GB2103154A - Liquid treatment of articles - Google Patents

Abstract

A printed circuit board (14) is etched by placing it in an inner tank (2) which itself is disposed in an outer tank (4). Etching solution is supplied to the inner tank (2) through an inlet (6) and flows upwardly over the circuit board (14). Turbulence is induced in the solution by baffles (12). The solution overflows the top edge of the inner tank (2) into the outer tank (4) and thence flows through an outlet (10). At the end of the etching operation, the inner tank (2) is drained through a drain hole (18) and water is supplied to the inlet (6) to wash the circuit board (14). Processes other than etching can be performed in a similar way. <IMAGE>

Description

SPECIFICATION Liquid treatment of articles This invention relates to the liquid treatment of articles. We use the term "liquid treatment" to means any process in which the articles are brought into contact with a liquid. The present invention particularly, although not exclusively, relates to the chemical etching and subsequent washing of printed circuit boards.

The material from which printed circuit boards are made is a thin panel of electrically insulating board coated with a layer of metal, usually copper.

During the manufacture of a circuit board, parts of the metal layer are etched from the surface of the board, to leave a desired configuration on the board to provide electrical connections. It is important to ensure that the rate of etching should be substantially constant over the entire surface of the metal layer. This requirement is difficult to achieve because the temperature of-the etching solution, and its concentration, vary during the etching process. These effects can be reduced to some extent by agitating the etching solution.

There are several methods of agitating the solution. For example, spray etching can be used, in which the etching solution is sprayed under pressure on to the circuit board through nozzles.

However, it is difficult to maintain a constant spray density over the entire working area, and some variation in the etching rate can occur.

Another known method is to use bubble etching, in which air is released into the bottom of a tank filled with the etching solution in which the board is immersed. As the bubbles rise, they agitate the solution to an extent depending on the quantity of air supplied. However, the greater the air flow into the solution, the smaller will be the area of contact between the layer to be etched and the solution. Consequently, bubble etching is a slow process and is prone to variation if the rate of air flow is excessive in any area.

A third method, generally confined to high volume installations, is to use a large tank of etching solution and to move the circuit boards in the manner of a paddle by means of an oscillating frame mounted above the tank. This method is efficient and gives good results, but the capital cost is very high.

After etching is complete, the circuit board has to be washed to remove all traces of the etching solution. The current practice is either to remove the board from the etching solution by hand and to wash it under a tap, or to move the board from the etching solution into a purpose-built wash tank, either manually or using a conveyor system.

According to the present invention there is provided apparatus for the liquid treatment of articles, the apparatus comprising a first container for receiving the articles, an inlet for liquid being provided at or adjacent the bottom of the first container, a second container being provided having an outlet at or adjacent the bottom, the first and second containers being disposed so that, in use, treatment liquid is supplied to the first container through the inlet, this liquid then flowing upwardly past the article or articles disposed within the first container and overflowing from the first container into the second container and flowing from the second container through the outlet.

Baffles may be provided on the inner wall of the first container to induce turbulence in the liquid as it flows upwardly past the article or articles.

Another method of inducing turbulence in the liquid, which may be used in addition to or instead of the baffles, is to introduce air, or other gas, into the liquid either before or after it enters the inner tank. For example, air may be introduced at the bottom of the inner tank.

According to another aspect of the present invention there is provided a method treating an article with a liquid, the method comprising placing the article in a first container, causing liquid to flow upwardly through the first container past the article, the liquid then overflowing from the first container into a second container.

Where the apparatus and process are used to etch a printed circuit board, the liquid may be a chemical etching solution. However, the apparatus may be adapted so that an etching solution and a washing liquid, such as water, may be selectively supplied to the container, so that the article may first be etched, and then washed.

For a better understanding of the present invention, and to show how it may be carried into effect, reference will now be made, by way of example, to the accompanying drawing, which shows apparatus for etching and subsequently washing a printed circuit board.

The apparatus shown in the Figure comprises a narrow inner tank 2 disposed within an outer tank 4. An inlet pipe 6 opens into the inner tank 2 at the bottom wall of the tank. The pipe 6 can receive either etching solution supplied from a reservoir by a pump 8, or water, selection being made by means of valves V1 and V3. An outlet pipe 10 extends from the bottom wall of the outer tank 4, and further valves V2 and V4 determine whether liquid discharged through the outlet pipe 10 is directed to waste or to the reservoir of etching solution.

The internal surface of the inner tank 2 is provided with baffles 12 which project inwardly and stop short of the middle of the tank. As shown in the Figure, a printed circuit board 14 is shown in the Figure, a printed circuit board 14 is suspended in the tank 2 by means of a clip 16 supported by the walls of the tank 4. There is a smaller diameter drain hole 18 in the bottom of the inner tank 2.

The apparatus shown in the Figure is used to etch and then to wash the circuit board 14. To do this, the valve V1 is closed and the valve V3 is opened, and the pump 8 is operated to supply a suitable etching solution through the pipe 6 into the lower region of the inner tank 2. The liquid flows upwardly through the tank 2, past the baffles 12, so inducing turbulence in the solution.

In particular, vortices are formed at the upper surfaces of the baffles 12. This promotes agitation of the fluid, and ensures as far as possible that all parts of the surface of the board 14 are always in contact with fresh solution. The turbulence can be enhanced if air or other gas is introduced into the etching solution through an aperture at the bottom of the inner tank 2. Some solution will flow through the drain hole 18, but the rate of flow through the drain hole 18 will be small compared to the rate of flow through the inlet 6. Continued introduction of the solution through the pipe 6 therefore results in overflow over the walls of the tank 2. This may occur over substantially the entire upper edge of the inner tank 2. The overflowing solution falls to the bottom of the tank 4 and leaves through the pipe 10.While etching solution is being supplied through the pipe 6, the valve V2 is closed and the valve V4 is open, so that the etching solution is returned to the reservoir. The condition of the etching fluid in the reservoir will need to be monitored so that the active constituents can be replenished if necessary.

When etching has proceeded for the required time, the valve V3 is closed and the pump 8 is turned off. The solution in the tank 2 flows through the drain hole 18 into the tank 4 and thence to the reservoir through the outlet pipe 10.

When the tank 2 is empty, the valve V4 is closed and the valves V1 and V2 are opened. In this condition, water is suppled to the inner tank 2 through the pipe 6 to wash the board thoroughly.

The overflowing water is discharged to the waste.

The supply of water is continued until the board 14 has been thoroughly washed and all traces of etching solution are removed. The board can then be removed, dried, and further processes applied as required. A new board can be placed in the tank 2, and the etching process begun again, after the water has been drained from the tank 2 through the hole 18.

The valves V1, V2, V3 and V4 may be controlled automatically, and, for examp!e, may be operated electrically so that they will close should the electrical supply fail. The pump may be operated by the same source of electric power as the valves.

In a simpler construction, the pipe 6 is supplied directly from the pump 8, and the pipe 10 discharges directly to the reservoir. The valves V1, V2, V3 and V4 are not required, nor is the pipework associated with the supply and discharge of water. With such apparatus, it is necessary to wash the etched boards in a separate operation, for example under a tap.

The description of the present invention in connection with an etching process followed by washing is only one example of the use to which apparatus in accordance with the present invention can be put. For example, apparatus as shown in the Figure could be used to provide a pure washing step, or a de-greasing process using a suitable solvent. Furthermore, the apparatus can be adapted to carry out a series of processes by passing different liquids in turn through the inner tank 1. The ability to perform a number of separate processes without physically moving the article to be treated provides significant advantages, particularly where some of the processes involve corrosive liquids.

Apparatus in accordance with the present invention can be constructed relatively economically, and provides consistent results.

Claims (20)

1. Apparatus for the liquid treatment of articles, the apparatus comprising a first container for receiving the articles, an inlet for liquid being provided at or adjacent the bottom of the first containing, a second container being provided having an outlet at or adjacent the bottom, the first and second containers being disposed so that, in use, treatment liquid is supplied to the first container through the inlet, this liquid then flowing upwardly past the article or articles disposed within the first container and overflowing from the first container into the second container and flowing from the second container through the outlet.

2. Apparatus as claimed in claim 1, in which the first container is disposed within the second container.

3. Apparatus as claimed in claim 2, in which, in use, treatment liquid overflows from the first container over substantially the entire upper periphery of the first container.

4. Apparatus as claimed in any one of the preceding claims, in which the inner wall of the first container is provided with baffles for inducing turbulence in the treatment liquid.

5. Apparatus as claimed in claim 4, in which the baffles extend inwardly from the inner wall of the first container and stop short of the middle of the first container.

6. Apparatus as claimed in any one of the preceding claims, in which a drain hole is provided out of the bottom of the first container to allow treatment liquid to drain from the first container to the second container.

7. Apparatus as claimed in any one of the preceding claims, in which means is provided for introducing gas into the treatment liquid.

8. Apparatus as claimed in claim 7, in which the gas introducing means comprises a gas supply aperture at the bottom of the first container.

9. Apparatus as claimed in any one of the preceding claims, in which the inlet is provided with means for connecting it to at least two different sources of treatment liquid.

10. Apparatus as claimed in any one of the preceding claims, in which the outlet is provided with means for connecting it to at least two receivers of treatment liquid.

11. Apparatus as claimed in claim 9 or 10, in which the connecting means comprise valves.

12. Apparatus as claimed in claim 1 in which the valves are automatically controlled.

13. Apparatus as claimed in any one of the preceding claims, in which a pump is provided for supplying treatment liquid to the inlet.

14. A method of treating an article with a liquid, the method comprising placing the article in a first container, causing liquid to flow upwardly through the first container past the article, the liquid then flowing from the first container into a second container.

15. A method as claimed in claim 14, in which turbulence is induced in the liquid as it flows upwardly through the first container.

16. A method as claimed in claim 14 or 15, in which the liquid is one of two liquids, and in which the method comprises: a) supplying the first liquid to the container, b) terminating the supply of the first liquid, c) emptying the first container, d) supplying the second liquid to the container, and e) terminating the supply of the second liquid.

17. A method as claimed in claim 16, in which the first liquid is an etching solution and in which the second liquid is water.

18. A method as claimed in any one of claims 14 to 17, which is a method of etching printed circuit boards.

1 9. Apparatus for the liquid treatment of articles substantially as described herein with reference to, and as shown in, the accompanying drawings.

20. A method of treating an article with a liquid substantially as described herein with reference to, and as shown in, the accompanying drawings.