High Speed Plating Device for Rectangular Sheets

The present invention concerns a high speed plating device for rectangular sheets, and more in particular it concerns a plating device which has an improved masking means and which uses an improved method of supplying the plating solution. Terminals of the copper plated, printed circuit board are generally imparted with the features as terminals-- hardness, wear resistance, electric properties, etc.-- by directly applying gold plating, or gold or rhodium plating over the nickel plating on the surface.

In the prior art, a plating method for terminals of the printed circuit board is known wherein the portions of the board which need not be plated is covered with a thin synthetic resin film and the peripheral portions are masked with adhesive tapes or resist material, and the board is dipped in the level controlled electroplating bath and charged with electricity for plating. However, this type of method requires preliminary preparations prior to the plating operation which automatically increase the costs in labour and materials. Plating at a high current density is impossible for this dipping method so that it takes a long period of time to obtain the required minimum thickness of the plated deposit. This method is further defective in that the thickness of the plating deposit is often uneven depending on the location of the object to be plated, distance between anodes and cathodes, and on the condition of electrolyte agitation and also in that these conditions are very hard to control.

The present invention was contrived so as to remove these defects by improving the masking means and by jetting the plating solution on the surface of the objects to be plated instead of dipping the object in the bath as in the prior art, thereby securing a plating device which performs the plating operation simply, securely and at a high speed.

The present invention aims at eliminating all the consumable materials such as resists or tapes which are required to protect the portions not requiring plating and at radically decreasing the labor and material costs by conducting the mechanical masking for the non-plated parts simultaneously with the plating operation.

Another object of the present invention is to remarkably reduce the area needed for installation of the plating device and to decrease the unevenness in the plating film at respective plated portions and on two faces by utilizing the constant jetting method.

Further objects of the present invention will become clear from the following explanation and the attached drawings.

One embodiment of the present invention is explained references being made to the drawing in which

FIG. 1 is a diagramatic oblique view showing an overall view of the high speed plating device with its main parts exploded;

FIG. 2 is a cross sectional view taken along the line II--II in FIG. 1;

FIG. 3 is a front view showing a printed circuit board used as one example of the rectangular sheet;

FIG. 4 is a partial oblique view showing an exploded view of a jetting means and

FIG. 5 is a diagram showing the plating solution being jetted.

In the drawing, (1) denotes a printed circuit board shown as an example of the rectangular sheet and (2) terminals aligned in the longitudinal direction of the bottom of the board (1) which are denoted also as (3), the portion to be plated.

The device in accordance with the present invention which plates the printed circuit board (1) as above described at a high speed comprises a masking means (4), a jetting means (5) and a circulating/feeding means for the plating solution. The masking means (4) is provided with a press plate (7) and a receiving plate (8) which makes up a pair and a pressure cylinder (9). This pair of press plate (7) and receiving plate (8) has a length exceeding that of the printed circuit board (1) and is provided on its opposing faces with masking sheets (10), (11) respectively. The masking sheets (10), (11) are made of rubber or some other material suitable for masking and acts also as a packing material. Above the said press plate (7) is positioned an upright guide scale plate (24), which has two pins (25) attached in such a way that the attaching position may be varied. As the printed circuit board (1) is invariably provided with a plurality of holes (26) (FIG. 3), the printed circuit board (1) may be hooked and hung by passing the pins (25) through these holes (26), and it is possible to adjust the position of the portions to be plated (3) relative to the plating liquid slit jet member, or the depth of the printed circuit board (1) relative to the jetting means (5) when the printed circuit board (1) is hung over the pins (25) by these holes. It is also possible to plate other types of printed circuit boards so long as the shape is the same without adjusting the positions; it is sufficient if the board is merely hung over the pins (25) of the guide scale plate (24). Instead of this "hanging method", the lower end of the printed circuit board may be supported by a support fixture of which the height is adjustable. The pressure cylinder (9) presses the press plate (7) toward the receiving plate (8) and the printed circuit board (1) is supported by the pressure between the press plate (7) and the receiving plate (8). If no pressure is applied, the printed circuit plate (1) can be removed freely from between the press plate (7) and the receiving plate (8) or conversely it may be placed therebetween. It is sufficient if at least one of the said pair of press plate (7) and receiving plate (8) can be moved for "pressurizing", but it is also possible to attach pressure cylinders to both of them for pressurizing.

The jetting means (5) comprises a nozzle member (27) having a specific structure and other accessories. At the top of the said nozzle member (27) there is provided an opening (14) to receive the portions to be plated (3) of the printed circuit board (1) and on both sides of the said opening (14) are positioned opposite each other and along the longitudinal direction two slit jet members (12), (13) for the plating solution. There are provided chargeable anodes (15), 16 on the said jet members (12), (13) all the way along the lengthwise edges thereof as shown in FIG. 4, sectioned into plural sections (15a-15e), (16d, 16e) and connected with a lead wire 28 respectively. Sectioning of the anode is quite important in maintaining the current density constant.

To the bottom of the said nozzle member (27) is attached a Y shaped pipe (29) joined to the piping through which the plating solution is instantly supplied to the jet members (12), (13). The nozzle member (27) is supported within a case (32) by a support plate (31) formed with a plurality of openings (30). The bottom of the case (32) is left open. The circulating/feeding means (6) for the plating solution comprises a pump (17), a plating solution tank (18) and various pipings. The tank (18) is open at the top to directly receive the bottom (opening) of the case (32) so that the plating solution jetted from the jet members (12), (13) does not remain in the case (32) but is returned to the tank (18) immediately through the openings (30) of the support plate (31) and the bottom opening of the case (32).

In the drawing, (19) denotes a housing for the device provided on its upper part with a slit (20) for allowing the printed circuit board (1) to be inserted and a storage recess (21) for containing the objects to be plated. (22) is an indicator panel while (23) is a control panel for plating.

The operations of the high speed plating device as above mentioned are now explained. With the pressure cylinder (9) turned "OFF", the printed circuit board (1) is hung by hooking the same to the guide scale sheet (24) having two pins (25) and the bottom end of the board is inserted between the press plate (7) and the receiving plate (8). Then, with the pressure cylinder (9) turned "ON", the printed circuit board (1) is supported between the press plate (7) and the receiving plate (8). The portion of the printed circuit board (1) which does not receive plating is mechanically, simply and securely masked with the masking sheets (10), (11) of both the press plate and the receiving plate and the unmasked portion (3) of the said board (1) which is to be plated is inserted into the opening (14) of the nozzle member (27) and positioned between the jet members (12), (13) for the plating solution. Electricity is charged to the terminals (2) as cathodes, and while charging anodes (15), (16), the circulating/feeding means (6) of the plating solution is operated. The plating solution flows under pressure from the pump (17) along the direction of arrow A (FIG. 1) through the Y shaped pipe (29) to the nozzle member (27) and is jetted instantly against the two surfaces to be plated through the two jet members (12), (13). Jetted plating solution (33) advances toward the object to be plated (3) as shown in FIG. 5 in the perpendicular direction (horizontal direction) and diverges into upward and downward streams as it crashes upon the surfaces. This phenomenon occurs instantly and simultaneously throughout the whole length of the portions to be plated (3) of the rectangular sheet. When the plating solution (33) contacts the portion to be plated (3), ionization occurs instantly and a uniform plated layer is achieved at a high speed. In this case, it is possible to selectively charge the anodes (15a-15e), (16d, 16e sectioned into a plural number corresponding to the length of the portions to be plated, and the readiness to correspond to the anodes (15), (16) in plating various printed circuit boards is improved and the electric current density can be controlled to be uniform.

Plating solution after the plating is completed flows in the direction of arrows (8) and C and is rapidly recovered into the tank (18) through the bottom opening of the case (32). The solution is then cycled and reused as the need arises.

The high speed plating device for rectangular sheet in accordance with the present invention as above mentioned achieves various advantages enumerated below.

a. Plating is completed by jetting the plating solution, thereby facilitating a use under a high electric current density.

This means the plating speed is about 5 times more (15 A/dm.sup.2, 14 sec., 1 .mu.) than that of the conventional dipping system (3 A/dm.sup.2, 70 sec., 1 .mu.).

b. Uniform jetting will achieve an even plating film thickness.

c. Since no masking materials such as resists and tapes are required, it becomes possible to reduce the number of steps in the operation, and to mechanically secure the sheet for plating only the required portions at once from both sides.

d. Since plating at a high speed is possible, the area needed for installation can radically be reduced for the same quantity production.

e. As the consumables for masking are no longer required, the plating time is shortened, the production per hour increased and contamination of the plating solution by masking agents avoided.

f. Soiling of the printed circuit board by dissolved lead, tin, etc. during soldering in the conventional dip plating is avoided since plating is performed at a high speed. This prolongs the life of the plating solution remarkably.

g. The additional advantage of this invention is that the gold plating over soldering is obtainable as a precipitate in an excellent condition by the high speed plating which is the major characteristic feature of the present invention.

Since the present invention offers plating of specific areas on both sides at the same time, let alone on one side, of the rectangular sheets which are not limited to the printed circuit board, such parts as connectors and contacts can also be processed in accordance with the present invention.