JP2012049363A - Method of manufacturing printed wiring board and printed wiring board - Google Patents

Abstract

PROBLEM TO BE SOLVED: To limit occurrence of troubles such as deficient copper plating due to insufficient supply of process liquid by supplying the process liquid to miniaturized through holes and non-penetrating via holes in surface treatment such as cleaning and electroless copper plating.SOLUTION: In surface treatment such as cleaning and electroless copper plating, a vertical system performing surface treatment such as cleaning and electroless copper plating at a low device cost is used. In order to supply process liquid to miniaturized through holes and non-penetrating via holes, copper clad laminates and detachable current plates for control of process liquid are arranged in a cage.

Description

  The present invention relates to a method of manufacturing a printed wiring board and a printed wiring board, and in particular, forms fine through-holes and non-through-holes that connect the front and back and inner layers to a copper-clad laminate, and then forms plating and circuit patterns. The present invention relates to a printed wiring board manufacturing method and a printed wiring board.

  In recent years, high-density multilayer printed wiring boards have been used in electronic devices due to demands for higher performance, higher functionality, and smaller size. This high-density multilayer printed wiring board mounts electronic components such as LSI, IC, and resistor. For this reason, the high-density multilayer printed circuit board requires through through holes, non-through through holes, and wiring patterns for electronic circuits that electrically connect the surface layer, the back layer, and the inner layer. A manufacturing process of the high-density multilayer printed wiring board will be described with reference to FIG. Here, FIG. 1 is a manufacturing process diagram of a high-density multilayer printed wiring board.

  As shown in FIG. 1B, a through-hole 3 and a non-through-hole 4 are drilled or lasered on a copper-clad laminate 2 formed with an inner layer wiring pattern 1 and subjected to lamination press in FIG. Drill holes with. In FIG. 1C, after the plating catalyst for cleaning the through-hole 3 and the non-through-hole 4 and making the inner wall conductive is formed, a copper film 5 is formed by an electroless copper plating method. The thickness of the plated copper film 5 varies depending on the process used, and is 0.2 μm to 25 μm. Thereafter, electrolytic copper plating is performed as necessary to form the outer layer wiring pattern 6 and the solder resist 7 as shown in FIG. 1D, thereby completing the high-density multilayer printed wiring board 8.

  With reference to FIG. 2, the plating defect mechanism at the time of fine through-hole plating will be described. In FIG. 2, as the pitch of the parts is reduced and the density is increased, the high-density multilayer printed wiring board forms fine through holes 9 and fine non-through holes 10 as shown in FIG. To do. Next, in the cleaning and electroless copper plating step, the perforated copper-clad laminate 11 is immersed in the treatment liquid 12 as shown in FIG. Using A), the liquid supply 14 is performed inside the through-hole and the non-through-hole, and the respective processes are performed. However, in the fine through-hole 9 and the fine non-through-hole 10, the supply amount of the processing liquid is remarkably reduced as shown in FIG. 2B (arrow B). For this reason, the plating defect 15 as shown in FIG. 2C is caused, and the incidence of defective connection between the through-hole and the non-through-hole is increased.

  As a countermeasure, when performing surface treatment processes such as cleaning and electroless copper plating, the copper-clad laminate is transported horizontally, and the treatment liquid is sprayed to spray through holes and non-through holes. There is a horizontal conveyance system to supply to. However, the horizontal conveyance method has a high apparatus cost and it is difficult to manage the concentration of the processing liquid. Furthermore, the horizontal conveyance method requires long-time processing in order to increase the plating thickness in electroless copper plating. For this reason, electroless copper plating is practically impossible with the horizontal conveyance method.

  On the other hand, in the vertical processing method, a copper-clad laminate 11 having through-holes and non-through-holes as shown in FIG. As in b), the substrate is immersed in a bath containing the treatment liquid 12 and subjected to surface treatment such as cleaning and electroless copper plating. The vertical processing method has a simple device configuration and is inexpensive. In addition, the vertical processing method is easy to manage the concentration of the processing solution, and can process a plurality of sheets simultaneously and has high productivity.

  However, as shown in the plan view of FIG. 3B, in the copper-clad laminate 11 with holes formed outside the cage 16, the flow of the treatment liquid is large. On the other hand, the copper-clad laminate on the inner side of the cage 16 has less processing liquid flow toward the center. For this reason, as described above, the copper-clad laminate on the inside of the cage 16 is highly likely to be short of the processing liquid supplied to the through through hole and the non-through through hole.

As a measure against supply shortage of treatment liquid, as a method of strengthening the agitation in the treatment liquid and promoting the flow of the treatment liquid, a method of directly applying a force to the cage 16 in which the copper clad laminate is inserted, and a treatment with a manufacturing facility Two methods of stirring the liquid itself are employed. As shown in FIG. 3B, the former includes a method in which the cage is reciprocated at a constant cycle (arrow C), and a method in which an impact is applied by a cylinder or a vibrator. However, if too much force is applied, there is a possibility that the cage will be damaged, or foreign matter may be generated from the movable part, causing a defect. The latter includes a method in which the treatment liquid is vibrated and agitated, and a method in which the diameter and strength of the air bubbling are changed and agitated. However, there are many problems such as an increase in apparatus cost, vibration, and generation of foreign matter from the stirring unit.
A method of improving the flow of the processing liquid in the shape of a cage that takes advantage of both is also employed. However, it is conceivable that the initial investment of the basket is increased and the filling amount of the substrate is decreased.

  Patent Document 1 discloses a method for processing micro-holes in a printed circuit board in which liquid supply generated by swinging a basket in vertical processing is promoted by a rectifying plate in the present invention. Patent Document 2 discloses an electroless plating method for a printed wiring board in which liquid generated by swinging a basket in vertical processing is promoted by a current plate. Patent Document 3 discloses a liquid stirring method that promotes liquid supply by a baffle plate using liquid that is generated by swinging a basket in vertical processing.

Japanese Patent Laid-Open No. 03-050792 JP 2009-077653 Japanese Unexamined Patent Publication No. 03-275130

  The present invention suppresses the occurrence of defects such as copper plating defects due to insufficient supply of processing liquid by supplying the processing liquid to fine through holes and non-through via holes in surface treatment such as cleaning and electroless copper plating liquid. With the goal.

  The above-described problem is a method of manufacturing a printed wiring board including a step of electroless copper plating on a through hole, and a step of attaching a removable rectifying plate to slits before and after a slit of a cage that holds the printed wiring board; A step of immersing in the electroless copper plating solution while reciprocating the ridge, and the rectifying plate has the same outer shape as the printed wiring board and increases the flow rate of the electroless copper plating solution. This can be achieved by a method for manufacturing a printed wiring board on which wings are formed.

  According to the present invention, it is possible to suppress the occurrence of defects such as copper plating defects due to insufficient supply of processing liquid.

It is a manufacturing-process figure of a high-density multilayer printed wiring board. It is a figure explaining the plating defect mechanism at the time of fine penetration through hole plating. It is a perspective view explaining a vertical processing type surface treatment. It is a top view explaining vertical processing type surface treatment. It is sectional drawing explaining the plating-thickness measurement position in the copper plating coverage ratio examination. It is a perspective view explaining a current plate structure. It is a top view explaining the flow of the process liquid at the time of use of a baffle plate. It is sectional drawing explaining the process liquid supply state to the penetration through hole by a baffle plate. It is sectional drawing explaining the angle of a baffle plate.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings using examples. The same reference numerals are assigned to substantially the same parts, and the description will not be repeated.

  First, the copper plating coverage will be described. Inventors etc. evaluated the through-hole through-hole part with copper plating as a scale which determines the supply shortage of a process liquid. The coverage ratio of the copper plating is obtained by Equation 1 based on the numerical values shown in the cross-sectional view after copper plating of the through through hole portion of FIG.

Circumference ratio with copper plating = ((a + b) / 2)) / ((c + d + e + f) / 4)) × 100 (Equation 1)
Where, a: plating thickness on the left side of the through-hole center in FIG.
b: Plating thickness on the right side of the through hole center
c: Plating thickness on the upper left side of the through hole entrance
d: Plating thickness on the upper right side of the through hole entrance
e: Plating thickness at the lower left side of the through hole entrance
f: Plating thickness at the lower right side of the through hole entrance That is, the copper plating coverage ratio is a ratio of the plating thickness at the center of the through hole to the plating thickness at the through hole entrance. Since the plating thickness at the center of the through hole becomes thin if there is insufficient supply of the processing liquid, it means that the processing liquid is supplied as the coating ratio with copper plating increases.

  Using MCL-E-67, glass epoxy resin copper-clad laminate and prepreg GEA-67 as the adhesive as the inner layer material of the high multilayer printed wiring board, a predetermined wiring pattern is formed on the inner layer material, and the interlayer and upper and lower surfaces After the prepreg was placed on the surface, 0.018 mm copper foil was stacked on the surface layer and laminated and adhered by a hot press to produce a copper-clad laminate 11 having a thickness of 2.4 mm.

  After machining through-holes with hole diameters of 0.15, 0.20, and 0.30 mm in the copper-clad laminate 11 with an NC drilling machine and polishing burrs on the front and back of the copper-clad laminate, foreign matter in the through-holes In order to completely remove water, washing was performed by high pressure water washing at 10 MPa.

  On the other hand, a material that can withstand a surface treatment solution such as cleaning and electroless copper plating shown in FIG. 5A is selected, and rectification is made by processing a wing 24 and an opening that are bent at a length of 30 mm and an angle of 45 degrees. A plate 25 was prepared. The outer shape of the rectifying plate 25 is the same as that of the copper-clad laminate 11. Since the electroless copper plating is high temperature and high alkali, the rectifying plate 25 is made of SUS304 as a material that can withstand these conditions.

  Next, as shown in FIG. 5B (a), the current plate 25 and the perforated copper-clad laminate 11 are alternately inserted into the cage 16. Note that the number of the rectifying plates 25 is the number of the laminated plates 11 +1, and the copper-clad laminated plate 11 is surrounded by the rectifying plates 25. With the cage 16 in which the rectifying plate 25 and the perforated copper-clad laminate 11 are alternately arranged, the desmear process for removing the resin (smear) welded to the inner wall of the through hole at the time of NC drilling and the inner wall of the through hole are made conductive. A plating catalyst treatment was performed.

  Subsequently, a film having a thickness of 25 μm was formed on the through-through hole and the surface by an electroless copper plating method using the cage 16. As shown in FIG. 5B (b), the electroless copper plating treatment was immersed in the treatment liquid 12, and the cage 16 was reciprocated in the plate thickness direction at a constant cycle. When the treatment liquid is pushed by the splash of the rectifying plate 25, a liquid flow (arrow D) in an oblique direction is generated with respect to the perforated copper-clad laminate 11.

  The liquid flow in the oblique direction generated by the rectifying plate shown in FIG. 6A becomes a turbulent flow by hitting the perforated copper-clad laminate 11 and the rectifying plate 25, and the flow rate (arrow E) supplied to the through-through hole. ) Will increase. For this reason, as shown in FIG.6 (b), the through through-hole 28 without a plating defect is formed.

  Next, outer layer wiring pattern formation and solder resist are formed on the copper-plated substrate, and the through-holes with copper plating in the through-holes of the completed multilayer printed wiring board are observed by cross-sectional observation of the through-through holes and determined by measuring the copper plating thickness did.

As a comparison, Table 1 shows the evaluation results including the copper plating coverage of the substrate subjected to electroless copper plating without inserting a rectifying plate, which is a conventional working condition.

Table 1 Results of evaluation of throwing power with copper plating
---------------------------------
With rectifier plate Without rectifier plate Through-hole diameter (mm) Length 30mm
45 degree angle
---------------------------------
0.30mm 100% 100%
0.20mm 100% 95%
0.15mm 95% 85%
---------------------------------

From Table 1, it can be seen that by using the rectifying plate, good throwing ability with copper plating to the through-through hole is obtained. Similarly, in the non-through hole, there is an effect of improving the throwing power by increasing the amount of liquid supplied.

With respect to the divergence angle of the rectifying plate, the divergence angle θ shown in FIG. Copper plating of 25 μm was performed. Next, an outer layer wiring pattern formation and a solder resist were formed on the copper plated substrate. Crossability of the through hole of the completed multilayer printed wiring board with copper plating was determined by observing the cross section of the through hole and measuring the thickness of the copper plating. The evaluation results are shown in Table 2.



Table 2 Evaluation results of wrapping performance with copper plating
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Through-hole diameter (mm) Current plate Current plate Current plate Current plate
Angle 15 degrees Angle 30 degrees Angle 45 degrees Angle 60 degrees ------------------------------------ −
0.30mm 100% 100% 100% 100%
0.20mm 95% 100% 100% 95%
0.15mm 90% 95% 95% 95%
--------------------------------------

From Table 2, it was found that good wrapping property with copper plating to the through-through hole can be obtained when the honeycomb angle θ of the rectifying plate 25 is in the range of 30 to 45 degrees.
The reciprocating motion of the cage 16 may be in a direction perpendicular to the thickness direction (the left-right direction in FIG. 5B (b)). Both the through hole and the non-through hole are through holes.

  According to the present embodiment, in the vertical method, in order to supply the liquid to the fine through hole and the non-through hole, the current plate for controlling the flow of the processing liquid can be attached and removed. Mixed flow production is possible, and the structure is simple and inexpensive.

  DESCRIPTION OF SYMBOLS 1 ... Inner layer pattern, 2 ... Copper-clad laminate, 3 ... Through-through hole, 4 ... Non-through-through hole, 5 ... Copper plating, 6 ... Outer layer pattern, 7 ... Solder resist, 8 ... Multilayer printed wiring board, 9 ... Fine Through holes, 10 ... fine non-through holes, 11 ... perforated copper-clad laminate, 12 ... treatment liquid, 15 ... deficient copper plating, 16 ... basket (ゴ), 24 ... honey (wings), 25 ... Current plate, 28 ... Through-through hole without plating defects.

Claims (4)

In the method for producing a printed wiring board comprising a step of electroless copper plating on the through hole,
Attaching a rectifying plate that can be attached to and detached from the slits before and after the slit of the bag that holds the printed wiring board; and
Dipping in the electroless copper plating solution while giving reciprocating motion to the reed, and
The method of manufacturing a printed wiring board, wherein the rectifying plate has the same outer shape as the printed wiring board and has a plurality of wings that increase a flow rate of the electroless copper plating solution. It is a manufacturing method of the printed wiring board according to claim 1,
The method of manufacturing a printed wiring board, wherein the wing is formed by sheet metal processing and bending a part of the main body of the current plate. It is a manufacturing method of the printed wiring board according to claim 2,
The method of manufacturing a printed wiring board according to claim 1, wherein a bending angle of the wing is in a range of 30 degrees to 45 degrees.   A printed wiring board manufactured by the method for manufacturing a printed wiring board according to claim 1.

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