DE102008050328A1 - Determining a solder volume contained in a solder bath, comprises performing a reference measurement, filling the solder bath with a known initial liquid reference solder volume, and cooling the solder under reproducible given conditions - Google Patents

Abstract

The method for determining a solder volume (V) (3) contained in a solder bath (1), comprises performing a reference measurement, filling the solder bath with a known initial liquid reference solder volume (V ref), cooling the solder under reproducible given conditions, measuring a reference flow TR(t), which represents a temporal flow of a temperature (T(t)) of the solder during the cooling process in a given temperature range including a melting temperature (T s) of the solder, and determining a reference parameter (KR) of the reference flow dependent of the solder volume. The method for determining a solder volume (V) (3) contained in a solder bath (1), comprises performing a reference measurement, filling the solder bath with a known initial liquid reference solder volume (V ref), cooling the solder under reproducible given conditions, measuring a reference flow TR(t), which represents a temporal flow of a temperature (T(t)) of the solder during the cooling process in a given temperature range including a melting temperature (T s) of the solder, determining a reference parameter (KR) of the reference flow dependent of the solder volume and then storing together with the reference solder volume, subjecting a solder operation, subsequently cooling the initial liquid solder under the given conditions used in the reference measurement for determining the actual solder volume present in the solder volume optionally changed based on the solder operation, measuring the temporal flow of the temperature (T(t)) of the solder during the cooling process in the given temperature range, determining a measurement parameter (K(V)) depending of the actual solder volume and corresponding to the reference parameter based on the temporal flow of the measured temperature, and approximately determining the solder volume to be determined based on the measurement parameter and the reference parameter. The reference solder volume corresponds to a volume minimum level (V min) given for the solder operation. The solder volume to be determined based on the measurement parameter and the reference parameter exceeds or falls below the actual volume. A first reference measurement is executed, in which the reference solder volume corresponds to the volume minimum level given for the solder operation. A second reference measurement is executed, in which the reference solder volume corresponds to a volume maximum level given for the solder operation. The solder volume to be determined is quantitatively determined based on the measurement parameter and the reference parameter using linear interpolation. The measurement parameters and the associated reference parameters are times, which require to cool the solder at a given reference temperature lying below the melting temperature of the solder during the cooling process, in which the temporal flow of the solder is minimum during the cooling process and at which a plateau-like passing section of the respective temperature flow ends. The measurement parameters and the associated reference parameters are time periods, during which the respective temperature flow is plateau-like. Independent claims are included for: (1) a solder plant for determining a solder volume contained in a solder bath; and (2) a method for operating a solder plant.

Description

The The invention relates to a method for determining a in a Lotbad a soldering system contained Lotvolumens and a soldering system for the execution of this Process.

Soldering is a thermal process for the cohesive joining of materials, the esp. is widely used in electrical engineering and electronics. In industrial manufacturing processes are z. B. electronic components Soldered on printed circuit boards. Known soldering methods are wave soldering, and selective soldering.

At the wave soldering Be electronic assemblies such. As printed circuit boards, with electronic Components assembled and over drove a solder wave. The solder wave is generated by that liquid solder ready in a solder bath through a gap is pumped. Selective soldering is a variant of the wave soldering, at the only defined parts of the assembly with the solder in contact come. This happens, for example, in that in a solder bath bereitstehendes liquid Lot through small nozzles is pumped whose size is adapted to the dimensions of the surfaces to be soldered are.

In both cases the solder bath will start with one to the size of the Lotbades filled custom predetermined volume of solder, so that in the solder bath a predetermined for the solderings optimal level is present. The provision of the optimal solder volume in the solder bath and the observance of a possible constant optimum level is crucial for the quality the soldering. Esp. hangs the precise one Function of the soldering pumps decisively present in the solder bath level of the lot.

in the Operation, however, is continuously consuming solder from the solder bath, which to a change the level leads. If the bath level drops below a for the soldering operation permissible Minimum level, so Lot must be refilled.

to Measurement of the level in the soldering bath is becoming common today a resistance measurement used in the one of the level in the solder bath more dependent Resistance between two electrodes introduced into the solder bath is measured. However, this measurement is largely due to contamination, by dross on the solder surface as well as by dross avoiding oil covers impaired on the solder bath. Deposits form on the electrodes over time the level measurement very much inaccurate or even impossible becomes.

The Measurement of the bath volume is esp. For solder baths with very low solder volume, Especially with bath volume of less than 10 liters of solder, very problematic since there are already minor soiling or deposits on the Electrodes can lead to significant measurement errors.

It It is an object of the invention to provide a method that a reliable Determining a solder volume located in a solder bath of a soldering system allows.

• – vorab mindestens eine Referenzmessung ausgeführt wird, bei der
• – das Lotbad mit einem bekannten zunächst flüssigen Referenzlotvolumen befüllt ist,
• – das Lot unter reproduzierbaren vorgegebenen Bedingungen abkühlt,
• – ein Referenzverlauf gemessen wird, der einen zeitlichen Verlauf einer Temperatur des Lotes während des Abkühlvorganges in einem vorgegebenen eine Schmelztemperatur des Lots einschließenden Temperaturbereich wiedergibt,
• – eine vom Lotvolumen abhängige Referenzkenngröße des Referenzverlaufs bestimmt wird und zusammen mit dem Referenzlotvolumen abgespeichert wird,
• – der Lötbetrieb aufgenommen wird, und nachfolgend
• – zur Bestimmung des aktuell im Lotbad befindlichen aufgrund des Lotbetriebes gegebenenfalls veränderten Lotvolumens jeweils das zunächst flüssige Lot unter den in den Referenzmessungen verwendeten vorgegebenen Bedingungen abgekühlt wird,
• – ein zeitlicher Verlauf einer Temperatur dieses Lotes während des Abkühlvorganges in dem vorgegebenen Temperaturbereich gemessen wird,
• – anhand des zeitlichen Verlaufs der gemessenen Temperatur eine den Referenzkenngrößen entsprechende vom aktuellen Lotvolumen abhängige Messkenngröße bestimmt wird, und
• – das zu bestimmende Lotvolumen jeweils anhand der Messkenngröße und der zugehörigen Referenzkenngrößen näherungsweise bestimmt wird.

For this purpose, the invention consists in a method for determining a solder volume contained in a solder bath, in which

• - at least one reference measurement is carried out in advance, in which
• - The solder bath is filled with a known initially liquid reference solder volume,
• Cooling the solder under reproducible predetermined conditions,
• A reference curve is measured, which represents a time profile of a temperature of the solder during the cooling process in a predetermined temperature range including a melting temperature of the solder,
• A reference variable of the reference curve which is dependent on the solder volume is determined and stored together with the reference solder volume,
• - The soldering operation is recorded, and below
• In order to determine the volume of solder currently present in the solder bath as a result of the soldering operation, in each case the initially liquid solder is cooled below the predetermined conditions used in the reference measurements,
• A time course of a temperature of this solder is measured during the cooling process in the predetermined temperature range,
• - Based on the time course of the measured temperature corresponding to the reference characteristics of the current Lotvolumen measured characteristic is determined, and
• - The volume of solder to be determined in each case on the basis of the measured characteristic and the associated reference Characteristics is determined approximately.

According to one In the first embodiment, a single reference measurement is carried out at the reference solder volume for the the soldering operation optimally suitable nominal volume corresponds, and it is based on the measurement characteristic and the Reference characteristic determined, whether the volume to be determined exceeds or falls below the nominal volume.

• – eine erste Referenzmessung ausgeführt, bei der das Referenzlotvolumen einer für den Lötbetrieb vorgegebenen Volumenuntergrenze entspricht,
• – eine zweite Referenzmessung ausgeführt, bei der das Referenzlotvolumen einer für den Lötbetrieb vorgegebenen Volumenobergrenze entspricht, und
• – es wird das zu bestimmende Lotvolumen anhand der Messkenngröße und der beiden Referenzkenngrößen mittels Interpolation quantitativ bestimmt.

According to a second embodiment

• A first reference measurement is carried out, in which the reference solder volume corresponds to a volume lower limit specified for the soldering operation,
• A second reference measurement is carried out, in which the reference solder volume corresponds to a volume upper limit specified for the soldering operation, and
• - The volume of solder to be determined is quantitatively determined on the basis of the measured characteristic and the two reference parameters by means of interpolation.

According to one first variant of the invention, the measurement parameters and the associated Reference characteristics the Times needed by the particular solder during the cooling process to a predetermined below the melting temperature of the solder lying Cool reference temperature.

According to one second variant, the measurement parameters and the associated reference parameters are the Times when the respective temperature course of the solder during the cooling process has a minimum.

According to one third variant, the measurement parameters and the associated reference parameters are the times to which a plateau-shaped extending portion of the respective temperature profile ends.

According to one fourth variant, the measurement parameters and the associated reference parameters are the Durations while where the respective temperature profile is plateau-shaped.

• – einem Lotbad zur Aufnahme von Lot,
• – einem Temperatursensor, der dazu dient, die Temperatur des Lots während des Abkühlvorganges in dem die Schmelztemperatur des Lots einschließenden Temperaturbereich zu messen, und
• – einer an den Temperatursensor angeschlossenen Auswerteeinheit zur Aufnahme der Referenzverläufe und der zur Bestimmung der Lotvolumina gemessenen Temperaturverläufe, zur Bestimmung der Referenzkenngrößen und der Messkenngrößen, und zur Bestimmung der zu bestimmenden Lotvolumina.

Furthermore, the invention comprises a soldering machine for carrying out the method according to the invention, with

• A solder bath for holding solder,
• A temperature sensor which serves to measure the temperature of the solder during the cooling process in the temperature range including the melting temperature of the solder, and
• - An evaluation unit connected to the temperature sensor for recording the reference curves and the measured for determining the Lotvolumina temperature curves, for determining the reference characteristics and the measurement parameters, and for determining the solder volumes to be determined.

Further the invention comprises a method for operating the soldering system according to the invention, in which determined by a utilization of the soldering system breaks be, and in the operating breaks the currently in Lotbad Lot volume according to the inventive method is determined.

• – eine Anzeige auf, die dazu dient, die Ergebnisse der mit der Anlage ausgeführten Volumenbestimmungen anzuzeigen, und/oder
• – sie weist eine an die Auswerteeinheit angebundene Schnittstelle auf, über die Ergebnisse der Volumenbestimmungen, gemessene Temperaturverläufe, Referenzverläufe, Messkenngrößen und/oder Referenzkenngrößen zur weiteren Anzeige, Nutzung oder Verarbeitung zugänglich sind.

According to one embodiment, the soldering system

• - an indicator used to display the results of the volume determinations carried out with the system, and / or
• It has an interface connected to the evaluation unit, via which results of the volume determinations, measured temperature profiles, reference curves, measurement characteristics and / or reference parameters for further display, use or processing are accessible.

One Advantage of the invention is that the inventive method insensitive to Impurities and deposits on the Lötbadoberfläche is, and that, esp. also with solder baths small lot volume provides very accurate and reliable results.

The Invention and further advantages will now be described with reference to the figures of Drawing in which an embodiment is shown, closer explains; like parts are provided in the figures with the same reference numerals.

1 schematically shows a soldering machine for carrying out the method according to the invention; and

2 shows three with the soldering of 1 recorded reference curves.

In 1 schematically shows a soldering machine for carrying out the method according to the invention. The soldering system is a wave soldering or Selektivlötanlage and has a Lotbad 1 on, in which in the soldering liquid solder 3 located. The liquid lot 3 is in the soldering operation by a from the solder bath 1 outstanding soldering 5 pumped out. The classic wave soldering is the soldering guide 5 For example, a wide gap, the selective soldering example, a nozzle. This results over the liquid level of the solder 3 in the solder bath 1 a solder wave 7 over which the assemblies to be soldered 9 by means of an assembly guide 11 be guided. The module shown as an example 9 includes a printed circuit board 13 and an electronic component 15 , The assembly guide 11 is in 1 indicated only in the form of a dashed line.

According to the soldering system has a device for determining the Lotbad 1 containing Lotvolumens. This includes a temperature sensor 17 which serves to raise the temperature of the solder 3 during a reproducible cooling process carried out under predetermined conditions in a melting temperature T _{S of} the solder 3 including temperature range. At the melting temperature T _S takes place a phase transition of the solder 3 instead, in which the first liquid solder 3 gradually freezes.

In the in 1 illustrated embodiment, the temperature sensor 17 arranged such that it is the temperature T of the solder 3 in the solder bath 1 as a function of the duration t of the cooling process. For example, one above the solder bath is suitable for this purpose 1 mounted infrared sensor. This variant is in 1 shown. Alternatively, the temperature measurement may also be by means of an outer wall of the solder bath 1 into the solder bath 1 introduced temperature sensor 19 respectively. This variant is in 1 also shown.

Furthermore, the device for determining the solder volume comprises a to the temperature sensor 17 respectively. 19 connected evaluation unit 21 based on the measured values of the temperature sensor 17 respectively. 19 in the manner explained in detail below determines the volume of solder to be determined. The lotbad 1 contained solder volume determines the fill level of the solder 3 in the solder bath 1 and thus indicates the bath level. The level or the level of the bath is crucial for the precise generation of the solder wave 7 , If the level is too low, too little solder will be produced 3 from the soldering 5 pumped out, he is too high may be too much solder 3 from the soldering 5 pumped out. During soldering, however, solder is continuously consumed, so that the solder volume and thus the level changes.

With the method according to the invention, it is possible that in the solder bath 1 To determine located solder volume, and perform on the basis of the solder volume precise monitoring of the bath level. The determination of the solder volume allows a demand-dependent addition of solder 3 in the respectively required for the soldering optimum amount.

The inventive method is based on the physical fact that the time course of the temperature T (t) of the Lotbad 1 contained lots 3 during a given conditions in a melting temperature T _{S of} the solder 3 Temperature range included reproducible cooling process sensitive to the volume of the solder bath 1 contained lots 3 depends. Even minor changes in the solder volume lead to a significantly changed temperature behavior. According to the invention, the time profile of the temperature T (t) is measured, a measured characteristic variable K (V) of the measured curve T (t) dependent on the current volume V is determined and based on the measured characteristic K (V) and at least one reference volume V _ref in the same way derived reference characteristic KR the current volume V determines.

To the currently in the solder bath 1 At least one reference measurement is carried out with the soldering system in advance, in which the solder bath 1 with a known solder volume V _{ref of} the solder 3 is filled.

If only one reference measurement is carried out, then the known solder volume V _{ref is} preferably a nominal volume V _{soll which is} optimally suitable for the soldering operation. On the basis of this single reference measurement can be determined very accurately and reliably, whether the volume of solder present in the determination exceeds or falls below the target volume V _soll .

Preferably, at least two reference measurements are performed. In particular, a first reference measurement is suitable for this, in which the known solder volume V _ref corresponds to a volume lower limit V _min specified for the soldering operation, and a second reference measurement in which the known solder volume V _ref corresponds to a volume upper limit V _max specified for the soldering operation. To increase the measurement accuracy with which the solder volume can subsequently be determined, it is of course also possible to carry out further reference measurements. Already based on two reference measurements provides the explained in detail below fiction however, already a very reliable quantitative determination of the solder volume V.

In the reference measurement, this is done in the solder bath 1 located initially liquid known solder volume V _ref under predetermined conditions in a reproducible manner cools. The starting point of the cooling process is preferably the solder bath heated to the soldering temperature T _L to be set anyway for the soldering operation 1 in which the liquid solder 3 the soldering temperature T _L has. For a cooling process to be carried out reproducibly under predetermined conditions, it is now sufficient for the starting time t _{0 of} the cooling process in 1 not shown heating the Lotbads 1 turn off and the lot 3 in the solder bath 1 to cool down. Starting with the starting time t ₀ is now via the temperature sensor 17 . 19 continuously a time course of a temperature T (t) of the solder 3 measured during the cooling process. The measurement is made over a predetermined melting temperature T _{S of} the solder 3 enclosing temperature range. At the melting temperature T _S, there is a phase transition of the solder 3 instead, in which the lot 3 stiffens. The time course of the measured with the known solder volume V _ref temperature T (t) is as a reference curve TR (t) of the evaluation 21 recorded and there, for example, in a memory 23 stored.

2 shows the reference curves TR _min (t), TR _soll (t), TR _max (t) of the three above-mentioned reference measurements. For the first reference measurement was the solder bath 1 filled with the predetermined volume for the soldering operation V _min . For the second reference measurement was the solder bath 1 filled with the optimum for soldering operation target volume V _soll . For the third reference measurement was the solder bath 1 filled with the volume upper limit V _max given for the soldering operation.

The three reference curves TR _min (t), TR _soll (t), TR _max (t) show the same fundamental characteristic characteristic of the phase transition. At the beginning of the measurement is the entire lot 3 liquid and has the soldering temperature T _L on. At the starting time point in time t _{0 of} the reference measurements, the heating is switched off. Here is the lot 3 exposed to the ambient room temperature and is left to itself, ie it is neither heated from the outside nor actively cooled. The lot 3 initially cools down continuously. Upon reaching the melting temperature T _S starts the phase transition. The lot 3 it cools briefly below the melting temperature T _{S of} the solder 3 From and rises through the energy released by the incipient phase transition energy back to the melting temperature T _S. All three reference curves TR _min (t), TR _soll (t), TR _max (t) have a minimum in this range. The time t ^M at which the respective minimum occurs is dependent on that in the respective reference measurement in the solder bath 1 existing reference solder volume V _ref and thus forms a dependent of the solder volume characteristic K ^{M of} the time course T (t). The larger the volume, the later the minimum occurs under otherwise identical cooling conditions. The minimum of the first reference curve TR _min (t) thus occurs at an earlier time t ^M _min , as a minimum of the second reference curve TR _soll (t), which _is present only at time t ^M _soll . The minimum of the third reference curve TR _max (t) occurs at an even later time t ^M _max , which is later than the time t ^M _soll , at which the minimum of the second reference curve TR _soll (t) occurs. Thus, the times t ^M _min , t ^M _{soll and} t ^M _{max form} reference parameters KR ^M _min = t ^M _min , KR ^M _soll = t ^M _soll and KR ^M _max = t ^M _max , which in the context of the respective reference measurement based on the respective reference curve TR _min (t), TR _soll (t), TR _max (t) in the evaluation unit 21 detected and in memory 23 together with the associated reference solder volume V _min , V _soll , V _max can be stored.

During the period of the phase transition, the temperature T (t) of the solder remains 3 almost constant. As a result, the time profile of the temperature T (t) in this region has a distinct plateau-shaped section in which the temperature T (t) practically does not change as a function of the time t until the phase transition ends. The duration Δt of this plateau-shaped section depends on that in the solder bath 1 located Lotvolumen and thus forms another dependent on the solder volume parameter K ^.DELTA.t the time course T (t). The more solder is contained in the solder bath, the longer it takes under otherwise identical cooling conditions until the entire quantity of solder has solidified. Accordingly, the duration Δt _{min of} the plateau-shaped portion of the first reference curve TR _min (t) is less than the duration Δt _{soll of} the plateau-shaped portion of the second reference curve TR _soll (t), which in turn is less than the duration Δt _{max of} the plateau-shaped portion of the third Reference curve TR _max (t). Thus, the duration .DELTA.t _min , the duration .DELTA.t _soll and the duration .DELTA.t _max reference characteristics KR ^.DELTA.t _Min = .DELTA.t _min , KR ^.DELTA.t soll = .DELTA.t _soll and KR ^.DELTA.t _max = .DELTA.t _max , which within the respective reference measurements in the evaluation 21 determined and stored together with the associated reference solder volume V _min , V _soll , V _max .

The point in time t ^p to which the plateau-shaped section ends forms a further parameter K ^p dependent on the volume of solder. The plateau-shaped portion of the first reference curve TR _min (t) ends at an earlier time t ^p _min than the plateau-shaped portion of the second reference curve TR _soll (t), which ends only at the time t ^p _soll . The plateau-shaped section of the third reference curve TR _max (t) ends at an even later point in time t ^p _max , which lies later than the time t ^p _soll at which the plateau-shaped section of the second reference rence curve TR _{should end} (t). Thus form the points in time t ^p _min, t _to ^p, and t ^p _max more reference parameters KR ^p _min = t ^p _min, KR ^p _soll = t _to ^p and KR ^p _max = t ^p _max in the framework of the respective reference measurement in the evaluation unit 21 determined and stored together with the associated reference solder volume V _min , V _soll , V _max .

Following the respective plateau-shaped section, ie after completion of the phase transition, the temperature in all three reference curves TR _min (t), TR _soll (t), TR _max (t) decreases again continuously. Also in this area, the temporal course of the measured temperature gives information about the associated solder bath 1 located solder volume. The larger the solder volume, the later the solder temperature reaches a predetermined below the melting temperature T _L reference temperature T _B under the same cooling conditions. The time t ^B to which the lot 3 the predetermined reference temperature T _B , which is below the melting temperature T _S , thus forms a further parameter K ^B dependent on the volume of solder. How out 2 the first reference curve TR _min (t) clearly falls short of the reference temperature T _B at the time t ^B _min , while the second reference curve TR _soll (t) reaches the reference temperature T _B only at the later time t ^B _soll . Thereafter, the third reference profile TR _max (t) falls below the reference temperature T _B at even later time t ^B _max . Thus, the times t ^B _min , t ^B _soll and t ^B _{max form} reference parameters KR ^B _min = t ^B _min , KR ^B _soll = t ^B _soll and KR ^B _max = t ^B _max , which are within the framework of the respective reference measurements in the evaluation unit 21 determined and stored together with the associated reference solder volume V _min , V _soll , V _max .

in the Following the reference measurements, the soldering operation is started. there Lot is consumed and the solder volume in the solder bath changes.

The changed due to the soldering operation and thus now unknown in the solder bath 1 Lot volume V can now be determined at any time by the currently Lotbad 1 located initially liquid soldered to the soldering temperature T _L 3 is cooled below the predetermined conditions used in the reference measurement, and the time course of the temperature T (t) of this solder ( 3 ) is measured during the cooling process in the predetermined temperature range. Subsequently, on the basis of this measured temperature profile T (t), one of the parameters K ^M , K ^Δt , K ^p , K ^B already described above in connection with the reference curves TR _min (t), TR _soll (t) and TR _max (t) is determined as derived from the volume V to be determined characteristic variable K ^M (V), K ^Δt (V), K ^p (V), K ^B (V) derived and to be determined solder volume V on the basis of this measurement parameter K ^M (V), K ^Δt ( V), K ^p (V), K ^B (V) and the respective reference characteristic KR ^M _min , KR ^M _soll , KR ^M _max , K ^Δt _min , K ^Δt _soll , K ^Δt _max , K ^p _min , K ^p _soll , K ^p _max , or K ^B _min , K ^B _soll , K ^B _{max are} approximately determined.

If only a single reference measurement _was carried out with the nominal volume V _soll , the determination of the unknown volume V is effected by a simple comparison of the measurement parameter K ^M (V), K ^Δt (V), K ^p (V), and / or K ^B ( V) with the associated reference characteristic KR ^M _soll , K ^Δt _soll , K ^p _soll , and K ^B _soll . And it is noted with the procedures below for the respective parameters K relationships whether the unknown volume V the target volume V _to above or below. K M (V) <KR M should → V <V should K .delta.t (V) <K .delta.t should → V <V should K p (V) <K p should → V <V should K B (V) <K B should· → V <V should K M (V)> KR M should → V <V should K .delta.t (V)> K .delta.t should → V <V should K p (V)> K p should → V <V should K B (V)> K B should· → V <V should K M (V) = KR M should → V = V should K .delta.t (V) = K .delta.t should → V = V should K p (V) = K p should → V = V should K B (V) = K B should· → V = V should

In addition, the difference may K ^M (V) - KR ^M _soll, K ^.DELTA.t (V) - K ^.DELTA.t _is to K ^p (V) - K ^p _to or K ^B (V) - K ^B _to between the respective measurement parameter K ^M (V), K ^Δt (V), K ^p (V) or K ^B (V) and the associated reference characteristic KR ^M _soll , K ^Δt _soll , K ^p _soll , K ^B _soll , be determined and as a measure of the size of possibly existing volume difference between the volume to be determined V and the target volume V soll _be used.

wenn als Kenngröße der Zeitpunkt t^M verwendet wird, an dem die Temperaturverläufe T(t) das Minimum aufweisen,

wenn als Kenngröße die Dauer Δt des plateauförmigen Abschnitts der Temperaturverläufe T(t) verwendet wird,

wenn als Kenngröße der Zeitpunkt t^p verwendet wird, an dem die plateauförmigen Abschnitt der Temperaturverläufe T(t) enden, und

wenn als Kenngröße der Zeitpunkt verwendet wird, an dem die Temperaturverläufe die vorgegebene Bezugstemperatur T_B unterschreiten., Liegen mehr als zwei Referenzmessungen vor, können natürlich Interpolationsverfahren entsprechend höherer Ordnung eingesetzt werden.If two reference measurements, in particular at the volume lower limit V _min given for the soldering operation and the upper volume limit V _max specified for the soldering operation, have been carried out, the unknown volume V is quantitatively determined. The respective characteristic quantities K are linearly dependent on the volume to a first approximation. The volume V to be determined is determined by means of one of the measurement parameters K ^M (V), K ^Δt (V), K ^p (V), or K ^B (V) and the associated reference parameter pairs KR ^M _min and KR ^M _max , K ^Δt _min and K ^Δt _max , K ^p _min and K ^p _max , and K ^B _min and K ^B _max performed linear interpolation determined quantitatively. This results in the volume V to be determined, depending on the choice of the characteristic K:

if the time t ^{M is} used as the parameter at which the temperature profiles T (t) have the minimum,

if the characteristic Δt of the plateau-shaped section of the temperature curves T (t) is used as the parameter,

if the time t ^p at which the plateau-shaped section of the temperature profiles T (t) ends is used as the parameter, and

if the point in time at which the temperature profiles fall below the predetermined reference temperature T _B is used as the parameter. If there are more than two reference measurements, of course, interpolation methods corresponding to a higher order can be used.

Basically, it's enough the multitude of volume-dependent Characteristics K a single to select and the determination of the volume V on the basis of the corresponding to determine the measured characteristic derived from the temperature profile and the associated reference parameters.

For each determination of solder volume V following the reference measurements, the soldering operation is performed for the duration of the cooling process and the solder is reheated 3 interrupted to the soldering temperature T _L. The duration of the interruption depends, among other things, on the size of the solder bath 1 , ie from the solder volume, from. The duration of the interruption is thus very small, especially in the case of small solder baths, especially in the case of solder baths with a filling volume of less than 10 liters, in which the initially mentioned form of level measurement is particularly inaccurate. An interruption of the soldering operation of 20-30 minutes is quite sufficient to the current in the solder bath 1 to determine the volume V to be located.

During operation of the soldering system, therefore, it is preferable to proceed in such a way that, based on the utilization of the soldering system in the soldering operation, operating pauses are determined in which, due to operational reasons, no printed circuit boards to be soldered are connected via the solder bath 1 be guided, and in these utilization-related already existing operating pauses currently located in the solder bath solder volume is determined according to the inventive method. This offers the advantage that the determination method according to the invention does not cause any delays. This process is preferably performed fully automated based on utilization data of the system, so that the system, for example, based on corresponding manufacturing data, for Be Determination of the volume V sufficiently long pauses and automatically switches to a stand-by mode by the method of the invention is carried out fully automatically.

In systems with very high utilization, the time t ^M at which the temperature profiles T (t) have the minimum is preferably used as the characteristic variable K ^M for the determination of the volume V. This has the advantage that the cooling process can be stopped after reaching the minimum, and the solder bath 1 can be heated again to the soldering temperature T _L. The for the solidification and the subsequent melting of the solder 3 the time required does not have to be fully available in this case.

Preferably, the soldering system has an additional display, which indicates the result of the volume determination. This can, for example, one to the evaluation 21 connected display 25 be, which includes a red and a green LED. This is controlled such that the green LED is lit as long as certain volume according to the invention larger than the target volume V is _intended. If the setpoint volume V setpoint _is undershot, the evaluation unit switches 21 the red LED turns on and the green one turns off. In the quantitative determination of the volume V is preferably an indication 27 used, for example, on the last volume V and / or its deviation from the target volume .DELTA.V = V - V _soll is displayed locally. In addition, the soldering system preferably exhausts via a to the evaluation unit 21 connected interface 29 are accessible via the results of the volume determinations, measured temperature profiles T (t), reference curves TR (t), parameters K and / or reference parameters KR for further display, use or processing.

1

solder bath

3

solder

5

solder guide

7

solder wave

9

to soldering module

11

assembly guide

13

circuit board

15

electronic component

17

temperature sensor

19

temperature sensor

21

evaluation

23

Storage

25

display

27

display

29

interface

Claims (10)

Method for determining a solution in a solder bath ( 1 ) Lot volume (V), in which - at least one reference measurement is carried out in advance, in which - the solder bath ( 1 ) is filled with a known initially liquid reference solder volume (V _ref ), - the solder ( 3 ) is cooled under reproducible predetermined conditions, - a reference curve TR (t) is measured, which shows a temporal course of a temperature (T (t)) of the solder ( 3 ) during the cooling process in a predetermined one melting temperature (T _S ) of the solder ( 3 ) includes a temperature range dependent on the solder volume (V) reference characteristic (KR) of the reference curve (TR (t))) and is stored together with the reference solder volume (V _ref ), - the soldering operation is recorded, and subsequently - Determination of the currently in the solder bath ( 1 ) located on the basis of the Lotbetriebes possibly changed Lotvolumens (V) in each case the first liquid solder ( 3 ) is cooled below the predetermined conditions used in the reference measurements, - a time course of a temperature (T (t)) of this solder ( 3 ) is measured during the cooling process in the predetermined temperature range, - based on the time course (T (t)) of the measured temperature a the reference characteristics (KR) corresponding to the actual solder volume (V) dependent measurement characteristic (K (V)) is determined, and - The volume of solder to be determined (V) in each case on the basis of the measured characteristic (K (V)) and the Referenzkenngrö ßen (KR) is approximated. Method according to Claim 1, in which a single reference measurement is carried out, in which the reference solder volume (V _ref ) corresponds to the setpoint volume (V _soll ) which is optimally suitable for the soldering operation, and - based on the measured characteristic variable (K (V)) and the reference parameter ( KR _soll ), it is determined whether the volume to be determined (V) exceeds or falls below the nominal volume (V _soll ). Method according to claim 1, in which - a first reference measurement is carried out, in which the reference solder volume (V _ref ) corresponds to a volume lower limit (V _min ) specified for the soldering operation, - a second reference measurement is carried out, in which the reference solder volume (V _ref ) is one for the soldering operation predetermined volume upper limit (V _max ) corresponds, and - the volume of solder to be determined (V) on the basis of the measured characteristic (K (V)) and the two reference parameters (KR _min , KR _max ) is determined quantitatively by means of linear interpolation. The method of claim 1, wherein the measurement characteristics (K ^B (V)) and the associated reference characteristics (KR ^B _min , KR ^B _should , KR ^B _max ) the times (t ^B , t ^B _min , t ^B _soll , t ^B _max ) are the Lot ( 3 ) during the cooling process to a predetermined below the melting temperature (T _S ) of the solder ( 3 ) lying reference temperature (T _B ) to cool. Method according to Claim 1, in which the measurement characteristics (K ^M (V)) and the associated reference characteristics (KR ^M _min , KR ^M _soll , KR ^M _max ) determine the times (t ^M , t ^M _min , t ^M _soll , t ^M _max ), in which the respective temperature profile (T (t), TR _min (t), TR _soll (t), TR _max (t)) of the solder ( 3 ) has a minimum during the cooling process. The method of claim 1, wherein the measurement characteristics (K ^p (V)) and the associated reference parameters (KR ^p _min , KR ^p _soll , KR ^p _max ) the times (t ^p , t ^p _min , t ^p _soll , t ^p _max ), to which a plateau-shaped extending portion of the respective temperature profile (T (t), TR _min (t), TR _soll (t), TR _max (t)) ends. Method according to Claim 1, in which the measurement parameters (K ^Δt (V)) and the associated reference parameters (KR ^Δt _{min ,} KR ^Δt _{soll ,} KR ^Δt _{max ) are} the time durations (Δt, Δt _min , Δt _soll , Δt _max ) during where the respective temperature profile (T (t), TR _min (t), TR _soll (t), TR _max (t)) is plateau-shaped. Soldering system for carrying out the method according to one of the preceding claims, comprising - a solder bath ( 1 ) for receiving solder ( 3 ), - a temperature sensor ( 17 . 19 ), which serves to increase the temperature of the solder ( 3 ) during the cooling process in which the melting temperature (T _S ) of the solder ( 3 ) temperature range, and - one to the temperature sensor ( 17 . 19 ) connected evaluation unit ( 21 ) for recording the reference curves (TR (t)) and the temperature curves (T (t)) measured for determining the solder volumes (V), for determining the reference parameters (KR) and the measuring characteristics (K (V)), and for determining the to be determined solder volumes (V). A method for operating a soldering system according to claim 8, wherein on the basis of a load of the soldering machine breaks are determined, and in the operating pauses currently in the solder bath ( 1 ) Lot volume (V) is determined by a method according to any one of claims 1 to 6. Soldering system according to claim 8, with an indication ( 25 . 27 ), which serves to display the results of the volume determinations carried out with the system, and / or to the evaluation unit ( 21 ) interface ( 29 ), on the results of the volume determinations, measured temperature profiles (T (t)), reference curves (TR (t)), measurement parameters (K (V)) and / or reference parameters (KR) are accessible for further display, use, or processing.