JP2009076553A - Electroless plating method of printed circuit board - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve a problem of insufficient supply of a plating liquid into a through-hole to lead to no formation of intended plating in that part due to difficulty of thorough removal of hydrogen bubbles generated in a through-hole and a non-penetrating through-hole in conventional plating by vibration or shaking in an electroless plating method of a printed circuit board having the non-penetrating through-hole. <P>SOLUTION: In the plating method of the printed circuit board, when electroless plating is performed on the printed circuit board immersed in the plating liquid while vibrating the printed circuit board, bubbling is also applied from below the printed circuit board by varying the flow rate. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a printed wiring board plating method. In particular, the present invention relates to a method of electroless plating while applying vibration to a printed wiring board.

  The printed wiring board is provided with through-holes and non-through-holes as needed. Generally, through-holes are formed by plating treatment such as electroless plating and then electrolytic plating. A conductor is formed in the hole. In the plating process, it is necessary that the plating solution is sufficiently supplied also into the through hole so that the plating is formed not only on the front and back surfaces of the printed wiring board but also in the through hole. At this time, hydrogen gas may be generated due to the electroless plating reaction and may remain in the through hole as a bubble. If it is not removed from the through hole, the plating reaction stops.

As a countermeasure for this, conventionally, in a plating tank in which a printed wiring board is immersed, the printed wiring board is vibrated during plating to quickly release hydrogen gas from the through hole (Patent Document 1). In addition to vibration, the electrolytic heat generated from the object to be plated is effectively cooled to quickly cool the object to be plated, and the air and dust removed from the through hole of the object to be plated can also be effectively removed. And aeration (bubble bubbling with air) (Patent Document 2).
JP 62-154798 A Japanese Patent Laid-Open No. 11-189880

However, in the plating by the above method, it is difficult to completely remove the hydrogen bubbles generated in the through through hole and particularly in the non-through through hole even if it is vibrated or simply combined with aeration. Therefore, it cannot be said that the plating solution is sufficiently supplied into the through hole, and the target plating is not formed in the through hole in that portion.
The present invention eliminates the hydrogen bubbles in the through hole of the printed wiring board, and the printed wiring board is sufficiently supplied with the plating solution in the through hole, particularly in the more difficult non-penetrating through hole. The object is to provide a plating method.

In the electroless plating method for a printed wiring board having a non-through hole, the present invention is adapted to increase or decrease the flow rate when plating while applying vibration to the printed wiring board immersed in an electroless plating solution. An object of the present invention is to provide a method for electroless plating of a printed wiring board, wherein the exposed bubbling is added from below the printed wiring board.
Another object of the present invention is to provide an electroless plating method for a printed wiring board as described above, wherein the bubbling flow rate has two levels and the weak flow rate is shorter than the strong flow time.

In the plating method of the present invention, when electroless plating is performed while vibration is applied to a printed wiring board immersed in a plating solution, bubbling with a strength of the flow rate is added from the lower side of the printed wiring board. As the plating solution pressure in the non-through-through hole is alternately compressed and released, the inflowing action and the outflowing action in which the plating solution tries to flow in alternately occur. Hydrogen bubbles generated in the non-penetrating through hole can be effectively pushed out of the non-penetrating through hole, and the plating solution can be sufficiently supplied into the non-penetrating through hole. Further, when the bubbling gas is air or oxygen, the oxygen concentration in the liquid periodically changes, and the hydrogen concentration also periodically changes accordingly. By periodically changing the hydrogen concentration, it is possible to shock the hydrogen bubbles and promote the release of the bubbles. Thereby, the plating solution can be sufficiently supplied into the non-through hole.
In addition, the bubbling flow rate has two levels, and the bubbling flow rate is set longer than the weak flow time, thereby sufficiently increasing the plating solution pressure in the non-through-hole, which is a dead end hole. Therefore, when it is released, hydrogen bubbles generated in the non-through hole can be effectively pushed out of the non-through hole.

  The non-penetrating through hole described in the present invention is an interstitial via hole which is a plated hole for connecting the layers of two or more conductor layers, with all the connecting holes not penetrating at the time of plating. (IVH) is included. In addition to the plated inner surface, filled vias that fill the entire hole with plating are also included.

In the bubbling described in the present invention, a gas such as air, oxygen or nitrogen is used as a bubbling gas, and these gases are discharged from a nozzle into a plating solution in the form of bubbles.
The gas is preferably an oxygen-containing gas, particularly air that contains a fixed amount of oxygen and can be easily supplied. Oxygen gas is related to the dissolved oxygen concentration in the plating solution. Generally, if the dissolved oxygen concentration in the plating solution is high, the plating solution is kept stable and the stability of the electroless plating solution is improved. It has been. Since the dissolved oxygen concentration in the plating solution tends to decrease due to the hydrogen gas generated by the electroless plating reaction, it is necessary to supply a sufficient amount.
The air bubbles are preferably fine air that is adjusted and discharged from an air nozzle. The amount of gas is preferably about 0.05 L / min to 0.07 L / min per 1 m ³ of the plating solution.
As the shape of the nozzle, there can be used a tubular one having a large number of holes, a porous resin tube, a cylindrical one having a blower side made of a ceramic porous body, and the like. The diameter of each hole of a tubular body having a large number of holes is about 0.1 mm to 2.0 mm, and all of them may be the same diameter or the diameter may be changed periodically.
The blow-out surface may be the upper surface in the case of a porous body, but in the case where a hole is made in a tubular body, it is staggered at a pitch of 3 mm to 10 mm at a position in two directions about 45 degrees away from the center of the tube to the lower surface. If it is provided in parallel, the gas can be easily blown out uniformly in the length direction of the tube.
The arrangement of the nozzle part is particularly elongated, in order to allow a plurality of printed wiring boards to be plated to stand and to blow out gas from below, the direction perpendicular to the surface direction of the printed wiring board is This is preferable because the amount of gas corresponding to each printed wiring is easily uniformized.
The method of giving strength to the air-flow rate is a method in which the air-flow rate applied from the lower side of the printed wiring board in the plating tank is made to have a strong and weak step and is repeated at regular time intervals. Hydrogen generated in the non-penetrating through hole by varying the plating solution pressure in the non-penetrating through hole by repeating the interval of 5 to 30 seconds with an amount of difference of about 1 to 3 times. This has the effect of effectively extruding the bubbles out of the non-penetrating through hole.

According to the method of applying vibration described in the present invention, one or more printed wiring boards are vertically arranged and mounted on a plating jig that supports the printed wiring board, and the plating jig is fixed to the plating jig. Attach to the vibration deaerator installed in the tank.
The vibration plating apparatus applies vibration acceleration of 1 to 3G to the printed wiring board through the plating jig by the vibration apparatus to vibrate the printed wiring board.

  The electroless plating solution described in the present invention is a general solution for plating an object to be plated with a reducing agent. In particular, a metal ion is reduced to deposit a metal, and a gas such as hydrogen or nitrogen is generated by the reaction. Things are included. For example, hydrogen gas is generated when formaldehyde is used as a reducing agent for copper ions, and nitrogen gas is generated when hydrazine is used as a reducing agent for nickel ions.

With the vibration plating apparatus of the present invention, gas (hydrogen or the like) generated by the plating reaction in the non-penetrating through hole is randomly pumped and degassed outside the non-penetrating through hole.
In addition, the electroless copper plating solution pressure inside and outside the non-penetrating through hole is changed so that the gas bubbles are defoamed outside the non-penetrating through hole and the electroless copper plating solution into the non-penetrating through hole. Thus, the electroless plating reaction in the non-penetrating through hole is effectively performed.

Hereinafter, the present invention will be described based on embodiments shown in the drawings.
FIG. 1 schematically shows an implementation state of the present invention in which a printed circuit board is installed in a vibration plating apparatus and plated by bubbling with strength.
The vibration plating apparatus includes a suspension jig 5 having a V-shaped portion 4 that is in contact with a V-shaped receiver 3 provided on the vibration table 1, and vibration is induced by vibration motors 2 provided at both ends of the vibration table 1. A cage-like plating rack jig 7 in which printed circuit boards 6 having through holes are vertically spaced is fixed by a fixing jig 8. The vibration table 1 is mounted on a support 10 for a spring table that extends from the bottom of the vibration device via a vibration-proof spring 9. Further, the cage-shaped plating rack jig 7 is submerged in an electroless copper plating tank 11 provided between the columns 10 for supporting the spring base. The air vent pipe 12 is inserted from the upper surface end of the electroless copper plating tank, and is bubbled from the nozzle 13 provided on the bottom surface.
FIG. 2 is an example of a vibration plating apparatus according to an embodiment of the present invention. FIG. 2 (a) is a front sectional view and 2 (b) is a side sectional view.
The plating magazine jig 19 that supports the printed circuit board 6 having a non-through hole has a length of 40 cm, a width of 53 cm, and a height of 50 cm. The basket-like plating rack jig 7 (60 cm in length, 86 cm in width, 108 cm in height, stainless steel square) is housed in two upper and lower rows.
The cage-shaped plating rack jig 7 is suspended by a suspension jig 5 and two V-shaped portions and V-shaped receptacles in total of two suspension jigs.
The nozzle of the air ventilation pipe 12 has a cylindrical shape with a diameter of 1.0 cm, and is 10 cm below the bottom surface of the cage-like plating rack jig 7. The nozzle holes have a diameter of 0.8 mm and are spaced at intervals of 5 cm. , Provided in two positions at 30 to 90 degrees (preferably 45 degrees) from the lower surface.

  Hereinafter, the present invention will be described based on examples. In addition, evaluation of the copper plating attachment property of a non-through-through-hole part was calculated | required by following Numerical formula 1 according to the numerical value shown in sectional drawing after copper plating of the non-through-through hole part of FIG.

ｃ：非貫通スルホール左側面のめっき厚
ｄ：非貫通スルホール右側面のめっき厚
ｅ：非貫通スルホール底面のめっき厚
ａ：非貫通スルホール入り口左側表面のめっき厚
ｂ：非貫通スルホール入り口右側表面のめっき厚

c: plating thickness of left side surface of non-through-through hole d: plating thickness of right side surface of non-through-through hole e: plating thickness of bottom surface of non-through-through hole a: plating thickness of left-side surface of non-through-through hole b: plating of right side surface of non-through-through hole Thickness

Example 1
MCL-E67WK (product name manufactured by Hitachi Chemical Co., Ltd.) glass epoxy resin copper-clad laminate (thickness 0.8 mm) as the core substrate material of the printed circuit board, and prepreg product name GEA- manufactured by Hitachi Chemical Co., Ltd. as the insulating layer material 67 (thickness 0.06mm), glass epoxy resin copper-clad laminate was formed on both sides of the inner layer circuit, copper foil with a thickness of 12μm was layered through a prepreg, and pressed and heated by a laminating press. A four-layer copper-clad laminate was produced.
This outermost layer was provided with a one-side closed type non-through hole (via top diameter 0.08 mm, 0.09 mm, 0.10 mm, 0.125 mm, insulating layer thickness 0.06 mm) by laser processing.
Next, when forming the one-side closed type non-through hole, a desmear process for removing the resin (smear) deposited on the inner wall of the through hole and a plating catalyst process for making the inner wall of the through hole conductive were performed.
Next, while giving a vibration of 2 G to the above-described four-layer copper-clad laminate according to the present invention, the flow rate is increased and decreased [strong flow rate: 0.07 L / L · min for 17 seconds, weak flow rate: 0.05 L / L · Applying an electroless copper plating method in which bubbling with air with a repetition of 10 seconds in minutes is applied from below the four-layer copper-clad laminate, electroless copper with a thickness of 12 μm is applied to the non-through-through holes and the substrate surface. A plating film was formed.
Next, the four-layer copper-clad laminate on which the copper plating film is formed is baked, developed, and etched by photographic method to form a connection circuit in which non-through-holes are connected. Cross-sectional observation of the inner wall portion of the non-through-through hole was performed by determining the ability of the through-through hole to be plated with copper by measuring the thickness of the copper plating.

(Comparative Example 1)
Except for air bubbling with a constant air flow rate (0.07 L / L · min), a 12 μm-thick copper plating film was formed on the non-through hole and the substrate surface by the electroless copper plating method in the same manner as in Example 1.
Next, similarly to Example 1, a connection pattern in which non-through holes are connected is formed on both surfaces of a printed circuit board on which a copper plating film is formed, and a cross-sectional observation of the inner wall of the non-through hole is performed by cross-sectional observation. Thickness measurement was performed to determine the ability of the non-penetrating through hole portion to be plated with copper.

(Comparative Example 2)
In the same manner as in Example 1 except that air bubbling was not applied, a 12 μm copper plating film was formed on the surface of the non-through hole and the substrate by electroless copper plating.
Next, similarly to Example 1, a connection pattern in which non-through holes are connected is formed on both surfaces of a printed circuit board on which a copper plating film is formed, and a cross-sectional observation of the inner wall of the non-through hole is performed by cross-sectional observation. Thickness measurement was performed to determine the ability of the non-penetrating through hole portion to be plated with copper.

Table 1 shows the results of evaluating the peripherality with copper plating of the non-through holes of Example 1, Comparative Example 1 and Comparative Example 2.

表１より、実施例及び比較例１、比較例２から、本発明の振動めっき装置及び流量に強弱をもたせたエアーバブリングを適用した無電解銅めっき方法により、非貫通スルーホールへの良好な銅めっき付き周り性を得ることができることがわかる。

From Table 1 and Example 1, Comparative Example 1 and Comparative Example 2, good copper to non-through holes is obtained by the electroless copper plating method using the vibration plating apparatus of the present invention and the air bubbling with the strength of the flow rate. It turns out that the surrounding property with plating can be obtained.

(Examples 2, 3, 4 and 5)
A non-through-through hole and a 12 μm copper plating film were formed on the substrate surface by a thick electroless copper plating method in the same manner as in Example 1 except that the strong flow time and the weak flow time of air bubbling were as shown in Table 2. .
Next, as in Example 1, a connection pattern in which non-through holes are connected is formed on both surfaces of a printed circuit board on which a copper plating film is formed, and a cross-sectional observation of the inner wall of the non-through hole with a via top diameter of 0.10 mm is performed. Then, the copper plating attachment property of the non-through-hole portion was determined by measuring the copper plating film thickness.

  Table 2 shows the results of evaluation of the peripheral property with copper plating of the non-through-holes having a via top diameter of 0.10 mm in Examples 2, 3, 4, 5 and Example 1.

表２より、強流量時間が、弱流量時間より長いほうが、同じか、短いより、貫通スルーホールへの良好な銅めっき付き周り性を得ることができることがわかる。

From Table 2, it can be seen that a better flowability with copper plating to the through-through hole can be obtained when the strong flow time is longer than the weak flow time than the same or shorter.

1 schematically shows an electroless plating method for a printed wiring board by a vibration plating apparatus and bubbling according to the present invention. The example of the vibration plating apparatus of the implementation state of this invention is shown. Sectional drawing after the plating of a non-penetrating through-hole part is shown typically.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Shaking table, 2 ... Vibration motor, 3 ... V-shaped receptacle, 4 ... V-shaped part, 5 ... Suspension jig, 6 ... Printed circuit board, 7 ... Plating rack jig, 8 ... Fixing jig, 9 ... Anti-vibration springs, 10 ... posts for receiving springs, 11 ... electroless copper plating tank, 12 ... air piping, 13 ... nozzles, 14 ... non-through holes, 15 ... electroless copper plating, 16 ... prepreg, 17 ... Copper foil, 18 ... core substrate, 19 ... plating magazine jig.

Claims (2)

  In the electroless plating method of a printed wiring board having a non-through hole, bubbling that gives strength to the flow rate is also applied when plating while vibrating the printed wiring board immersed in an electroless plating solution. An electroless plating method for a printed wiring board, wherein the method is applied from below the printed wiring board.   2. The method of electroless plating of a printed wiring board according to claim 1, wherein the bubbling flow rate is in two stages and the weak flow time is shorter than the strong flow time.

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