WO1986006925A1

WO1986006925A1 - Printed circuit boards and transfers therefor

Info

Publication number: WO1986006925A1
Application number: PCT/GB1986/000248
Authority: WO
Inventors: Ernest Bourne
Original assignee: Boorman, Paul, Anthony
Priority date: 1985-05-10
Filing date: 1986-05-09
Publication date: 1986-11-20
Also published as: AU5867386A; GB8511861D0

Abstract

A transfer arrangement to form a printed circuit on a board (10) comprises a thin flexible carrier sheet on which are superimposed individual layers formed of different materials, for example by printing. A first layer (12) may be formed of an alkali soluble material, a second layer (14) of a solvent soluble material, and a third layer (16) of a solder resist material. Each of the layers has a predetermined image so that when the transfer arrangement is applied to the board (10) and the carrier removed, the board (10) can be subjected to various chemical treatments, for example etching, solder application, and gold plating, with the layers (12, 16) being chemically removed inbetween successive treatments, the treatments thereby being restricted to those parts of the board (10) not masked at the appropriate time by any of the layers. The transfer arrangement can therefore be used to produce the printed circuit board with no printing facilities being required by the user on site which has many advantages over established methods of production.

Description

_ _

Printed Circuit Boards and Transfers Therefor

This invention relates to the production of components having surface areas presenting different materials, particularly but not exclusively printed circuit boards, and transfer arrangements for use in such production. The term 'material' as used in this Specif¬ ication is intended to embrace both a single substance material and a material comprising a mixture of substances.

Presently the manufacture of printed circuit boards involves a number of both printing and treatment operations which are carried out at the place of manufacture, involving skilled operators.

It is an object of the present invention to provide for a simplified method of production, resulting in considerable saving in cost, machinery, materials, site area and skilled personnel.

According to one aspect of the present invention there is provided a transfer arrangement for use in forming a component having at least two surface areas presenting different materials, the arrangement comprising at least two layers removably super¬ imposed one upon another, one of the layers forming a carrier for the other layer, and the other layer being formed in a predetermined design, whereby, when the arrangement is transferred to a component and the carrier is removed, the other layer is retained on the component to extend over a part of the surface thereof, and thereby control subsequent treatment of the surface of the component and enable at least two surface areas to present different materials. Preferably there are provided a plurality of the other layers, each of which is formed of a material different to the others, whereby at least some of the other layers can be selectively removed by different respective chemical treatments. The other layers may comprise a first layer adapted to remain permanently on the compon¬ ent and additional layers each adapted to be selectively removed. One of the other layers to be removed can be formed for example of an alkali soluble material, and another of the other layers to be removed may be formed for example of a solvent soluble material. The carrier may be formed of a sheet of flexible material.

The layers may be superimposed one upon another by printing or by dye stamping.

An adhesive may be included for retaining the or the respective other layer on the component.

According to another aspect of the present invention there is provided a method of producing a component having at least two surface areas presenting different materials, the method comprising providing a transfer arrangement having at least two layers remov¬ ably superimposed one upon another, one of the layers forming a carrier for the other layer, and the other layer being formed in a predetermined design, applying the transfer arrangement to a compon¬ ent and removing the carrier to expose a predetermined surface area uf the component, applying a first treatment to the component which is effective on the exposed surface area, and removing the other - , ~ -

layer.

Preferably the transfer arrangement is provided with a plural¬ ity of other layers, each formed of a material different to the others, whereby, after the application of the first treatment and removal of the respective layer to expose a further surface area of the component, further treatments are applied to the component and each of the remaining other layers is chemically removed after a respective one of said further treatments, whereby each of said further treatments is effective only on a previously exposed surface area of the component.

The other areas to be removed may include a layer formed of an alkali soluble material and a layer formed of a solvent soluble material.

Prior to application of the transfer arrangement, the component may be plated with an electrically conductive material such as copper. The first treatment may comprise etching of the copper in the exposed surface area, one of the further treatments may comprise applying a solder layer to the exposed surface area, and another of the further treatments may comprise gold plating the exposed surface area.

The invention also provides a printed circuit board comprising a board in the form of a component with a printed circuit as produced by the method according to any of the- four preceding para¬ graphs, and electrical components mounted on the board in electrical connection with the printed circuit.

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The connections for the electrical components may extend through the board to connect with the printed circuit. The electri¬ cal connections may be secured by solder, a sheet of solder resist material masking the area of the board other than selected areas, on which applied solder is to be effective. The solder resist material may have an identification legend provided thereon.

Further the invention may provide a method of producing a printed circuit board, the method including providing a transfer arrangement comprising a layer of a solder resist material and a layer in the form of a legend superimposed on a removable carrier layer, transferring the arrangment to a board and removing the carrier layer,^' whereby the layer of the solder resist material remains on the board, having openings therein aligning with selected areas of the board, and applying solder to the board whereby to be effective only in the selected areas.

The solder resist material and legend layers may be printed on the carrier layer.

An embodiment of the present invention will now be described by way of example only with reference to the accompanying drawings, in which :-

Fig. 1 is a plan view of a component with a transfer arrange¬ ment applied thereto, prior.to any treatment;

Fig. 2 is a view similar to Fig. 1 after the component has been subjected to a first treatment;

Fig. 3 is a view similar to Fig. 2 after one layer of the transfer arrangement has been removed;

Fig. 4 is a view similar to Fig. 3 after the component has been subjected to a further treatment;

Fig. 5 is a view similar to Fig. 4 after a further layer of the transfer arrangement has been removed;

Fig. 6 is a view similar to Fig. 5 after the component has been subjected to yet a further treatment; and

Fig. 7 is a view similar to Fig. 6 showing the component in its finished form.

In the production of a printed circuit board, a board for example in the form of a fibreglass laminate is drilled at pre-set locations determined by the subsequent required positioning of elec¬ trical components on the board at respective locations on a printed circuit. The surface of the board is then conditioned with the drilled holes being smoothed and radiussed at the ends by means of vapour honing. Thereafter the board can be copper plated, for example by panel plating, a layer of electroless copper being formed prior to a layer of electrolytic copper.

To enable forming of the printed circuit on the board 10 there is provided a transfer arrangement. This arrangement comprises a stable carrier in the form of a thin sheet of a flexible material (not shown) on which are superimposed individual layers formed of different materials. Each of these layers has a predetermined design or image and the imaged layers can be formed by any known printing method or by dye stamping.

In one example the first image layer on the carrier may be lormed of an alkali soluble material, the next layer formed of a solvent soluble material, and a final layer formed of a solder resist material. Suitable means may be provided for enabling registration of the imaged layers on the carrier.

To form a printed circuit on the board 10, the image transfer comprising the carrier and the superimposed image layers is applied to a surface of the board 10, with the carrier outermost, and matching location positions on the transfer and the board 10 provide for registration. For retaining the transfer on the board 10, any suitable form of adhesive may be utilised, and in one example a thermosetting or other adhesive may be incorporated in the solder resist material. In Fig. 1, where the carrier has been removed, the transfer on a component 10 comprises a first layer 12 formed of the alkali soluble material, a second layer 14 formed of the solvent soluble material, and a third layer 16 formed of the solder resist material.

When the component 10 is then subjected to an etching treat¬ ment, the exposed areas of copper, i.e. the areas not masked by the layers 12, 14, 16, are removed to expose the fibreglass surface 17 (Fig. 2). Thereafter the first layer 12 is individually removed by the application of an alkali solution which dissolves the material to leave an exposed copper pad 18 (Fig. 3). The component 10 is then dipped in a solder bath provided with hot air knives to level the solder, and the solder affixes to the exposed copper pad 18 but not to any other area of the component surface (Fig. 4).

Thereafter a solvent solution is applied to the component to dissolve and therefore remove the layer 14 and this exposes a copper finger 20 and a copper bus-bar contact 22 (Fig. 5). The component can then be dipped in a bath for gold plating with the bus-bar contact 22 remaining outside the bath so as to provide the electri¬ cal contacts necessary for gold plating. The finger 20 is the only part of the component surface plated with gold (Fig. 6). To comp¬ lete the printed circuit board, the component 10 is then trimmed around the edge to retain only the soldered pad 18, the gold plated finger 20 and an interconnecting strip 24 on which the layer 16 ^•remains as a solder resist track cover (Fig. 7). It will be apprec¬ iated that the layer 16 is also an etch resist or gold plating resist material.

It will of course be appreciated that this description with reference to the drawings shows a single pad 18, contact finger 20, and track 24 for illustration only and that any design of circuit can be printed using such a transfer arrangement.

When the printed circuit board is completed by the attachment uf electrical components, it is appropriate to apply a final layer of solder to the pads which receive the component connections. For this purpose a further transfer arrangement (not shown), particul¬ arly if further insulation is required, comprises a stable carrier formed of a thin sheet of a flexible material on which is super- - -

imposed a layer of a solder resist material and a layer in the form of a legend or notation as desired to be applied to the printed circuit board. Suitable means are provided for registration of the layers on the carrier. The solder resist layer has the form of a mask formed with apertures which, when the transfer is applied to the circuit board and the carrier is removed, apertures align with the pads. Thus when solder is applied it affixes only to the desired areas.

Where no legend is required, it will be appreciated that the transfer will comprise a carrier and solder resist insulation layer only.

In a conventional method of producing a printed circuit board • an electroless copper coat is first applied to a laminate and printing of a first image is required for electrolytic copper plating and tin lead plating. After copper plating and tin lead plating the first printed image is removed and etching takes place. Next tin lead is chemically removed in areas where gold plating is required, areas which are to be immersed in a gold plating bath but which do not require gold plating having to be masked. After gold plating the mask is removed, the board is degreased, a solder mask is printed on the first side and dried and a solder mask is printed --n the second side before stoving.

The advantages of the present invention will therefore be apparent in that there are no printing facilities required by the user on site, leading to a saving in floor area and equipment cost - 9 - T/GB8./00248 etc., as well as maintenance costs. No skilled printing operators will be required and there will be considerable reduction in consum¬ ables such as films, inks and chemicals. Further, environmental controls will be reduced, storage area will be reduced and there will be reduced product handling. In applications where electrical components are attached by being laid on the printed tracks, for example surface mounted, the consequence is that more tracks are required on one surface of the board resulting in greater packing density. The invention is particularly suitable in such applica¬ tions as extremely narrow track widths can be achieved.

It is to be appreciated that a transfer having only one layer may be utilised, and also that more layers than those described with reference to the drawings can be provided on a transfer. Further, two or more transfers may be utilised in producing a printed circuit board. For example a first transfer may be used to form a plated area and a second transfer may then be used to apply a solder resist mask protecting the plated area during further treatment, possibly using further transfers. The number of layers relate to the number of processes required and individually with the related process can be considered for example as a plating system, an etching system, a solder resist system, a resistor paste system, or a conductor paste/ink system, in, of course, any sequence. In the embodiment specifically described, the alkali solution may be a caustic soda solution while the solvent may be methylene chloride or white spirit, but the choice of chemicals and solutions used is dependent on the layer materials used. _ ^ _ 86/00248

The use of a transfer to apply the solder resist mask and selectively the legend overcomes problems which can otherwise result when applying solder, as the solder may otherwise affix to the sides of tracks, not covered by a solder resist material. Where tracks are close together such solder can lead to bridging of the tracks.

Various modifications may be made without departing from the invention. For example the board used may be a double sided non- plated copper board or a laminated copper foil board. The image layers may be formed by other than printing. Instead of hot air levelling in the solder bath, hot oil levelling or tin lead plating may be utilised.

Claims

Claims :

1. A transfer arrangement for use in forming a component having at least two surface areas presenting different materials, charact¬ erised in that the arrangement comprises at least two layers remov¬ ably superimposed one upon another, one of the layers forming a carrier for the other layer (12, 14 or 16), and the other layer (12, 14 or 16) being formed in a predetermined design, whereby, when the arrangement is transferred to a component (10) and the carrier is removed, the other layer (12, 14 or 16) is retained on the component (10) to extend over a part of the surface thereof, and thereby con¬ trol subsequent treatment of the surface of the component (10) and enable at least two surface areas to present different materials.

2. A transfer arrangement according to claim 1, characterised in that there are provided a plurality of the other layers (12, 14, 16), each of which is formed of a material different to the others, whereby at least some of the other layers (12, 14, 16) can be selectively removed by different respective chemical treatments.

3. A transfer arrangement according to claim 2, characterised in that the other layers comprise a first layer (16) adapted to remain permanently on the component and additional layers (12, 14) each adapted to be selectively removed.

4. A transfer arrangement according to any of the preceding claims, characterised in that the or each other layer (12, 14, 16) is superimposed by printing.

5. A method of producing a component having at least two surface areas presenting different materials, characterised in that the method comprises providing a transfer arrangement having at least two layers removably superimposed one upon another, one of the ^• layers forming a carrier for the other layer, and the other layer (12, 14, 16) being formed in a predetermined design, applying the transfer arrangement to a component (10) and removing the carrier to- expose a predetermined surface area of the component (10), applying a first treatment to the component (10) which is effective on the exposed surface area, and- removing the other layer (12, 14, 16).

6. A method according to claim 5, characterised in that the transfer arrangement is provided with a plurality of other layers (12, 14, 16), each formed of a material different to the others, whereby, after the application of the first treatment and removal of the respective layer (12) to expose a further surface area of the component (10), further treatments are applied to the component (10) and each of at least some of the remaining other layers (14, 16) is chemically.removed after a respective one of said further treatments, whereby each of said further treatments is effective only on a previously exposed surface area of the component (10).

7. A printed circuit board characterised by a board in the form of a component (10) with a printed circuit as produced by the method of any of claims 5 or 6, and electrical components mounted on the board in electrical connection with the printed circuit.

8. A printed circuit board according to claim 7, characterised in that the electrical connections are secured by solder, a sheet of solder resist material masking the area of the board other than selected areas, on which applied solder is to be effective.

9. A method of producing a printed circuit board, characterised by providing a transfer arrangement comprising a layer of a solder resist material and a layer in the form of a legend superimposed on a removable carrier layer, transferring the arrangement to a board and removing the carrier layer, whereby the layer of the solder resist material remains on the board, having openings therein aligning with selected areas of the board, and applying solder to the board whereby to be effective only in the selected areas.

10. A method according to claim 9, characterised in that the solder resist material and legend layers are printed on the carrier layer.