WO2002103750A2

WO2002103750A2 - Ball grid array

Info

Publication number: WO2002103750A2
Application number: PCT/GB2002/002598
Authority: WO
Inventors: Michael Notter
Original assignee: Astrium Limited
Priority date: 2001-06-18
Filing date: 2002-06-06
Publication date: 2002-12-27
Also published as: AU2002311433A1; GB0114724D0; WO2002103750A3

Abstract

A ball grid array is used on a macroscopic scale as a suspended stripline. The array construction comprises a stack of substrate circuit layers with space regions formed between adjoining layers and a number of conductive ball spacer members distributed at predetermined positions at the space regions. The array has structural stiffness and mechanical strength and it provides both thermal and electrical conductivity pathways between layers and is also convenient and cheap to manufacture using existing technology. The array finds utility for various space-borne or terrestrial printed circuit antenna applications.

Description

A BALL GRID ARRAY

FIELD OF THE INVENTION This invention relates to a ball grid array and to a method of manufacturing the same for use in space-borne or terrestrial printed circuit antenna applications.

BACKGROUND OF THE INVENTION

A dual polarised antenna design devised by ASTRIUM having a layout as shown schematically in Figure 1 , comprises a sandwich of two tripiate slot antennas in which the lower radiating aperture is etched into the groundplate of the upper radiating element. Blockage is eliminated or substantially reduced by gridding the upper radiating element so that it acts as a polarisation filter - being responsive to V (vertical polarisation of the electric field) and transparent to H (horizontal polarisation of the electric field) for example. Similarly, the lower radiating element responds to H and is reflective to V.

In the radiator design shown in Figure 1 , tiered rings of mode suppression pins surround the radiators to suppress the excitation of 'parallel-plate' waveguide modes. While known radiator designs employ pins that provide rf screening, their physical arrangements are such that they make use of pins straight through the radiator structure and that means that it is difficult to control the electrical contacts internally made in the structure. Also, the unavoidable need for lossy dielectric mechanical support substrates in the structure leads to energy losses and cost disadvantages. OBJECTS AND SUMMARY OF THE INVENTION

The present invention aims to overcome or at least substantially reduce some of the above mentioned drawbacks.

It is a principal object of the present invention to provide a convenient and cost- effective method of manufacturing low-loss printed circuit antenna systems for space applications.

It is another principal object of the present invention to provide a ball grid array on a macroscopic scale which has structural stiffness and mechanical strength characteristics and which provides electrical and/or thermal conductivity pathways during operation.

It is another principal object of the present invention to provide a ball grid array which functions as a suspended stripline (transmissive medium) for printed circuit antennas for example.

In broad terms, the present invention resides in the concept of utilising ball members in place of mode suppression pins in an otherwise known radiator type providing a novel ball grid array design on a macroscopic scale well-suited to suspended stripline applications and having improved rf performance/transmissive characteristics.

According to one aspect of the present invention there is provided a ball grid array comprising; a first, for example base substrate, layer; a second, for example top substrate, layer; one or more intermediate layers being adapted and arranged to be positioned between the first and second layers, the layers in use defining a stack of layers with space regions formed between adjoining layers of the array; and a number of conductive ball members being distributable at predetermined positions at the space regions so that in use of the array, the ball members provide support to the layers enabling the array to form a thermally and/or electrically transmissive pathway.

According to another aspect of the present invention there is provided a ball grid array comprising: a first layer; a second layer; one or more intermediate layers positioned between the first and second layers providing three or more layers with space regions formed between adjoining layers of the array; and a number of conductive ball spacer members distributed at predetermined positions at the space regions providing support to the layers and enabling the array to form a suspended stripline transmission medium.

In accordance with an exemplary embodiment of the invention which will be described hereinafter in detail, there are a plurality of conductive ball members transversely arrayed on top of one and another in a linear array and each ball member is spatially separated from its immediate neighbouring ball member(s) by an intermediate substrate layer. Also, in this embodiment, there are conveniently a plurality of spaced-apart conductive ball members laterally arrayed in a linear array in each of the space regions of the structure. In the preferred embodiment, each of the ball members is placed into direct contact with an upper adjoining layer and a lower adjoining layer of the arrayed structure. This can be suitably achieved by ensuring that each ball member is adhesively or solder contacted with the respective upper and lower adjoining layers of the array. Conveniently, the ball members are made to make contact with the metal plated hole portions (vias for example) formed in the various layers of the structure. The presence of the hole formations in the structure contributes toward an enhancement in the thermal and electrical conductivity characteristics of the structure provided the ball members are positioned contiguously in adjacent substrate layers.

Preferably, the space regions of the array structure comprise air-filled regions. Alternatively, if desired, the space regions could be filled with liquid dielectric material.

The conductive ball members can be advantageously made of different kinds of metallic material. Preferably, the ball members are made of copper material or aluminium material.

Further, the ball members may have different sizes, allowing a number of substrate thicknesses within the stack. Note that each distinct substrate in the stack has equal-sized balls.

It is to be appreciated that the present invention extends to a radiating system incorporating the above mentioned ball grid array. The present invention also extends to a method of manufacturing the above mentioned ball grid array on a macroscopic scale, the method comprising: forming a first, for example base substrate, layer; forming a second, for example top substrate, layer; forming one or more intermediate layers between the first and second layers so as to define three or more layers with space regions formed between adjoining layers of the array; and distributing a number of conductive ball members at predetermined positions at the space regions so that in use of the array the ball members provide support to the layers enabling the array to form a thermally and/or electrically transmissive pathway.

It is to be appreciated that the ball grid array of the present invention can be implemented at reasonable cost and it has utility for various space-borne or terrestrial applications.

The above and further features of the invention are set forth with particularity in the appended claims and together with advantages thereof will become clearer from consideration of the following detailed description of an exemplary embodiment of the invention given with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 shows schematically an ASTRIUM radiator design, namely a dual- polarised printed circuit antenna example (prototype design); Figures 2 to 4 show the V-H port S-parameters and radiation pattern characteristics along the principal V & H axes of the radiator of Figure 1 ; and

Figure 5 is a schematic view of a ball grid array embodying the present invention.

DETAILED DESCRIPTION OF AN EXEMPLARY EMBODIMENT

As previously mentioned, Figure 1 shows an ASTRIUM radiator design 1 comprising a sandwich of two ASAR-type tripiate slot antennas 5, 5' in which the lower radiating aperture is etched into the groundplate of the upper radiating element. The positions of the mode suppression pins 6, as shown in the figure, surround the radiators to suppress the excitation of "parallel plate" waveguide modes. The radiation pattern V-H axis definition is shown on the figure for clarity. The typical radiation pattern characteristics of the radiator design 1 of Figure 1 are shown in Figures 2 to 4 and it can be seen from these figures that

(a) there is a V-H port isolation >30 dB;

(b) there is a 15 dB input return loss bandwidth of 300 MHz; and

(c) there are low cross-polar levels along the principal planes.

Referring now to Figure 5 there is schematically shown therein a preferred ball grid array 10 embodying the present invention. The ball grid array 10 as shown in the Figure, comprises a stack of thin spaced apart stiff dielectric layers (typically of the Rogers RO4003 or glass-reinforced plastic substrate type) comprised by a base substrate layer 11 at its lower end, three intermediate substrate layers 12, 13, 14 and a top substrate layer 15 at its upper end. The layers 11 , 12, 13, 14, 15 are mutually spaced apart in a transverse axial direction to provide a formation of four laterally-directed space regions (Gaps 01 to 04) between the respective adjoining layers of the array 10. As shown, two laterally spaced apart columns of ball members are distributed at predetermined locations in the Gaps 01 to 04, the first column being comprised by four ball members 25, 26, 27, 28 at one side of the array 10 and the second column being comprised by four ball members 35, 36, 37, 38 at an opposed side of the array 10. In the embodiment thus, there are (a) two laterally spaced ball members per space region defining laterally a linear array in each of the space regions (Gaps 01 to 04) and (b) two spaced apart columns of ball members defining two transversely-directed linear arrays and whereupon each ball member in each column is spatially separated from its immediate neighbouring ball member(s) by the presence of an intermediate substrate layer.

As shown in Figure 5, each ball member is placed into direct contact with an upper adjoining layer and a lower adjoining layer of the array. Conveniently, the upper and lower end surfaces of the ball members are adhesively or solder contacted 30 about the hole portions 'A' (vias) which are pre-formed in the layers to facilitate the thermal and electrical conductivity characteristics of the array 10 in use. Different sized vias 'B' are also shown to be formed in a centre part of the array and other balls (not shown) can be secured at these sites if desired. The ball members can have varying sizes and can be made of different kinds of metallic material. Preferably, the ball members are made of copper (Cu) material and their typical dimensions (including the type of cladding and the diameter dimensions) are provided in Figure 5.

Advantageously, the space regions comprise air-filled regions. However, if required, the space regions could alternatively comprise liquid dielectric-filled regions.

In operation of the thus described ball grid array of the invention, it will be understood that while it provides the characteristics of Figures 2 to 4 when applied to a radiator system of the kind shown in Figure 1 it provides many definite advantages, from both the rf and manufacturing standpoints, over the known arrangement 1 by virtue of replacing the pins by ball members at positions 6, namely:

(a) the ball diameters can be accurately specified and hence the laminate spacing is known precisely;

(b) no orientation of the ball spacers is required during assembly, so accurate positioning is easy and the tooling cost is relatively cost effective;

(c) during application of the conducting adhesive layer, the ball to plane contact supports the formation of a meniscus (by means of capillary action) which is contained within the ball cross-section. This leads to good rf performance repeatability through the avoidance of unwanted adhesive fillets; (d) the array construction has structural stiffness and mechanical strength; (e) by^' suspending the substitute circuit carriers (layers), the array construction is suited to suspended stripline applications;

(f) the array construction has thermal and electrical conductivity pathways;

(g) the array construction is energy-efficient by avoiding the need for lossy solid dielectric supportive substrate spacers; and

(h) the array construction is such that it provides control over the way the electrical contacts are made internally in the structure.

The above described array construction 10 of the invention is manufactured by forming at least three/a stack of layers with space regions formed between adjoining layers and distributing a number of conductive ball members at predetermined positions at the space regions. Note that the particular order of these steps is not critical to the method of the invention. Thus, it is possible in the method of the invention to mount first a ball onto a base substrate layer and thereafter, to mount an intermediate substrate layer on top of the ball and to repeat this procedure of mounting so as to successively build up a number of layers with ball spacer members, thereby enabling the aforementioned array 10 to be produced.

Having thus described the present invention by reference to a preferred embodiment, it is to be appreciated that the embodiment is in all respects exemplary and that modifications and variations are possible without departure from the spirit and scope of the invention. For example, the performance of the embodiment could be improved, if desired, by changing the number/size of the ball spacers in the lateral and/or transverse axial directions of the array and/or by changing the dielectric medium in the space regions or by changing the number/size of the layers. Note that the term 'ball member' in this specification is taken to mean any sphere/ball or any member which is substantially ball/spherical-shaped. Further while in the described embodiment the dielectric medium in the space regions is air, the arrangement could alternatively be such that the dielectric medium in the space regions is a liquid. The balls could also be made of any kind of metallic material, ie not just made of copper as in the described embodiment; the balls could be made of another metal, aluminium for example, or of an alloy material with suitable conducting properties. It is to be noted that the ball and layer dimensions in the embodiment are given by way of example only and that these dimensions could easily be changed and the technical effect of the invention would still be realised.

It is envisaged that the present invention finds utility for various space-borne or terrestrial applications.

Claims

1. A ball grid array comprising; a first, for example base substrate, layer; a second, for example top substrate, layer; one or more intermediate layers being adapted and arranged to be positioned between the first and second layers, the layers in use defining a stack of layers with space regions formed between adjoining layers of the array; and a number of conductive ball members being distributable at predetermined positions at the space regions so that in use of the array, the ball members provide support to the layers enabling the array to form a thermally and/or electrically transmissive pathway.

2. An array as claimed in claim 1 wherein there are a plurality of conductive ball members transversely arrayed on top of one and another in a linear array and each one of the ball members is spatially separated from its neighbouring ball member(s) by said one or more intermediate substrate layers.

3. An array as claimed in claim 1 or claim 2 wherein there are a plurality of spaced-apart conductive ball members laterally arrayed in a linear array in each of the respective space regions.

4. An array as claimed in claim 1 or claim 2 or claim 3 wherein each of the ball members is in contact with an upper adjoining layer and a lower adjoining layer of the array.

5. ^" An array as claimed in claim 4 wherein said each of the ball members is adhesively or solder contacted with said upper and lower adjoining layers of the array.

6. An array as claimed in any of the preceding claims wherein the space regions comprise air-filled regions.

7. An array as claimed in any of the preceding claims wherein the ball members are made of copper material.

8. An array as claimed in any of claims 4 to 7 wherein the substrate layers are provided with hole portions, vias for example, about which each of the ball members are in contact, facilitating a thermal conductivity pathway and/or electrical conductivity pathway in the array.

9. A ball grid array comprising: a first layer; a second layer; one or more intermediate layers positioned between the first and second layers providing three or more layers with space regions formed between adjoining layers of the array; and a number of conductive ball spacer members distributed at predetermined positions at the space regions providing support to the layers and enabling the array to form a suspended stripline transmission medium.

10. A radiating system incorporating a ball grid array as claimed in any of the preceding claims.

11. A method of manufacturing a ball grid array on a macroscopic scale, the method comprising: forming a first, for example base substrate, layer; forming a second, for example top substrate, layer; forming one or more intermediate layers between the first and second layers so as to define three or more layers with space regions formed between adjoining layers of the array; and distributing a number of conductive ball members at predetermined positions at the space regions so that in use of the array the ball members provide support to the layers enabling the array to form a thermally and/or electrically transmissive pathway.

12. A method as claimed in claim 11 further comprising binding each of the ball members to an upper adjoining layer and a lower adjoining layer of the array using a binding means, an adhesive or solder for example.

13. A ball grid array or method of manufacturing a ball grid array substantially as described herein with reference to the accompanying drawings.