METHOD AND ARRANGEMENT FOR HEATING A COMPONENT

Abstract: The invention relates to a method and arrangement for heating at least one component (14) of a circuit board comprising one or plural layers (10 and 11). At least one component (14) to be heated is then heated with at least one heat resistor (15) associated with the circuit board.

Description: METHOD AND ARRANGEMENT FOR HEATING A COMPONENT FIELD OF THE INVENTION The invention relates to a method for heating at least one component on a circuit board, said circuit board comprising one or plural layers. The invention also relates to an arrangement for heating a component on a circuit board, which comprises at least one layer and which comprises one or plural components to be heated. BACKGROUND OF THE INVENTION Circuit boards that are meant to be used within a broad temperature range, are usually designed to dissipate heat well. Heat is conducted or conveyed from components to cooling elements, to support structures and/or to the environment. This solution functions well in warm and hot conditions, but in cold conditions the cooling is often even too efficient and the temperature of the components falls to the extent that it can disturb the operation of the apparatus concerned. The operation of an apparatus functioning in cold conditions can be secured by using components intended for military use, said components being designed to function within a broad temperature range, or by heating an apparatus comprising standard components. Since components intended for military use are expensive and each component usually has only one manufacturer, a prior art solution relies on heating the whole apparatus concerned, which typically involves heating the frame, the air space in the apparatus and its cooling fins, in addition to the circuit boards. This requires high heating power. Often a heating arrangement such as this also increases the size of the apparatus concerned, which is particularly disadvantageous when small size and high degree of integration are aimed at. In addition, all components are then subject to an equal amount of heating power, even if some of them would not need to be heated. The heating of components is also described in the US Patent 5,539,186, which is enclosed herein as a reference. A solution according to the US Patent 5,539,186 concerns a multi-layer board, in which a layer comprises a resistive heating film structure for heating a circuit board. SUMMARY OF THE INVENTION An object of the present invention is thus to provide a method and arrangement for heating components, in said method and arrangement heating power being reduced by heating only components that need to be heated, instead of the frame, air space and cooling fins of a whole apparatus. This is achieved with a method described in the preamble, said method being characterized in that one or plural components to be heated are heated with at least one heat resistor associated with a circuit board and that the circuit board's own conduction material is used as the material of the heat resistor. An arrangement of the invention is characterized in that a circuit board comprises at least one heat resistor arranged in connection with it, said heat resistor being arranged to heat at least one component on the circuit board and that the material of a heat resistor is the conduction material of the circuit board. The method of the invention offers considerable advantages. Compared with prior art, the amount of heating power needed is much smaller, because heating can be focused more carefully on the desired components, which enables avoiding the heating of elements that need not necessarily to be heated. The degree of integration of the heating arrangement can also be increased. BRIEF DESCRIPTION OF THE DRAWINGS In the following the invention is described in greater detail with reference to examples shown in the attached drawings, in which Figure 1 illustrates a multi-layer circuit board and Figure 2 illustrates a layer of a circuit board comprising a heat resistor and Figure 3 illustrates a layer of a circuit board comprising plural heat resistors. DESCRIPTION OF PREFERRED EMBODIMENTS A solution of the invention can be utilized in different circuit board solutions, particularly in multi-layer circuit boards comprising discrete components. Let us now examine more closely a method of the invention. One or plural heatable components of a circuit board of one or plural layers, said components being responsible for the actual operation of the circuit, are heated using at least one heat resistor associated with the circuit board. The heat resistor is then in the immediate vicinity of or in contact with the component to be heated. In the solution of the invention heating is preferably performed with a heat resistor integrated into a circuit board layer. The components to be heated perform the actual desired operation of the circuit board, for instance signal processing in a transceiver of a digital radio system. In the invention, the heatable components can, in turn, be any components whatsoever, e.g. mechanical, electronic or optical components. Typically the stabilizing of the operating temperature of a processor used in signal processing is important. Heating is performed by feeding direct current or alternating current power into the resistor, whereby the resistor warms up. Any typically resistive prior art resistor material can be used as a resistor. The resistor material used in the circuit board, such as copper, is preferably used as the material of the resistor. The material of a heat resistor can, however, also be any other material conducting electricity reasonably well, of which metals are a typical example. When alternating current is being fed into a heat resistor, at least a partly capacitive or inductive load impedance can also function as a resistor. In a single-layer circuit board in particular the heat resistor can be arranged directly below a sufficiently large component responsible for the actual operation of the circuit board, the heat resistor then heating the component above it by obtaining its heating power preferably from the same operating voltage as the component responsible for the actual operation of the circuit board. Let us now examine the inventive arrangement and method on the basis of Figures 1 , 2 and 3. Figure 1 is an explosion view illustrating the circuit board. A circuit board usually comprises an even number of layers, but for the sake of simplicity the structure of the circuit board in Figure 1 comprises three layers 10 and 11 , of which the bottommost and the topmost layers 10 are the switching circuit boards 10 of the components 14 performing the desired operation and between said layers 10 is a heat resistor layer 11 with a heat resistor 15. Heating can thus be focused on the circuit board and its components, instead of the whole apparatus concerned. In the inventive solution the power source of the heat resistor is preferably the power, i.e. the operating voltage, used by the components 14 needed for the actual operation of the circuit board. The heat resistor 15 can, however, also be heated by a separate power source 12. The heating power of the heat resistor 15 can preferably be adjusted according to need, for which purpose the power source 12 is for instance controlled with a control means 13 monitoring the temperature of the components 14. The control means 13 can monitor the temperature around the components, such as the temperature of the air, the temperature of the circuit 10 or the temperature of the heatable component 14 and, if the temperature is too low, heating is activated. If a predetermined variation in temperature is allowed for the components 14 responsible for the actual operation of the circuit board, then the control means 13 is, at its simplest, a switch which in cold conditions switches the heating on and in warm conditions turns it off. The control means 13 can, however, preferably also control the power fed by the power source 12 to the resistor 15. In this case, the colder the environment, the circuit board 10 or one or plural components 14 are, the more heating power is preferably fed. The control means 13 is an electronic thermometer conforming to prior art and furnished with at least one measuring head 131 , 132 and 133, which measure the temperature of the environment, the circuit board 10 or the component 14. Figure 2 shows the circuit board layer 11 in greater detail. The layer 11 in this example comprises one heat resistor 15, which is used for heating all components in the layers 10. The form of the heat resistor can differ quite considerably from the one shown in Figure 2, because the form is not essential to the invention. Since the heat resistor 15 is close to the components 14 of the layer 10, they heat effectively. The heat resistor 15 can substantially cover the whole layer 11 of the circuit board, as shown in Figure 2, or the heat resistor 15 can be arranged on only a part of the surface of the layer 11. Figure 3 illustrates a more efficient embodiment of the inventive solution than the above. The heat resistor layer 11 in this example comprises plural heat resistors 15. The inventive solution thus allows heating different components 14 responsible for the actual operation of the circuit board in a different way. Components generating a lot of heat in their own operation are heated less than components generating little heat. Heating power can be varied for instance by using heat resistors 15 with impedances of a different magnitude. This allows the components 14 responsible for the actual desired operation in the different layers 10 of the circuit board to be heated independently, irrespective of each other. In addition, when a solution similar to the one shown in Figure 1 is used, the control means 13 can preferably measure the temperature of each component 14 separately with measuring heads 131 , 132 and 133 and guide the heating power of the power source 12 to each component separately. Since each component 14 responsible for the actual operation of the circuit board has its own heat resistor 15, the resistors 15 can have small values, whereby a low operating voltage is sufficient for them. This enables using for instance the operating voltage meant for logic also as the power source for heat resistors 15. The means 12, 13, 131 , 132 and 133 are not, however, essential to the invention. Even though the invention is described above with reference to an example shown in the attached drawings, it is apparent that the invention is not restricted to it, but can vary in many ways within the inventive idea disclosed in the attached claims.

Claims: CLAIMS 1. A method for heating at least one component (14) on a circuit board, said circuit board comprising one or plural layers (10 and 11), characterized in that one or plural components (14) to be heated are heated with at least one heat resistor (15) associated with the circuit board and that the circuit board's own conduction material is used as the material of the heat resistor (15). 2. A method according to claim ^characterized in that when a multi-layer circuit board is concerned, one or plural layers (11) of the circuit board are used as the circuit containing the heat resistors (15). 3. A method according to claim ^characterized in that when a plurality of different components (14) are heated, each component (14) is heated independently. 4. A method according to claim 1, characterized in that one or plural heat resistors (15) use a different power source (12) for generating heating power than the components (14) to be heated. 5. A method according to claim 1, characterized in that when the components (14) that need to be heated differ from one another, said components (14) are heated with different heating power. 6. A method according to claim 1, characterized in that the heating power of one or plural heat resistors (15) are adjusted according to need. 7. A method according to claim 1 or 6, characterized in that the temperature of one or plural components (14) to be heated is measured and the heating power of one or plural heat resistors (15) is automatically adjusted according to the temperature of the components (14) to be heated. 8. A method according to claim 2, characterized in that one or plural innermost layers (11) of a multi-layer circuit board or a part of a layer are used as a circuit in which one or plural heat resistors (15) are arranged. 9. A method according to claim ^ characterized in that the component (14) to be heated is heated with the heat resistor (15), which is below the component (14) in the same layer as said component (14). 10. An arrangement for heating a component on a circuit board, which comprises at least one layer (10 and 11) and which comprises one or plural components (14) to be heated, characterized in that the circuit board comprises at least one heat resistor (15) arranged in connection with it, said heat resistor being arranged to heat at least one component (14) on the circuit board and that the material of the heat resistor (15) is the conduction material of the circuit board. 11. An arrangement according to claim 10, characterized in that when a plurality of different components (14) are heated, more than one heat resistors (15) are arranged to focus heating on each said component (14) separately. 12. An arrangement according to claim 10, characterized in that the layer (11) comprising one or plural heat resistors (15) is operationally connected to a different power source (12) than the components to be heated (14). 13. An arrangement according to claim 10, characterized in that when the components (14) to be heated differ from one another, the heating power of the heat resistors (15) responsible for heating said components (14) varies. 14. An arrangement according to claim 10, characterized in that the arrangement comprises means (13) for substantially measuring the temperature of the components (14) to be heated and for automatically adjusting the heating power of one or plural heat resistors (15). 15. An arrangement according to claim 10, characterized in that the heat resistor (15) is below the component (14) to be heated, in the same layer as said component (14) to be heated. 16. An arrangement according to claim 10, characterized in that one or plural innermost layers (11) of a multi-layer circuit board, or a part of a layer, is a circuit comprising one or plural heat resistors (15).

Inventors: ISTERI ARI, ISTERI, ARI
Applicants: ISTERI ARI, NOKIA TELECOMMUNICATIONS OY, ISTERI, ARI
Application year: 1997
Main classification: H05K7
IPC codes: H01L23, H05B3, H05K1, H05K3, H05K7