WO2000055874A1

WO2000055874A1 - Electrical components and circuit assembly

Info

Publication number: WO2000055874A1
Application number: PCT/EP2000/001343
Authority: WO
Inventors: Stephen J. Battersby
Original assignee: Koninklijke Philips Electronics N.V.
Priority date: 1999-03-13
Filing date: 2000-02-18
Publication date: 2000-09-21
Also published as: GB9905742D0

Abstract

Electronic components (1) are fabricated on a glass substrate (10) which is opaque rather than transparent so that the components can be used reliably in pick and place machines that employ visual location techniques to find and select the components. The use of opaque substrates (10) eliminates the need to make expensive modifications to pick-and-place machines. Problems associated with the optical recognition system of the machine viewing the thin film device structure (11, 12, 13) by looking through the substrate (10) from the remote side of the component are also avoided. This can be important where orientation of the device is of concern, for example when placing thin film components. Transparent glass substrate materials that are suitable for use in the fabrication of electronic components, are treated during manufacture of the substrate to make the substrate substantially opaque. Suitable materials are added to the substrate melt and different materials may be used to give the substrate different colours.

Description

ELECTRICAL COMPONENTS AND CIRCUIT ASSEMBLY

The present invention relates to electrical components having a thin-film structure supported on a glass substrate, a method of assembling a circuit having at least one such component and a circuit assembled by the method. In particular the present invention relates to the use of such components in or with circuit assembly apparatus.

Known techniques for the mass production of electronic circuitry include the use of machines for selecting individual components and placing the components in the correct location on a circuitry carrier or circuit substrate for mounting thereon, such as a printed circuit board or the like. One principle for mounting the components is so-called "Surface Mount Technology (SMT)" where the components are attached to the surface of a printed circuit board. SMT components can be small compared with equivalent components having leads, which allows components to be mounted more densely.

One particular category of machines used to select and place the components on the circuitry carrier is that of so called pick-and-place machines. An example of such a machine is described in published patent application number WO-A-97/22238 which is incorporated herein by reference. Components supplied to the machines need to be located before selection and orientation operations can be performed on those components. One way of locating, selecting and orientating the components is to employ visual techniques for example in the form of optical recognition systems, whereby the machine is provided with a video camera or the like allowing it to "see" the components so that the machine can handle them. While this can provide satisfactory performance in many applications, problems can arise when the components are largely transparent because they cannot be seen properly by the machine. The component may be rendered largely transparent for a number of different reasons, although it is common for the component to be largely transparent if the component substrate is largely transparent. Largely transparent materials are normally difficult to distinguish from the background they are viewed against. Examples of such components include those formed on glass substrates although the problem can occur with substrates formed of other materials that are generally clear or transparent. As described in GB-A- 2 141 584 it is advantageous to use glass substrates to produce low cost components and GB-A-2 141 584 describes low cost thin film capacitors having an insulating substrate of glass.

Consider an example of one type of electrical component having a largely transparent substrate with a thin film device formed on a first surface of the substrate. The device will not necessarily occupy the whole area of the first surface. If only a fraction of the surface area is occupied, then even if the component is orientated so that an optical recognition system views the first surface directly, the area occupied by the device can be too small to be reliably seen by the optical recognition system. Because the substrate of the component is largely transparent, the component is not detected at all.

If the device does cover a sufficient surface area so as to be detectable by the optical recognition system, it is still critical that the optical recognition system views the surface from a particular direction. If the component is orientated to cause the optical recognition system to view the component from the side or the end of the component, the component may not be detected. This is because the device can present to the recognition system a visible area that is too small to be detected. This is particularly likely where the device structure is relatively thin as is the case for thin film devices. Once again, because the substrate of the component is largely transparent, the component is not detected at all.

In some cases component packing techniques cause individual components to be supplied to pick-and-place machines with a random orientation and the possibility of individual components being undetectable merely due to their particular orientation with respect to the optical recognition system causes unacceptable problems. Other examples of components may be detectable by optical recognition systems due to the presence of component contacts, even if the component substrate is largely transparent. Such contacts can also provide information to an optical recognition system about the orientation of an individual device. For some of these components when used in certain applications it can be sufficient merely to identify the contacts of the component and place the component in the circuit to establish electrical connection. However, in other instances, for example where the component is a thin film device, the particular orientation of the component is important to ensure that the thin film device is correctly located with respect to the circuit carrier. This requires knowledge of which surface of the substrate carries the thin film structure.

In this respect particular problems arise where the substrate is largely transparent. Assuming the device of the component is large enough to be detected when viewed directly, it can also be seen, and therefore detected, when viewed indirectly by looking through the substrate material. The component may appear the same to a pick and place machine when the thin film structure device is viewed directly or viewed through the substrate from the side of the component remote from the device, especially if the substrate is thin. Therefore the orientation of the component cannot be determined to the extent that is required. If a component is electrically connected to the circuit correctly but with the incorrect physical orientation, circuit and / or component performance can be affected, for example when operating in high frequency circuits. In such circuits it is often preferred for the thin film component to be mounted with the thin film structure closest to the circuit carrier.

Thin film device structures can be reflective to light but problems can still be encountered when detecting and orientating these components for the reason described above.

It is an object of the present invention to provide electrical components having glass substrates that can be visually located by assembly machines more easily than would be the case for components not benefiting from the present invention. In accordance with a first aspect of the present invention there is provided an electrical component having a thin-film structure supported on a glass substrate, wherein the glass substrate is visually more distinct than the thin-film structure so as to permit a visual identification of the location of the component by identification of the substrate. Thus, the glass substrate may be substantially opaque.

Because the component is formed on a substrate that is visually more distinct than the thin film structure, the component can be used in machines, such as pick-and-place machines, that rely on visual techniques to locate the devices. By forming the devices on a substrate that would otherwise be largely invisible to the machine, there is no requirement to implement costly modifications to the location or handling apparatus of the machine. Additional steps that may otherwise be considered during component manufacture for making a component visible to such machines may be omitted. Advantageously this can reduce manufacturing costs. Making the glass substrate visually more distinct than the thin film structure can assist in identifying the surface of the substrate that the thin film structure is supported on.

In accordance with the second aspect of the present invention there is provided a method of assembling a circuit comprising a circuit substrate and a component of the present invention. The component is visually identified by an optical recognition system of a pick-and-place machine, is picked up by the machine and is placed in a component area of the circuit substrate.

In accordance with a third aspect of the present invention there is provided a circuit assembled by the method of the present invention, wherein the circuit comprises at least two different components of the present invention. The different components are visually distinguished from each other by a difference in colour for their glass substrate.

Other aspects and optional features of the present invention appear in the appended claims, to which reference should now be made and the disclosure of which is incorporated herein by reference. The present invention will now be described by way of example only with reference to the accompanying diagrammatic drawings wherein:

Figure 1 is a cross-sectional view of a component of the present invention in the form of a thin film capacitor; and Figure 2 is a cross-sectional view of a component of the present invention in the form of a thin film transistor.

It should be noted that the drawings are diagrammatic and not drawn to scale. Relative dimensions and proportions of parts of the Figures have been shown exaggerated or reduced in size for the sake of clarity and convenience in the drawings. The same reference signs are generally used to refer to corresponding or similar features in the different embodiments.

Referring to Figure 1 a thin film capacitor 1 includes a first conductive film 11 formed on the surface of an electrically insulating substrate of glass 10, an insulating film 12 formed on the surface of the first conductive film 11 and a second conductive film 13 formed on the surface of the insulating film 12. The first and second conductive films provide bottom and top capacitor plates respectively and each film may be of a metal material. The insulating film 12 provides the capacitor dielectric and is of a suitable material, for example Si₃N₄. The first conductive film 11 and the second conductive film 12 may be made from gold, for example. The capacitor is provided with terminals denoted as 14 and 15 respectively and the structure is covered with a protective layer 16.

Figure 2 shows two thin film transistors (TFT's) 2a and 2b connected in an integrated circuit, with the boundary between the devices indicated by the broken line 3. Each transistor is supported on a common electrically insulating substrate of glass 10. Each transistor 2a and 2b includes a first conductive film 11a and 11 b respectively, formed on the surface of the glass substrate 10. Conductive films 11a and 11b provide separate gate electrodes for transistor 2a and 2b respectively and each film may be of a metal material. An insulating film 12 is formed to cover each of the conductive films 11a, 11 b and the surface of the glass substrate 10. The insulating film 12 serves as a gate dielectric of the TFT's. A semiconductor film is formed on the insulating film 12 and is divided into two parts 14a and 14b to provide a separate semiconductor body of each TFT 2a and 2b respectively. Each transistor 2a and 2b is provided with a separate source electrode 13a and 13b respectively of conductive film and each may be of a metal material. Finally a conductive film drain electrode 13c is provided which is common to the two transistors. This electrode may be of a metal material.

For each component, either in the form of a capacitor, transistor or otherwise, the glass substrate 10 is visually more distinct than the thin film structure formed by elements 11 , 12, 13,14a and 14b so as to permit visual identification of the location of the component by identification of the substrate 10.

The substrate may be more distinct for any one or more of a number of reasons. In all of the illustrated embodiments the glass substrate 10 is more impervious to light than the thin-film structure 11 , 12, 13,14a and 14b. However it is not necessary for the substrate 10 to be totally opaque and indeed in terms of a given amount of bulk material the substrate may even be less impervious to light then the thin film structure material. The important requirement is that the substrate is visually more distinct than the thin film structure and this may be by virtue of a substrate that has sufficient surface area and/or volume and is at least partially opaque to light at a particular wavelength.

The substrate allows an optical recognition system to identify which surface of the substrate the thin film structure is on since the thin film structure will have a different appearance when viewed directly than it does when viewed through the substrate.

The substrate 10 may be translucent or partially transmissive and may have a different colour (for example black, red, blue or green) and in this case different colours may be used to give a visual indication of different components or different component characteristics, such as tolerance value.

In one example a thin film capacitor is formed on a substrate of opaque glass. Glass is a preferred substrate because it is low cost and has a good surface finish suitable for the fabrication of components thereon. Certain types of glass are preferred, and one example is Type 1737 glass manufactured by Corning. This glass has physical characteristics suitable for the fabrication of components. Boro Silicate Glass is generally preferred to Soda Lime Glass due to the detrimental effect the latter can have on certain materials commonly used in the manufacture of electronic components.

Opaque glass substrates can be produced by adding suitable materials to the glass melt. Glass may be rendered opaque by colouring it by the standard techniques used in the glass industry, for example by the addition of oxides of transition elements or rare earth elements. In this example the resulting glass substrate is black. A large number of individual thin-film capacitors are produced on each glass substrate using typical semiconductor-like fabrication processes, as will be understood by the person skilled in the art and the role of the substrate is simply that of a support for the over-lying layers. The individual capacitors are then obtained by dividing the glass substrate appropriately at regions of the plate between the individual capacitors to produce discrete devices. The discrete devices are typically 1 mm x 0.5mm x 0.4mm in size. Optionally, a silicon dioxide layer or other insulating buffer layer may be formed on the surface of the glass substrate prior to depositing the other layers that make up the electrical component.

The finished components may be supplied to circuit assembly machines, such as pick and place machines that rely on visual techniques to locate the components. The components can be fed into the machine using conventional techniques such as the use of bulk, tape, stick or tray feeders. Indeed, certain types of components or batches of components may be formed on substrates having a different colour for easy identification of components and reduction in the likelihood of feeding wrong components into the machine. It would also be possible to programme the machine to recognise and use only components having a substrate of a particular colour. While the present invention has been described in relation to thin film capacitors and thin film transistors, this is not to be construed as a limitation. Indeed other types of thin film components such as thin film inductors may be provided. Integrated thin film components employing a number of similar or different thin film devices may also be formed on substrates of this invention and opto-electronic devices could be produced. The components could be active or passive. The overall area of the component is visually distinct because of the opaque nature of the substrate material. In other words, the bulk of the component is non-transparent to at least one wavelength of light. The wavelengths may fall in any one or more of the visible, infrared or ultraviolet bands. From reading the present disclosure, other modifications will be apparent to persons skilled in the art. Such modifications may involve other features which are already known in the design, manufacture and use of systems and devices and component parts thereof and which may be used instead of or in addition to features already described herein.

Claims

1. An electrical component (1 ; 2a, 2b) having a thin-film structure (11 , 12, 13; 11a, 11b, 12, 13a, 13b, 13c, 14a, 14b) supported on a glass substrate (10), wherein the glass substrate (10) is visually more distinct than the thin-film structure so as to permit a visual identification of the location of the component by identification of the substrate (10).

2. A component in accordance with Claim 1 , wherein the thin-film structure (11 , 12, 13) forms a capacitor.

3. A component in accordance with Claim 1 or 2, wherein the glass substrate (10) has a larger opaque volume than the thin film structure.

4. A component in accordance with Claim 1 , 2 or 3 wherein the glass substrate (10) has a larger opaque surface area than the thin film structure.

5. A component in accordance with any one or more of Claims 1 to

4, wherein the glass substrate (10) is substantially opaque.

6. A component in accordance with claim 5, wherein the glass substrate (10) is substantially black.

7. A method of assembling a circuit comprising a circuit substrate and a component (1 ; 2a, 2b) as claimed in any one of Claims 1 to 6, wherein the component is visually identified by an optical recognition system of a pick-and-place machine, is then picked up by the machine and is placed in a component area of the circuit substrate.

8. A circuit assembled by a method in accordance with Claim 7 and including at least one component as claimed in any one of claims 1 to 6.

9. A circuit assembled by a method in accordance with claim 7, wherein the circuit comprises at least two different components each of which is in accordance with one or more of Claims 1 to 6, wherein the different components are visually distinguished from each other by a difference in colour for their glass substrate.