JP3747043B2 - Manufacturing method of three-dimensional circuit board - Google Patents

Description

The present invention relates to a method for manufacturing a three-dimensional circuit board.

In recent years, circuit boards have achieved the miniaturization of electronic equipment by reducing the distance between circuit patterns, that is, the pitch, to the limit in accordance with the so-called light, thin and small market needs, and technology for saving resources and energy. Development is required. Therefore, circuit patterns are formed on both the front and back surfaces of the circuit board, and through-hole conductor layers that electrically connect both circuit patterns are formed. And in order to drill this through hole, conventionally, it was by mechanical work using a drill, but in recent years, through holes have been formed simultaneously with the molding of circuit boards by injection molding. (Patent Documents 1, 2, and 3).
JP 61-239694 A JP 63-128181 A US Patent No. 4424095

A basic manufacturing method of the conventional three-dimensional circuit board 11 will be described with reference to FIGS. 5 to 7. Circuit patterns 31, 31..., 41, 41. And a through hole 51 electrically connected between the circuit patterns on both sides is formed, and the diameter of the through hole is on the order of several tens of microns. For injection molding, a cylindrical pin for through-hole molding is used in a mold, and the diameter of this pin is also in the order of several tens of microns, for example, 30 to 50 microns. The inner diameter of the circular through hole 51 is the same straight shape, and the ratio of the thickness of the circuit board 21 to the inner diameter of the through hole 51, the so-called aspect ratio is limited to about 5 times, and this 5 times If it is within the range, the electroless plating can be deposited, but if it exceeds 5 times, the electroless plating is difficult or impossible to deposit.

  However, as the electronic equipment is miniaturized, the inner diameter of the through hole 51 must be as small as several tens of microns as described above in order to reduce the pitch of the circuit patterns 31 on the circuit board. As a result, when the aspect ratio is high, when a circuit board is molded with a molding die, the die, particularly the pin for through-hole molding, cannot withstand the liquid injection flow resistance, and accidents that cause damage frequently occur. Furthermore, there is a problem that the aspect ratio becomes high and does not precipitate beyond the deposition limit of electroless plating.

Therefore, the problem to be solved by the present invention is that a method of manufacturing a three-dimensional circuit board that prevents damage to the molding pins of the mold, ensures the deposition of plating, and thereby narrows the circuit pitch to the limit. Is to provide.

The first feature of the method of manufacturing a three-dimensional circuit board according to the present invention, by forming a through hole by molding pin in the primary molded article is injection molded of dielectric material, plating on both surfaces of a circuit board consisting of the primary molded article processed by forming a predetermined circuit pattern made of a conductive material, there is forming a conductive layer for electrically connecting both sides of the circuit pattern of the circuit board in the through hole, the shape of the through-holes adjacent It is narrow in the direction between circuit patterns and long in the circuit extending direction. As described above, the shape of the through hole exposed from the circuit pattern is narrow in the direction between adjacent circuit patterns and long in the circuit extending direction, and examples thereof include a rectangle and an ellipse.

  The second feature is that the shape of the through hole sectioned in the thickness direction of the circuit board is tapered. The taper shape means that the through hole is tapered in the direction of the circuit between adjacent circuit patterns and further expanded in the circuit extending direction of the circuit pattern, or the direction between the circuit patterns or the circuit extending direction. One of these is tapered and opened.

Furthermore, the third feature is that a partition is formed on a circuit board between circuit patterns. This is because, as described above, since the circuit pitch is formed extremely narrow, paste solder is used when soldering and mounting a lead wire terminal, for example, on this circuit pattern. There is a risk of short-circuiting between adjacent circuit patterns due to scattering, and this partition is for preventing this scattering.

  Further, the fourth feature is that the through hole is a blind through hole in which the through hole is filled with plating.

The effect of the present invention is to prevent breakage of the mold, particularly the molding pin, and to allow reliable deposition of plating, so that the circuit pitch of the three-dimensional circuit board can be narrowed to the limit. Furthermore, it is possible to prevent solder from being scattered during mounting and to prevent a short circuit. In particular, if the through hole is a blind through hole, the flux cleaning process at the time of solder mounting can be omitted, and further, the outflow of solder can be prevented, so that the reliability of the three-dimensional circuit becomes higher.

Referring to FIGS. 1 to 3, to describe the structure of a three-dimensional circuit board 1 according to the present invention, the primary molded article to a plating treatment to the surface of the circuit board 2, the material of the insulating material, as shown in FIG. 1 Are formed with conductive circuit materials, and predetermined circuit patterns 4, 4... Are formed on the back surface as shown in FIG. On the circuit board 2, as shown in an enlarged view in FIG. 2, conductor layers 5a of through holes 5, 5... For electrically connecting the circuit patterns 3, 3,. .

  The inner surface shape of the through holes 5, 5... Is narrow in the direction between adjacent circuit patterns 3, 3, that is, in the left-right direction in FIG. 1, and is long in the circuit extending direction, that is, in the up-down direction in FIG. In this rectangular shape, not only the upper end opening 5b but also the lower end opening 5c of this through hole is narrow in the direction between adjacent circuit patterns 4, that is, in the horizontal direction in FIG. 3, and in the circuit extending direction, that is, in the vertical direction in FIG. Long. That is, it is rectangular. The shape of the through hole 5 is not limited to a rectangular shape, and may be an elliptical shape that is long in the vertical direction. Therefore, the molding pin for the through hole 5 having such a shape can be used with a larger diameter than the conventional one, and the risk of breakage of the pin is reduced.

  The cross-sectional shape of the circuit board 2 in the thickness direction, as shown in FIG. 2, is a taper shape expanding from the upper end opening 5b on the surface of the through holes 5, 5... is there. Therefore, the lower end opening 5c opened in the circuit pattern 4 on the back surface of the circuit board 2 is about twice as large as the upper end opening 5b on the front surface, as is clear when FIG. 1 is compared with FIG. It has become. At the same time, the width of the circuit pattern 4 on the back surface of the circuit board 2 is also about twice that of the circuit pattern 3 on the front surface. As shown in FIG. 2, the tapered shape of the through hole 5 is the inter-circuit direction between the circuit patterns 3, 3,..., 4, 4. In addition to the direction, the circuit patterns 3 and 4 have a taper shape that expands in the circuit extending direction, that is, in both the vertical directions of FIGS. However, the shape is not limited to such a shape expanded in both directions, and is expanded toward one of the adjacent circuit patterns 3, 3,..., 4, 4,. An open tapered shape may be used.

  Thus, by making the through hole 5 tapered, even if the aspect ratio is apparently 10 times, for example, the aspect ratio is substantially about 5 times. Therefore, the inside of the through hole is a catalyst solution or an electroless solution. Smoothly circulates and flows, ensuring catalyst deposition and plating deposition. Further, the through-hole forming pins themselves can be formed in a trapezoidal cross section, and the risk of breakage is significantly reduced.

  In recent years, the pitch of the circuit patterns 3 and 4 has been extremely narrowed to near the limit. Therefore, when soldering and mounting, for example, a lead wire terminal to this circuit pattern, this solder, particularly in a paste form Since there is a risk that the splash of solder will be scattered and the circuit patterns 3 and 3 adjacent to each other will be short-circuited, a partition wall 6 is formed between the circuit patterns in order to prevent this scattering.

  Next, with reference to (A)-(F) of FIG. 4, the manufacturing process of the three-dimensional circuit board which concerns on this invention is demonstrated. FIG. 4A shows a primary molded product 20 formed by injecting a plating grade liquid crystal polymer into the cavity with the mold closed, and the outer shape of the primary molded product is the circuit board 2 which is the final product. In this primary molded product, a through hole 5 is formed by a molding pin. As this liquid crystal polymer, an aromatic polyester is used. The primary molded product 20 is plated, but first, as shown in FIG. 4B, the surface becomes a surface 20a roughened by chemical etching. The etching process is performed, for example, by heating an alkaline aqueous solution in which caustic soda or caustic potash is dissolved at a predetermined concentration to a predetermined temperature and immersing the primary molded product 20 for a predetermined time. Thereafter, the primary molded product 20 is inserted into the mold again. At this time, a cavity having a shape having a predetermined gap is formed on the outer periphery of the primary molded product 20 in the mold, and with this mold closed, an axylene group-containing polyvinyl alcohol resin (for example, a mask agent) , “Ecomati AX” (trade name of Nippon Synthetic Chemical Industry Co., Ltd.) is injection molded to form a secondary molded product 200 in which a mask 7 is formed on a predetermined surface as shown in FIG. Therefore, as shown in FIG. 4D, a catalyst 8 made of palladium, gold, or the like is applied to the roughened surface 20a of the secondary molded product 200. This catalyst application is a known method. For example, after the secondary molded product 200 is immersed in a mixed catalyst solution of silver and palladium, the catalyst is activated with an acid such as hydrochloric acid or sulfuric acid to deposit palladium on the surface. Alternatively, a relatively strong reducing agent such as stannous chloride is adsorbed on the surface and immersed in a catalyst solution containing noble metal ions such as gold. At this time, since the through hole 5 is tapered as described above, the catalyst solution Circulates smoothly and deposits gold on the surface reliably.

  Next, as shown in FIG. 4 (E), the secondary molded product 200 is heated in hot water to elute the portion of the mask 7 formed by the secondary molding into hot water. When the secondary molded product 200 is placed in hot water at 80 ° C. for 10 minutes, “Ecomati AX” is completely dissolved in the hot water. Therefore, as shown in FIG. 4F, the catalyst application portion is plated to form circuit patterns 3 and 4. At this time, since the through hole 5 is tapered as described above, this through hole is formed. Since the electroless solution smoothly circulates and flows inside, plating can be formed reliably. For this plating, chemical copper plating or chemical nickel plating is used. Finally, the process of forming the conductive circuit by removing the moisture inside by heat treatment is completed, and the three-dimensional circuit board 1 is completed.

  In the three-dimensional circuit board 1 in the above embodiment, an electronic element is solder-mounted on one circuit pattern, for example, the circuit pattern 3 on the upper surface, and the circuit pattern 4 on the opposite side is used as a contact. The flux or solder passes through the through hole 5 and flows out to the contact surface of the circuit pattern 4, so that the function as a contact may be hindered.

  Therefore, another embodiment will be described with reference to FIGS. 8 to 10. The through hole 5 is filled with a plating 30, and the inside of the filled plating is a cone-like hollow shape. The lower end is a circuit pattern 40 on the lower surface. Other configurations are the same as those of the above-described embodiment, and are denoted by the same reference numerals. Therefore, according to this embodiment, the flux cleaning process at the time of solder mounting can be omitted, and further, the outflow of solder can be prevented, so that the reliability of the three-dimensional circuit becomes higher.

  As an application example of the invention, the folding part between the circuit part of the folding cellular phone and the liquid crystal display surface can be used as a connector for connecting via a coaxial cable.

Circuit board top view Aa line expanded sectional view of FIG. Bottom view of circuit board (A)-(F) is sectional drawing which shows a manufacturing process Plan view of conventional example Aa line sectional view of FIG. Bottom view of conventional example Plan view showing another embodiment Bb line sectional view of FIG. Bottom view in another embodiment

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 3D circuit board 2 Circuit board 3 Circuit pattern 4 Circuit pattern 5 Through hole 6 Bulkhead
20 Primary molded product 30 Circuit pattern 40 Circuit pattern

Claims (4)

Forming a through hole with a molding pin in a primary molded product injection-molded with an insulating material ,
Forming a predetermined circuit pattern made of a conductive material by plating on both surfaces of a circuit board consisting of the primary molded article,
A forms a conductive layer for electrically connecting both sides of the circuit pattern of the circuit board in the through hole,
The method of manufacturing a three-dimensional circuit board , wherein the shape of the through hole is narrow in a direction between adjacent circuit patterns and long in a circuit extending direction. 2. The method of manufacturing a three-dimensional circuit board according to claim 1, wherein a cross-sectional shape of the through hole is tapered toward at least one direction between adjacent circuit patterns and a circuit extending direction. 3. The method for manufacturing a three-dimensional circuit board according to claim 1, wherein a partition wall is formed between adjacent circuit patterns. 4. The method of manufacturing a three-dimensional circuit board according to claim 1, wherein the through hole is a blind through hole in which the inside of the through hole is filled with plating.

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