GB2224164A

GB2224164A - An Improved circuit board

Info

Publication number: GB2224164A
Application number: GB8922696A
Authority: GB
Inventors: Howard Lawrence
Original assignee: BICC PLC
Current assignee: Balfour Beatty PLC
Priority date: 1988-10-11
Filing date: 1989-10-09
Publication date: 1990-04-25
Anticipated expiration: 2009-10-09
Also published as: GB2224164B; GB8823770D0; GB8922696D0

Abstract

A printed circuit board has a multiplicity of holes comprising five groups (4, 5, 6, 7 and 8) each arranged in an identical sub-pattern of columns and rows. On one major surface of the board, metal pads (12) overlying or bounding plated-through holes of each group are electrically connected to arrays of "footprints" (20-23) to which can be soldered the leads of any one of a limited range of small outline surface mounted components. On each major surface of the board, any one of a limited range of dual-in-line packages can be mounted on the board by inserting the pins of the package into plated-through holes of one of the groups (4, 5, 6, 7 and 8) of holes. <IMAGE>

Description

AN IMPROVED CIRCUIT BOARD This invention relates to circuit boards of the kind comprising a substantially rigid board of which at least the major surfaces are of electrically insulating material, which carries on one or each of its major surfaces a pattern of strips and/or pads of metal or metal alloy of high electrical conductivity, usually but not necessarily copper, and which has, extending through the board and underlying the electrically conductive metal strips and/or pads, a multiplicity of mutually spaced holes. Circuit boards of this kind will hereinafter, for convenience, be referred to as "circuit boards of the kind described".

The invention is particularly concerned with effecting electrical connection between electrically conductive metal strips and/or pads of a circuit board of the kind described and the leads of a surface mounted component of the kind generally known, and hereinafter referred to, as a small outline surface mounted component or an S.O. surface mounted component, and/or the pins of a dual-in-line package, which leads and pins are mutually spaced around at least a part of the periphery of the component or package, as the case may be.

The holes of circuit boards of the kind described are either arranged in a pattern of rows and columns with the centres of adjacent holes being spaced by n or in an array of rows and columns with the: centres-at adjacent holes spaced by -multiples:' at n# .in circuit boards of the kind described currently in general use n is 2.54mm.

The leads of S.O. surface mounted components currently in use are mutually spaced around at least a part of the periphery of the component, usually but not necessarily at 2 intervals, in order that the component is compact and therefore provides for a high packing density on a circuit board. Since the spacing of the leads of S.O. surface mounted components is not compatible with the spacing of the holes in a circuit board of the kind described, it is the current practice to effect electrical connection between the leads of a S.O. surface mounted component and appropriate electrically conductive metal strips and/or pads of a circuit board of the kind described by means of an adaptor having pins which are appropriately spaced for electrical connection in holes in the circuit board and having an array of contacts of metal or metal alloy of high electrical conductivity which are electrically connected to said pins by electrically conductive tracks on the surface of the adaptor and which are so mutually spaced apart that the leads of an S.O. surface mounted component can be soldered or otherwise electrically connected thereto. Such contacts are generally known, and for convenience hereinafter will be referred to, as "footprints".The number of S.O. surface mounted components having arrays of leads differing from one another is large and, hence, the number of adaptors that a manufacturer must provide, and the number of adaptors that a user must hold, with arrays of footprints differing from one another to accommodate the different arrays of leads of such S.O. surface mounted components is also large.

The pins of dual-in-line packages currently in general use are mutually spaced along at least each of two opposite substantially parallel sides of the package, usually but not necessarily at intervals of n, but the number of pins in the lines of the pins of packages and/or the spacing between the two lines of pins of packages can differ from one another depending upon the type of the package. For example, in one range of packages the number of pins in the packages can be any even number in the range 8 to 44 and the spacing between the two lines of pins of the packages can be 3n to 6n.

It is an object of the present invention to provide an improved circuit board of the kind described having at least one group of the multiplicity of holes arranged in a sub-pattern and, on at least one major surface of electrically insulatingmaterial overlyingthe group of holes, at least one array of "footprints" of metal or metal alloy of high electrical conductivity, which group of holes and array of "footprints" are suitable for use in directly electrically connecting any one of a limited range of dual-in-line packages and/or any one of a limited range of S.O. surface mounted components to the circuit board.

According to the invention, in the improved circuit board at least one group of the multiplicity of holes extending through the rigid board are arranged in a sub-pattern of columns and rows and underlie or are bounded by pads of metal or metal alloy of high electrical conductivity on each major surface of the board, the columns (or rows) of the group of holes being arranged in two sub-groups of three columns (or rows) on opposite sides of a central column (or row), the pitch between neighbouring holes in the columns (or rows) being n, the pitch between neighbouring holes of adjacent columns (or rows) of each sub-group being n and the pitch between neighbouring holes of the central column (or row) and of the nearer column (or row) of each sub-group being 3n;; on the first major surface of the rigid board, in one of the sub-groups of columns (or rows) of holes each pad overlying or bounding a hole in the middle column (or row) of said sub-group is electrically interconnected to the pad overlying or bounding the hole which lies in the same row (or column) in the central column (or row) of the group of holes by a strip of metal or metal alloy of high electrical conductivity extending between said row (or column) and an adjacent row (or column) of said sub-group, in the other sub-group of columns (or rows) of holes each pad overlying or bounding a hole in the middle column (or row) of said other sub-group is electrically connected to a strip of metal or metal alloy of high electrical conductivity which extends between the row (or column) in which said hole lies and an adjacent row (or column) of said other sub-group into the gap between the central column (or row) of the group of holes and the nearer column (or row) of said other sub-group, and in each sub-group of columns (or rows) of holes each pad overlying or bounding a hole in the column (or row) of the sub-group nearer the central column (or row) of the group of holes is electrically connected to a strip of metal or metal alloy of high electrical conductivity which extends between but is spaced from the pad overlying or bounding the hole which lies in the same row (or column) in the middle column (or row) of the sub-group and the pad overlying or bounding the hole which lies in the same row (or column) in the central column (or row) of the group of holes, the metal strips on said first major sUr#ace: of the rigid board-over at least a part or parts of their#lengths :con'stituting "footprints" to which the leads of an S.O. surface mounted component can be soldered or otherwise electrically connected; and on the second major surface of the rigid board in each sub-group of columns: (or rows) of holes, each pad overlying or bounding a hole in one outer column (or row) of said sub-group is electrically interconnected to the pad overlying or bounding the hole which lies in the same row (or column) in the other outer column (or row) of said sub-group by a track of metal or metal alloy of high electrical conductivity extending between said row (or column) and an adjacent row (or column) of said sub-group.

The arrangement is such that any S.O. surface mounted component selected from the limited range of S.O. surface mounted components can be mounted on the circuit board by soldering or otherwise electrically connecting its leads to "footprints" on the first major surface of the rigid board and any dual-in-line package selected from the limited range of dual-in-line packages can be mounted on the circuit board on either of its major surfaces by inserting the pins of the package into holes of said group of holes in the rigid board.

Preferably, the internal boundary surface of each hole is plated with metal or metal alloy of high electrical conductivity and is electrically connected to the pad on each major surface of the board overlying the hole, each hole effectively being what is known in the art as a "plated through hole".

To enable an S.O. surface mounted component to be readily soldered to "footprints" on the first major surface of the rigid board in such a way as to reduce the risk of misalignment of the leads of the component with the "footprints" to which they are to be soldered and/or of "solder bridging" between adjacent "footprints" and pads, preferably a masking layer overlies the first major surface and has appropriately shaped holes through which are exposed the "footprints" and pads to which the leads of S.O. surface mounted components are to be soldered. The masking layer forms a raised surface profile and the shaped holes serve to guide the leads of an S.O. surface mounted component into alignment with the "footprints" or pads to which they are to be soldered.A masking layer may also overlie the second major surface of the rigid board and have appropriately shaped holes through which are exposed the pads on said second major surface.

On said first major surface of the rigid board, in each sub-group of columns (or rows) of holes the metal strip electrically connected to each pad overlying or bounding a hole in the middle column (or row) of said sub-group may also extend into.' the gap between the middle column (or row) af saidzsub::-group#and' the the column (or row) of said sub-group remote from the central column (or row) of the group of holes and each pad overlying or bounding a hole in the middle column (or row) of said sub-group may have electrically connected thereto a strip of metal or metal alloy of high electrical conductivity which extends towards but is spaced from the hole which lies in the same row (or column) in the column (or row) of said sub-group which is remote from the central column (or row) of the group of rows.

One or each sub-group of holes of the group of holes may have at least one supplementary column (or row) of holes which is remote from the central column (or row) of the group of holes, the or each supplementary column (or row) of holes in a sub-group being suitable for ground and voltage connections.

On each major surface of the rigid board, the or each group of holes arranged in the aforesaid sub-pattern of columns and rows may be surrounded by a peripherally continuous bus of metal or metal alloy of high electrical conductivity, the peripherally continuous bus on each major surface of the rigid board being suitable for power distribution or for use as a ground plane. Where each major surface of the board carries two or more groups of holes each arranged in the aforesaid sub-pattern of columns and rows, preferably the columns (or rows) of each group extend substantially parallel to the columns (or rows) of holes of the other group or groups and the bus surrounding each group is electrically interconnected to the bus surrounding the or each other group.

On the second major surface of the rigid board the or each group of holes may have extending between the central column (or row) of the group and each sub-group of holes a bus of metal or metal alloy of high electrical conductivity which is electrically interconnected with the bus surrounding the group.

Additionally, on said second major surface of the rigid board, a pattern of tracks of metal or metal alloy of high electrical conductivity may extend between adjacent holes of the columns and rows of the or each group and be directly or indirectly connected to the bus surrounding the group.

On one or each major surface of the rigid board, the pads, tracks and/or strips of metal or metal alloy of high electrical conductivity may be applied directly to the electrically insulating major surface of the rigid board and the holes of the or each group of holes may extend through the overlying metal pads, or the metal pads, tracks and/or strips may be carried on a flexible sheet of electrically insulating material which is separately formed; with; respect:' -to ,and##:is is secured to the major surface of the rigid board. In the. latter.

case, preferably the or each flexible sheet is made ofan electrically insulating plastics material having such inherent elasticity that, when a pad on the flexible sheet is pierced by a pin, the inherent elasticity ot the plastics material tends to urge the metal or metal alloy of the pierced pad into electrical contact with the pin.

The invention is further illustrated by a description, by way of example, of a preferred circuit board having groups of holes and, on one major surface of the rigid board of the circuit boardr arrays of "footprints" of high electrical conductivity for use in directly electrically connecting any one of a limited range of dual-in-line packages and/or surface mounted components to the circuit board, with reference to the accompanying drawings, in which: Figure 1 is a plan view of the first major surface of the rigid board of the preferred circuit board with an overlying masking layer omitted; Figure 2 is a fragmental plan view of the first major surface of the rigid board drawn on a greatly enlarged scale; Figure 3 is a plan view of the second major surface of the rigid board of the preferred circuit board with on overlying masking layer omitted; and Figure 4 is a fragmental plan view of the second major surface of the rigid board drawn on a greatly enlarged scale.

Referring to the drawings, the preferred circuit board comprises a rigid board 1 of electrically insulating material having, extending through the board, a multiplicity of mutually spaced holes arranged in a pattern of rows and columns. The multiplicity of holes comprise five groups 4, 5, 6, 7 and 8 of holes each arranged in an identical sub-pattern of columns and rows and the columns of each group of holes are arranged in two sub-groups of three columns 9 and 11 on opposite sides of a central column 10, the pitch between neighbouring holes in the columns being 2.54mm, the pitch between neighbouring holes of adjacent columns of each sub-group 9 and 11 being 2.54mm and the pitch between neighbouring holes of the central column 10 and of the nearer column of each sub-group 9 and 11 being 3.81mm.

Each sub-group 9 of holes of each group 4, 5, 6, 7, and 8 of holes has two supplementary columns 14 and 15 of holes which are remote from the central column 10 of the group of holes. The sub-group 11 of holes of the group 6 of holes has two supplementary columns 16 and 17 of holes which are remote from the central column 10 of the group of holes.

Extending alongside the supplementary, co#umfls 16- and 17 of holes and#indapen#dent#of the groups 4, 5, -6, 7 and' 8 of holes are six columns:18 of holes,. the pitch between neighbouring holes in each of;these columns being 2.54mm and the pitch between neighbouring holes-of adjacent columns of these columns also being 2.54mm.

On the major surface 2 and on the major surface 3 of the rigid board 1 respectively, each of the multiplicity of holes is bounded by a pad 12 and 13 of copper and the internal boundary surface of each hole is plated with copper integral with the pads bounding the hole on the two major surfaces of the board so that the hole is effectively what is known in the art as a "plated through hole".

As will be seen more clearly on referring to Figure 2, on the major surface 2 of the rigid board 1, in the sub-group 11 of holes of each group 4, 5, 6, 7 and 8, each pad 12 bounding a hole in the middle column of this sub-group is electrically interconnected to the pad bounding the hole which lies in the same row in the central column 10 of the group by a strip 20 of copper which extends between this row and an adjacent row of the sub-group into the gap between the middle column of the sub-group and the column of the sub-group remote from the central column 10.In the sub-group 9 of holes of each group 4, 5, 6, 7 and 8 of holes, each pad 12 bounding a hole in the middle column of the sub-group 9 is electrically connected to a strip 21 of copper lying between the row in which the hole lies and an adjacent row of the sub-group and extending from the gap between the central column 10 of the group and the nearer column of the sub-group 9 to the gap between the middle column of the sub-group 9 and the column of the sub-group 9 remote from the central column 10.In each sub-group 9 and 11 of holes each pad 12 bounding a hole in the column of the sub-group nearer the central column 10 of each group of holes is electrically connected to a strip 22 of copper which extends between but is spaced from the pad bounding the hole which lies in the same row in the middle column of the sub-group and the pad bounding the hole which lies in the same row in the central column 10 of the group of holes. In each sub-group 9 and 11 of holes also, each pad 12 bounding a hole in the middle column of the sub-group has integral with the pad a strip 23 of copper which extends towards but is spaced from the pad which bounds the hole lying in the same row in the column of the sub-group remote from the central column 10.The metal strips 20, 21, 22 and 23 on the first major surface 2 of the rigid board l constitute "footprints" to which the leads of an S.O. surface mounted component can be soldered.

On the first major surface 2 of the rigid board 1, the groups 4, 5, 6, 7 and 8 of holes are surrounded by a peripherally continuous bus 30 of copper, which bus over a part of its peripherally continuous length overlies the holes in.-the supplementary column 15 of; the sub-group 9 of the group 4 and the hoSes in the supplementary column 17 adjacent the. sub-group 11 of the group 8. Additionally, the holes of the supplementary columns 15 of the groups 5, 6, 7 and 8 underlie supplementary buses 31 of copper which are integral with the peripherally continuous bus 30 at each of their ends.

The pads 12 bounding holes in the outermost columns of the columns 18 and lying in the same row are electrically connected by strips 36 of copper.

A masking layer (not shown) overlies the first major surface 2 of the rigid board 1 and has appropriately shaped holes through which are exposed the "footprints" and pads 12 to which the leads of S.O.

surface mounted components can be soldered. The masking layer forms a raised surface profile and the shaped holes in the masking layer serve to guide the leads of an S.O. surface mounted component into alignment with the "footprints" or pads 12 to which they are to be soldered.

As will be seen more clearly on referring to Figure 4, on the second major surface 3 of the rigid board 1, in each sub-group 9 and 11 of holes in each group 4, 5, 6, 7 and 8 of holes, each pad 13 bounding a hole in one outer column of the sub-group is electrically interconnected to the pad bounding the hole which lies in the same row in the other outer column of the sub-group by a track 25 of copper extending between the row and an adjacent row of the sub-group. The groups 4, 5, 6, 7 and 8 of holes are surrounded by a peripherally continuous bus 40 of copper which, over part of its peripherally continuous length, overlies the holes in the supplementary column 14 adjacent the sub-group 4 and the holes in the supplementary column 16 adjacent the sub-group 11 of the group 8.The holes in the supplementary columns 14 of the sub-groups 5, 6, 7 and 8 underlie supplementary buses 41 of copper which, at each of their ends, are integral with the peripherally continuous bus 40. Additionally, in each group 4, 5, 6, 7 and 8 there is interposed between the central column 10 and the adjacent sub-groups 9 and 11 supplementary buses 42 of copper which, at each of their ends, are integral with the peripherally continuous bus 40.

On the second major surface 3, in each group 4, 5, 6, 7 and 8 the supplementary column 15 of holes is separated from the adjacent column of holes of the sub-group 11 of the adjacent group, if present, by a track 26 of copper which, at each of its ends, is integral with the peripherally continuous bus 40. Lying between adjacent holes of the central column 10 of each group 4, 5, 6, 7 and 8 are tracks 27 of copper which are integral with the supplementary buses 42- and extend between adj;acent holes -of -the neighbourin'g coumns of.

holes of the-sub-groups 9 and 11. Tracks:28 of copper integral with each supplementary bus41 in each#group: extend between adjacent holes in the neighbouring column of holes of the sub-group 11 and tracks 29 of copper integral with each supplementary bus 41 extend between adjacent holes of the supplementary column 15 and between adjacent holes of the beighbouring column of holes of the sub-group 9.

The pads 13 bounding holes in the middle two columns of the columns 18 and lying in the same row are electrically interconnected together by strips 37 of copper and the pads bounding holes in the second and fifth columns of the columns 18 and lying in the same row are electrically interconnected by strips 38 of copper lying between adjacent rows of holes.

A masking layer (not shown) overlies the second major surface 3 of the rigid board 1 and has appropriately shaped holes through which the pads 13 on the second major surface are exposed.

Any S.O. surface mounted component selected from a limited range of S.O. surface mounted components can be mounted on the preferred circuit board by soldering or otherwise electrically connecting its leads to "footprints" on the first major surface 2 of the rigid board 1 and any dual-in-line package selected from a limited range of dual-in-line packages can be mounted on the preferred circuit board on either of its major surfaces 2 and 3 by inserting the pins of the package into holes of one of the groups 4, 5, 6, 7 and 8 of holes in the rigid board.

Claims

CLXIMS: .

1. A circuit board -of' tha kind deacribed,#wherein wherein at least one group of the multiplicity.of holes extending through the rigid board are arranged in a sub#'p-attern of columns and rows and underlie or are bounded by pads of metal or metal alloy of high electrical conductivity on each major surface of the board, the columns (or rows).

of the group of holes being arranged in two sub-groups of three columns (or rows) on opposite sides of a central column (or row), the pitch between neighbouring holes in the columns (or rows) being n, the pitch between neighbouring holes of adjacent columns (or rows) of each sub-group being n, and the pitch between neighbouring holes of the central column (or row) and of the nearer column (or row) of each sub-group being 3n 7;; on the first major surface of the rigid board, in one of the sub-groups of columns (or rows) of holes each pad overlying or bounding a hole in the middle column (or row) of said sub-group is electrically interconnected to the pad overlying or bounding the hole which lies in the same row (or column) in the central column (or row) of the group of holes by a strip of metal or metaJ alloy of high electrical conductivity extending between said row (or column) and an adjacent row (or column) of said sub-group, in the other sub-group of columns (or rows) of holes each pad overlying or bounding a hole in the middle column (or row) of said other sub-group electrically connected to a strip of metal or metal alloy of high electrical conductivity which extends between the row (or column) in which said hole lies and an adjacent row (or column) of said other sub-group into the gap between the central column (or row) of the group of holes and the nearer column (or row) of said other sub-group, and in each sub-group of columns (or rows) of holes each pad overlying or bounding a hole in the column (or row) of the sub-group nearer the central column (or row) of the group of holes is electrically connected to a strip of metal or metal alloy of high electrical conductivity which extends between but is spaced from the pad overlying or bounding the hole which lies in the same row (or column) in the middle column (or row) of the sub-group and the pad overlying or bounding the hole which lies in the same row (or column) in the central column (or row) of the group of holes, the metal strips on said first major surface of the rigid board over at least a part or parts of their lengths constituting "footprints" to which the leads of an S.O. surface mounted component can be soldered or otherwise electrically connected; and on the second major surface of the rigid board in each sub-group of columns (or rows) of holes, each pad overlying or bounding a hole in one outer column or row) of said sub-group-: is:, ele#ctrica1ly# #interconnected'. to the, pad- overlying or-.bounding the hole which lies in .thersamefl row (or column) in:the other outer column (or row) of said sub-group by a track of metal'o,r metal alloy of high electrical conductivity extending between said row (or column) and an adjacent row (or column) of said sub-group.

2. A circuit board as claimed in Claim 1, wherein the internal boundary surface of each hole is plated with metal or metal alloy of high electrical conductivity and is electrically connected to the pad on each major surface of the board overlying the hole, each hole thereby effectively constituting a "plated through hole".

3. A circuit board as claimed in Claim 1 or 2, wherein a masking layer overlies the first major surface and has appropriately shaped holes through which are exposed the "footprints" and pads to which the leads of S.O. surface mounted components are to be soldered.

4. A circuit board as claimed in any one of the preceding Claims, wherein a masking layer overlies the second major surface of the rigid board and has appropriately shaped holes through which are exposed the pads on said second major surface.

5. A circuit board as claimed in any one of the preceding Claims, wherein, on said first major surface of the rigid board, in each sub-group of columns (or rows) of holes the metal strip electrically connected to each pad overlying or bounding a hole in the middle column (or row) of said sub-group extends into the gap between the middle column (or row) of said sub-group and the column (or row) of said sub-group remote from the central column (or row) of the group of holes.

6. A circuit board as claimed in any one of the preceding Claims, wherein, on said first major surface of the rigid board, in each sub-group of columns (or rows) of holes each pad overlying or bounding a hole in the middle column (or row) of said sub-group has electrically connected thereto a strip of metal or metal alloy of high electrical conductivity which extends towards but is spaced from the hole which lies in the same row (or column) in the column (or row) of said sub-group which is remote from the central column (or row) of the group of holes.

7. A circuit. board as claimed in any one of the preceding Claims, wherein one or each sub-group of holes of the group of holes has at least one supplementary column (or row) of holes which is remote from the central column (or row) of the group of holes, the or each supplementary column (or row) of holes in a sub-group being suitable for ground and voltage connections.

8. A circuit board as claimed in any one of the preceding Claims, wherein, on each major surface of the rigid board, the or each group of holes arranged in the aforesaid #ub#-pattern of columns.and raws,- is:'# surrounded by a peripherally continuous bus of'. metal ar-:metal alloy of high electrical conductivity.

9. A circuit board as claimed in any one of#Claims 1 to 7 in which each major surface of the board carries two or more groups of holes each arranged in the aforesaid sub-pattern of columns and rows, wherein the columns (or rows) of each group extend substantially parallel to the columns (or rows) of holes of the other group or groups.

10. A circuit board as claimed in Claim 9, wherein, on each major surface of the rigid board, each group of holes arranged in the aforesaid sub-pattern of columns and rows is surrounded by a peripherally continuous bus of metal or metal alloy of high electrical conductivity, the bus surrounding each group being electrically interconnected to the bus surrounding the or each other group.

11. A circuit board as claimed in Claim 8 or 10, wherein, on the second major surface of the rigid board, the or each group of holes has extending between the central column (or row) of the group and each sub-group of holes a bus of metal or metal alloy of high electrical conductivity which is electrically interconnected with the bus surrounding the group.

12. A circuit board as claimed in Claim 11, wherein, on the second major surface of the rigid board, a pattern of tracks of metal or metal alloy of high electrical conductivity extends between adjacent holes of the columns and rows of the or each group and is directly or indirectly connected to the bus surrounding the group.

13. A circuit board as claimed in any one of the preceding Claims, wherein, on one or each major surface of the rigid board, the metal pads, tracks and/or strips are carried on a flexible sheet of electrically insulating material which is separately formed with respect to, and is secured to the major surface of, the rigid board.

14. A circuit board as claimed in Claim 13, wherein the or each flexible sheet is made of an electrically insulating plastics material having such inherent elasticity that, when a pad on the flexible sheet is pierced by a pin, the inherent elasticity of the plastics material tends to urge the metal or metal alloy of the pierced pad into electrical contact with the pin.

15. A circuit board of the kind described substantially as hereinbefore described with reference to and as shown in the accompanying drawings.