JP2008098327A - Method of processing inside of holes of printed circuit board - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of processing the inside of holes of a printed circuit board that reliably allows a processing solution to pass through through-holes with a hole diameter of 0.3 mm or less and an aspect ratio of over 15, and allows the processing solution to pass through each hole distributed in the surface evenly and uniformly. <P>SOLUTION: Liquid current directed to a predetermined direction flows on one surface of the printed circuit board which is soaked in a processing solution, and a difference in flow velocity arises between the front and back of the printed circuit board. According to Bernoulli's theorem, a surface with a faster flow velocity has a negative pressure, thus facilitating drawing and flowing the processing solution into the through-holes. In order to flow a liquid current in a predetermined direction on one surface of the printed circuit board, a nozzle is disposed at a position along one surface of the printed circuit board, and the outlet of the nozzle is directed to a direction substantially parallel with the printed circuit board for processing solution discharge. Furthermore, a current plate is provided at a position along one surface of the printed circuit board, and the processing solution is flown into between the printed circuit board and current plate. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a processing method for easily passing a processing solution such as water or a chemical solution through a through hole formed in a printed circuit board.

  When cleaning and processing the inside of a through hole formed in a printed circuit board with water or a chemical solution, a method of spraying a processing liquid perpendicularly to the hole as shown in FIG. 4 is widely used (see Patent Document 1).

Japanese Patent Laid-Open No. 2003-37351

  In the method of Patent Document 1, as the aspect ratio (thickness / hole diameter) of the printed circuit board increases, insufficient processing such as processing liquid residue or foreign substance residue is likely to occur in the hole, and this is more efficient. There was no way to treat the inside of the small hole.

  The object of the present invention is to pass the treatment liquid efficiently and surely through the through-holes even when the aspect ratio of the printed circuit board is large, and to uniformly distribute the treatment liquid to each hole distributed in the surface. An object of the present invention is to provide an in-hole processing method for a printed circuit board that can be passed.

  In order to achieve the above object, the present invention is characterized in that a liquid flow in a certain direction is caused on one side of a printed circuit board immersed in the processing liquid, and a flow rate difference is generated between the front and back surfaces of the printed circuit board. Draw in. In order to generate a liquid flow in a certain direction on one side of the printed circuit board, a nozzle is arranged at a position along one side of the printed circuit board, and the processing liquid is discharged so that the nozzle outlet is substantially parallel to the printed circuit board. Further, a rectifying plate is provided at a position along one side of the printed circuit board, and the processing liquid is poured between the printed circuit board and the rectifying plate.

  Since the flow of the processing liquid is generated only on one side of the printed circuit board, the higher the flow velocity, the lower the pressure compared to the opposite side, and the processing liquid is sucked through the through hole. In addition, as the flow rate difference between the front and back of the printed circuit board increases, the effect increases, and the processing capacity increases because the amount of processing liquid passing through the through hole increases. Since the surface of the printed circuit board has the same processing conditions as a constant flow velocity is obtained on a wider surface, a flow straightening plate is provided at a position along one side of the printed circuit board, and the processing liquid is poured between the printed circuit board and the flow straightening plate. The generated liquid flow rate can be kept constant over a wide range, and the processing of the printed circuit board becomes more uniform. If the discharge amount from the nozzle is constant, the flow rate of the processing liquid increases and the effect increases as the rectifying plate is brought closer to the substrate. Further, it becomes possible to efficiently pass the treatment liquid into the through hole having a hole diameter of 0.3 mm or less and an aspect ratio exceeding 15.

Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings.

  Example 1 will be described with reference to FIG.

  Two types of glass epoxy printed circuit board 4 of 600 × 500 mm having a plate thickness of 3.8 mm and 5.3 mm are prepared, and a through hole 5 is formed in each with a drill diameter of 0.25 mm, an aspect ratio of 15.2 and an aspect ratio of 21. Two samples were made. Further, a jet nozzle 1 for processing liquid was installed beside the conveyor roll 2 of the horizontal transfer type processing apparatus. At this time, the ejection nozzle 1 is set so that the processing liquid flows substantially parallel to the printed circuit board 4 (for example, the ejection nozzle 1 is installed so as to have an inclination of −45 degrees to +45 degrees with respect to the printed circuit board 4. Desirably, it may be parallel to the printed circuit board 4), and the flow rate of the processing liquid is adjusted to 15 L / min.

  In order to confirm that the treatment liquid flows in the through hole in this state, use an electroless copper plating solution as the treatment liquid to deposit plated copper, and measure the degree of growth of the copper film between the printed circuit board surface and the inside of the hole after cross-sectional polishing. And compared. If the plating solution passes through the hole more than a certain amount, the surface and the inside of the hole will have the same plating thickness, but if it does not pass or if the passing amount is small, the copper ions in the hole are consumed and the copper film growth stops Or, the reaction is slower than the surface, and the plating thickness inside the hole becomes thin.

  The two types of printed circuit boards 4 are subjected to general pretreatments such as conditioning, soft etching, catalyst application, and activation using a vertical dip type copper plating apparatus, and then the horizontal transfer type processing apparatus is used. Electrolytic copper plating was applied. The conveyor conveyance speed at this time was conveyed at 0.4 m / min, and processing was performed until the total plating time reached 2 hours 30 minutes. As the electroless copper plating solution, a plating solution for thickening generally used in a printed circuit board was used.

  The through hole portions of the two types of printed circuit boards thus manufactured were each subjected to cross section polishing by 50 holes, and the plating thickness deposited on the surface portion of the printed circuit board and the plating thickness deposited on the central portion of the through hole were measured with a metal microscope. As a result, in the sample having an aspect ratio of 15.2, copper having a surface portion of 4.91 μm and a through-hole center portion of 4.93 μm is deposited, and the surface and the inside of the hole have approximately the same plating thickness and the throwing power of the center portion of the hole ( The hole center portion plating thickness / surface portion plating thickness × 100) was 100%, but in the sample having an aspect ratio of 21.2, the surface portion was 4.85 μm and the through hole center portion was 4.16 μm. %.

  Moreover, in the comparative evaluation similarly performed by the prior art which sprays a process liquid perpendicularly | vertically with respect to a printed circuit board, a through-hole center part 3.08micrometer with respect to the surface part 4.87micrometer with the sample of aspect ratio 15.2; Since the throwing power was 63%, it was proved that the amount of treatment liquid passing through the through hole could be increased by the present invention.

  A second embodiment will be described with reference to FIG.

  A glass epoxy printed circuit board 4 of 600 × 500 mm and a thickness of 5.3 mm was prepared, and a sample with an aspect ratio of 21.2 was prepared by drilling a through hole 5 with a drill diameter of 0.25 mm. Moreover, the baffle plate 6 was installed beside the printed circuit board beside the conveyor roll 2 of the horizontal conveyance type processing apparatus. The distance between the printed circuit board and the rectifying plate was 5 mm, and a part of the rectifying plate was bent at an angle of 45 ° in order to flow the processing liquid therebetween, and the processing liquid was jetted from the nozzle 1 toward the rectifying plate. The discharge rate of the treatment liquid was 15 L / min as in Example 1. As a result, the sprayed processing liquid is collected between the printed circuit board and the current plate, and can flow along the printed circuit board at a constant flow rate.

  In order to confirm that the treatment liquid flows in the through hole in this state, an electroless copper plating solution was used as the treatment liquid as in Example 1.

  The printed circuit board 4 is subjected to general pretreatments such as conditioning, soft etching, catalyst application, and activation using a vertical dip type copper plating apparatus, and then electroless copper plating is performed using the horizontal transfer type processing apparatus. gave. The conveyor conveyance speed at this time was conveyed at 0.4 m / min, and processing was performed until the total plating time reached 2 hours 30 minutes. As the electroless copper plating solution, a plating solution for thickening generally used in a printed circuit board was used.

  The printed board thus produced was subjected to cross-sectional polishing, and the plating thickness deposited on the surface of the printed board and the plating thickness deposited at the center of the through hole were measured with a metal microscope. As a result, in the sample having an aspect ratio of 21.2, copper having a surface portion of 4.99 μm and a center portion of the through hole of 4.94 μm was deposited, and the surface and the inside of the hole had almost the same plating thickness and the throwing power of the center portion of the hole ( The hole center portion plating thickness / surface portion plating thickness) was 99%, which was higher than Example 1.

  Therefore, it can be seen that the processing effect on the through hole of the printed circuit board is further improved by installing the current plate. These are summarized in Table 1.

  Example 1 and Example 2 are characterized in that a liquid flow in a certain direction is caused on one side of a printed circuit board immersed in the processing liquid, and by generating a flow velocity difference between the front and back of the printed circuit board, from Bernoulli's theorem As shown in FIG. 3, the surface having a high flow rate becomes negative pressure, and the processing liquid can be easily drawn into the through hole. In order to generate a liquid flow in a certain direction on one side of the printed circuit board, a nozzle is arranged at a position along one side of the printed circuit board, and the processing liquid is discharged so that the nozzle outlet is substantially parallel to the printed circuit board. Furthermore, by providing a current plate at a position along one side of the printed circuit board and pouring the processing liquid between the printed circuit board and the current plate, the generated liquid flow rate can be kept constant over a wide range, and the processing in the hole of the printed circuit board can be performed. It becomes more uniform in the plane and the effect is improved.

  In addition, when the hole diameter is 0.3 mm or less and the aspect ratio exceeds 15, the treatment liquid is efficiently and surely passed, and the treatment liquid is uniformly and uniformly distributed to each hole distributed in the surface. Can pass through.

Sectional drawing of the processing method of Claim 1 Sectional drawing of the processing method using the baffle plate described in Claim 2 Schematic diagram of the liquid flow direction in which the through hole portion of FIGS. 1 and 2 is enlarged Cross-sectional view of conventional processing method

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Spray nozzle 2 Conveyor roll 3 Pressing roll 4 Printed circuit board 5 Through hole of printed circuit board 6 Current plate

Claims (2)

In the processing method in a hole in a horizontal transfer type processing apparatus of a printed circuit board,
With the nozzle installed on one side of the printed circuit board in the processing liquid, the processing liquid is ejected from the nozzle so as to cause a flow velocity difference between the front and back of the printed circuit board.
An in-hole processing method for a printed circuit board, wherein the processing liquid is passed through a through hole formed in the printed circuit board. In the printed circuit board in-hole processing method according to claim 1,
A rectifying plate is installed substantially parallel to the printed circuit board, a processing liquid is poured between the rectifying plate and the printed circuit board, the processing liquid is flowed substantially horizontally with the printed circuit board, and a flow velocity is applied to the front and back of the printed circuit board. A method for in-hole processing of a printed circuit board characterized by causing a difference.

Images