ASSEMBLY PROCESS AND STATION

Technical field

This invention relates to an assembly process and an assembly station for electronic cards, in particular a soldering process and a soldering station for assembling electronic cards designed for controlling electric motors.

Background art

In general, a rotating electrical machine of known type, such as, for example, an electric motor illustrated in international patent document WO2013008180 in the name of the same Applicant as this invention, comprises a casing having inside a stator, rigidly constrained to the casing, and a rotor, for example with permanent magnets, rotatably constrained to the casing.

An electronic module or control electronics, connected to the stator and inserted in the casing, comprises, schematically, a printed circuit, a plurality of conductor tracks and electronic power components, both of the SMD {Surface Mount Device) type and the PTH (Pin Through Hole) type, which are positioned on the printed circuit and connected to it and/or to the conductor tracks. More specifically, the PTH type components have respective pins soldered to the conductor tracks.

A cap closes the casing to form a closed container from which connection terminals protrude for the power supply of the control electronics.

For the soldering of the pin through hole components to the electronic card, for example an inductor and capacitors to which explicit reference will be made without thereby limiting the scope of the invention, it is preferable to use high power soldering systems which allow soldering to be performed in a few seconds, for example two, in order to limit the overall time for assembling the motor. There are substantially two high power systems, the laser soldering type and the so-called "micro-flame" soldering of substantially known type. Schematically, these systems increase the temperature of the tracks to the melting temperature of the tin which is dispensed, at the pins of the component, from a corresponding dispensing device.

The power supply tracks, usually made of tin-plated copper, are prepared to receive the capacitors and the inductor; in embodiments the tracks do not actually have holes for the pins of the components but simply soldering zones in which the pins must be positioned.

As mentioned, the soldering systems must increase the temperature of the tracks to the melting temperature of the tin to allow the tin to wet the tracks and perform the soldering of the corresponding component.

In the case, for example, of soldering with a micro-flame, in a soldering cycle, the flame is switched on for a predetermined soldering time.

After a predetermined preheating time with the flame on, the tin is dispensed at a predetermined speed and with a preset quantity by means of a suitable dispensing unit.

After dispensing the tin, the dispenser is switched off and post-heating is performed to allow the tin to melt in the expected manner, after which the flame is moved away or switched off at the end of the soldering time.

Certain variabilities of the process parameters, for example, the "wettability" of the tracks, that is, the capacity of the copper to retain or absorb the tin, or the variation of the coefficient of convection, that is, how the energy passes from the flame to the tracks, determine an increase in the temperature of the tracks over time with a law which does not correspond to that expected.

The soldering temperature required by the process may therefore be reached in different times with respect to those expected and may not be forecast whilst, in general, the soldering time set in the machine is, as mentioned, predetermined. In these circumstances, therefore, the temperature reached by the tracks in the soldering time may not be as desired, for example following the variation of the coefficient of heat exchange between the flame and the copper with consequent defects in the soldering.

More specifically, the defect is determined by the fact that the tin may be dispensed when the tracks are too cold or too hot.

In the first case the tin does not melt completely and does not fill the soldering zone whilst in the second case the tin runs without soldering. In both of the above-mentioned cases, the defective card must either be rejected or re-worked with a consequent increase in the times and costs. In this context, the main aim of this invention is to obviate the above- mentioned drawbacks.

Disclosure of the invention

The aim of this invention is to provide an assembly process and an assembly station which make it possible to reduce the soldering defects. The technical purpose and the aim specified are substantially achieved by an assembly process according to claim 1 and an assembly station according to claim 1 1.

Brief description of drawings

Further features and advantages of this invention are more apparent in the detailed description below, with reference to a preferred, non-limiting embodiment of an assembly station as illustrated in the accompanying drawings, in which:

Figure 1 illustrates a schematic block diagram of an assembly station according to this invention;

Figure 2 illustrates a schematic perspective view, with some parts cut away for greater clarity, of an electronic module at least in part assembled in the station of Figure 1 ; Figure 3 illustrates the electronic module of Figure 2 in a different perspective view, with some parts cut away for greater clarity.

Detailed description of preferred embodiments of the invention

With reference to Figure 1 , the numeral 1 denotes an assembly station according to this invention.

The station 1 is preferably designed for assembling an electronic module or electronic card, illustrated at least partly in Figure 2, labelled 100, for an electric motor not illustrated.

In general, a rotating electrical machine of known type, such as, for example, an electric motor illustrated in international patent document WO2013008180 which is referred to herein in its entirety for the purposes of a complete description, comprises a casing having inside a stator, rigidly constrained to the casing, and a rotor, for example with permanent magnets, rotatably constrained to the casing.

The electronic module 100 is connected to the stator and inserted in the casing whilst a cap closes the casing to form a closed container from which connection terminals protrude for the power supply of the control electronics.

The card 100, substantially known, comprises, schematically, a printed circuit 1 10, a plurality of conductor power tracks 102 and electronic power components, both of the SMD (Surface Mount Device) type and the PTH (Pin Through Hole) type, which are positioned on the printed circuit 1 10 and connected to it and/or to the conductor tracks 102.

The components of the PTH type are suitably connected to the tracks 102 even if corresponding mounting holes are not actually present.

For simplicity of description, reference is made below to a single conductor track 102.

The card 100 in the example illustrated comprises an inductor 103 and a first and a second capacitor 104 and 105. The inductor 103 has respective power supply pins 103a, 103b and the capacitors 104 and 105 have respective power supply pins 104a, 104b, 105a, 105b.

The inductor 103 and the capacitors 104 and 105 are of the PTH type and are soldered to a respective power supply conductor track 102.

The conductor track 102 has soldering zones or areas 106a, 106b, 107a, 107b, 108a, 108b designed to receive, respectively, the pins 103a, 103b, 104a, 104b and 105a, 105b of the components 103, 104, 105.

The assembly station 1 , only described as regards those parts necessary for an understanding of this invention, comprises means for soldering the pins 103a, 103b, 104a, 104b, 105a, 105b to the conductor track 102.

The soldering means comprise means for heating the conductor track 102 and at least one device for dispensing a soldering material, for example tin, on the conductor track 102 in the zones 106a, 106b, 107a, 107b, 108a, 108b, at the power supply pins 103a, 103b, 104a, 104b and 105a, 105b of the electronic components 103, 104, 105 suitably positioned on the track 102.

In the embodiment illustrated by way of example, the assembly station 1 is crossed by a conveyor 2 for feeding the electronic cards 100, schematically shown by a corresponding block, of substantially known type.

The components 103, 104 and 105, not illustrated, are positioned on the cards, in known manner 100; the cards 100 are moved along a feed direction V.

The station 1 comprises a first, a second and a third soldering substation 3, 4, 5, preferably roboticized.

The soldering means comprise means for heating the conductor track and a device for dispensing soldering material in each substation 3, 4, 5.

Preferably, the heating means are of the high-power type and in the preferred embodiment illustrated comprise a "micro-flame" device 6, of substantially known type and not described in more detail, in each substation 3, 4, 5.

A micro-flame device or system generally comprises a generator in which the electrolysis of water occurs, that is, the electrical separation of water into hydrogen and oxygen which are then channelled, collected and mixed with alcohol and sent under pressure to a nozzle where the combustion occurs, triggered by a piezoelectric mechanism.

Each device 6 comprises, in short, a generator 7 connected with a nozzle

8 for dispensing a mixture of gases, in general hydrogen and oxygen, for supporting, in use, a corresponding flame not illustrated.

Preferably, for the uses which are described in more detail below, each device 6 comprises, at the respective nozzle 8, a pressure sensor 9.

Preferably, in the first soldering substation 3, a first flame is provided for soldering a first pin 103a of the inductor 103.

Preferably, in the second soldering substation 4, a second flame is provided for soldering the second pin 103b of the inductor 103.

Preferably, the first pin 103a to be soldered is the highest one between the pins 103a and 103b with reference to figure 2.

Preferably, in the third soldering substation 5, a third flame is provided for soldering the four pins 104a, 104b, 105a, 105b of the capacitors 104 and 105.

The solderings for fixing the pins 103a, 103b, 104a, 104b, 105a, 105b are schematically illustrated and denoted by the label S.

Preferably, the soldering means comprise, in each substation 3, 4, 5 a respective device 10 for dispensing soldering material, for example tin.

According to this invention, the station 1 comprises means for measuring the temperature of the conductor track 102 operating, in particular, during the soldering of the components 103, 104 and 105.

Preferably, the means for measuring the temperature are of the type without contact, that is they are able to measure the temperature of the track 102 without physical contact with it. Preferably, the means for measuring the temperature comprise, for each substation 3, 4, 5, a pyrometer 1 1 of substantially known type and not described in detail.

In short, the pyrometer 1 1 reads the irradiation of the infrared rays from the track 102 to determine the temperature of the source, in this case, the track 102.

The assembly station 1 comprises a computerised command and control unit, schematically illustrated as a block 12, in communication with the soldering means and with the temperature measurement means.

More specifically, the unit 12 is preferably at least in communication with the pyrometers 1 1 and with the devices 10 for dispensing the soldering material.

The unit 12 is designed for operating each device 10, in the respective substation 3, 4, 5, upon reaching a corresponding predetermined first temperature value V1 of the track 102, in particular in the soldering zones 106a, 106b, 107a, 107b, 108a, 108b, suitable for soldering the corresponding component 103, 104, 105.

In practice, with reference to a substation 3, 4, 5, the unit 12 is configured for operating the dispensing device 10 upon reaching the first temperature value V1 of the conductor track 102 measured by the temperature measurement means, in particular by the pyrometer 1 1.

The unit 12 is also configured for controlling each device 6, in particular the respective generator 7, in such a way as to suitably switch on and off the respective soldering flame.

More specifically, the unit 12 is configured for switching off, in each substation, the heating means, in particular the micro-flame devices 6, upon reaching a second predetermined temperature value V2 of the conductor track 102 measured by the temperature measurement means, in particular by the pyrometers 1 1 .

In order to optimise the soldering temperatures, the unit 12 is preferably configured for processing a first temperature value VM1 measured by the temperature measuring means, in particular by the pyrometers 1 1 , at least in a zone 200 for measuring in the conductor track 102 and estimating a corresponding temperature value VS1 of the conductor track 102 at the zones 106a, 106b, 107a, 107b, 108a, 108b, in the substation 3, 4, 5 in question.

In alternative embodiments not illustrated for sake of simplicity, the track 102 comprises a plurality of measurement zones 200 preferably a different one for each single soldering. Conveniently, a respective measuring zone 200 is selected, for each soldering S, which allows the temperature of the corresponding soldering zones 106a, 106b, 107a, 107b, 108a, 108b to be measured, or calculated, in an optimum manner.

For convenience of description, reference is made hereinafter to a single measuring zone 200.

The computerised command and control unit 12 is configured for comparing the estimated temperature value VS1 of the conductor track 102 at the zones 106a, 106b, 107a, 107b, 108a, 108b, in the substation 3, 4, 5 in question, with the above-mentioned first temperature value V1 and actuating the respective dispensing device 10 if the estimated temperature value VS1 of the conductor track 102 reaches the corresponding first temperature value V1 .

To guarantee the switching off of the flame in such a way that the track 102 does not overheat, the computerised command and control unit 12 is configured for processing a second temperature value VM2 measured by the means for measuring the temperature in the measurement zone 200 in the conductor track 102 and estimating a corresponding temperature value VS2 of the conductor track 102 at the zones 106a, 106b, 107a, 107b, 108a, 108b, in the substation 3, 4, 5 in question.

The computerised command and control unit 12 is configured for comparing the estimated temperature value VS2 of the conductor track 102 at the zones 106a, 106b, 107a, 107b, 108a, 108b with the second temperature value V2 and switching off the heating means, in particular the generators 7, if the estimated temperature value VS2 of the conductor track 102 reaches the second temperature value V2.

In general, the trend of the temperatures in the tracks 102 is preferably calibrated, in the unit 12, for correlating the measured value VM1 , VM2 in the measuring zone 200 with the value in the soldering zones 106a, 106b, 107a, 107b, 108a, 108b where the pins 103a, 103b, 104a, 104b, 105a, 105b of the components 103, 104, 105 must be soldered.

The measurement of the temperature in the soldering zone 106a, 106b, 107a, 107b, 108a, 108b is therefore performed indirectly, that is, estimated from the temperature in the respective measuring zone 200.

The flow rate of the mixture of gases to the nozzles 8 of the substations 3, 4, 5 is influenced by the pressure of the gases at the nozzle 8; a pressure which can drop over time.

A reduction in the flow rate causes a loss of power with consequent variability of the heating times of the track 102.

In order to optimise the heating times, the computerised command and control unit 12 is in communication with the above-mentioned pressure sensors 9 to obtain significant information regarding the flow rate of gas to the nozzles 8.

Advantageously, the computerised command and control unit 12 is configured for adjusting the pressure of the mixture of gases at the nozzles 8 as a function of the temperature of the conductor track 102.

In use, the process for assembling the electronic card 100 according to this invention comprises a step of soldering the power supply pins 103a, 103b, 104a, 104b, 105a, 105b on the conductor tracks 102.

The soldering step comprises, in each substation 3, 4, 5, a step of heating the conductor tracks 102 using the heating means, in particular using the micro-flame devices 6.

The soldering step comprises, in each substation 3, 4, 5, a step for dispensing soldering material, using the corresponding dispensing device 10, on the conductor tracks 102, in the areas 106a, 106b, 107a, 107b, 108a, 108b at the power supply pins 103a, 103b, 104a, 104b, 105a, 105b. The process comprises, in each substation 3, 4, 5, a step of monitoring the temperature of the conductor tracks 102 to check the reaching of the first predetermined temperature value V1 of the conductor tracks 102 in the soldering zones 106a, 106b, 107a, 107b, 108a, 108b, which is optimum in particular for the melting the tin, in such a way as to dispense the soldering material when the value 108b is reached in the soldering zones 106a, 106b, 107a, 107b, 108a, 108b.

The tin melts completely filling the soldering zone without running.

To avoid overheating of the solderings S, in particular after dispensing the soldering material, the process comprises monitoring the temperature of the conductor tracks 102 in the soldering zones 106a, 106b, 107a, 107b, 108a, 108b in order to switch off the flame of the devices 6 when the second predetermined temperature value V2 is reached.

As mentioned, the temperature is measured using the pyrometers 1 1 which measure the temperature of the tracks 102 without contact with them.

In a preferred embodiment, the temperature is measured, if possible, directly in the soldering zones or areas 106a, 106b, 107a, 107b, 108a, 108b.

In a preferred embodiment, the temperature is measured on the track 102 on the opposite sides to the soldering areas 106a, 106b, 107a, 107b, 108a, 108b as it substantially correspond to the temperature of the soldering areas 106a, 106b, 107a, 107b, 108a, 108b.

In a preferred embodiment, the temperature is measured by measuring the temperature in the measurement zone 200 which preferably does not coincide with the zones 106a, 106b, 107a, 107b, 108a, 108b for soldering the components 103, 104, 105.

Advantageously, the process comprises a step of processing the temperature value VM1 in the measuring zone 200, or in the measuring zones 200, to obtain an estimate of the temperature value VS1 in the corresponding soldering area 106a, 106b, 107a, 107b, 108a, 108b and switching on the devices 10 for dispensing the tin when the estimated value VS1 corresponds to the preset temperature value V1.

Advantageously, the process comprises a step of processing the temperature value VM2 in the measuring zone 200 to obtain an estimate of the temperature value VS2 in the corresponding soldering area 106a, 106b, 107a, 107b, 108a, 108b and switching off the flame when the estimated value VS2 corresponds to the preset temperature value V2. In other words, the process comprises estimating the temperature of the tracks 102 at the areas 106a, 106b, 107a, 107b, 108a, 108b based on the temperature measurement in the zone 200 or in the respective zones 200 and controlling accordingly the corresponding dispensing device 10 in the respective substation 3, 4, 5.

In a substantially similar manner, the process comprises estimating the temperature of the tracks 102 at the soldering areas 106a, 106b, 107a, 107b, 108a, 108b based on the temperature measurement in the zone 200, preferably close to the respective soldering zone, and switching off accordingly the corresponding micro-flame device 6 in the respective substation 3, 4, 5.

Advantageously, to overcome possible differences in the emission coefficient of the surface of the tracks 102 which could distort the temperature measurement performed with the pyrometer 1 , the process comprises a step of blackening the measuring zone 200.

The zone 200 coloured black offers the same emission coefficient for each card 100 and for each pyrometer 1 1 .

A preferred embodiment of the process according to this invention also comprises monitoring the pressure at the nozzle 8 using the corresponding pressure sensor 9.

As mentioned, the pressure at the nozzle 8 indicates the flow rate of gas and, therefore, the power of the flame so, preferably, the process comprises a step of adjusting the pressure at the nozzle so as to optimise the heating times.

In a preferred embodiment, the process comprises a step of adjusting the power of the flame as a function of the temperature in the soldering zones 106a, 106b, 107a, 107b, 108a, 108b to avoid over-temperatures on the track 102.

In practice, the process controls, by feedback as a function of the temperature of the track, the power of the flame to keep the temperature of the track 102 below a maximum permissible limit.

In a preferred embodiment, the flame has a preset maximum power value until the soldering zones 106a, 106b, 107a, 107b, 108a, 108b reach the temperature expected for the soldering in a relatively short period of time, after which the power of the flame changes to a lower value to maintain the expected temperature, remaining, however, below a preset maximum limit.

Advantageously, the reading or the estimation of the temperature in the soldering zones forms a control for the dispensing of the soldering material and the time the flame is switched on, which are no longer preset but are a function of temperature of the tracks 102.

In practice, the pre-heating time for heating the tracks 102 to the temperature necessary for melting the tin and the pre-heating time to allow the tin to melt in the expected manner and prevent the tracks from overheating excessively is monitored.

The power of the flame is also preferably adjusted to prevent the track exceeding a predetermined maximum temperature value, guaranteeing at the same time the reaching of the soldering temperature in a short time. Advantageously, the use of the pyrometer also allows the temperature reached by the tracks due to the previous soldering to be taken into account, adjusting as a consequence the times for switching on the flame. The definition of a measuring zone or pyrometer measuring point avoids the possibility of differences between the surfaces of different conductor tracks so as to overcome possible measurement errors.