Patent Application
20240359246
The invention relates to control of a preheating process. In particular, the invention relates to a method of controlling a preheating process for preheating a board for use in a soldering machine.
Selective soldering machines are used to solder electronics components to boards, such as to printed circuit boards (PCBs). The boards pass through the machine and undergo a soldering process to connect the components to the board. The soldering process typically includes the application of flux to the joints between the components and the board, preheating the components and the board, and applying solder to the connections between the components and the board.
The board is preheated to evaporate alcohol from previously applied flux, and to reduce the thermal shock to the board when solder is applied thereto. Typically, the board enters a preheating chamber, which may be the same chamber as a fluxing chamber and/or a soldering chamber. Once in the preheating chamber a heating unit, which faces a surface of the board, emits heat to heat the board.
The heating unit may comprise an infra-red (IR) heating unit which comprises strips of IR bulbs. Heat emission from the IR bulbs is controlled by controlling the voltage supplied to the IR bulbs. The heat emission determines the amount of heat transfer from the IR bulbs to the board. Clearly, if one or more bulbs begins to deteriorate, or has different operating properties to other IR bulbs, then this causes deviation from the target temperature and so the board is not heated to the required temperature.
The heating unit may comprise a forced convection preheating unit. In forced convection preheating, at least one electrical heater is situated between at least one fan and the electronics board. The heater/s emit heat, and the fan/s create air flow to transport the heat to the board. The heat transfer to the board is controlled by controlling the voltage supplied to the heater/s, or by controlling the rotation speed of the fan/s using a frequency inverter, with the actual fan speed being measured using an encoder. If any one of the fan/s or the heater/s deteriorate or have different operating parameters than other fan/s and/or heater/s, then this may cause deviation from the target temperature and so the board will not be heated to the required temperature.
In order to correct for differences between the required board temperature and the actual board temperature, it is known to use a temperature probe to measure the ambient temperature between the heating unit and the board, or to measure the temperature of the board at a discrete location. If the temperature measured using the temperature gauge is different to that which is expected, then the heating unit can be adjusted accordingly to emit more, or less, heat. As the boards are preheated in a production line, adjustments are sometimes calculated from measurements taken during preheating of one board, and the adjustments are implemented for subsequent boards. This means that the board from which temperatures are measured is not heated by an adjusted amount, and so is preheated to an incorrect temperature, and subsequent boards are preheated with an adjustment that is calculated for a preceding board.
Another limitation of this method is that each temperature gauge only measures the temperature at one location, and, due to the high processing speeds of soldering machines, it is not usually feasible to measure the temperature at multiple locations using the same temperature gauge. Instead, the number of temperature gauges can be increased to measure the temperature at multiple locations, but this is expensive and cumbersome. Furthermore, even if more temperature gauges are used, each temperature gauge will only measure the temperature at a specific location, leaving the temperature of most of the board unmeasured.
This means that hot and cold spots on the boards caused by deterioration of IR lamps, heater/s and/or fan/s, or incorrect heating unit settings for example, often go undetected. These hot and cold spots can lead to board warpage, thermal damage to the board at hot spots, or thermal shock during soldering of cold spots. Board warpage may lead to failed placement of electronic components, and ultimately to the scrapping of the board and electrical components. Furthermore, suboptimal performance of parts of the heating unit often goes undetected due to hot or cold spots on the boards being undetected.
Furthermore, overheating of all or some of the board can lead to the de-activation of flux which has been applied to the board in preparation for a soldering process. The flux contains activators, which are chemicals, which, when activated, prevent oxidation and support the wetting of the metal surface for soldering, at certain activation temperatures. These temperatures are typically 150° C. or higher. If the board is preheated to greater than the activation temperature of the activators, then insufficient chemistry might remain for the flux to effectively prevent oxidation and to effectively support the wetting of the metal surface.
It would therefore be beneficial to overcome at least some of these limitations.
According to a first aspect of the present invention, there is provided a method of controlling a preheating process for preheating a board in preparation for processing of the board in a soldering machine, the method comprising the steps of:
Advantageously, this means that the heat output from the heating unit to each board can be adjusted, such that the amount and/or distribution of heat transferred to the board is optimised to prevent overheating and board warpage, and to reduce thermal shock when solder is applied to the board.
The preheating process may take place in the soldering machine such that the method is for controlling a preheating process in the soldering machine. Processing of the board in the soldering machine may include the application of flux to the board and/or the application of solder to the board, to solder one or more electrical components onto the board.
The heating unit might be located facing a lower, or bottom, side of the board. The heating unit may be located facing an upper side, or topside, of the board. The heating unit may comprise a topside heating unit and a bottom side heating unit, the topside heating unit facing an upper side, or topside, of the board and the bottom side heating unit facing a lower, or bottom, side of the board.
Obtaining a temperature profile of the board may comprise using a thermal imaging camera to obtain a thermal image or a thermal video of the board. The thermal image or the thermal video of the board may include at least a part of the surface of the board which is heated by the heating unit. The thermal image or the thermal video may be of the surface of the board which is heated by the heating unit. The thermal image or the thermal video of the board may include at least a part of a surface of the board opposite to the surface which the heating unit is configured to heat. The thermal image or the thermal video of the board may be of the surface of the board opposite to the surface which the heating unit is configured to heat.
Advantageously, a thermal image or a thermal video of the board may provide the distribution of heat across the entire surface, thereby allowing hot or cold spots to be identified. The heating unit can then be adjusted to bring hot and cold spots to the correct temperature. This can be used to provide evenly distributed preheating, as well as to minimise overheating, warpage and/or heating damage to the board. Additionally, or alternatively, a thermal image or a thermal video of the board may provide temperature measurements of electrical components. The heating unit can then be adjusted to avoid overheating of the components. Advantageously, a thermal video of the board may allow the preheating process to be monitored over time, which may enable the identification of trends which indicate a requirement for maintenance, repair, and/or replacement of any components of the heating unit.
Obtaining a temperature profile of the board may comprise using one or more pyrometers to measure the temperature at one or more respective positions on the board. The pyrometers may be movable for measuring various locations on the board.
The heating unit may comprise a plurality of bulbs, for example infra-red bulbs. Providing electrical power to the heating unit may comprise providing electrical power to each bulb. Obtaining a profile of heat output from the heating unit may comprise measuring the current drawn by each bulb, or the temperature of each bulb. Adjusting the electrical power provided to the heating unit may comprise adjusting the electrical power provided to at least one bulb of the plurality of bulbs. Adjusting the electrical power provided to the heating unit may comprise adjusting the electrical power provided to each bulb of the plurality of bulbs independently. The plurality of bulbs may face a lower, or bottom, side of the board. The plurality of bulbs may face an upper side, or topside, of the board. The plurality of bulbs may be arranged in a topside heating unit and in a bottom side heating unit, the topside heating unit facing an upper side, or topside, of the board and the bottom side heating unit facing a lower, or bottom, side of the board.
The heating unit may be or comprise a forced convection unit. The forced convection unit may comprise at least one fan and at least one heater. Providing electrical power to the heating unit may comprise providing electrical power to the at least one fan to control a rotation speed of the at least one fan and/or providing electrical power to the at least one heater to control the amount of heat emitted by the at least one heater. Obtaining a profile of the heat output from the heating unit may comprise measuring air flow temperature and/or air flow rate at at least one location in an air flow path from the fan. Adjusting the electrical power provided to the heating unit may comprise adjusting the electrical power provided to the heater and/or to the fan. The forced convection unit may face an upper side, or topside, of the board. The forced convection unit may face a lower, or bottom, side of the board. The heating unit may comprise two forced convection units, one forced convection unit arranged in a topside heating unit and one forced convection unit arranged in a bottom side heating unit, the topside heating unit facing an upper side, or topside, of the board and the bottom side heating unit facing a lower, or bottom, side of the board.
The topside heating unit may comprise the plurality of bulbs and the bottom side heating unit may comprise the forced convection unit. Alternatively, the bottom side heating unit may comprise the plurality of bulbs and the topside heating unit may comprise the forced convection unit. Controlling the rotation speed of the at least one fan may comprise using an encoder to measure the rotation speed. Controlling the rotation speed of the at least one fan may comprise using a frequency inverter to control the rotation speed.
The electrical power provided to the heating unit may be adjusted so as to reduce the range of temperatures in the temperature distribution on the board.
The board may be an electronics board and the process may further comprise obtaining a temperature profile of one or more electrical components which are connected to the board. The process may further comprise adjusting the electrical power provided to the heating unit to maintain the temperature of the or each component to below a respective overheating temperature. Advantageously, this reduces the risk of, or prevents, overheating damage to the or each electrical component. The one or more components may be connected to the board in preparation for soldering to the board, for example after the preheating process.
According to a second aspect of the present invention, there is provided a method of maintaining a heating unit, the heating unit being used in the aforementioned method of controlling a preheating process, the method comprising using a controller to store data relating to:
Advantageously, monitoring data in this way can be used to improve operational efficiencies, to predict lifetimes of components and of equipment, and to detect faults and/or damage early.
According to another aspect of the invention there is provided a preheating apparatus for preheating a board in preparation for processing of the board in a soldering machine, the apparatus comprising:
The heating unit might be located facing a lower, or bottom, side of the board. The heating unit may be located facing an upper side, or topside, of the board. The heating unit may comprise a topside heating unit and a bottom side heating unit, the topside heating unit facing an upper side, or topside, of the board and the bottom side heating unit facing a lower, or bottom, side of the board.
The sensor may comprise a thermal imaging camera. The thermal imaging camera may be configured to obtain a thermal image or a thermal video of the board. The thermal imaging camera may be configured to obtain a thermal image or a thermal video of the board in order for the apparatus to obtain a temperature profile of the board.
The thermal imaging camera may be located such that, in use, the thermal image or the thermal video of the board includes at least a part of a surface of the board opposite to the surface which the heating unit is configured to heat. The thermal imaging camera may be located such that, in use, the thermal image or the thermal video of the board includes at least a part of the surface which is heated by the heating unit, in use.
The sensor may comprise one or more pyrometers to measure the temperature at one or more respective positions on the board. The pyrometers may be movable for measuring various locations on the board.
The heating unit may comprise a plurality of bulbs, for example infra-red bulbs. The power supply circuitry may be configured to provide electrical power to each bulb. The control circuitry may be configured to adjust the electrical power provided to at least one bulb of the plurality of bulbs. The control circuitry may be configured to adjust the electrical power provided to each bulb of the plurality of bulbs independently.
The plurality of bulbs may face a lower, or bottom, side of the board. The plurality of bulbs may face an upper side, or topside, of the board. The plurality of bulbs may be arranged in a topside heating unit and in a bottom side heating unit, the topside heating unit facing an upper side, or topside, of the board and the bottom side heating unit facing a lower, or bottom, side of the board.
The sensor may be configured to obtain a profile of heat output from the heating unit by measuring the current drawn by each bulb, or the temperature of each bulb.
The heating unit may be a forced convection unit comprising at least one fan and at least one heater. The power supply circuitry may be configured to provide electrical power to the at least one fan to control a rotation speed of the at least one fan and/or to provide electrical power to the at least one heater to control the amount of heat emitted by the at least one heater. The control circuitry may be configured to adjust the electrical power provided to the heater and/or to the fan.
The forced convection unit may face an upper side, or topside, of the board The forced convection unit may face a lower, or bottom, side of the board. The heating unit may comprise two forced convection units, one forced convection unit arranged in a topside heating unit and one forced convection unit arranged in a bottom side heating unit, the topside heating unit facing an upper side, or topside, of the board and the bottom side heating unit facing a lower, or bottom, side of the board.
The topside heating unit may comprise the plurality of bulbs and the bottom side heating unit may comprise the forced convection unit. Alternatively, the bottom side heating unit may comprise the plurality of bulbs and the topside heating unit may comprise the forced convection unit.
The sensor may be configured to obtain a profile of heat output from the heating unit by measuring air flow temperature and/or air flow rate at at least one location in an air flow path from the fan.
The power supply circuitry may be configured to control the rotation speed of the at least one fan by using an encoder to measure the rotation speed and a frequency inverter to control the rotation speed.
The control circuitry may be configured to adjust the electrical power provided to the heating unit so as to reduce the range of temperatures in the temperature distribution on the board.
The control circuitry may be configured to store data relating to the electrical power provided to the heating unit. The control circuitry may be configured to store data relating to the profile of heat output from the heating unit and/or the temperature profile of the board. The control circuitry may be configured to store data relating to adjustment made to the electrical power provided to the heating unit. The control circuitry may be configured to monitor the data to identify trends which indicate a requirement for maintenance, repair, and/or replacement of any components of the heating unit.
According to another aspect of the invention there is provided a soldering machine comprising the aforementioned preheating apparatus.
Example embodiment(s) of the invention are illustrated in the accompanying drawings, in which:
The illustrative embodiment relates to a method controlling a preheating process in a soldering machine.
The method is intended for use in a selective soldering machine. However, the method can be used with any soldering machine.
Referring to
The heating unit 1 is configured to heat a surface 21 of the board 2 when the board 2 is in a preheating position. In the preheating position the surface 21 faces the bulbs 11 and is spaced therefrom.
In this example each bulb 11 comprises a temperature sensor (not shown) and/or a current sensor (not shown). Each temperature sensor, if present, is provided proximal to the respective bulb 11 and measures the temperature surrounding the bulb 11. Each current sensor, if present, measures the electrical current drawn by each bulb 11. The temperature sensors and/or current sensors are in communication with a controller. The controller may otherwise be referred to as control circuitry.
In this example the heating unit 1 is connected to an electrical power supply (not shown) via electrical cables 12. The electrical cables 12 thereby provide power supply circuitry. In this example the heating unit 1 and/or power supply are in communication with the controller.
In this example a chamber sensor 3 is provided to measure ambient conditions between the board 2 and the bulbs 11. The ambient conditions may include, for example, temperature and/or humidity. The chamber sensor 3 is in communication with the controller. It will be appreciated that while one chamber sensor 3 is shown in this example, any number of chamber sensors 3 may be provided. It will be appreciated that the chamber sensor 3 is located between the bulbs 11 and the board 2 if the bulbs 11 are facing a bottom side of the board 2. If bulbs 11 face both the topside and the bottom side of the board 2 then a chamber sensor 3 is located between the topside bulbs 11 and the board 2 and between the bottom side bulbs 11 and the board 2.
In use, in this example, electrical power is provided to each bulb 11. Electrical power may be provided to each bulb 11 consecutively, or to any number of bulbs 11 simultaneously. The temperature sensors and/or current sensors measure the output of each bulb 11 to test the functionality of each bulb 11. Functionality is checked by ensuring that the heat emitted by each bulb 11 is as expected by the controller.
Adjustments to the electrical power may be made if the heat output from each bulb is different to an amount that is expected. Temperature and/or current may be measured over the full length of each bulb 11, or only over a part of the length of each bulb 11.
In this example the chamber sensor 3 is also used to determine the ambient conditions between a conveyor (not shown), on which the board 2 is moved to the preheating position, and the heating unit 1. The ambient conditions may be the temperature and/or the humidity. The controller may adjust the power supplied to each bulb 11 to alter the ambient conditions between the conveyor and the heating unit 1.
The board 2 is moved, on the conveyor, to the preheating position. The controller determines an amount of power to be provided to each bulb 11 to emit a predetermined amount of heat, the amount of heat being calculated, or estimated, to heat the surface 21 of the board 2 to a desired temperature. The power supply provides the power to the bulbs 11 to heat the surface 21 of the board 2 according to the calculation.
The temperature sensors and/or current sensors may continue to measure the output of each bulb 11 to obtain a profile of the heat output from the heating unit 1. From this profile an amount and distribution of heat transferred from the heating unit 1 to the board 2 can be calculated. If temperature sensors are used, then the controller obtains the amount of heat emitted from each bulb 11 to determine the profile of heat output. The controller may also calculate the heat transfer to the surface 21 of the board 2, based upon the distance between the heating unit 1 and the board 2. If current sensors are used, then the controller calculates an expected heat emission of each bulb 11 based upon the current drawn by, and the voltage provided to, each bulb, to determine the temperature profile. This expected heat emission may then be used to calculate an expected heat transfer to the surface 21 of the board 2.
In this example the controller also continues to obtain measurements of temperature and/or humidity between the board 2 and the heating unit 1, from the chamber sensor 3. The controller may then adjust the electrical power supplied to each bulb 11 to adjust ambient conditions between the board 2 and the heating unit 1 if these are incorrect. Furthermore, if temperature is measured by the chamber sensor 3 then this may be used to determine the temperature profile of heat output from the heating unit 1. Furthermore, temperatures measured by the chamber sensor 3 may be used to calculate an amount of heat transferred from the heating unit 1 to the board 2. Either or both of a humidity measurement or a temperature measurement from the chamber sensor 3 may be used by the controller in determining a profile of heat output from the heating unit 1, and in calculating the amount and distribution of heat transferred from the heating unit 1 to the surface 21 of the board 2, using measurements of temperature and/or current at each bulb 11.
Once the controller has obtained a profile of heat output from the heating unit 1, the controller adjusts the electrical power provided to the heating unit 1 to adjust the heat output from the heating unit 1 to the board 2. The adjustments reduce the difference between the desired board temperature and the actual board temperature. The adjustments reduce the variations in temperature across the surface 21 of the board 2, to reduce the severity of hot and cold spots. The adjustments may be made for the same board 2 or may be made for a subsequent board 2 in the production line. Alternatively, if the board 2 is a calibration board, then the calibration board is inserted, periodically, into the soldering machine to be heated, to make any adjustments to the power supply to each bulb 11.
In this example the controller also stores data, from the start of the process and/or during operation, pertaining to the electrical power provided to each bulb 11, adjustments made to the electrical power provided to each bulb 11, measurements from the temperature sensor and/or the current sensor at each bulb 11, and/or the obtained profile of the heat output from the heating unit 1, and/or the calculated amount and/or distribution of heat transferred from the heating unit 1 to the board 2, for maintaining the method of preheating a board 2. The controller processes the data such that trends or anomalies in the data, which may be indicative of problems with parts of the soldering machine, of a requirement for maintenance or replacement, or of incorrect operating parameters, may be identified. Identification may be by the controller, by a separate computer, and/or by an operator. The data, or trends in the data, may also provide lifetime predictions for parts of the soldering machine, for example providing a lifetime expectation of each bulb 11.
Further sensors may be present and in communication with the controller. An example of another sensor is a temperature sensor in an exhaust, the exhaust extracting air from the area between the conveyor and the heating unit 1. Another example is a sensor which measures production room conditions. These sensors may be used in calculating the profile of the amount and/or distribution of heat transferred to the board, for example.
Turning now to
In this example the thermal imaging camera 4 is configured to obtain a thermal image, or a thermal video, of the surface 21 of the board 2. The thermal imaging camera 4 may obtain at least one thermal image of all of the surface 21 of the board 2 or may obtain at least one thermal image of only a part of the board 2. The board 2 may be moved to a position where the thermal imaging camera 4 is able to obtain the necessary thermal image/s of the surface 21, for example the thermal imaging camera 4 may obtain thermal image/s after the board 2 has been preheated. The thermal imaging camera 4 may also obtain image/s of the board 2 via one or more mirrors, such that the thermal imaging camera 4 can be positioned away from the heating unit 1. The thermal imaging camera 4 may instead face a bottom side of the board, and obtain a thermal image, or thermal images, of the bottom side, or multiple thermal imaging cameras may be used to capture thermal images of both the topside and bottom side of the board 2. The controller obtains the profile of the amount and/or distribution of heat transferred from the heating unit 1 to the board 2 from the thermal image/s captured by the thermal imaging camera 4. The thermal imaging camera 4 may be used to provide a temperature profile of the board. The temperature profile may be obtained instead of, or alongside, the profile of heat output from the heating unit.
In this example, the board temperature sensor 5 is used to obtain a temperature at a discrete location on the board 2. Whilst one board temperature sensor 5 is shown, it will be appreciated that any number of board temperature sensors 5 may be used. Also, whilst the board sensor 5 is shown, in
The temperature profile of the board 2 may be obtained during the preheating routine for the board 2, and adjustments made to the preheating of the same board 2, or the profile may be obtained after preheating and the adjustments made to subsequent boards 2. Also, as with the previous example, the board 2 may be a calibration board which is inserted, periodically, into the soldering machine to be heated, and adjustments to the electrical power provided to the bulbs 2 made for subsequent electronics boards.
Also, in this example, the profile obtained using the thermal imaging camera 4 and/or data measured using the board temperature sensor 5 may be stored by the controller for use in maintaining the method of preheating a board 2.
It will be appreciated that the method of preheating a board 2 using bulbs 11 may include any combination of temperature sensor on each bulb 11, current sensor on each bulb 11, chamber sensor 3, thermal imaging camera 4, board temperature sensor 5, or any other suitable sensor.
Turning now to
The forced convection heating unit 10 has a fan 101 and at least one heating element 102. The fan 101 and the heating element/s 102 are located inside of a pressure chamber 104 and are connected to an electrical power source (not shown). In this example at least one pressure chamber temperature sensor 105 is provided which measures the air temperature inside of the pressure chamber 104. The pressure chamber temperature sensor 105 is in communication with the controller. The forced convection heating unit faces the board 2, which, as in the previous examples, may be an electronics board or a calibration board. The heating element/s 102 is/are located between the fan 101 and the board 2. When electrical power is provided to the heating element/s 102 the heating element/s emit/s heat, and the fan blows air past the heating element/s. The heated air heats a surface 21 of the board 2 which faces the heating element 1 when the board 2 is in a preheating position. The fan 101 has a frequency inverter (not shown) which controls the rotation speed thereof. The fan 101 has an encoder 103 which is used to measure the rotation speed of the fan 101. The electrical power supply, frequency inverter, and encoder are in communication with the controller.
The fan may have maintenance sensors installed thereupon, the maintenance sensors measuring operating parameters, such as current, vibration, or temperature, of moving parts of the fan. Maintenance sensors are in communication with the controller such that the controller can monitor operating parameters of the fan to identify indicators of damage such as wear.
In this example a plurality of chamber sensors 3′ are provided, which are configured to measure a gas temperature between the conveyor and the heating unit 10. In this example the chamber sensors 3′ measure the temperature proximal to the conveyor. The chamber sensors 3′ may be used to obtain a profile of heat output from the heating unit 10. If a forced convection heating unit 10 is provided which faces the bottom side of the board 2 then chamber sensors 3′ are located between this forced convection heating unit 10 and the board 2.
As in the example described with reference to
As in the previous example, the temperature profile of the board 2 is obtained using the thermal imaging camera 5′ and/or the board temperature sensor 5′. Also, as in the previous example, the profile of heat output from the heating unit 10 is obtained using the chamber sensor 3′ and/or the pressure chamber temperature sensor 105. This obtained profile of heat output may be used to calculate amounts and/or distributions of heat transferred to the board 2. The controller may then adjust the power supplied to either of the heating element/s 102 or the fan 101, or adjust the rotation speed of the fan 101 using the frequency inverter, to adjust the heat output from the heating unit 10 to the board 2, in the same way that power to the bulbs 11 is adjusted in the example described with reference to
As in the previous example, data measured from any of the sensors, the temperature profile of the board 2, the profile of heat output from the heating unit 10, calculated amounts and/or distributions of heat transfer from the heating unit 10 to the board 2, and adjustments may be stored and processed by the controller such that trends or anomalies in the data, which may be indicative of problems with parts of the soldering machine, of a requirement for maintenance or replacement, or of incorrect operating parameters, may be identified.
In any of the aforementioned examples, the obtained profile/s may also be used to monitor the preheating process, and the controller may provide warnings or alarms if the deviation is temperature across the surface 21 of the board 2 is too high, for example greater than 30°. Similarly, any of the stored data may be used by the controller to monitor the preheating process, and provide an alarm or warning is a problem is identified.
Also, in the aforementioned examples, storing and processing data may be used for lifetime predictions of parts of the soldering machine or of products, such that maintenance can be scheduled in an optimal manner. Also stored may be the identification of each board, to which the data relates, so that the data store may be used for quality managing processes, for example, to determine which boards to inspect after processing.
Referring now to
Referring now to
Thermal images such as that of
Referring now to
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Referring now to
Referring now to
The thermal images shown in
The following numbered clauses are provided:
Clause 1. A method of controlling a preheating process in a soldering machine, the method comprising the steps of:
Clause 2. A method according to clause 1, wherein obtaining a temperature profile of the board comprises using a thermal imaging camera to obtain a thermal image of the board.
Clause 3. A method according to either of clause 1 or clause 2, wherein:
Clause 4. A method according to clause 1 or clause 2, wherein:
Clause 5. A method according to clause 4, wherein the rotation speed of the at least one fan comprises using an encoder to measure the rotation speed and a frequency inverter to control the rotation speed.
Clause 6. A method according to any preceding clause, wherein the electrical power provided to the heating unit is adjusted so as to reduce the range of temperatures in the temperature distribution on the board.
Clause 7. A method of maintaining a preheating system, the preheating system comprising a heating unit as used in the method of controlling a preheating process according to any preceding clause, the method comprising using a controller to store data relating to:
| Number | Date | Country | Kind |
|---|---|---|---|
| 21190885.0 | Aug 2021 | EP | regional |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/US2022/039904 | 8/10/2022 | WO |
