GB2237580A

GB2237580A - A method for plating a hole and adjacent surface portion of a printed circuit board

Info

Publication number: GB2237580A
Application number: GB8924832A
Authority: GB
Inventors: Ronald Frederick Lester
Original assignee: GEC Marconi Ltd; Marconi Co Ltd
Current assignee: BAE Systems Electronics Ltd
Priority date: 1989-11-03
Filing date: 1989-11-03
Publication date: 1991-05-08
Also published as: GB8924832D0

Abstract

A method of selectively plating a hole in a printed circuit board so as to form a solder pad at the same time as plating a hole in the board comprises placing a suitably shaped member with an aperture in it about the hole such that the aperture of the member defines the region that is to be plated on the surface of the board so as to correctly orientate plating apparatus eg. the electroplating apparatus of GB 2214931. A seeding layer may be first deposited, the member removed and the delivery head of the plating apparatus applied such that it seals about the seeded layer, and the seeded layer then electroplated.

Description

A Method for Plating a Hole and Adiacent Surface Portion of a Substrate.

This invention relates to a method and apparatus for plating a hole in a substrate and a surface portion immediately adjacent to the hole, and in particular to such a hole in a printed circuit board.

Many printed circuit boards have holes in them which are plated. The holes may extend partially through the board or straight through from one surface to the other. Such plated holes may electrically connect either side of the board, connect intermediate conductive layers within a multi-layer printed circuit board, or provide connection points for the pins of surface mounted devices.

These holes in a circuit board are occasionally damaged. This may either be due to the hole not being properly plated when the board was manufactured, or may be due to components having been removed from the board, whereupon, in the process of removal, the extraction of a pin through the hole has damaged the plating within the hole.

When a hole is damaged, it may be necessary to selectively repair that hole, or a plurality of damaged holes individually, without interfering with the rest of the circuit board or other components.

Apparatus for selectively replating a hole is described in our co-pending UK patent application number 8806544. This apparatus comprises a delivery head which has a rubber end portion which seals about the hole to be plated. The delivery head provides a means of passing fluids required in the plating process into the hole.

Each hole is usually surrounded by a solder pad, which is an annular portion on the surface of the board about the hole, being an extension of the plating within the hole. If this has also been damaged or removed then it may be difficult to align the delivery head with respect to the hole. Furthermore, the above apparatus cannot be used to replace the surface portion.

This invention provides a method, and apparatus for effecting a method, of selectively plating a hole in a substrate and a surface portion immediately adjacent to the hole, comprising placing an apertured member over the hole such that the aperture defines the surface portion to be plated. By using this method a surface portion immediately adjacent to the hole may be plated.

The operator may select the area to be plated with ease before it is obscured by a delivery head, for example.

Preferably, the method includes the steps of using the apertured member to locate a delivery head through which fluid used in plating the portion and hole can be applied.

The invention is now described by way of example only with reference to the accompanying drawings in which: Figure 1 shows a plating apparatus as disclosed in our co-pending application 8806544 to be used with the present invention; Figure 2A illustrates schematically a printed circuit board to which the invention may be applied; Figure 2B is an enlargement of the part designated A of Figure 2A; Figure 2C is a cross-section through the line I I Figure 2B; Figure 3 illustrates a prior art method of plating a hole; Figure 4 illustrates a method in accordance with the invention; and Figure 5 illustrates apparatus for use with the invention described with reference to Figure 4.

Referring to Figure 1, there is illustrated apparatus as disclosed in our co-pending UK application 8806544 comprising two vessels 1 and 2 for applying a fluid through a hole 3 in a dielectric substrate 4.

These vessels contain electrodes 5 for electro plating the inner surface of the hole 3.

The apparatus may be used to plate a damaged hole, which may have been drilled out, in a circuit board, without the need to remove other components such as the resistor 6. This avoids the expense of having to replace the whole circuit board, making this apparatus very attractive for use on multi-layer circuit boards.

Although the Figure illustrates the use of two vessels 1 and 2 for through-hole plating, a solitary modified vessel may be employed for applying the necessary chemicals used in plating a hole which does not pass completely through the board.

Figure 2A is a schematic illustration of a situation to which the present invention may be applied, and shows a circuit board 7 having holes 8 within it, some of which are surrounded by solder pads 9 of various shapes. Two such solder pads have been removed, leaving holes 10.

In Figure 2B the portion A of Figure 2A is shown enlarged, and in cross-section in Figure 2C. The coating 11 on the wall of the hole 8 in substrate 7 effectively continues on to the surface of the substrate to form an annular solder pad 9 about the hole. A leg has been removed from hole 10 and in the process has removed the conductive lining from the hole so that the different layers in the multi-layer substrate 7 are no longer electrically connected. It is therefore necessary to replace this layer, and in addition the missing solder pads.

Figure 3 discloses a method that has been previously used with the apparatus of Figure 1 for plating a hole, and comprises, as illustrated at A, placing a large bore seal 12 on the end of the delivery head 13 connected to the vessel 1 of Figure 1. This is then placed on the substrate 14 over the hole 15 and solder pad 16. Appropriate fluids are then flushed into the hole in order to clean it. The seal 12 is then replaced with a tapered seal 17 shown in B which seals on the solder pad 16. In this arrangement a seeding layer 19 is laid down comprising palladium obtained from a tin palladium solution applied via the delivery head 13. The delivery head can be correctly positioned upon the solder pad 16 for when the seal 17 is in position an annular portion of the solder pad can still be seen and used to locate the seal.The positioning of the delivery head and seal is not crucial providing the hole is covered by the seal, and the seal joins all round with the solder pad 16.

If a solder pad is not present as illustrated in C then it is more difficult to align the delivery head 13 on the hole 15, for the delivery head when near to position masks the precise location of the hole. Furthermore if the delivery head is not correctly positioned the seeding layer will not be concentric about the hole. Therefore when the seal 17 is again replaced with the wider seal 12, as indicated in D, and the plating solution applied, the resultant solder pad will also be off centre, the plating only being laid down on areas which are seeded. However, if a solder pad 16 were already in existence, as illustrated in D, then the off setting of the plating 19 would in this situation have no adverse effect.

Figure 4 illustrates a method employing the present invention whereby the delivery head 20 with à large seal 21 is placed over the hole 22 which has had its solder pad broken away. The area is then cleaned by passing cleaning fluid from the delivery head, the delivery head then being removed. As illustrated in B a member 23 (as shown in Figure 5A) having a aperture 24 within it, is placed over the hole such that an area 25 which it is desired to plate at the same time as plating the hole 26 is defined by the aperture in the member. A tapered seal 27 is then attached to the delivery head 20 which seals on the member 23, the member being of a soft silicon rubber compound.

Seeding solution is passed from the delivery head 20 which coats the areas exposed to leave a seeded layer 28. The delivery head is then removed and the seal replaced with a wider seal. This is placed over the hole and the seeded regions after the member 23 has been removed. A plating solution is applied which coats all the seeded regions such as to replate the hole and form a solder pad 29 on the surface.

If the hole described in the above method passes completely through the circuit board then similar methods may be applied simultaneously to both sides of the board so that the hole may be through plated.

Figure 5A shows two members X and Y one of which may be selected for placing over a hole to be plated in the method previously described. The apertures in these two members are round and square respectively but may be any shape for which it is desired to produce a solder pad, some standard shapes being illustrated in 5B.

The members X and Y have adhesive portion 30 for maintaining them in position on the circuit board prior to the delivery head being applied to the apertures 31 or 32. These members are prepared by stamping a silicon rubber strip 33 illustrated in 5C to which two lines of adhesive 34 and 35 have been applied, these shapes are then pressed out as and when required.

Claims

1. A method of selectively plating a hole in a substrate and a surface portion immediately adjacent to the hole, comprising placing an apertured member over the hole such that the aperture defines the surface portion to be plated.

2. A method as claimed in claim 1 wherein the substrate is a printed circuit board.

3. A method as claimed in claim 1 or 2 including the step of using the apertured member to locate a delivery head through which fluid used in plating the portion and hole is applied.

4. A method as claimed in claim 3 wherein the fluid deposits a seeding layer on the walls of the hole and surface portion.

5. A method as claimed in claim 4 including the steps of removing the member after applying the fluid, applying the delivery head such that it seals with the substrate about the seeded layer, and electroplating the seeded layer using a fluid applied by the delivery head.

6. A method as claimed in any preceding claim for through-hole plating including the step of placing one member on each major surface of the substrate over the hole.

7. A method as claimed in claim 3, 4, 5 or 6 wherein the delivery head has an interchangeable sealing portions which are selected for different stages of the method.

8. A method as claimed in any preceding claim wherein the member comprises an adhesive area.

9. A method as claimed in any preceding claim wherein the member is substantially planer.

10. A method as claimed in any preceding claim wherein the member consists substantially of silicon rubber.

11. A method as claimed in any preceding claim wherein a plurality of members are derived from a strip.

12. A method as claimed in any preceding claim wherein a member is selected from a plurality of members having different shaped apertures.

13. Apparatus for putting a method as claimed in any preceding claim into effect.

14. A method of plating a hole substantially as illustrated and described with reference to Figures 4 and 5 of the accompanying drawings.

15. Apparatus for plating a hole substantially as illustrated and described with reference to Figures 4 and 5 of the accompanying drawings.