DE102018120865A1 - Dispensing a solder paste - Google Patents

Abstract

A method of dispensing a paste during a printing process, the paste being dispensed in an amount that is dependent on the number of workpieces remaining to be printed in the current production run.

Description

The invention relates to a method for dispensing a conductive paste during a printing process, to a control system, to a computer program product and to a printing machine.

Background and state of the art

Just like that in 1 As shown schematically, industrial screen printing machines typically bring a conductive printing medium 1 , such as a solder paste or conductive ink, on a flat workpiece 2 , such as a printed circuit board, by passing the conductive print medium through a pattern of openings 3 in a sieve 4 (sometimes referred to as a foil or stencil) using an angled blade or squeegee blade 5 mounted on a printhead (not shown). During a printing process, the doctor blade becomes 5 in one direction X over the sieve (or grid) 4 moves, causing the conductive medium 1 into the openings 3 is transferred, which process is commonly referred to as a "pressure stroke". For convenience, the term "paste" is used throughout this specification to refer to jointly conductive print media, including solder pastes and conductive inks. The paste is conventionally stored in a container, such as a cartridge or a crucible (or pot), and is dispensed from the bottom of this container by pressurizing the top thereof, typically using a pressurized air source. The printing press includes a paste dispenser that removably holds the container to allow the container to be replaced when the paste is used up. It is difficult to accurately determine the amount of paste remaining in the container, but the container is typically provided with a sensor to indicate to an operator of the printing press when the container is nearly empty and requires replacement. The output profile is fully adjustable by optimizing the speed, pressure, position and frequency of the output. Workpieces are typically printed in separate production or print runs in which a plurality of the same workpieces (ie workpieces printed using the same stencil) are sequentially printed. These output profile values are set during a single production run.

The paste dispenser is operable to dispense a lot of paste onto the stencil, around an elongated "stain" or "sausage" or paste that is parallel to the pressure blade along a line from the start position of the print stroke and the size of the workpiece is calculated, and which is of sufficient length to ensure that all openings within the screen pattern receive paste during printing. The amount of paste dispensed in one dispense is sufficient to print a plurality of workpieces sequentially so that dispenses can be spaced in time to cause minimal interruption in the printing. The volume of the paste on the stencil significantly affects the quality and efficiency of the printing process, and it is therefore important that this volume falls within a predetermined optimal range - for example, if the spot size is too small, then the pressure the paste will apply to the Exerts openings, reduced, which can lead to insufficient filling of the openings and ultimately to insufficient conductive connections. If the spot size is too large, the pressure that the paste will exert on the openings will increase, which may cause paste to bleed out (or bleed) under the stencil, excessive paste on the pad, and even short circuit on the workpiece.

In addition, too large a spot size can result in poor curl (or poor curl) of the paste and thus insufficient filling of the openings, as well as the risk of paste drying out on the upper surfaces of the doctor blades which [dried-out paste] in the paste stain can fall back and block openings. Furthermore, very large stain sizes and non-frequent replenishment (or refilled amounts) can influence the flow content (or flow content) of the stain, which can noticeably change the printing properties and possibly even the reflux properties. Too large a paste volume can also cause paste to be wasted. The settings for the profile of the paste dispensing process are specific to the product (i.e. the workpiece) on the press. This enables the use of profile specific values for the product and the solder paste. To ensure that the volume of paste on the stencil is within the optimal range, the volume is estimated and, if necessary, a set amount of paste is automatically dispensed by the dispenser.

During printing, the activity of the pressure blade on the dispensed paste tends to cause the paste to form into a roll or cylinder and the volume of the paste on the screen can be estimated, for example by measuring the dimensions of the roll. A particularly simple technique is to assume that the roll is of approximately circular cross-section, in which case the volume of the paste can be derived directly from the height of the roll, it being noted that the lateral extent of the roll can be limited by paste baffles attached to the printhead. The paste roll can either be measured during a printing stroke, in which case the shape of the roll is directly influenced by the doctor blade (as in 1 is shown), or between pressure strokes, in which case the roller tends to sag (or sink). In practice, therefore, the role is not uniformly circular, but this approximation can be improved to address this difference, for example using empirical volumetric data obtained from an experiment.

Other volume estimation techniques are known in the art. A simple configuration provides a mechanically attached sensor that "looks down" to measure the height of the paste roll at one position. If the specified height of the paste roll (" Zroll ”) Below a certain predetermined height (eg“ zmin ", as in 1 shown), causes the set volume of the paste to be dispensed, this volume being set such that, following dispensing, the height of the paste roll immediately follows the maximum height (“ Zmax “), Which has been designed for reliable printing, is achieved but not exceeded. A more complex and expensive alternative is to use a laser to measure the height of the paste roll directly, which in turn causes the set volume of the paste to be dispensed when the height falls below a predetermined value, such as Zmin. Laser systems of this type can be problematic with regard to the optical path of the laser, which is at risk due to blocking by paste, and because considerable associated equipment is required.

Such systems are automatic, effective and reliable. However, a problem has been identified in that they can suffer from efficiency problems. In particular, such systems are not flexible because they cause a set volume of paste to be dispensed whenever the paste volume on the stencil falls below a predetermined value. As noted above, workpieces are typically printed in separate production runs. Following the production run, a new production run can be started to print a different type of workpiece, which may require a significantly different configuration of the printing press, including a new template. If the next production run uses the same paste as the previous production run, the paste roll can sometimes be transferred to the next stencil to save money and reduce waste. However, if the blade size is changed, it is impossible to predict how much paste will be used in addition to the transfer roller. This creates problems for standard automatic dispensing profiles and therefore multiple dispensing operations are required, resulting in production line downtime.

There are other problems if the new production run requires the use of a different type of paste. In these cases, any paste that was dispensed on the old template during the previous production run will be discarded. Waste disposal of this wasted paste is not only expensive, but can also have an adverse impact on the environment.

The present invention seeks to overcome this problem.

In accordance with the present invention, this goal is achieved by providing an influencing (or intervention) mechanism so that the amount of paste dispensed depends on the progress of the production run.

This concept of the invention is expanded to provide a fully flexible control mechanism for the paste dispensing process, in particular to enable the dispensing of relatively small volumes of paste, and also to provide an alternative mechanism for estimating the paste volume on the stencil without a fixed sensor or laser use.

Summary of the invention

1. i) Bereitstellen eines Steuerungssystems, das zu der Maschine zugehörig (oder mit ihr verbunden) ist,
2. ii) Bereitstellen eines Ausgebers, der betriebsfähig ist, ein leitendes Druckmedium aus einem Vorratsbehälter auszugeben, um einen Flecken (oder Tropfen) von leitendem Druckmedium auf einem innerhalb der Druckmaschine angeordneten Sieb (oder Raster) auszubilden, wobei der Ausgeber mittels des Steuerungssystems gesteuert wird,
3. iii) in dem Steuerungssystem, Einstellen der Anzahl von Werkstücken, die innerhalb des Produktionslaufs gedruckt werden sollen,
4. iv) während des Druckens, Überwachen der Anzahl von Werkstücken, die in dem Produktionslauf zu drucken verbleiben,
5. v) während des Produktionslaufs, Abschätzen des Volumens des leitenden Druckmediums auf dem Sieb, und
6. vi) Ausgeben einer Menge des leitenden Druckmediums während des Produktionslaufs, um das Volumen des leitenden Druckmediums auf dem Sieb innerhalb eines vorbestimmten Bereichs für den Produktionslauf aufrechtzuerhalten,

wobei im Schritt vi) das leitende Druckmedium in einer Menge ausgegeben wird, die von der Anzahl der Werkstücke, die in dem Produktionslauf zu drucken verbleiben, abhängt.According to a first aspect of the present invention, there is provided a method for dispensing a conductive printing medium during a sequential printing printing process, with conductive paste by a printing press, of a plurality of workpieces within a production run of [same] workpieces, the method comprising the following steps having:

1. i) providing a control system which is associated with (or connected to) the machine,
2. ii) providing a dispenser operable to dispense conductive media from a reservoir to form a patch (or drop) of conductive media on a screen (or grid) located within the press, the dispenser being controlled by the control system,
3. iii) in the control system, setting the number of workpieces to be printed within the production run,
4. iv) during printing, monitoring the number of workpieces remaining in the production run to be printed,
5. v) during the production run, estimating the volume of the conductive printing medium on the screen, and
6. vi) dispensing an amount of the conductive print media during the production run to maintain the volume of the conductive print media on the screen within a predetermined range for the production run,

wherein in step vi) the conductive print medium is dispensed in an amount that depends on the number of workpieces remaining in the production run to be printed.

According to a second aspect of the present invention, there is provided a control system for use with the method according to any preceding claim, the control system having a processor.

According to a third aspect of the present invention, there is provided a printing press having the control system of the second aspect.

According to a fourth aspect of the present invention, there is provided a computer program product for enabling the control system according to one of the first three aspects.

Other specific aspects and features of the present invention are set out in the accompanying claims.

list of figures

• 1 zeigt schematisch eine bekannte Druckanordnung,
• 2 zeigt schematisch ein beispielhaftes Drucksystem zum Ausführen des Verfahrens der vorliegenden Erfindung, und
• 3 ist ein Ablaufdiagramm, das ein beispielhaftes Verfahren gemäß der vorliegenden Erfindung beschreibt.

The invention will now be described (not to scale) with reference to the accompanying drawings, in which:

• 1 schematically shows a known printing arrangement,
• 2 Figure 3 schematically shows an exemplary printing system for carrying out the method of the present invention, and
• 3 FIG. 10 is a flowchart describing an exemplary method in accordance with the present invention.

Detailed description of preferred embodiments of the invention

An embodiment of the invention will now be described with respect to 2 which schematically shows a printing system for carrying out a printing method according to the present invention. A control system 11 is provided which has a processor for controlling the output process at least from a printing press. The control system is a printing press 10 belonging to it, as in the embodiment described here, it can form part of it, for example an “on-board” computing means, or it can be at least partially distant from it in other embodiments, for example a separate PC, a laptop, a mobile device or another computing means , which can optionally be able to operate other equipment or machines. The control system 11 is capable of operating, executing or accessing a computer program, such as software, embedded software, cloud-based software, etc., for controlling at least the output process of the printing press. The control system 11 is trained to provide production run information 12 to receive, in particular information that sets the number of workpieces that are to be printed within a production run, but optionally also the optimal output positions on the screen that is to be used within this production run, and information that relates to the expected paste consumption per Workpiece that is printed within this production run. Such production run information 12 can be at least partially entered by an operator. It should be noted that the control system 11 is also operable to monitor the number of workpieces remaining to print in a current production run, for example by receiving information about the number of workpieces printed, for example from a dedicated sensor (not shown) or from an external source (not shown) ), and this with the set number of workpieces that are to be printed within the production run, such as that from the production run information 12 is obtained is compared. The information relating to optimal dispensing positions and the expected paste consumption can be generated automatically by a separate program or processing means, for example from Gerber data provided by an operator, or it can be derived within the control system itself, for example from such Gerber data , The control system 6 is also designed to output signals from a sensor 13 to receive a paste storage container 16 is assigned and the is operable to detect when the container is substantially empty and therefore needs replacement. The control system is optional 11 also set up to output the signal from a sensor 14 for monitoring the paste roll height, which is received by the control system 11 can be interpreted to indicate the height of the paste roll on the sieve and which can consequently be used to directly estimate the volume of the paste on the sieve. Such a sensor can be used as described above 14 have a laser or a simpler height measurement sensor. The control system 11 is also set up to be a paste dispenser 15 to control the operable paste from the paste storage container 16 Output to a stain (or drop) of paste on a sieve that is inside the press 10 is arranged to form, such paste dispensers are well known per se in the art.

As noted above, the control system can 11 be operable to estimate the volume of paste on the sieve by measuring the volume from the output of the paste roller height monitoring sensor 14 is calculated as previously discussed. However, in an alternative embodiment, this calculation is not performed, and instead the paste volume estimate can be performed by calculating the paste consumption during the current production run, by the number of workpieces printed in the production run, with the amount of conductive print media that was used during the Production run has been output, is correlated.

In more detail, the volume of the paste coming from the paste dispenser 15 in a standard dispense is either directly known, or it can be determined empirically, or it can be [at least] partially derived from at least one of the group consisting of: an output nozzle characteristic, an output pressure of the conductive print medium, and one Stroke length of a print head of the printing press, which print head is used during the production run.

The number of standard paste dispensing operations performed during a print run can also be done using the control system 11 be monitored.

Furthermore, the volume of paste consumed per workpiece during the production run can be determined in a variety of ways. For example, the volume of the paste can be derived at least partially experimentally. One option to do this could be to print a plurality of workpieces until a set paste volume has been consumed, then the average paste volume consumed per workpiece can be easily calculated. Other options will be apparent to those skilled in the art. Alternatively or additionally, a value for the volume of the conductive pressure medium consumed per workpiece during the production run can be at least partially derived from the combined volume from all openings provided in the screen. Assuming that there is no waste of paste (e.g. any paste baffles used in the press work perfectly), that the openings are completely filled with paste during a printing process, and that separation of the screen and the workpiece is 100% paste transfer leads from the sieve to the workpiece, then, at least as an initial approximation, the paste volume consumed per workpiece will equal the total internal volume of all openings within the opening pattern of the sieve. Of course, in reality the filling, the transfer and the waste will not be perfect. However, it is possible to apply an empirically determined correction factor to at least partially compensate for such inefficiencies.

wobei:

• V_Sieb das Volumen von Paste auf dem Sieb ist,
• C ein empirisch bestimmter Korrekturfaktor ist,
• m die Anzahl von Ausgabevorgängen ist, die bisher in dem aktuellen Produktionslauf ausgeführt worden sind,
• V_d das Volumen der Paste ist, das in einem standardmäßigen Pastenausgabevorgang ausgegeben wird,
• n die Anzahl von Werkstücken ist, die bisher während des Produktionslaufs gedruckt worden sind, und
• V_w das Pastenvolumen ist, das während des Produktionslaufs pro Werkstück verbraucht wird.

With these values (ie the paste volume coming from the paste dispenser 15 is output in a standard dispense, the number of dispenses previously performed in the current production run, and the volume of paste consumed per workpiece during the production run) and by monitoring the number of workpieces previously printed during the production run , the volume of paste on the sieve can be estimated by the following equation. $${\text{V}}_{\text{SLEB}}~\text{C}\left({\text{mV}}_{\text{d}}-{\text{nV}}_{\text{w}}\right).$$

in which:

• V _{sieve is} the volume of paste on the sieve,
• C is an empirically determined correction factor,
• m is the number of dispensing processes that have been carried out in the current production run,
• V _{d is} the volume of paste that is dispensed in a standard paste dispensing process
• n is the number of workpieces that have been printed during the production run, and
• V _{w is} the paste volume consumed per workpiece during the production run.

Whichever method is used to estimate the volume of paste on the sieve, this estimate is made by the control system 11 used the paste dispenser 15 to control. Just like the previous one in relation to the 1 For optimum print quality, it is important that the volume of paste on the screen be maintained within a predetermined optimal range. Usually, this area is set by an operator of the printing press and can vary widely depending on preferences, the type of paste and the opening pattern that will be printed. If it is estimated that the volume of paste on the screen is below or at least approaching the lower extent of this area, the control system causes the paste dispenser 15 performs a dispensing operation in which an amount of paste is discharged onto the sieve, the quantity or volume of the discharged paste being such that the volume of the paste on the sieve subsequent to dispensing does not exceed the upper extent of the predetermined range.

In accordance with the present invention is the control system 11 operable to control the dispensing process so that the paste is dispensed in an amount that depends on the number of workpieces remaining in the production run to be printed. In a preferred embodiment, if the number of workpieces remaining in the production run is below a predetermined number, sufficient conductive media is dispensed to maintain the volume of conductive media on the screen within a portion of the predetermined range, the Sub-area has an average that is lower than an average of the predetermined range. As a non-limiting example, the predetermined range could be selected to be between, for example, 10 cm ³ and 13 cm ³ so that the average is 11.5 cm ³ . In this case, the partial area could be selected such that it is between 10 cm ³ and 11 cm ³ , for example, so that the mean value is 10.5 cm ³ . This methodology effectively means that an amount of paste is dispensed that is less than the standard amount of paste that is dispensed during the initial part of the production run.

In this way it can be ensured that the remaining workpieces to be printed in the production run are printed with a sufficient amount of paste, and that there is nevertheless minimal waste of the paste when the production run is ended.

It will be apparent to those skilled in the art that progress must be monitored during the production run so that the number of workpieces remaining to be printed for the control system 11 is known. However, this information is typically known in known systems so that the production run can be adequately controlled.

The dependency of the section and the number of remaining workpieces to be printed at which the reduced output characteristic is triggered can be set by an operator or it can be set by the control system 11 be proposed. For example, the reduced output characteristic could be triggered, for example, if there are 10 workpieces remaining to be printed within the current production run, and this will result in any paste that is dispensed while printing these workpieces with a reduced volume compared to a standard volume ,

A methodology according to an embodiment of the present invention is shown as a flow diagram in FIG 3 explained. This flow chart shows the operations that are performed while the production run is printing. It should be noted that this flowchart details only key steps in the printing and dispensing process, for example, it does not include details regarding the transfer or inspection of workpieces because they remain similar to known methods.

In one step A a volume of paste on the sieve is estimated using any of the methods described above.

When it is estimated that the volume of the paste is within a predetermined acceptable range (step B ), the system can then continue to print (step H ), ie a workpiece is printed.

If in step B it is estimated that the paste volume is outside the predetermined acceptable range (step B ), then the control system checks (step C ) the proximity to the end of the production run, i.e. the number of workpieces that remain to be printed, and in particular whether this number is less than the predetermined number.

If the production run is not near the end, then the control system does 11 in step D that a standard amount of paste is dispensed.

Following the output process in step D will (in step e ) carried out a check whether the paste container is sufficiently full. This check checks if there is enough paste left in the container to perform another standard paste delivery if found (step C ) that the production run is still far from the end, or alternatively, if there is enough paste left for a reduced paste dispensing operation as the production run approaches the end. If there is not enough paste, then in step F the container replaced. Another check can be carried out (step e ) only to ensure that the new container is filled correctly. The method can then go to the printing step H Continue.

If in step C it is determined that the number of workpieces remaining to be printed is smaller than the predetermined number, then in the step G a reduced amount of paste is dispensed, and a printing operation is performed at the step H executed.

Following the step printing process H checks the control system 11 whether the production run is complete (step I ). If so, the process can end, otherwise the process returns to step A and the volume of the paste on the sieve is again estimated.

The above-described embodiments are exemplary only, and other possibilities and alternatives within the scope of the invention will become apparent to those skilled in the art. For example, towards the end of the production run, the amount of paste dispensed can be gradually reduced or "shut down". The amount of paste dispensed could also be reduced if it is determined that the paste container is empty.

LIST OF REFERENCE NUMBERS

1 -

conductive printing medium

2 -

workpiece

3 -

opening

4 -

scree

5 -

doctor blade

10 -

press

11 -

control system

12 -

Tracking information

13 -

Paste container sensor

14 -

Paste tip height monitoring sensor

15 -

paste dispenser

16 -

Paste reservoir

Zmax -

maximum paste roll height that is determined for printing

Zmin -

Minimum paste roll height that is determined for printing

Zroll -

Paste tip height

Claims (14)

A method for dispensing a conductive printing medium during a printing process for sequential printing, with a conductive paste by a printing press, from a plurality of workpieces within a production run, the method comprising the following steps: i) providing a control system which is associated with the printing press, ii) providing a dispenser operable to dispense a conductive print medium from a reservoir to form a stain of the conductive print medium on a screen located within the press, the dispenser being controlled by the control system, iii) in the control system, setting a number of workpieces to be printed within the production run, iv) during printing, monitoring the number of workpieces remaining in the production run to be printed, v) during the production run, estimating the volume of the conductive printing medium on the screen, and vi) dispensing an amount of the conductive print medium during the production run to maintain the volume of the conductive print medium on the screen within a predetermined range for the production run, wherein in step vi) the conductive print medium is dispensed in an amount that is supplied by the Number of workpieces remaining to print in the production run depends. The procedure according to Claim 1 , wherein in step v) estimating the volume of the conductive print medium on the screen comprises measuring the height of a roll of the conductive print medium on the screen. The procedure according to Claim 2 , wherein the height of the roll of the conductive printing medium on the screen is measured using a sensor. The procedure according to Claim 2 wherein the height of the roll of the conductive printing medium on the screen is measured using a laser. The procedure according to Claim 1 , wherein in step v) estimating the volume of the conductive printing medium on the screen comprises correlating the number of workpieces printed in the production run with the amount of the conductive printing medium dispensed during the production run. The procedure according to Claim 5 , comprising deriving a value for the volume of the conductive printing medium that is needed per workpiece during the production run. The procedure according to Claim 6 , wherein the value for the volume of the conductive pressure medium that is used per workpiece during the production run is at least partially derived experimentally. The method according to one of the Claims 6 and 7 , wherein the value for the volume of the conductive pressure medium needed per workpiece during the production run is at least partially derived from the combined volume from all the openings provided in the screen. The method according to one of the Claims 5 to 8th , wherein the amount of the conductive printing medium discharged during the production run is at least partially derived from at least one of the group consisting of: a discharge nozzle characteristic, a discharge pressure of the conductive printing medium and a stroke length of a print head of the printing press used during the production run. The method of any preceding claim, wherein in step vi), if the number of workpieces remaining to be printed in the production run is below a predetermined number, sufficient conductive media is dispensed to accommodate the volume of conductive media on the screen within maintain a partial area of the predetermined area, the partial area having an average value that is lower than an average value of the predetermined area. The method according to any one of the preceding claims, wherein the conductive media container is replaced prior to step vi) if it does not contain sufficient conductive media to dispense the amount of conductive media in step vi), the amount depending on the number of workpieces, which remain in the production run to be printed depends on. A control system for use with the method according to any one of the preceding claims, comprising a processor. A printing press, having the control system according to Claim 12 , A computer program product for enabling the control system according to one of the preceding claims.

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