GB2157006A - Testing printed circuit board assemblies - Google Patents

Abstract

A mother/daughter printed circuit board assembly including a power interlock. A conductive loop is formed by interconnecting conductive paths (6) formed between edge connections (5a, 5b) on the daughter boards (2). The conductive paths (6) are interconnected through edge connectors (3) by conductive tracks (7) on the motherboard (1). The electrical continuity of the loop is determined by a short circuit sensor (13) which operates a switching control (14) to switch on the power to the assembly. <IMAGE>

Description

SPECIFICATION Electronic circuit assemblies Background of the invention The present invention relates to electronic circuit assemblies in which a plurality of electronic subassemblies are connected together by connection means.

For example, the subassemblies may comprise printed circuit boards and the connection means may comprise a larger circuit board. In this case the larger circuit board is known as a mother board and the other circuit boards are known as daughter boards. The electrical interconnections between the daughter boards and the mother board are established via edge connections on the daughter boards which co-operate with edge connectors mounted on the mother board. It is common for large numbers of daughter boards, for example, more than one hundred, to be mounted on a single mother board. Difficulties have been experienced with these assemblies in ensuring that every one of the daughter boards is correctly inserted in its respective edge connector.If a daughter board is not correctly inserted it will be appreciated that all of the connections may not be established and in this case, when electrical power is applied to the assembly, damage to components on the daughter board can occur.

It has previously been proposed in US Patent 3 710 197 to arrange the edge connections on a circuit board in such a way that those edge connections carrying power for the components on the board are established only after all of the other connections. This arrangement, however, only ensures that no power is prematurely applied to an individual circuit board until that board is fully inserted.

One object of the present invention is to ensure that no power can be applied to the whole circuit assembly until all of the circuit boards are fully inserted.

Summary of the invention According to the present invention an electronic circuit assembly includes: a plurality of detachable electronic subassemblies; means for establishing at least one conductive loop extending through all of the subassemblies when the subassemblies are correctly attached to the electronic circuit assembly; and control means operable to check the electrical continuity of the conductive loop and, in response to such continuity being determined, to effect the application of electrical power to the electronic circuit assembly.

Brief description of the drawing A mother/daughter printer circuit board assembly will now be described, by way of example, with reference to the accompanying drawing, in which; Figure 1 is a schematic illustration of a mother daughter circuit board arrangement including means for controlling the application of power to the assembly, and Figure 2 shows one of the daughter boards.

Description of the preferred embodiment Referring to the drawing, a circuit board assembly comprises a mother board 1 which carries a number of daughter boards 2. The daughter boards 2 and the mother board 1 each carry circuitry, (shown in simplified form on the daughter board only). Twenty daughter boards have been shown but it will be understood that in practice many more daughter boards, for example, a number in excess of one hundred could be carried on a single mother board. Edge connectors 3 are secured to the motherboard 1 and contain connector elements 4, (only one of which is shown for clarity), which co-operate with corresponding conductive connection portions 5 on the daughter boards 2 to provide interconnections between the circuitry carried on the daughter boards and the circuitry of the mother board.The edge connectors 3 also provide the means by which the daughter boards 2 are supported on the motherboard 1.

Two of the connection portions 5, designated 5a and 5b, on each of the daughter boards 2 are connected by a conductive track 6 (Figure 2). Further conductive tracks 7 on the motherboard 1 interconnect those connector elements 4 which engage the connection portions 5a and 5b of the daughter boards as shown. A conductive track 8 connects one of the connector elements 4 associated with a connection portion 5a on the daughter board to a conductive track 9 connects one of the connector elements associated with a connection portion 5b to a conductive connection portion 11 on the motherboard. The connection portions 10 and 11 are arranged to co-operated with another edge connector 12 which may, for example, be carried on a support frame.

A short circuit sensor 13 is connected between the connection portions 10 and 11 of the motherboard by the edge connector 12 and a switching control 14 is arranged to switch on power to the circuit asssembly in response to a signal from the short circuit sensor 13.

It will be realised that the conductive tracks 7 on the motherboard, by interconnecting the connector elements 4 as shown, are effective to connect all of the conductive tracks 6 extending between the conductive portions 5a and 5b in series when all of the daughter boards are inserted. A conductive path extending through all of the daughterboards is thereby formed and this conductive path is extended via conductive tracks 8 and 9 to form a conductive loop extending between the connection portions 10 and 11 of the motherboard.

Thus, when all of the daughter boards are correctly inserted in their respective sockets 3 on the motherboard and the motherboard is inserted in the socket 12 a complete conductive loop will be formed and connected to the short circuit sensor.

Only when the daughter boards are correctly inserted in each of the sockets 3 can this condition be attained. When this condition is attained the short circuit sensor reacts to produce a signal which causes the switching control 14 to switch on the power to the circuit assembly. If one or more of the daughter boards is not correctly inserted the conductive portions 5a and 5b will not make contact with their corresponding conector elements 4 and thus a complete conductive loop will not be formed. In this case the short circuit sensor 13 will not react and the power will not be switched on to the circuit assembly.

It will be seen that the described arrangement provides a convenient means to ensure that electrical power cannot be applied to the circuit assembly unless all of the circuit boards are correctly inserted.

Different ones of the conductive connection portions 5 may be interconnected for different types of daughter boards. The connector elements 4 on the motherboard are arranged to correspond with the conductive portions 5 of a particular type of daughter board. Thus, electrical power cannot be applied to the assembly if a daughter board of the wrong type is inserted.

It will also be realised that, although a particular mother/daughter board arrangement has been described, the invention is equally applicable to other arrangements in which the circuit boards are differently disposed in relation to one another. Furthermore, in the described embodiment it will be noted that the structure comprises two levels of circuit board, i.e. daughter boards and mother board. In another form of the invention additional levels may be provided, for example, a number of motherboards may be carried on a further larger circuit board. In this case, also, will be realised that a complete conductive loop may be formed extending through all of the circuit boards. However, if desired, a separate conductive loop may be employed for the boards of each level or, indeed, for other groups of the boards.

Claims (5)

1. An electronic circuit assembly including: a plurality of detachable electronic subassemblies; means for establishing at least one conductive loop extending through all of the subassemblies when the subassemblies are correctly attached to the electronic circuit assembly; and control means operable to check the electrical continuity of the conductive loop and, in response to such continuity being determined, to effect the application of electrical power to the electronic circuit assembly.

2. An assembly as claimed in Claim 1, in which said electronic subassemblies each include a series of conductive connection portions and a first conductive path interconnecting a pair of said conductive connection portions; and including connection means carrying a plurality of connections arranged to connect with the electronic subassemblies, the connectors having connector elements for engagement with corresponding connection portions on the subassemblies and a plurality of second conductive paths interconnecting connector elements of different connectors in such a way that said first and second conductive paths are connected in series to form said conductive loop.

3. An assembly as claimed in Claim 2, in which different ones of the conductive connection portions are interconnected on different types of electronic subassembly so that, when the connector elements are arranged to correspond with particular types of electronic subassembly, the electrical power cannot be applied to the circuit assembly if an electronic subassembly of the wrong type is connected.

4. An assembly as claimed in Claim 2 or 3, in which said electronic subassemblies are printed circuit boards and said conductive connection portions are arranged along at least one edge of the circuit board, and in which said connection means is a further printed circuit board and said connectors are printed circuit board edge connectors.

5. An electronic circuit assembly constructed as hereinbefore described with reference to the accompanying drawing.