GB2266727A

GB2266727A - Conveyorised system for electroplating PCBs or plates e.g. with photoresist

Info

Publication number: GB2266727A
Application number: GB9209108A
Authority: GB
Inventors: Kevin Oswald Laidler
Original assignee: Individual
Current assignee: Individual
Priority date: 1992-04-27
Filing date: 1992-04-27
Publication date: 1993-11-10
Also published as: GB9209108D0

Abstract

The conveyor moves a succession of substrates along a horizontal plane, then down into the electroplating solution and up out of the solution before levelling on to the horizontal plane again electrical contact with the substrate being by means of a rotating fixture containing a series of contacts which only apply electrical current when in contact with the substrate. The system will produce a more evenly plated coating on various sized material without the need to hold the work in jigs and without mechanical action to prevent carry over of chemicals. <IMAGE>

Description

HORIZONTAL CONVEYORISED ELECTRODEPOSITED PHOTORESIST This invention relates to a horizontal conveyorised system for electrodepositing photoresists.

Photoresists can now be electrodeposited on to most conductive surfaces for example a copper based printed circuit board or stainless steel plate to be chemically milled. Latest equipment to carry out this process involves the vertical immersion of the substrate to be plated into a tank of plating solution. The substrate is retained in a holding jig which is conductive. An electrical charge is applied to the substrate through the contacts on the jig for a given period of time.

Conventional plating either cathodic or anodic then takes place. Conventional vibration is applied to the substrate to remove gas bubbles generated during the plating process on the surface of the substrate. These bubbles would prevent plating causing a pin hole effect on the surface of the substrate.

The vibration techniques can be mechanical, ultrasonics, air or liquid sparging etc which will cause the substrate to vibrate, shake off the gas bubbles thus allowing them to float to the surface of the solution.

Conventional plating in this method involves loading and unloading the work into suitable jigs. The immersion into plating solution of the substrate is carried out by hand or automatic hoist. Contact with the chemistry or fumes given off can not be fully avoided by either method.

Substrate of differing widths requires different work holding jigs and in any event loading and unloading work is inefficient and time consuming.

According to the present invention by changing the production method from vertical immersion to horizontal conveyorised processing the production method is greatly improved. Apart from the obvious handling improvements utilising readily available automatic conveyor load and unload machinery, there are no jigs involved. Work of varying sizes can be placed on the conveyor for automatic process through the plating solution. Contact with the chemistry by the operator is removed and since the conveyors have covers, the fumes are not free to enter the operational environment. By creating a negative pressure inside the process chamber, fresh filtered air enters the equipment so preventing uncontrolled escape of fumes.

The present invention is a means of horizontal conveyorised plating of photo resists though not restricted to photo resists but applying to any electroplating process of a similar nature. The substrate to be conveyed is loaded on a horizontal conveyor. The conveyor moves the substrate into the process chamber. The conveyor in the process chamber is concave, thus allowing the substrate to move down into the solution and up out of the solution levelling onto the horizontal plane (FIG 1).

The degree of slope of the conveyor and therefore the substrate will enable gas bubbles generated during the plating process to be more likely to move from the underneath of the substrate than any trapped on a substrate on a horizontal plane. Plating therefore takes place when the substrate is at the angle created by entering or leaving the process chamber.

Vibration techniques previously discussed will assist with the removal of the gas bubbles from the surface of the substrate. A benefit of the sloping conveyor surface and thus the angle of the substrate is that surplus chemistry on the surface of the substrate will drain off back into the process chamber as the substrate is transferred to the next process. This will prevent cross contamination of chemistry without the need to have mechanical methods of removing the chemistry, such as squeeze rollers, which could damage the substrate.

To apply the electrical current the present invention proposes a rotating electrical contact (FIG2). This contact will need to be conductive and as such will be prone to plating itself. Should the contact become plated it will no longer be conductive. The revolving contact can be used either under solution or above the solution dependant on the length of the substrate.

In the event that the substrate is a laminate of two conductive surfaces divided by an insulating panel, as in the case of a printed circuit board, a revolving contact must be applied to both surfaces i.e. a contact on the top and the bottom sides of the substrate.

The revolving contact will consist of a number of conductive points which only apply electrical current when in contact with the substrate. These contact points can be, but are not restricted to, a series of contacts on the circumference of a roller or wheel. (FIG 3) The contact point touching the substrate is insulated from the other contact points mounted on the roller or wheel.

The plating solution will not plate the contact which is in contact with the substrate but were the contact a conductive roller or wheel, any area not in contact with the substrate would be plated. As the substrate moved and the roller or wheel turned, areas of the roller or wheel which had been plated would come into contact with the substrate. The surface which had become plated by a photo resist would in effect be an electrical insulator and the plating process would cease.

This invention of a revolving series of electrical contacts receiving and passing on electricity only at a time when in contact with the substrate will allow plating to take place whilst the substrate is moving on the conveyor.

Whilst the revolving contacts can be fitted above the liquid level of the plating solution they can also function whilst immersed in the plating solution.

This invention of revolving contacts will offer additional benefits. In conventional plating the electrical contact is made at the top of the substrate. The bulk of the substrate which is immersed in the solution receives the electrical current from only the top jig mounted electrical contacts. The substrate which is conductive will by virtue of the size of the item in relation to the distance the top of the substrate and the bottom of the substrate are from the electrical contacts will plate unevenly. This will be caused since there will be an electrical resistance created by the surface of the substrate. Plating will be wedge shaped with the greater plating depths achieved the closer to the electrical contact.

Since this invention conveys the substrate through the electrical contacts, all of the surface receives a more equal electrical current. For slow moving substrates or lengthy plating times, a series of rotating electrical contacts such as but not restricted to rollers can be fitted. These will ensure a more even distribution of electrical current.

This invention which creates a revolving series of contacts will enable substrates to move through the contacts without damage caused to the substrate by non revolving contacts which would be prone to scratch the surface of a substrate.

This invention when utilising the revolving contacts in the form of a roller or rollers will allow substrates of varying sizes to be processed. The conveyor can be loaded with substrates of various widths or a number of separate substrates side by side. Since the revolving electrical contacts are in the form of rollers covering the full width of the conveyor, the various substrates will make contact with the electrical contact roller whatever their size.

Claims

1. A horizontal conveyorised system for electroplating photo resists.

2. A horizontal conveyorised system for electroplating conductive materials.

3. A horizontal conveyorised system for electroplating conductive materials of different sizes without holding jigs.

4. A horizontal conveyorised system for electroplating conductive materials utilising a revolving fixture containing numerous electrical contacts.

5. A horizontal conveyorised system for electroplating conductive materials which needs no mechanical action to prevent carry over cross contamination of chemistry.

6. A horizontal conveyorised system for electroplating conductive materials with a more even plated surface.