JPH0468400B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an apparatus for electroplating printed circuit boards. More specifically, the present invention relates to an improvement in a so-called continuous movable electroplating apparatus in which a printed circuit board is moved in a constant direction during the plating process. Conventionally, in the electroplating of printed circuit boards, a rack 3 on which a plurality of printed circuit boards are usually attached is immersed in a plating tank 1 between a pair of copper anodes 4, as shown in FIGS. 1 and 2. This was done by standing still for a certain period of time and then taking it out.
In order to increase productivity, a large number of plating tanks are arranged in parallel, and the immersion time in the plating tanks and the washing tank are controlled by using carrier bars and rationally, sometimes by computer control. By adjusting the travel time and other factors, the operation is essentially continuous. However, in this plating method, there is a limit to increasing the number of tanks, so in order to obtain higher productivity, it is necessary to increase the size of the plating tank.
At present, plating is carried out on a substrate area of 0.4 m ² per rack, or 2 m ² in large cases. Increasing the size of the plating equipment in this way increases the weight per rack, and the carrier bar to support and move the rack needs to be structurally robust, making the entire equipment larger. .
Moreover, the burden on the workers who attach, detach, and move the racks increases. Furthermore, the biggest quality problem with the carrier bar method is the variation in plating thickness.
For example, if electrolytic copper plating is applied to a thickness of 25 μm at 1 m ² per rack, the plating thickness at the center will be 25 μm.
It is often experienced that when the thickness reaches 30 to 50μ, the peripheral area reaches 30 to 50μ. That is, as shown in FIG. 3, due to the uneven distribution of current density, a problem arises in that the plating thickness is thicker in the shaded area 5 than in other areas in one substrate and one rack. In order to solve this problem, a common method is to provide a sacrificial plate on the outside of the rack to prevent the above phenomenon. Although this method has certain effects, it is not perfect, and the current situation in the industry is that the thickness distribution of electroplating is unavoidable to some extent. This variation in plating thickness may be due to instability of the plating conditions, but it is recognized that the larger the plating area, the larger the variation. Therefore, it has been desired to develop an electroplating method that reduces the plated area per rack and is suitable for mass production. Recently, the plating tank has been changed to a long one-tank type,
Arrange the power supply rails in a monorail shape until the printed circuit board to be plated has the specified thickness.
Continuously movable electroplating devices that move in the longitudinal direction and perform plating while remaining in a movable state have been studied. This method is sometimes called the push-shear bar method, and is used in practical applications such as chrome plating of automobile parts, but in the field of printed circuit boards, there are only limited examples of this method. be. This continuously movable electroplating device has been recognized to have the advantage of producing printed circuit boards with small variations in plating thickness while ensuring productivity comparable to large-area carrier bar systems with a small area per rack. However, the reason why it is not widely used in this field is as follows. The first reason is that even though the plating condition is good during stable operation, this method is susceptible to small changes in conditions, such as a partial malfunction of the aeration nozzle or variations in current density. The influence is large, and once the conditions are disrupted, it takes time to recover, and during that time, the yield drops significantly due to quality defects. The second reason is that this is also a problem unique to the long single-tank plating tank. That is, under normal operating conditions, the printed circuit boards to be plated in the plating tank are arranged throughout the tank, and the plating thickness of the printed circuit boards in each rack is relatively stable. This seems to be because the current density provided by the rectifier is evenly distributed across the printed circuit board. On the other hand, when the work is started and when the work is finished, there is a tendency for the plating thickness to become thicker overall and to be more variable than when the racks are arranged all over. Naturally, two or more racks are arranged in a long plating tank, and it is difficult to increase productivity unless approximately 20 to 50 racks are arranged. Therefore, printed circuit boards that are plated between the start of work and the time when the steady state is reached, and from the steady state until the end of the work, are likely to have different plating thickness and distribution from printed circuit boards that are plated in the steady state. Strict quality standards are a major cause of lower yield. Furthermore, in the case of industrial circuit boards that require through-hole plating, the number of circuit boards produced per lot is often several to several dozen, and it is practically difficult to apply this method to such small-lot printed circuit boards. In this way, the continuous movable electroplating method using a long one-tank method has a more compact overall equipment compared to the carrier bar method, requires less capital investment, and when produced under steady operation, the distribution of plating thickness is Despite its recognized advantages such as small size, it has not yet been widely applied as a plating method for printed circuit boards, as described above. The present invention has been made from this point of view, and by improving the conventional continuously movable electroplating apparatus, it can be made small while taking advantage of the advantages such as small capital investment and compact equipment volume. Even for lot-sized printed circuit boards,
It is an object of the present invention to provide an electroplating device for printed circuit boards that can consistently perform plating with a stable and good thickness distribution. That is, the present invention provides an electroplating apparatus in which anodes are arranged on both sides of a long plating tank passage, and a printed circuit board that is easily disposed between the two electrode plates is continuously moved to electroplate the printed circuit board. ,
The present invention relates to an electroplating device for printed circuit boards, characterized in that weirs are provided at appropriate intervals on both sides. The present invention will be explained below based on the drawings. FIG. 4 is a plan view illustrating an embodiment of the present invention. The printed circuit board to be plated according to the present invention is manufactured by steps not shown in the drawings, for example, as roughly described below. First, glass cloth, paper, etc. are impregnated with epoxy resin, phenol resin, etc. to produce a prepreg, copper foil is adhered to both sides of this prepreg, and the resin is cured to obtain a copper-clad board. Next, holes (through-holes) that pass through the front and back of the copper-clad board are made at necessary locations, and chemical copper plating is applied to the inner side walls of the through-holes and the entire front and back surfaces of the copper-clad board to a thickness of about 0.3 to 1μ. After ensuring the conductivity of the entire board, for example, this perforated board (printed board) is subjected to the electroplating of the present invention, and the entire board is coated with a uniform plating bath. The printed (wiring) board plated according to the present invention has a circuit printed on its surface, undergoes operations such as etching and soldering, and is used as a printed wiring board for consumer or industrial applications such as TVs and computers. A printed circuit board to be plated by the method of the present invention is first subjected to pretreatment such as water washing and acid washing in a pretreatment device 6, and then immersed in a plating bath 1. The printed circuit board is mounted on a rack 3, and is continuously advanced (moved) in a fixed direction approximately in the center of the plating tank 1 with copper anodes 4 arranged on both sides, and is copper plated.
The material is subjected to post-processing such as washing with water in the post-processing device 7 and then pulled up. The rack is suspended from a rail 8 installed above the plating apparatus by a suitable conductive hanging device, and is advanced through the plating apparatus. Current is passed through this rail, and the printed circuit board becomes the cathode. The copper anode may be, for example, a suitable titanium steel container filled with copper balls. In the present invention, "continuous" movement of the printed circuit board includes cases in which the printed circuit board moves at a constant speed from the pre-processing device to the post-processing device without stopping, as well as cases in which the printed circuit board moves on both sides. There is also intermittent movement that repeats progressing and stopping at fixed time or fixed distance intervals, such as stopping between a pair of copper anodes, then moving forward, and stopping again between the next pair of copper anodes. This refers to the operation of sequentially plating while being immersed in a plating tank and moving through the tank, and there is no problem even if the movement and stopping is repeated during the process. It should be noted that the movement of the rack is carried out by a suitable moving device, which is not shown in FIG. Next, the greatest feature of the present invention is that each one or more copper anodes, preferably 2 to 5 copper anodes, are oriented substantially perpendicularly to the direction in which the printed circuit board advances, on both sides of the plating bath. A pair of weirs 9 are provided on the surface. As a result, variations in plating thickness were significantly reduced, and plating efficiency, ie, yield, was improved. The reason for this is not clear, but it may be that the unnecessary flow of the plating solution, that is, the non-uniform flow of the ionized plating metal, is made uniform by the weir 9. Generally, in a plating tank, in order to make the plating bath uniform, a nozzle is placed at the bottom of the tank, through which air is passed, and the bath is stirred by aeration. If the nozzle becomes clogged, the bath may not be agitated uniformly and the plating thickness may become uneven.
When a weir is provided, non-uniformity in the amount of plating can also be prevented by stopping the energization of the part within the weir surrounding the nozzle. It is desirable that the distance between the pair of weirs 9, 9 be less than half the distance between the pair of anodes. If this interval is too wide, it will be difficult to achieve the objectives of the present invention, such as reducing variations in plating thickness, so it is better to keep this interval as narrow as possible, but if it is too narrow, it will be difficult to achieve due to operational reasons. In the event of vibration, the printed circuit board and weir may come into contact and damage the surface, so it is necessary to provide a minimum distance to avoid contact between the printed circuit board and the weir due to easy vibration. There is. The preferred range of the distance between the weirs is less than half the distance between the anodes.
Furthermore, even if the distance between the anodes is less than half, it is still 150 mm.
Exceeding this is not preferable as it reduces the effectiveness of the weir. Other examples of plating conditions are as follows. Current density 2~5A/dm ² bath composition Cu 28~32g/, NH3 ₃ ~5ml/
Copper pyrophosphate plating solution bath consisting of 200 to 250 g of P ₂ O ₇ PH 8 to 10 Bath temperature 40 to 60°C Easy movement speed 0.3 to 0.7 m/min The above examples use a copper pyrophosphate plating solution. This is an example of a case and is not intended to limit the scope of the present invention. That is, all plating methods for printed circuit boards, such as acidic copper sulfate plating and solder plating, can be applied without problems. Naturally, there is no problem in adding commonly used brighteners, rust preventives, etc. to the above-mentioned plating solution. Example 1 A glass cloth-reinforced epoxy resin copper-clad laminate having a thickness of 1.6 mm was cut into 400 mm x 280 mm, and through-holes were drilled in a pattern corresponding to a double-sided digital device wiring board. The number of through holes in this pattern is 1904 holes for the hole diameter of 0.8 mmφ,
The 1.2mmφ one has 48 holes. This material was plated to a thickness of 0.3 μm using a conventional chemical copper plating method using a palladium catalyst, and then electroplated using an electroplating apparatus according to the present invention, aiming at a plating thickness of 25 μm. An outline of the plating device and plating conditions used at this time is as follows. External shape: Reciprocating type as shown in Figure 4, the width of the plating layer is 400mm, the length is 2630mm, and the depth is 1050mm.
It is. On the inlet side of this device, there are two washing tanks and one
There are 1 dilute sulfuric acid tanks and 3 water washing tanks on the outlet side. Cathode: Arranged in a monorail loop through the center axis of the tank.The height is 550 mm from the top of the tank.
It is located at mm. However, in order to overcome the partition wall between the plating tank and the front and rear washing tanks, a 950mm upward stroke will be provided. Therefore, only this part has a height of approximately 2,700 mm. Anode: Copper balls with an initial diameter of approximately 75 mm were filled in a titanium steel cylinder and placed at approximately 180 mm intervals so as to face each other with a printed circuit board to be covered. The anode spacing was 540 mm. Weir: A weir plate was provided for every three of the above anodes with a center spacing of 150 mm. Rack: 40 racks of 550 mm x 1000 mm were prepared in a plating tank, and each rack was operated with two printed circuit boards that had been chemically copper plated. Rectifier: 4 rectifiers are installed, and 1 rectifier
Now they are in charge of 10 racks. Plating solution: A copper pyrophosphate plating solution adjusted to pH 8.5 to 9.0 was used. The liquid temperature was set at 55°C. Plating speed: The rack was adjusted to advance in steps of 1 minute and remain in the plating solution for a total of 40 minutes. Air ration: Air piping with holes of appropriate diameter was provided at the bottom of the plating liquid tank on both sides, and air ration was performed using a compressor. Current density was adjusted to 3.5 A/dm ² . The prepared printed circuit board was plated under the above conditions, its thickness distribution was measured, and the pass ratio according to the pass criteria was determined. The results are shown in Table 1, and it was confirmed that the thickness distribution of the taming performed by this method was extremely stable. The thickness was measured using a microderm at four ends (points 15 mm from the two sides) and five points in the center of the printed circuit board. Comparative Example 1 Electroplating was performed in the same manner as in Example 1, except that the weir plate used in Example 1 was not provided in the plating tank, and the pass ratio was determined. The results are in Table-1
The accuracy of the variation in plating thickness is slightly inferior to that of Example 1, and the quality at the start and end of operation tends to be inferior compared to the steady state. Comparative Example 2 The printed circuit board that had undergone chemical copper plating used in Example 1 was plated using a conventional 12-tank carrier bar type plating device. The size of the rack at this time was approximately ^2m2 , and six substrates were arranged in one rack.Operating conditions such as plating solution and current density were kept as similar as possible to those in Example 1. It was set to Table 1 shows the results of examining the accuracy of variation in plating thickness.

【table】

【table】 [Brief explanation of the drawing]

Figures 1 and 2 are plan views explaining the prior art;
The figure is an elevational view in which the printed circuit board is easily arranged, and FIG. 4 is a plan view illustrating the method of the present invention. 1... Plating tank, 2... Printed circuit board, 3... Rack, 4... Anode, 5... Part to be thickly plated, 6...
Pre-processing device, 7... Post-processing device, 8... Rail, 9...
Weir.

Claims (1)

[Claims] 1. Anodes are arranged on both sides of a long plating tank passage,
An electroplating apparatus for electroplating printed circuit boards, which performs electroplating by continuously moving a printed circuit board whose center part is easily installed, and which is characterized in that weirs are provided at appropriate intervals on both sides. 2. Claim 1, in which a pair of weirs is provided on both sides of the plating bath, oriented approximately perpendicularly to the printed circuit board advancing direction, for every 2 to 4 copper anodes.
Apparatus described in section. 3. The device according to claim 1 or 2, wherein the distance between the pair of weirs is less than half the distance between the pair of anodes.