating part 130 Heating land part 131 Groove (dent)
140 Through hole 141 Rolled copper foil 220 Counter electrode 230 Preliminary solder 230A Fused solder 230B Extra solder 321, 322,... 326 (320) Welding side land 321a, 322a,. 336 (330) Heating land portion 430 Heating land portion 431 Groove (concave portion)
435 holes H pulse heater

Claims (11)

A flexible printed circuit board,
An insulating layer having a first surface and a second surface and having a through hole extending between the first surface and the second surface;
A first metal land portion provided on the first surface around an opening defined on the first surface by the through hole;
A second metal land portion provided on the second surface around an opening defined on the second surface by the through hole;
A metal connecting portion provided inside the through hole and connecting the first metal land portion and the second metal land portion;
A recess is formed in the first metal land to fluidly connect the through hole and the outside of the first metal land to each other.
A second metal land portion, on the second surface, surrounding the periphery of the opening defined by the through hole on the second surface ;
The flexible printed circuit board is a flexible printed circuit board that is soldered to a mating electrode using a heater, and a top portion of a first metal land portion is a contact surface where a heating surface of the heater is contacted. A flexible print in which air in the through hole is discharged to the outside of the first metal land through the recess when the heating surface of the heater is brought into contact with the contact surface of the first metal land. substrate.   The flexible printed circuit board according to claim 1, wherein the metal connection portion is provided on an inner peripheral surface of the through hole.   The flexible printed circuit board according to claim 2, wherein the metal connection portion is provided on the entire inner peripheral surface of the through hole.   The flexible printed circuit board according to claim 1, wherein the metal connection unit covers a side surface of the insulating layer that defines the through hole.   The first metal land portion is a disk-shaped member that covers the through hole, and the recess is a slit that extends in a radial direction of the disk-shaped member and divides the disk-shaped member into two parts. The flexible printed circuit board according to claim 1. The flexible printed board according to claim 1, wherein the recess is a groove. The flexible printed circuit board according to any one of claims 1 to 6, wherein a solder escape portion is provided on the wiring connected to the second metal land portion. The flexible printed circuit board according to any one of claims 1 to 7, wherein the first metal land portion in which the concave portion is formed includes a plurality of land portions arranged in a staggered manner. Each of the recesses of the plurality of lands is a groove, and an extension line along a longitudinal direction of a groove of one of two adjacent lands of the plurality of lands and a length of a groove of the other. 9. The flexible printed circuit board according to claim 8, wherein extension lines along the direction do not coincide with each other. The flexible printed circuit board according to claim 1, wherein the second metal land has a ring shape. The through-hole is defined by being surrounded by a side surface of the insulating layer extending between a first surface and a second surface, and the through-hole is formed over the entire side surface of the insulating layer that defines the through-hole. The flexible printed circuit board according to any one of claims 1 to 10, further comprising a metal connecting portion.

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