GB2040499A - Methods of Manufacturing Electrical-circuit Layouts and Items for Use Therein - Google Patents

Abstract

A method of laying out the circuit artwork required as a preliminary to photographic and etching processes in the production of printed circuits, is carried out by application to a sheet (20) of overlay (or print-transfer) elements (30, 40, 50, 60), that each carry print of a multiplicity of parallel lines whereby in the one application of each element there is established on the sheet (20) at least one section of the length of a multiplicity of parallel circuit connections. The parallel lines of print on some elements (30, 60, include angled offsets, and some (30), of these have lines that are cranked to provide bridge portions. Print- representations of two rows of circular or other terminal pads extend transversely of the lines on certain (30) of the latter elements, so that these elements carry the print- representations of the terminal pads and individual parallel circuit- connections to them, required for mounting dual in-line integrated circuits on the printed-circuit board, whereby the whole pattern for pack interconnection can be established by the one application of such element to the sheet. The different types of element or symbols are stored on reels to be drawn off one at a time for use and can have an adhesive layer for attaching to the sheet. <IMAGE>

Description

SPECIFICATION Methods of Manufacturing Electrical-circuit Layouts and Items for Use Therein This invention relates to methods of manufacturing electrical-circuit layouts and items for use therein.

Electrical-circuit layouts involving artwork representing the desired pattern of circuitconnections are utilized in the production of printed and like circuits. The artwork is reduced and printed photographically, and is then converted from the photographic print by etching or deposition into a corresponding pattern of eiectrically-conductive paths and pads on a board or other carrier. The carrier supports integrated circuits or other discrete components in the finished device, electrical connection to and from the components necessary to achieve the desired circuit-function being made via the electricallyconductive paths and pads laid down in accordance with the artwork.

The artwork required for the circuit layout is in general executed by application of opaque or translucent items to a transparent sheet. In particular opaque or translucent tape is applied to the sheet along the line of each required connection path. Points in the pattern where pads are to be provided for terminal connections are established by application to the sheet of appropriately-shaped items which, like the tape, are opaque or translucent. The artwork is provided to an enlarged scale, but it is nonetheless necessary to apply the tape and other items to the sheet with considerable care and accuracy in order to ensure that the electricallyconductive paths and pads produced from it after reduction in scale, conform to close tolerances on location and spacing required for the finished device.

The application of the tape or other items to the sheet is often tedious and time-consuming.

This is especially so where integrated circuits are mounted on the carrier in individual packs, each such pack normally requires fourteen or more individual terminal connections, and accordingly a substantial number of closely-spaced parallel lines of tape are required to be applied individually to the sheet in respect of each circuit.

It is one of the objects of the present invention to simplify manufacture of electrical-circuit layouts. Another of the objects of the invention is to provide items for use by way of aids to such manufacture.

According to one aspect of the present invention there is provided a method of manufacturing an electrical-circuit layout that includes artwork representation on a sheet of a multiplicity of parallel circuit-connections, wherein an element carrying print of a multiplicity of parallel lines is applied to the sheet such that said print provides by the one application of said element to the sheet the said representation of said circuit connections along at least part of their length.

According to another aspect of the present invention an item for use in the manufacture of an electrical-circuit layout consists of an element which carries print of a multiplicity of parallel lines and which is adapted to be applied to a sheet to establish thereon in the one application representation by said print of a multiplicity of parallel circuit connections along at least part of the length of such connections in the said layout.

The said element specified in respect of each of the above-mentioned aspects of the invention is preferably an element of photographicallytransparent film that is adapted to be applied to the said sheet to adhere thereto as an overlay; the under-surface of the film may in this latter respect be coated with a pressure-sensitive adhesive. The print may be carried on the upper-surface of the film but is preferably carried on the under-surface so as to be protected during handling and when the film is applied to and overlays the sheet.

Instead of establishing the print on the sheet by means of an overlay, it might be transferred to the sheet from the element by, for example, a drytransfer technique, and the element may accordingly be adapted appropriately for this.

The print provided on the said element may consist simply of a multiplicity of parallel straight lines, but lines including angled offsets and/or other features may be involved. Furthermore, the print may include representation of a set of terminal pads and parallel circuit-connections to those pads or to at least some of them. More specifically in the latter respect, the print may represent two parallel rows of pads and parallel paths crossing both rows and connecting respectively with different ones of the pads; elements provided with such a print are of especial advantage in the provision of layouts incorporating integrated circuits in dual in-line or flat packs.

A A multiplicity of identical elements each as referred to in the preceding paragraphs, may be provided to aid manufacture of circuit layouts, the elements being arranged so that they can be conveniently withdrawn in turn for application in provision of the artwork required. More specifically, the elements may conveniently be provided in a reel, the elements being carried on a common backing strip in the reel from which they can be peeled individually and in turn as the strip is unwound from the reel.

A method of manufacturing an electrical-circuit layout and items for use in such method, all in accordance with the present invention, will now be described, by way of example, with reference to the accompanying drawings, in which~ Figure 1 shows a portion of a printed-circuit board produced from an electrical-circuit layout manufactured in accordance with the present invention; Figure 2 shows a portion of the electricalcircuit layout from which the printed-circuit board of Figure 1 is produced; Figures 3 to 6 show draughting aids used in the manufacture of the electrical-circuit layout of Figure 2; and Figures 7 to 1 1 illustrate other forms of draughting aid and their use.

Referring to Figure 1, the printed-circuit board 1 carries a multiplicity of integrated circuits that are contained within individual dual in-line packs 2 arranged in spaced columns and interconnected with one another by printed-circuit paths 3 on a surface 4 of the board 1. Further printed-circuit paths 5 are carried on the other-surface of the board 1 for the purpose of establishing ground and voltage-rail connections with the packs 2.

Connections to the paths 3 and 5 are made from each pack 2 via two sets of eight parallel wireleads 7 that extend laterally from opposite sides of the pack 2 with the corresponding leads 7 of the two sets aligned one with the other. The leads 7 are bent downwardly to connect with individual pads 8 that are provided in two parallel rows on the surface 4, each lead 7 extending down through the board 1 via a plated-through hole 9 centrally-located within the pad 8 on the surface 4 and a corresponding pad 10 on the other surface.The majority of pads 8 are connected to the paths 3 on the surface 4, but where connections of leads 7 to the paths 5 are to be established these are made via the individual pads 10 on the other surface. (The packs 2 would normally be mounted, according to current practice on the reverse side of the board from the main tracks provided by the paths 3, but the opposite is shown in Figure 1 for the purpose of clearer illustration).

The paths and pads on both surfaces of the board 1 are provided according to conventional practice, by etching. The metal-conductor patterns required on the two surfaces are in this respect etched from thin metal cladding that originally covers both surfaces on the board 1.

The etching process involves initial definition of the conductor-pattern required by printing photoresist material in that pattern on the cladding. The print is obtained photographically by reduction from a master circuit-layout. The master circuitlayout utilized in this way to define the conductor pattern required for the surface 4, is illustrated in Figure 2.

Referring to Figure 2, the circuit layout consists of artwork that is executed on a sheet 20 in accordance with the pattern required for the paths 3 and pads 8. The sheet 20 is transparent so that the artwork may be executed against the background of a standard grid and thereby established with a high degree of accuracy. A high degree of accuracy is required in execution of the artwork in order that the various elements, in this case the paths 3 and the pads 8, of the final metal-pattern shall each be dimensioned and located appropriately relative one to the other, within the tight tolerances necessary to ensure that the electrical connections and insulation required for the intended circuit-operation are achieved.

According to conventional practice the artwork of Figure 2 would be executed by application of opaque or translucent tape to the transparent sheet 20. An individual length of tape would be applied to the sheet to lay down the line appropriate to each path 3. The circles required for the pads 8 might similarly be laid down individually, but draughting aids are available that enable representations of the two rows of pads appropriate to an in-line pack to be laid down as one. The aids available in the latter respect carry print of two rows of circles or other shapes on a transparent strip that may be used as an overlay to the transparent sheet. The spacings between the rows and between the shapes in the rows correspond accurately to the standard spacings required for the mounting of dual in-line packs having regard to the particular degree of enlargement used for the layout.Thus by the application of an aid of this nature as an overlay to the transparent sheet wherever a pack is to be provided, it is possible to establish accurately in the one operation the disposition of pads required for that pack.

Although aids already available can be utilized as indicated above, to reduce the labour involved in preparation of circuit-layouts, the major task of taping-in the lines required for the printed-circuit paths, remains. Such task is particularly tedious and time consuming where large areas of closelyspaced and parallel paths are involved, and is especially so where it is necessary that these paths incorporate angled offsets.

With the specific printed-circuit board illustrated in Figure 1, fifteen parallel paths 3 extend from one pack 2 to the other in each column, and because of the alignment between the pads 8 such paths 3 necessarily incorporate repeated angled offsets, first to one side and then to the other, adjacent to each pack location.

Angled offsets, which are also involved at other locations as illustrated in Figure 1, require repeated accurate and clean cutting of the tape, and accurate positioning of individual small lengths of tape to join, at the appropriate angle, with the main lengths with precision in the extent of overlap. Taping-in of the multiplicity of lines required to define the paths 3 would accordingly take considerable time and involve significant tedious and repetitious labour.

The present invention enables a considerable amount of the tedious and repetitious taping that would normally be necessary to manufacture an electrical-circuit layout such as that of Figure 2, to be avoided. In particular there is provided in accordance with the present invention, draughting aids as illustrated in Figure 3. Such aids each consist of an element 30 of photographically-transparent acetate film (having a thickness, for example, of 0.025 mm) that carries printed circles 31 and parallel lines 32 appropriate to the required (enlarged) representation in the artwork of the pads 8 and their adjacent portions-including angled offsets-of the connecting paths 3.The elements 30, which are carried together on a reel of paper strip 33 such that they can be readily withdrawn in turn for use, each have an under-coating of pressure-sensitive adhesive to retain them on the strip 33. The strip 33 has a surface coating of an easy-release silicone so as to enable the element 30 to be easily peeled off when required for application in the circuit-layout. The pressuresensitive adhesive used for the under-coating of the elements 30 is of a nature to facilitate sliding adjustment of the location of the element 30 on the sheet 20 during application; the adhesive is effective to provide a tight bond under firm pressure, when the correct location has been achieved.

Other aids provided in accordance with the present invention to facilitate manufacture of the layout of Figure 2 are illustrated in Figures 4 to 6.

These other aids consist respectively of elements 40, 50 and 60 provided in exactly the same way as the elements 30, but in these cases the printing is of parallel lines alone. The lines 41 and 51 of the elements 40 and 50 are all straight and such aids can be utilized to avoid the need for extended lengths of parallel taping; the line spacings are different in the two cases, and other aids with other spacings and different thicknesses of line may be provided. In the case of the elements 60 the parallel lines are provided with successive angular offsets of 45 degrees; these aids may be cut for example as indicated by the broken lines 61, to provide by the portion between the lines 61, an overlay appropriate to the provision of single angular offsets in the otherwise-straight paths.

In all cases, the elements (30, 40, 50, 60) may be adapted to meet a particular draughting requirement by cutting to remove part of the printing on them.

The manner in which the various aids illustrated in Figures 3 to 6 are utilized to provide the layout illustrated in Figure 2, is indicated for one column of packs 2 by use of broken outline referenced in accordance with the elements from which each part of the artwork is built up.

Elements 30 are applied as overlay wherever a pack 2 is to be located, representation of the pads 8 and the adjacent parts of the paths 3 required for each pack 2 being laid down simply by peeling the next element 30 from the backing strip 33 and applying that element to the sheet 20 in the appropriate location. In the case illustrated by Figure 2 only fifteen paths 3 are required, so the sixteenth line 32 is cut from the element 30 (as indicated in one instance in Figure 3 by the broken line 34). Thus the repetitive and tedious taping-in of fifteen lines having double angledoffsets to represent the paths 3, and the separate application of circles representing the pads 8, is avoided at each pack-location, being reduced simply to the application to the sheet 20 of an element 30 peeled from the backing strip after the unwanted sixteenth line 34 has been removed.The paths 3 are then completed by application of lengths of elements 50 in the gaps between successive elements 30 of each column, the elements 50 being applied in each case with fifteen of the lines 51 aligned with and interconnecting respectively the fifteen lines 32 o the elements 30; the unwanted sixteenth line 51 is removed by cutting. Other parts of the layout are executed as illustrated in Figure 2 by application to the sheet 20 of the elements 40 and 60 in cut lengths.

As indicated above, aids other than those illustrated may be provided to meet the varying needs that are encountered. For example, aids corresponding to those illustrated in Figure 6 may be provided printed with longer straight sections, and perhaps too, such as more readily to enable angled offsets both to the left and to the right to be executed. Also Figure 7 shows the form of an element 70 that may be utilized as an alternative to that of Figure 3.

Referring to Figure 7, the element 70, like the element 30, incorporates two parallel rows of eight pad-representing circles 71 (other shapes could of course be utilized). Fourteen parallel lines 72 cross the two rows of circles 71, leaving two circles 71 (corresponding to lead Nos 8 and 16 of the standard dual in-line pack nomenclature) without connection lines. All the lines 72 extend in both directions from their respective circles 71; this is in contrast to the case of the lines 32 for which it is only each alternate line 32 that extends in both directions from the respective circle 31.

A preferred second alternative form of element to that of Figure 3 is shown in Figure 8.

Referring to Figure 8, the element 80 in this alternative incorporates two parallel rows of eight pad-representing circles 81 (other shapes could be utilized), together with sixteen lines 82. Only one circle 81 is in this case left unconnected, but there is also one line 82 that is free of connection to a pad-representation.

A further aid that may be utilized is illustrated in Figure 9 which shows the form of an element 90 that consists of a series of cranked lines of similar configuration to alternate lines of the elements 30 and 70 described above.

Referring to Figure 9, the element 90 incorporates simply eight parallel lines 91 that across the width of the element 90 each have angled offsets of forty-five degrees, first one way and then the other, to present an overall cranked configuration. Such element is applicable in the provision of layout-connections to pads where offsets are required, and may be utilized in whole or in part to this end. In the latter respect and as illustrated in Figure 10, an element 90 may be applied (as indicated within broken line 90), directly in the layout, whereas lines 91 and parts of them, cut from the same form of element, may be applied (as indicated within broken lines 91) to achieve individual connections.

In the provision of the layouts required for the opposite surfaces of the board (or each surface where multilayer boards are involved), it is necessary to maintain very accurate registration between the patterns on the respective surfaces.

More especially in the example of the board 1 of Figure 1, it is necessary to ensure that the pads 8 and 10 on the two surfaces of the board 1 are in precise registration with one another so that the holes 9 are centrally located with respect to them.

This accuracy of registration required in the finished board necessitates a very high degree of accuracy of registration as between the layouts from which the circuit-patterns for the two (or more) surfaces are to be produced. The present invention provides a method by which this can be readily achieved, involving the provision initially of a layout incorporating representations of pads and other circuit elements for which registration is required as between opposite board-surfaces, photographing the layout or otherwise to provide a reversed-image print thereof, and then applying to this print and the layout (or an unreversed image print thereof) elements to represent circuitry required for the opposite board-surfaces respectively.

When using the latter technique in relation to the example of board 1, a layout comprising simply representations of pads where pads 8 and 10 (and any others) are required) is first produced.

In particular representation of the pads required for the packs 2 are laid down on a sheet of transparent-plastic film by application to the sheet of elements such as illustrated in Figure 11, as overlays to the sheet. The draughting aid of Figure 11 carries print of two rows of circles 111 on a transparent strip 11 2. The spacings between the rows and between the circles 111 in the rows correspond accurately to the spacings required for the packs 2. Once the pad-layout has been completed this is photographed and a reversed print is then produced on a transparent sheet, so that this print and the pad-master itself, can be used to provide the master layouts for the two surfaces.

Draughting-aid elements such as those illustrated in Figures 3 to 9 are applied as overlays to the pad-master and the print in accordance with the circuit patterns required on the respective surfaces. The patterns are applied with appropriate alignment and registration with the pad representations already established on the pad-master and print, so as thereby to ensure the appropriate through-the-board relationship between them. In particular, elements such as those of Figures 3, 7 and 8 that already incorporate pad representations, are applied where appropriate to the pad-master (or print) to locate such pad-representations (31,71,81) directly on the corresponding pad representations of the pad-master.This overlaying of pad representation on pad-representation enables extremely high accuracy of alignment and location of the element on the pad master to be achieved very easily and quickly. More especially, the element can be placed on the pad-master over the relevant row of pad-representations and then quickly adjusted in position before pressure is applied to secure it finally in place on the master, by reference to the required and easilydiscernable registration between the central 'white-eyes' of the pad-representing areas of the element and master. The pad representations on the applied element need not be of the same shape as those on the master for achievement of the desired accuracy in this.

Where draughting-aid elements such as those of Figures 4 to 6 and 9 not involving pad representations, are utilized, these can readily be aligned with pad-representation of the padmaster, against the background grid used during taping. Elements having the same bridge-pattern of lines as that of the elements of Figure 9 but with more (and slightly larger) lines at the smaller line pitch required for connection to in-line packs, may be found to be particularly useful in this respect. Such may be utilized instead of elements of the form illustrated in Figure 8, to establish the pack-connection pattern, where the pad representations appropriate to pack location have already been established in the layout.

Claims (14)

Claims

1. A method of manufacturing an electricalcircuit layout that includes artwork on a sheet to represent a multiplicity of parallel circuitconnections, wherein an element carrying print of a multiplicity of parallel lines is applied to the sheet to be retained thereon such that said print provides representation of said circuit connections along at least part of their length by the one application of said element to the sheet.

2. A method according to Claim 1 wherein each of the said lines includes a cranked portion by which part of the line is displaced laterally with respect to the remainder of that line.

3. A method according to Claim 1 or Claim 2 including the steps of establishing representations of spaced terminal pads on said sheet and applying said element to the sheet whereby at least some of said lines are aligned in register with respective ones of the pad-representations to represent circuit connection to those represented pads, and wherein at least some of said lines extend through the spaces between respective pairs of said pad-representations.

4. A method of manufacturing an electrical circuit layout in which artwork representation of a multiplicity of parallel electrical-circuit connections is produced on a sheet for subsequent conversion to printed-circuit form, comprising a first step of providing a plurality of film elements each carrying print of a multiplicity of parallel lines. and a second step of applying the said elements in turn to the said sheet, the application of each said element to the sheet including adhering that element to said sheet as an overlay thereto, the print lines of that element providing representation on the sheet of said circuit connections along part of their length in the one application of that element to the sheet, and the different elements being applied to the sheet in turn to provide representation thereon of successive parts of said length.

5. A method according to Claim 4 wherein at least some of the elements include a multiplicity of parallel lines each of which includes a cranked portion by which part of the line is displaced laterally with respect to the remainder of that line.

6. An item for use in the manufacture of an electrical-circuit layout, consisting of an element which carries print of a multiplicity of parallel lines and which is adapted to be applied to a sheet to establish thereon in the one application representation by said print of a multiplicity of parallel circuit connections along at least part of the length of such connections in the said layout.

7. An item according to Claim 6 wherein said lines are parallel to one another throughout their entire length and each includes a cranked portion by which a part of the line is displaced laterally with respect to the remainder of that line.

8. An item according to Claim 6 or Claim 7 wherein said element carries printed areas representing terminal pads and spaced from one another in a row extending transversely to said lines, alternate ones of said lines extending through the spaces between respective pairs of said areas, and at least some of the others of said lines extending in alignment with, so as effectively to intersect, respective ones of the said areas.

9. An item according to Claim 8 wherein said element carries two parallel rows of said padrepresenting areas, the two rows being spaced apart from one another and extending transversely to said lines with different ones of the said areas of one row contacting alternate ones of said liens within the displaced parts of those lines, and with different ones of said areas of the other row contacting others of said lines beyond the said displaced parts to those said other lines.

10. An item for overlaying-application to a sheet in the manufacture of an electrical-circuit layout that is adapted for subsequent photographic conversion to printed-circuit form, said item consisting of an element of photographically-transparent film having upperand under-surfaces, a coating of pressuresensitive adhesive on the under-surface for retaining the element to said sheet, and photographically-distinct print on one of said surfaces to represent terminal-pads and connecting paths thereto for an integrated-circuit device to be incorporated with said printed circuit, said print comprising two interlaced sets of parallel printed lines extending across said one surface to represent said connecting paths, each of said sets comprising a multiplicity of lines that are parallel to one another throughout their entire length and each of said lines including a cranked portion by which a part of the line is displaced laterally with respect to the remainder of that line, and two parallel rows of mutually-spaced printed areas representing respective ones of said terminal pads, each said row extending transversely to the two sets of lines with different ones of the said areas of one row contacting different ones of the said first set of lines within the said displaced parts of those lines, and with different ones of said areas of the other row contacting different ones of the said second set of lines beyond the said displaced parts thereof.

11. An item for use in the manufacture of an electrical-circuit layout, substantially as hereinbefore described with reference to any of Figures 3 to 9 of the accompanying drawings.

12. An aid for use in the manufacture of an electrical-circuit layout in which representations of a multiplicity of parallel electrical connections are applied to a sheet, said aid comprising a multiplicity of identical items according to any one of Claims 6 to 11 retained together for selective withdrawal one at a time in turn from said aid for application to said sheet.

13. A method of manufacturing an electricalcircuit layout according to any one of Claims 1 to 5 using items in accordance with any one of Claims 6 to 11.

14. A method of manufacturing an electricalcircuit layout, substantially as hereinbefore described with reference to any of Figures 2 to 11 of the accompanying drawings.