GB2248345A

GB2248345A - Edge soldering of electronic components

Info

Publication number: GB2248345A
Application number: GB9021006A
Authority: GB
Inventors: Andrew Neil Stubbings
Original assignee: STC PLC
Current assignee: STC PLC
Priority date: 1990-09-27
Filing date: 1990-09-27
Publication date: 1992-04-01
Anticipated expiration: 2010-09-27
Also published as: GB9021006D0; GB2248345B

Abstract

A printed circuit board (10) has channels (17) formed across the edges of the board. The channels are electroplated with metal to be in electrical connection with tracks (11, 12) on the board. A liquid crystal display of the same size as the board is mounted on the board and has wire leads extending vertically from the display. The leads lie in the channels and are soldered to the channels. The channels may be formed by drilling holes through an oversized board, plating the inside surfaces of the holes with metal, and cutting through the board along a line which passes across the holes to trim off the edge of the board. <IMAGE>

Description

Edge soldering of electronic components This invention relates to the mounting of components such as liquid crystal displays, vacuum fluorescent displays, LED displays and any other type of substrate or component with leads which are required to be fixed so as to make an electrical connection with printed circuit board or other substrate along its edges. Other components/substrates include, integrated circuits, resistors, capacitors, connectors, wire leads, hybrids and PCB's.

In the field of compact electronic equipment it is often required to provide a liquid crystal display and associated control circuitry on a printed circuit board where the mounting constraints are such that the board and the display have to be substantially the same size. This means that the matrix address connections of the display, in the form of vertical wires on two opposed edges of the display, need to be soldered to edge connections on the associated printed circuit board.

In the past, where the display and the board are of differering sizes the connections between the display and the board have been made by so-called 'gull-wing' connection pieces soldered at one end to the board and at the other end to the display. This is expensive and time consuming and cannot be used where the board and the display are the same size.

Another approach is to use flexible connection foils with printed circuit tracks which can be bent around the edge of the board. These are expensive and unreliable. Frequently solder connections to the flexible connectors are unsatisfactory.

If the vertical connection wires of the display are simply soldered to the edges of the connection tracks on the board there is insufficient contact area between the wire and the track to provide a reliable solder connection. If the wires are bent over so that their end portions lie on the tracks a much larger contact area is provided for soldering but assembling a board and display with bent-over connecting wires requires the wires to be bent over after the display and the board have been mounted together. The natural resilience of the wires always causes the bent over portions to spring away from the board so that they do not actually lie against the tracks, i.e. there is a small angled gap between the end portion of the wire and the track which gap has to be filled with solder.It is not practical to slide the board edgewise into position behind the display after the wires have been bent.

According to the invention there is provided a printed circuit board having a plurality of edge connections comprised of plated metallic portions on the edge surfaces of the board, said plated metallic portions being in electrical contact with individual tracks of the printed circuit on the board.

In a preferred embodiment of the invention said plated metallic portions are formed as plated metallic channels across the edges of the board.

The invention also provides a method of forming edge connections to tracks on a printed circuit board, the method including the steps of fabricating a printed circuit board having larger dimensions than those required in the finished board, drilling holes through the board, said holes being disposed so as to be subsequently divided by the edges of the finished board, metallicplating said holes to form electrical connections to printed circuit tracks on the board and trimming the board through the holes to leave plated channels across the finished edges of the board.

Embodiments of the invention will now be described with reference to the accompanying drawings, in which: Fig. 1 shows a perspective view of edge connection channels on a printed circuit board; Fig. 2 shows a sectional side elevation of the board of Fig. 1; Fig. 3 shows a plan view of the board of Fig.

1; Figs 4-6 shows stages in the fabrication of the board of Fig. 1.

Referring generally to the drawings, a printed circuit board 10 is fabricated by conventional techniques e.g. selective etching of a copper clad board, to form the required printed circuit tracks 11.

Referring to Figs. 4-6 the board is initially fabricated oversize with pads or lands 12 extending over what will be the final edge of the board as indicated by the dotted line 13. Holes 14 are drilled through the board, the holes being positioned so as toextend partially over the area defined by the dotted line 13. The diameter of the holes 14 is slightly less than the width of the pads 12. The holes 14 are then metallicplated through from one surface of the board to the other surface in conventional manner. After plating further holes 15, of larger diameter than the holes 14, are then drilled through the board such that the holes 15 intersect the holes 14 within the area defined by the dotted line 13.

Then a router or other suitable tool is used to cut the board along the dotted line 13 to remove the unwanted portion 16. The result is that the remaining portions of the plated through holes form plated channels 17 across the edge of the board. These channels provide an accurate location for the wire leads 18 extending vertically from an overlying liquid crystal display (not shown) and form a substantial contact area for solder 19 when the wires are soldered in place. The fabricating of the board can be completed by lightly bevelling the top and bottom edges 20a, 20b of the board to remove excess copper and reduce the likelihood of excess solder bridging the gaps between adjacent channels.

It is also practical to apply a solder resist coating to the top and bottom surfaces of the board after it has been etched to form the tracks and pads.

This will further reduce the likelihood of solder blobs reaching across from one channel to the next and facilitates the removal of excess solder.

Claims

1. A printed circuit board having a plurality of edge connections comprised of plated metallic portions on the edge surfaces of the board, said plated metallic portions being in electrical contact with individual tracks of the printed circuit on the board.

2. A printed circuit board according to claim 1 wherein said plated metallic portions are formed as plated metallic channels across the edges of the board.

3. A printed circuit board according to claim 2 wherein said plated metallic channels are formed as plated through holes which holes are subsequently divided by removal of an edge portion of the board.

4. A printed circuit board substantially as described with reference to the accompanying drawings.

5. A method of forming edge connections to tracks on a printed circuit board, the method including the steps of fabricating a printed circuit board having larger dimensions than those required in the finished board, drilling holes through the board, said holes being disposed so as to be subsequently divided by the edges of the finished board, metallicplating said holes to form electrical connections to printed circuit tracks on the board and trimming the board through the holes to leave metallicplated channels across the finished edges of the board.

6. A method of forming edge connections to tracks on a printed circuit board substantially as described with reference to the accompanying drawings.

7. A method of mounting a liquid crystal display on a printed circuit board of substantially the same dimensions as the displays, wherein the board is fabricated with channels across edges of the board, said channels being coated with plated metal which is in electrical connection with associated printed circuit tracks on the board, and the display is mounted on the board with wire lead connections extending vertically from the display and locating in said channels, the wire leads being soldered to the metallic plating in their respective channels.

Amendments to the claims have been filed as follows

8. A method of forming edge connections to tracks on a printed circuit board, the method including the steps of fabricating a printed circuit board having larger dimensions than those required in the finished board, drilling first rows of holes through the board each row being parallel to an adjacent edge of the board, said holes being disposed so as to be subsequently divided by the edges of the finished board, metallic plating said holes to form electrical connections with printed circuit tracks on the board, drilling second rows of holes of larger diameter than the holes for the first rows so that each hole of a second row intersects a corresponding hole of a first row within the area of the finished board to leave a portion only of the metallic plated hole in electrical connection with the tracks, and trimming the board through said second rows of holes whereby said portions form metallic plated channels across the finished edges of the board.