GB2396976A

GB2396976A - Assembly and method for interconnecting printed circuit boards using a PLCC socket and frame

Info

Publication number: GB2396976A
Application number: GB0230356A
Authority: GB
Inventors: Achim Hohmann; Karl-Ludwig Farnkopf
Original assignee: Motorola Inc
Current assignee: Motorola Solutions Inc
Priority date: 2002-12-31
Filing date: 2002-12-31
Publication date: 2004-07-07
Also published as: GB0230356D0

Abstract

An assembly for connecting printed circuit boards (12,10), comprising a PLCC (Plated Leadless Chip Carrier) socket (4) and a contact frame (2), the contact frame being dimensioned to fit at least partly inside the PLCC socket (4). The PLCC socket (4) is attached to a first printed circuit board (12), the contact frame (2) is attached to a second printed circuit board (10), and the contact frame is located inside the PLCC socket, in electrical contact with the PLCC socket and in mechanical abutment to two or more interior walls of the PLCC socket. A corresponding method is also provided. The assembly can be fabricated with surface mount technology, is compact and very strong.

Description

1 2396976 Assembly and Method for Interconnecting Printed Circuit Boards

Technical Field

The invention relates to the field of printed circuit-board interconnection.

Background

Printed circuit-boards (PCBs) are the supports most commonly used for mounting electronic components. They are widely used throughout modern manufacturing.

Printed circuit boards extend in two dimensions. They are usually flat, and may have components on both the upper and lower surfaces.

A need may arise to interconnect the surfaces of two or more printed circuit boards. This interconnection is usually done in such a way as to place two boards in parallel planes, with a relatively narrow gap between the boards. The boards may be permanently connected together, or may be detachably connected.

In a known prior art arrangement, the interconnection of printed circuit boards is achieved by means of a multicontact connector block. This connector block must be handplaced. It is located in 'throughhole' soldering pads. These are pads that penetrate through the surface of the printed circuit board.

The prior art technique, of using a multiconnector block, is a costly process.

This connection system cannot easily be automated.

There is a need for a more efficient detachable interconnection technique for printed circuit boards.

A. ee: .:A. *: . - . 2 '. . ... . Summarv of the Invention An assembly in accordance with the invention has the features of appended claim 1. A method in accordance with the invention comprises the steps of appended claim 7.

Further advantageous features and steps of preferred embodiments of the invention are provided by apparatus and methods in accordance with the appended dependent claims.

Brief description of the drawing

Figure 1 shows part of an arrangement in accordance with the invention, in plan view. 1'

Figure 2 shows a side-elevation view of an arrangement in accordance with the invention.

Detailed description of the preferred embodiment

An assembly for connecting printed circuit boards in accordance with the present invention is shown in appended figures 1 and 2.

Figure 1 is a plan view of part of an arrangement in accordance with the invention. Figure 1 shows a printed circuit board 10.

Figure 2 shows a side-elevation view of an arrangement in accordance with the invention. The upper part of figure 2 shows the printed circuit board 10, in side- view. The lower part of figure 2 shows a printed circuit board 12, in side view.

The assembly for connecting printed circuit boards in accordance with the present invention comprises a plated leadless chip carrier (PLCC) socket 4, and a contact frame 2. The contact frame 2 is dimensioned to fit at least partly inside e. : À . e: 3. -. ... . the PLCC socket 4. In use of the assembly, PLCC socket 4 is attached to the first printed circuit board 12. The contact frame 2 is attached to the second printed circuit board 10. The contact frame 2 is located inside the PLCC socket 4, in electrical contact with the PLCC socket and in mechanical abutment to two or more interior walls of the PLCC socket.

The contact frame therefore provides both electrical and mechanical connection between the two printed circuit boards 12 and 10, via the connectors in the interior surface of PLCC socket 4. Contact frame 2 has electrical contacts on its outer surface. These contacts provide electrical connection to some or all of the contacts on the interior walls of PLCC socket 4. Clearly this electrical connection can be used to facilitate electrical connection between components that are attached to the surfaces of the two printed circuit boards.

In order to provide mechanical rigidity, at least two sides of contact frame 2 must touch the interior walls of PLCC socket 4. In a preferred arrangement, contact frame 2 is square, and is sized such that all four sides touch the interior walls of PLCC socket 4. In this case, contact frame 2 fits exactly inside PLCC socket 4.

Contact frame 2 is preferably the same height as PLCC socket 4, measured in a vertical axis that is perpendicular to the planes of the printed circuit boards.

However, this is not necessarily the case. If contact frame 2 is higher than PLCC socket 4, then it can only be inserted partially into PLCC socket 4.

A further enhanced feature of the invention is that the contact frame 2 may provide space within its perimeter for other components to be attached to the second printed circuit board 10. In figure 1, some of the placed parts 8 are shown within the area of second printed circuit board 10 that is bounded by contact frame 2. Other components 8 lie outside of the area.

The contact frame 2 may be adapted to be surface soldered to the second printed circuit board 10. The PLCC socket 4 and contact frame 2 may be À . . . - . 4. . adapted to be re-flow soldered to the first and second printed circuit boards 12,10 respectively.

When PLCC socket 4 and contact frame 2 are surface mounted components, several advantages may be achieved. Firstly, an automatic insertion machine tool can be used to place the socket and frame on their respective locations.

Contact frame 2 may comprise a central flat access point 6, adapted for the nozzle of an insertion head to pick up and place the contact frame precisely.

This is quicker and cheaper than manually assembling components that need to be located precisely in through holes in the printed circuit boards. Secondly, the printed circuit boards do not need 'keep out' areas, underneath the socket and frame, where through holes need to run. Instead, the areas underneath the socket and frame can be used to run electrical connectors. During the reflow soldering itself, no 'retainer' is needed to fix the connector in place, as was the

case with prior art circuit board connectors.

The invention may extend to a stack of two or more printed circuit boards 12,10, each printed circuit board being connected to an adjacent board by an assembly as described above. The assembly described above provides a very compact way of joining two printed circuit boards. When a stack of several printed circuit boards has interconnectors as described above between each board, the compact nature of this invention is particularly appreciable.

The assembly for connecting printed circuit boards described above is mechanically very strong. Some of this strength results from the fixing of the PLCC socket 4 to first printed circuit board 12. PLCC sockets are themselves very robust. The use of PLCC sockets for mounting expensive semiconductor processors has lead to fixing techniques that are highly developed.

Importantly, the assembly of the present invention is detachable. So first circuit board 12 can be detached from second circuit board 10. This can be done by exerting force in a direction perpendicular to the planes of the boards. When the two boards detach, clearly PLCC socket 4 will remain soldered to first printed circuit board 12, and contact frame 2 will remain soldered to second printed

- -

À À À . . À.. . .:. À. . circuit board 10. The advantage of being able to detach the boards is that this makes components on the boards more accessible. The components can then be replaced or cleaned more easily, thereby extending the useful life of the printed circuit boards.

Further in accordance with the present invention, a method for connecting printed circuit boards 12,10, comprises attaching the PLCC socket 4 to the first printed circuit board 12, and attaching the contact frame 2 to the second printed circuit board 10, the contact frame being dimensioned to fit at least partly inside the PLCC socket. The method then involves inserting contact frame 2 into PLCC socket 4, thereby placing the contact frame both in electrical contact with the PLCC socket, and in mechanical abutment to two or more interior walls of the PLCC socket.

An automated pick and place insertion head may perform steps a) and b). A further enhancement to the invention would be to insert other components within the perimeter of the contact frame, in attachment to the second printed circuit board 10.

The method may comprise surface soldering contact frame 2 to the second printed circuit board 10. The PLCC socket 4 and contact frame 2 may be reflow soldered to the first and second printed circuit boards 12, 10 respectively. The step of re-flow soldering the contact frame may use PLCC 4 as a retainer.

Clearly, the method of the present invention may be extended to stacking more than two printed circuit boards. A stack of two or more printed circuit boards may be created by connecting each printed circuit board to an adjacent board by a method as described above.

Claims

À À -: À: A. I: 6 À,. À ; Claims 1. An assembly for connecting printed

circuit boards (12,10), comprising: a) a PLCC socket (4); b) a contact frame (2), the contact frame being dimensioned to fit at least partly inside the PLCC socket (4); and c) whereby, in use of the assembly, the PLCC socket (4) is attached to a first printed circuit board (12), the contact frame (2) is attached to a second printed circuit board (10), and the contact frame is located inside the PLCC socket, in electrical contact with the PLCC socket and in mechanical abutment to two or more interior walls of the PLCC socket
2. An assembly in accordance with claim 1, wherein the contact frame (2) has space within its perimeter for other components to be attached to the second printed circuit board (10).
3. An assembly in accordance with claim 1 or claim 2, wherein the contact frame (2) is adapted to be surface soldered to the second printed circuit board (1 o).
4. An assembly in accordance with any previous claim, wherein the PLCC socket (4) and contact frame (2) are adapted to be reflow soldered to the first and second printed circuit boards (12, 10) respectively.
5. An assembly in accordance with any previous claim, wherein the contact frame (2) comprises a central flat access point (6), adapted for the nozzle of an insertion head to pick up and place the contact frame precisely.
6. A stack of two or more printed circuit boards (12,10), each printed circuit board being connected to an adjacent board by an assembly in accordance with any previous claim.

- À : 7, . ;
7. A method for connecting printed circuit boards (12,10), comprising: a) attaching a PLCC socket (4) to a first printed circuit board (12); b) attaching a contact frame (2) to a second printed circuit board (10), the contact frame being dimensioned to fit at least partly inside the PLCC socket; and c) inserting the contact frame (2) into the PLCC socket (4), thereby placing the contact frame: (i) in electrical contact with the PLCC socket, and (ii) in mechanical abutment to two or more interior walls of the PLCC 1 0 socket.
8. A method in accordance with claim 7, wherein an automated pick and place insertion head performs steps a) and b).
9. A method in accordance with claim 7 or claim 8, further comprising inserting other components within the perimeter of the contact frame (2), in attachment to the second printed circuit board (10).
10. A method in accordance with any of claims 7-9, further comprising surface soldering the contact frame (2) to the second printed circuit board (10).
11. A method in accordance with any of claims 7-10, further comprising reflow soldering the PLCC socket (4) and contact frame (2) to the first and second printed circuit boards (12,10) respectively.
12. A method in accordance with claim 1 1, whereby the step of re-flow soldering the contact frame (2) uses the PLCC (4) as a retainer.
13. A method of assembling a stack of two or more printed circuit boards (12,10), by connecting each printed circuit board to an adjacent board by a method in accordance with any of claims 7-12.