GB2477993A

GB2477993A - Mechanical assembly methods for PCB boards using sets of edge solder pads

Info

Publication number: GB2477993A
Application number: GB1002986A
Authority: GB
Inventors: Geoffrey David Horn
Original assignee: Individual
Current assignee: Individual
Priority date: 2010-02-23
Filing date: 2010-02-23
Publication date: 2011-08-24
Anticipated expiration: 2030-02-23
Also published as: GB201002986D0; GB2477993B

Abstract

Printed circuit boards (PCBs) are connected together to form larger assemblies by providing sets of solder pads, at least one set arranged along at least one edge of one the boards. This may allow a large board to be assembled from smaller modular boards (see figs 5a, 5b, 6, 7) and may be of use in prototyping or education. The boards are arranged so that mating edges of two boards are parallel and solder pads on each are aligned so that either a solder joint of wire link can connect adjacent pads. The pads are designed with a plated through hole that improves the adhesion of the pad to the board and mechanical strength. The hole is set back from the edge, but not too far. Preferably the pad is at the edge of the PCB a distance B in the range 1 mm to 2.5mm, with the plated hole having a diameter greater than 0.6mm. If the hole is 0.7mm in diameter, the pad size may be a minimum of 1mm by 1.5mm.

Description

I

Design and placement of pads for mechanically assembling multiple printed circuit boards together to form one intergraded printed circuit board.

Description

This invention is a reliable and economical method of connecting modular electronic/electrical circuits or printed circuit boards together to form custom circuits or a custom printed circuit board. All circuit boards using this system will be compatible with each other irrespective of the manufacturer. The design of the interconnecting pads and placement of these pads make the method unique. The other unique feature of this system is the use of blank boards and boards for mounting to achieve the desired shape and mounting holes. This method varies from other patents in that it is economical and practical to produce.

It must be noted that this is a tested and proven method of connecting circuit boards together and not the electrical circuits, these circuits are connected by standard methods for example wiring of circuits together or through connectors etc. Connecting boards together via this method does not require the board to be on the same plane, boards can be connected at right angles to each other. This method of connecting boards together requires no knowledge of other boards to which they may be connected allowing persons without knowledge of other products to produce a product that would integrate with the system. Different boards can be connected together irrespective of size, shape, orientation or alignment as long as connection sides are parallel with each other.

Background of the invention

Producing customised electronic circuit boards is expensive and time consuming whether being used for prototyping, testing a concept or small volume productions. The use of connecting modular circuits together simplifies the task thus saving money and effort.

With the size of electronic components getting smaller and smaller, there are difficulties associated in using these components due to their size. Some of these components are so small they require special skills and equipment to use them. To add to this problem certain components are only manufactured in these small packages. This prohibits the use of these small components to the majority of people.

At present some component manufacturers still produce product in a variety of packages for the older components but the tendency is to change to the small packages as the market dictates. These larger packages can be easily used but these have the following disadvantages:- 1. Costly to manufacture.

2. Expensive to ship and store due to size and weight.

I Circuits produced with these components are large and therefore costly.

Most of the present production of electronic components is in surface mount packages which are difficult to use by students and developers. This system would alleviate this problem by supplying a method by which they can easily be used. There are a limited number of adaptor boards available but have size disadvantages and require additional circuits to be incorporated into, for example, a proto board.

Development boards supplied by component manufacturers are designed to prove the concept of a product and contain additional circuitry that is usually irrelevant to the required design, thus taking up unnecessary space and cost. These boards would be of more benefit if they could be made in functional modules or components and combined as required.

It is apparent that a number of circuit boards that can be connected together to form one circuit board would be advantageous to a number of people especially if they can produce their own designs which do not have any restraints due to existing circuits.

The practical implementations of these ideas present challenges.

These are explained below:-The requirement to connect boards of any size, shape, orientation or alignment together. This has two challenges, the first being a uniform pattern on the edge of the board that will allow alignment of pads irrespective of the arrangement or orientation of the boards. The problem arises with the pad at the corner of the board. This problem is easily illustrated with a photo shown in fig2. This is a photo of standard mats that can be placed side by side to form a larger mat. This works well until you try to connect them in a different arrangement from what was intended, the pattern does not allow for this. To correct this problem and still have the required strength in this connection the corner pads need to be offset to the centre of the board. This is of particular importance on very small boards where only the corner pads are used.

Illustration figure 5a and 5b shows that different boards of different sizes and orientation can be interconnected using the correct placement of pads.

Mechanical interlocking patterns have the disadvantage of being very expensive to implement, especially due to the high accuracy required because of rigidity of the boards.

The advantage of using pads placed along the edge of the board is low cost therefore making the mechanical method uneconomical to use for a low cost system.

The other challenge is in the design of the interconnecting pads. Standard pads do not have the required bonding strength with the circuit board substrate or strength in the copper track.

This is illustrated in photo figure 3 where it can be seen that the pad will easily break away from the board even if there are tracks connected to the pad.

The way to overcome the problem is to place a plated through-hole through the pad as this does provide mechanical strength via the plated hole, but as standard pads where the hole is placed in the centre of the pad a different problem arises where the through-hole plating is pulled through the side of the board making this an impractical solution. This is illustrated ip photo figure 4.

To overcome these problems the design of the pad and its associated plated through-hole is very important. The pad must reach the edge of the board to allow easy connection to the adjacent board via a solder joint or wire link. The exact position for the plated through-hole is critical with regard to its placement from the edge of the board. The pad will easily become disconnected from the board. If the plated through-hole is far from the edge of the board and if the plated through-hole is close to the edge of the board, the plated through-hole and pad will easily become disconnected from the boards.

It can be seen that the design of the interconnecting pads with the associated plated through-hole is an important part of the design feature and critical to the success of this type of assembly.

To understand the importance of the design of the interconnecting pads we need to consider the forces that can be applied to the interconnection. For example if we joined two 100mm wide boards together, fixed the two side and applied a force at right angles to the connection between the boards, the force exerted on the interconnection would be the width of the board divided by the thickness multiplied by 2. A standard board is approximately 1.6mm thick using the formula below.

F = length/thickness x 2 x applied force Using a force of 1Kg we get Force = 100 x 2 xl/1.6 Force 125Kg With the need to be RoHS compliant we need to use lead free solders, these solder joints are stronger than the copper bonding of printed circuit boards thus requiring a special design for the interconnecting pads.

In practice the size of the plated through-hole would determine the distance from the edge of the board. The size of the hole to provide the strength required should be greater than 0.6mm, illustrated in drawing figure 1 Dimension A. The distance from the edge of the board to the edge of the hole shall be greater than 1.0mm but not greater than 2.5mm, illustrated in drawing figure 1 Dimension B. The pad size would be greater than these dimensions, illustrated in drawing figure 1 Dimension C and D. For example plated through-hole size of 0.7mm and the distance from the edge of the hole to the edge of the board, a distance of 1mm, the associated pad size for this combination would be greater than this typically 1mm x 1.5mm size or larger.

An example of a board connected at right angles to each other is illustrated in photo figure 5.

An example of a number of boards connected together using this interconnecting system is illustrated in photo Figure 6

Claims

Claims 1. By using the correct design of pads and the positioning of such pads it is possible to mechanically connect circuit boards or modules together irrespective of size, shape, alignment or orientation as long as the mating edges are parallel with each other.
2. In the assembly method according to claim 1, in which the standard specification allows different manufacturers to contribute to this system without prior knowledge of other circuits.
3. In the assembly method according to claim 1, in which circuit boards can be easily connected together without additional hardware.
4. In the assembly method according to claim 1, in which each circuit board has the ability to mechanically interconnect with each other by a set of solder pads along the edge of the circuit boards irrespective of size, shape, alignment or orientation as long as mating edges are parallel with each other.
5. In the assembly method according to claim 1, where electrical interconnections between different circuit boards can be made in a number of ways, for example wire links between boards, plugs and sockets, wire links into sockets, etc.
6. In the assembly method according to claim 1, may be used with circuit boards consisting of pads, tracks and via for mounting and connecting circuits, or complete circuits with components.
7. In the assembly method according to claim 1, may be used with boards requiring pads only for mechanical connection between boards and holes to enable mounting or fixing of boards.
8. In the assembly method according to claim 1, may be used with single layer or multi layer circuits.
9. In the assembly method according to claim 1, can be used with blank boards used to fill empty spaces or achieve the desired final board size and shape.
10. In the assembly method according to claim 1, can be used with boards of any shape as long as the mating edges are parallel with each other for example square, rectangle triangle, polygon etc. Amendment to the claims have been filed as follows Claims 1. A method of assemblmg circuit boards or modules together irrespective of size, shape, alignment or orientation as long as the mating edges are parallel with each other, having solder pads placed at regular intervals around the edge of the boards, by offsetting the corner solder pads by half the width of the pads to the centre of the board, all solder pads with the same spacing are able to align with adjacent boards so that the solder pads may be soldered together thus creating a single circuit board or module ensuring the correct design of the solder pads with it's associated plated through hole will provide the mechanical strength required.2. In the assembly method according to claim 1, circuit boards can be easily connected together by soldering pads without the use of additional hardware.3. In the assembly method according to claim 1, multiple boards can be connected along one edge as pads will align with each other.4. In the assembly method according to claim 1, pads are used for connecting boards together are not used for electrical interconnections between boards as this can be achieved in a number of ways, for example wire links between boards, plugs and sockets, wire links into sockets, etc. 5. In the assembly method according to claim 1, boards used with this method of construction can have pads, tracks and via for mounting components and connecting circuits, or complete circuits with components.6. In the assembly method according to claim 1, blank boards with pads around the edge of the boards together with holes in the centre of the boards are used for mounting or fixing of boards.7. In the assembly method according to claim 1, boards can be single layer or multi-layer circuit construction.* . 8. In the assembly method according to claim 1, blank boards with only the pads along the edge of the boards are used to fill in empty spaces or achieve the desired final board size and * * shape.9. In the assembly method according to claim 1, plated through-holes are used to provide the required mechanical strength. * r. * *r* ** r* * (