GB2130021A

GB2130021A - Electrically connecting printed circuit boards

Info

Publication number: GB2130021A
Application number: GB08329258A
Authority: GB
Inventors: Lennart B Johnson; William B Walkup
Original assignee: Teradyne Inc
Current assignee: Teradyne Inc
Priority date: 1982-11-12
Filing date: 1983-11-02
Publication date: 1984-05-23
Also published as: FR2536216A1; GB2130021B; JPH0451955B2; FR2536216B1; DE3340975C2; JPS59101784A; SE8306228D0; SE459057B; CA1207047A; GB8329258D0; DE3340975A1; DE3340975C3; SE8306228L

Abstract

A plurality of daughter printed circuit boards (12) are detachably mounted on a backplane (14) and electrically connected to a bus bar (16, 17) on the same side of the backplane via contacts (18) on the daughter boards that mate with contact portions (20) of the bus bar. A plurality of parallel contacts (28) provide increased current carrying capacity. <IMAGE>

Description

SPECIFICATION Electrically connecting printed circuit boards The invention relates to systems for detachably mounting a plurality of daughter printed circuit boards (PCBs) on a backplane.

Backplanes are printed circuit boards or metal plates on the upper side of which "daughter" PCBs are detachably mounted perpendicularly to the backplanes for easy removal and replacement while the circuit is still being powered. One way of electrically connecting the daughter boards to other daughter boards, the backplane, and other circuitry is by providing metallised surface portions near the edges of the daughter boards and inserting them between the forked prongs of electrical connectors that are secured to the backplane. Another way of making electrical connection to the daughter boards involves using post and box connectors.The connectors secured to the backplane often have connector posts extending from the lower side of the backplanes for receiving wires connecting selected pairs of posts, and bus bars are often connected to a line of connector posts under the backplane to distribute voltage to a plurality of posts. These connections to the daughter boards are typically designed to carry small amounts of current; thus, a large number of contacts are connected in parallel when large amounts of current are needed.

It has been discovered that space can be conserved and better electrical connection between the components on the daughter boards and the bus bars can be provided, to result in less current resistance and increased reliability, by mounting the bus bar on the same side of the backplane as the daughter boards, and providing the daughter boards with contacts that directly mate with contact portions on the bus bars. In preferred embodiments, the bus bar contact portions comprise a male portion extending along the length of the bus bar and transversely to the backplane; the daughter board contacts have forked prongs for engaging the male portion, and a daughter board has more than one forked contact for mating with a single bus bar to provide increased current carrying capacity.In one embodiment the bus bar is connected to the backplane via a dielectric housing, and in another embodiment the bus bar has connector posts that extend through holes in the backplane.

The structure and operation of one presently preferred embodiment of the invention will now be described by way of example with reference to the accompanying drawings, in which: Fig. 1 is an elevation, partially broken away, of apparatus embodying a system for detachably mounting a plurality of daughter printed circuit boards on a backplane.

Fig. 2 is a perspective view, partially broken away, of the Fig. 1 apparatus, with a daughter board shown disconnected from the backplane.

Fig. 3 is a perspective view, partially broken away, showing an alternative bus bar construction for use in said apparatus.

Referring to Figs. 1 and 2, there is shown daughter board mounting system 10 including daughter boards 12 mounted on backplane 14 and electrically connected to bus bars 1 6, 1 7 via female contacts 18 engaging mating male contact portions 20 of bus bars 16, 17. Although not completely shown on Figs. 1 and 2, daughter boards 1 2 each have a plurality of female contacts 18 on them for making electrical connection with bus bars 16, 17 and other bus bars not shown. On the portions of daughter boards 12 not shown, there also are other contacts for making electrical connection between the components on different daughter board via, for example, wire wrapped connector posts.

Bus bars 1 6, 17 are made of copper and in their present embodiment have 0.140" (3.5 mm) high and 0.150" (3.8 mm) wide base portions 22 under vertically extending male portions 20, which in this embodiment are 0.025" (0.6 mm) thick. Bars 16, 1 7 are mounted on and electrically insulated from backplane 14 by dielectric housings 24.

Capacitor 30 is directly connected between bus bars 1 6, 17. Bus bar 17 is connected to lead 32 by screw 34 for screwing into threaded hole 36, and bus bar 17 has connector 38 attached to it for receiving lead 37, which is held in place by a set screw 39. The bus bar used for ground is mounted lower than the other voltage distributing bus bars to guarantee that when daughter boards 12 are connected, they make electrical contact with the ground bus bar first.

Female contacts 18 are the well known tuning fork type contacts meeting United States military specification MIL-C-28754, and each can carry 5+ amps. They are soldered to metallised portions on daughter boards 12 and are embedded in insulators 26, which are shaped to provide a snug fit within the upwardly extending portions of housings 24 when the forked prongs 28 are slid over male portions 20. Portions of contacts 18 attached to daughter boards 12 are positioned vertically in line, and are electrically connected in parallel, thus providing increased current carrying capacity without using up space along the width of boards 12.

In operation, daughter boards 12 can be easily attached and electrically connected to backplane 14 by lowering them to engage the bus bars and other connectors on the backplane. Because the ground bus bar is higher than the other bus bars, the daughter boards make contact with ground first to prevent damage to the components.

Because the bus bars are on the same side of the backplane as the daughter boards and are directly connected to the daughter boards, space is conserved and there is good electrical conduction between the components on the daughter boards and the bus bars. Placing the bus bars on the same side as the daughter boards also provides space for easily attaching capacitors between the bus bars and avoids the problem of interference of the bus bars with the wires wrapped to connector posts.

Other embodiments of the invention are within the scope of the appended claims. By way of example, as is shown in Fig. 3, one can use bus bars 40, having connector posts 42 for making electrical connection with conducting portions of backplane 44. Also in addition to copper, other rigid, electrically conducting materials such as phosphor bronze and brass can be used for the bus bars.

Claims

1. Apparatus for detachably mounting a plurality of daughter printed circuit boards on a backplane, said system comprising a backplane, at least one bus bar mounted on one side of said backplane, said bus bar being made of electrically conductive material and having accessible contact portions, a plurality of daughter printed circuit boards mounted on said backplane on said one side transversely to said backplane, said daughter boards each having at least one daughter contact shaped to mate with a said accessible contact portion.

2. Apparatus as claimed in claim 1, wherein said contact portions comprise a male portion extending transversely to the backplane along the length of said bus bar, and said daughter contacts are female contacts with forked prongs that engage opposite sides of said male portion.

3. Apparatus as claimed in claim 2, wherein there are a plurality of female contacts on a said daughter board for making connection with a common said bus bar, said female contacts for said common bus bar being attached to said daughter board along an axis transverse to both said bus bar and said backplane.

4. Apparatus as claimed in claim 2 or 3, wherein said bus bar is mounted on said backplane via a dielectric housing.

5. Apparatus as claimed in claim 4, wherein said bus bar has a portion below said male portion that has a larger width than said male portion.

6. Apparatus as claimed in any one of the preceding claims, wherein said bus bar has connector posts that extend through said backplane.

7. Apparatus as claimed in any one of the preceding claims further comprising a second bus bar and a capacitor connected between said bus bars.

8. Apparatus as claimed in any one of the preceding claims, wherein there are two bus bars, and one said bus bar is higher than the other bus bar.

9. Apparatus as claimed in any one of the preceding claims, wherein said bus bar is made of copper, phosphor bronze, or brass.

10. Apparatus as claimed in claim 2 or any one of claims 3 to 9 as dependent upon claim 2, wherein said male portion is 0.022" (0.56 mm) thick.

11. Apparatus as claimed in any one of the preceding claims, wherein each said daughter connector has sufficient current carrying capacity to carry at least 5 amps.

12. Apparatus for detachably mounting printed circuit boards on a backplane substantially as hereinbefore described with reference to, and as shown in, the accompanying drawings.

13. A printed circuit board and backplane assembly substantially as hereinbefore described, and as shown in, the accompanying drawings.

14. A method of mounting a printed circuit board on a backplane substantially as hereinbefore described with reference to the accompanying drawings.