DE102019201549A1 - Method for monitoring a screw connection - Google Patents

Abstract

The invention relates to a method for monitoring a screw connection (30) of at least two components (31, 34) in which a minimum (46) and maximum value (45) for the tightening torque and a minimum value (45) for determining the quality of the screw connection (30) (49) and a maximum value (48) for the rotational angle of a component is defined, which together define a process window in which the screw (30) is considered good, wherein the starting point (47) of the rotation angle determination by a torque threshold (51) defines is. An increase in the slope of the torque with respect to its maximum gradient must be below a defined limit in the process window.

Description

The invention relates to a method for monitoring a screw connection.

In modern assembly technology, the screw connection is still one of the most important types of connection. The variety of screws in the screw technology has changed significantly compared to earlier. Methods for calculating bolt connections and newly developed bolting methods offer the possibility of significantly reducing the size of the bolts. The result is smaller and lighter screws, which leads to a significant reduction in raw materials and weight and greatly reduces the space required for screwing.

Screwed connections also play an important role in the field of projection exposure systems for semiconductor lithography, in particular in EUV projection exposure systems. Due to the here typically low installation space available and the drastic consequences of the failure of a gland there are increased requirements.

A threaded connection is a detachable connection that joins two or more parts together to behave as one part among all the operating personnel. Of crucial importance for operational safety is obtaining sufficient residual prestressing force (residual clamping force). If the operating force during operation so large that it releases the biasing force, the screw can solve depending on the operating load or even break. The biasing force can be increased by increasing the stress cross section by using several or more screws, increasing the screw quality, which makes it possible to increase the assembly biasing force with the same screw size, or by using more accurate screwing methods, so that the screw can be better utilized. increase. The screwing methods can achieve a more accurate statement about or even a smaller dispersion of the achieved preload force on the basis of the monitored parameters during screwing, such as the torque, the slope of the torque and / or the exceeded angle of rotation. The measured torque when tightening the screw is composed of the thread friction, the Unterkopfreibung, for example between a nut and a support and the biasing force together, the high dispersion of the threaded friction and the Unterkopfreibung make it difficult to determine the biasing force.

Known tightening methods are disclosed, for example, in the training documents of the company IBES Elektronik GmbH, which are published under http://www.ibes-electronic.de/SchulungsunterlagenNeutral.pdf.

A method for improving the bolting described therein is a torque controlled tightening method in which the torque D [Nm] is monitored and a minimum D _min [Nm] and maximum torque D _max [Nm] are defined, which describe a range in which the Screw is tightened. As a result, the torque used in comparison to a purely subjective tightening the screw is reproducible. In addition, a range for the exceeded rotation angle W [degree] is defined by a minimum W _min [deg] and maximum rotation angle W _max [deg], for example, to detect a seizure of the thread or a plastic deformation of the screw head. The quality of the gland is defined by the achievement of the process window, which is defined by the minimum and maximum values of the ranges for the torque and the angle of rotation. The described method has the disadvantage that it still involves the high variability of the thread friction and the undercutting friction.

Another known method monitors the rotation angle, this is only when a defined threshold of the torque D _threshold [N,], in which the joining operation, that is, the settling effects in the thread and under the head of the screw, have been completed is determined. This method can bring the screw into the plastic range regardless of the torque, so that the thread friction and the Unterkopfreibung have no influence on the determination of the biasing force. Nevertheless, this method also defines a minimum and maximum torque for the same reasons as above. The quality of the screw connection is also defined by reaching the process window.

The methods described above have the disadvantage that the tolerable glands do not always meet the requirements.

The object of the present invention is to provide a method which solves the above-described disadvantages of the prior art.

This object is achieved by a method having the features of the independent claim. The subclaims relate to advantageous developments and variants of the invention.

In a method according to the invention for monitoring a screw connection of at least Two components are defined for determining the quality of the screw a minimum and a maximum value for the tightening torque and a minimum and maximum value for the rotation angle of the one component, which together define a process window in which the screw is considered good. Furthermore, the starting point of the rotation angle determination is defined by a torque threshold, wherein a slope decrease of the torque with respect to its maximum slope in the process window must be below a defined limit. The definition of a limit value for the slope drop in relation to the maximum slope of the torque has the advantage that the fluctuation of the thread friction and the undercarriage friction are taken into account in the definition of the limit value and thus have a smaller influence on the prestressing force. In addition, for example, a crack in one of the components or a strong plastic deformation, in which the slope changes sharply over a relatively small angle of rotation, can be detected advantageously. The slope drop can be evaluated during tightening or after reaching the process window and used to assess the quality of the fitting.

In particular, the limit value of the slope drop can be smaller 20 , especially smaller 10 , especially smaller 5 be the maximum slope. The higher the preload for the given screw is to be exploited without risking the failure of the screw, the more accurately the slope of the torque, which is a measure of the bias and thus the elongation of the screw is monitored. The smaller the permitted value, the further the distance to a possible failure of the screw connection.

In a variant of the method, the starting point of the rotational angle determination can be defined by a gradient threshold value of the torque. This has the advantage that glands where the torque curve is very flat, resulting in high friction and / or high deformation in the thread (and thus on a non-standard thread) and / or high friction under the head and / or on can indicate a crack in one of the components can be filtered out.

In addition, an area can be defined for the torque threshold. Experiments have shown that a certain fluctuation of the torque at which the slope reaches the threshold value for defining the starting value of the rotational angle determination has no influence on the quality of the screw connection.

The start condition for the determination of the angle of rotation can also be defined, for example, by reaching the gradient threshold value below the defined range up to the upper value of the range of the torque threshold value.

In a variant of the method, the starting point can be defined by the reaching of the gradient threshold value within the defined range of the torque threshold value.

Furthermore, the method can be repeated if the maximum torque is reached only after reaching the maximum angle of rotation. This can always be the case if the plastic deformation of the surface roughness and the Unterkopfreibung especially at the first tightening a screw lead to a very shallow curve. Experiments have shown that the slope of the torque increases with a further screw connection and a defined process window, which is defined by the minimum and maximum values of the torque and the rotation angle, is achieved.

In this case, for example, the limit value for the slope drop for the first and further repetitions of the method can be defined differently. In the case of a first screw connection, a partial plastic deformation of one of the two components can already occur, as a result of which the behavior in the boundary region is influenced to a plastic deformation. With a constant value for a further screw connection, this can lead to excessive plastic deformation and even failure of the screw connection.

In particular, the value for the slope drop for a second, third or further implementation of the method can be smaller. Reducing the value advantageously minimizes the risk of failure or increased risk of pre-damage.

In addition, the method may be limited to two repetitions. As tests have shown, the risk of failure and pre-damage is too great for more than two repetitions of the procedure. In particular, a failure when screwing should be avoided.

• 1 den prinzipiellen Aufbau einer EUV-Projektionsbelichtungsanlage,
• 2 eine schematische Darstellung einer Schraubverbindung
• 3 ein Diagramm zur Darstellung einer Verschraubung
• 4 ein weiteres Diagramm zur Darstellung einer Verschraubung

Embodiments and variants of the invention will be explained in more detail with reference to the drawing. Show it

• 1 the basic structure of an EUV projection exposure system,
• 2 a schematic representation of a screw connection
• 3 a diagram showing a screw connection
• 4 another diagram showing a screw connection

1 shows an example of the basic structure of an EUV projection exposure system 1 for microlithography, in which the invention can find application. An illumination system of the projection exposure apparatus 1 points next to a light source 3 an illumination optics 4 for illuminating an object field 5 in an object plane 6 on. One by the light source 3 generated EUV radiation 14 as optical useful radiation is by means of a light source in the 3 integrated collector aligned so that they are in the area of a Zwischenfokusebene 15 undergoes an intermediate focus before moving to a field facet mirror 2 meets. After the field facet mirror 2 becomes the EUV radiation 14 from a pupil facet mirror 16 reflected. With the aid of the pupil facet mirror 16 and an optical assembly 17 with mirrors 18 . 19 and 20 become field facets of the field facet mirror 2 in the object field 5 displayed.

Illuminated is a in the object field 5 arranged reticle 7 that of a schematically represented Reticlehalter 8th is held. A merely schematically illustrated projection optics 9 serves to represent the object field 5 in a picture field 10 into an image plane 11 , Pictured is a structure on the reticle 7 on a photosensitive layer in the area of the image field 10 in the picture plane 11 arranged wafers 12 , by a wafer holder also shown in detail 13 is held. The light source 3 can emit useful radiation, in particular in a wavelength range between 5 nm and 30 nm.

The invention can also be used in a DUV system, which is not shown. A DUV system is in principle like the EUV system described above 1 constructed, in a DUV system mirrors and lenses can be used as optical elements and the light source of a DUV system emits a useful radiation in a wavelength range of 100 nm to 300 nm.

2 shows a schematic representation of a screw 30 of two components 31 . 34 , A first as a head 31 formed component comprises an internal thread 33 and a head bottom 32 , with a second as a body 34 trained component a rejuvenation 35 with an external thread 36 and an edition 37 includes. The head 31 gets on the body 34 screwed until the bottom 32 Of the head 31 on the pad 37 the body is firmly attached. It can also be between the head 31 and the body 34 be arranged another component. The head 31 and the body 34 can also be formed on a component such as a screw with which then any two other components can be screwed. The screw connection 30 is tightened so tight that the expected operating forces are smaller than the preload force, which never leads to a detachment of the top of the head 32 from the edition 37 of the body 34 or the other component comes. The preload is due to the elasticity of the body 34 can be generated and determined by the determination of different parameters when putting on the head 31 , such as the tightening torque, hereinafter referred to as torque, the rotation angle of the head 31 and the slope of the torque can be adjusted. The torque consists of the friction in the thread, also referred to as thread friction, the friction between the bottom 32 Of the head 31 and the edition 37 , which is also referred to as Unterkopfreibung, and the bias together.

3 shows a diagram representing the curve of the torque D [Nm] and the slope S [Nm / degrees] of the torque over the rotation angle W [degrees]. The torque D [Nm] is plotted on the left vertical axis of the diagram and there is a minimum torque _threshold D from bottom to top _Threshold [Nm] 51 , a maximum torque _threshold D _{Threshold max} [Nm] 50 , a minimum torque Dmin [Nm] 46 and a maximum torque D _max [Nm] 45 Are defined. The rotation angle W is plotted on the horizontal axis and a starting point for the rotation angle determination W _Start [degree] 47 , a minimum rotation angle Dmin [degrees] 48 and a maximum angle of rotation D _max [degrees] 49 Are defined. On the right vertical axis, the slope of the torque S [Nm / deg] is applied, only one threshold value S _threshold [Nm / deg] 52 is defined. The diagram also shows a torque curve 40 and a slope curve 41 , which is shown in dashed lines, both of which are plotted against the angle of rotation W [degrees]. The slope curve 41 includes a maximum slope S _max [Nm / deg] 43 and a minimum slope S _min [Nm / deg] 44 where S _min 44 the minimum slope after reaching the maximum slope S _max 43 Are defined. The desired quality of the screw connection 30 is reached, on the one hand, within the range between minimum 51 and maximum torque threshold 50 the slope of the torque the threshold of the slope 52 has exceeded. On the other hand, the slope of the slope may not fall below a certain value, until in the further course of the curve, the torque D [Nm] the process window 42 has reached. The process window 42 is due to the area between minimal 48 and maximum rotation angle 49 in the horizontal direction and the area between minimal 46 and maximum torque 47 defined in the vertical direction. Of the maximum slope of the curve is determined by the following formula: $$\text{lead waste}=\left(1-\frac{SteiGun{G}_{min}}{SteiGun{G}_{max}}\right)*100$$

For example, the slope drop may not exceed 30 , in particular not greater than 20 and in particular not greater than 10 be. A further increase in slope does not have a negative impact on the screw connection 30 because the preload is not generated by plastic deformation.

If one of the above-described requirements does not apply, the screw connection is required 30 out of tolerance.

4 shows another diagram, which is also the torque D [Nm] on the rotation angle W [degrees] when tightening a screw 30 represents. On the vertical axis is the torque D [Nm] with the minimum D _min [Nm] 46 and maximum torque D _max [Nm] 45 and on the horizontal axis the rotation angle W [degrees] with the minimum W _min [degrees] 48 and maximum rotation angle W _max [degrees] 49 and the starting value of the rotation angle determination Wstart [degree] 47 applied. The diagram contains three curves 60 . 61 . 62 , where the first curve 60 the first time tightening a screw 30 shows. This is the first screw when reaching the maximum torque 45 aborted, without an assessment of the first screwing is made; it serves only a first leveling of unevenness or roughness.

The conditions at the second screwing are through the curve 61 Here, the process window is indeed reached, but the curve flattens towards the end, so that the slope drop of the curve 62 in this range is above the defined limit and the screw is considered to be outside the tolerance.

Accordingly, now a third screw is made, the torque curve through the curve 62 is illustrated. Here all required criteria are fulfilled and the screw connection is considered as within the tolerance. A new release does not logically take place.

Tests have shown that tightening the screw 30 Only twice should be repeated, otherwise the flat slope of the torque D [Nm] on another cause such as a crack in the head 31 or body 34 is due.

By combining the two in the 3 and the 4 described method, the quality of the screw 30 and thus minimize scrap, which has a positive effect on the manufacturing costs of the devices produced by the screwing.

LIST OF REFERENCE NUMBERS

1

Projection exposure system

2

facet mirror

3

light source

4

illumination optics

5

object field

6

object level

7

reticle

8th

Reticlehalter

9

projection optics

10

field

11

image plane

12

wafer

13

wafer holder

14

EUV radiation

15

Between field focal plane

16

Pupil facet mirror

17

module

18

mirror

19

mirror

20

mirror

30

screw

31

head

32

bottom

33

inner thread

34

body

35

rejuvenation

36

external thread

37

edition

40

torque curve

41

slope curve

42

process window

43

Maximum slope S _max [Nm]

44

Minimum slope S _min [Nm]

45

Maximum torque D _max [Nm]

46

Minimum torque Dmin [Nm]

47

Starting point rotation angle measurement W _Start [degree]

48

Minimum rotation angle W _max [degrees]

49

Maximum rotation angle W _min [degrees]

50

Maximum Threshold Torque D _{Threshold Max} [degrees]

51

Minimum Threshold Torque D _Threshold [degrees]

52

Threshold slope S _threshold [Nm / deg]

60

First turn

61

Second turn

62

Third turn

Claims (10)

Method for monitoring a screw connection (30) of at least two components (31, 34), wherein a minimum (46) and maximum value (45) for the tightening torque is defined for determining the quality of the screw connection (30), - a minimum ( 48) and a maximum value (49) for the angle of rotation of a component (31) is defined, which together define a process window in which the screw (30) is considered good, wherein the starting point (47) of the rotation angle determination by a torque threshold ( 51), characterized in that a slope drop of the torque with respect to its maximum pitch (43) in the process window must be below a defined limit. Method according to Claim 1 , characterized in that the limit value of the slope drop is less than 20, in particular less than 10, in particular less than 5. Method according to one of Claims 1 or 2 , characterized in that the starting point (47) of the rotation angle determination by a slope threshold (52) is defined. Method according to one of the preceding claims, characterized in that a range (50, 51) is defined for the torque threshold value (51). Method according to one of Claims 3 or 4 characterized in that the starting point (47) for determining the angle of rotation is defined by reaching the gradient threshold (52) up to the upper value (50) of the range of the torque threshold (50, 51). Method according to one of Claims 3 to 4 , characterized in that the starting point (47) of the rotation angle determination by the reaching of the slope threshold value (52) within the defined range of the torque threshold (50, 51) is defined. Method according to one of the preceding claims, characterized in that the method is repeated when the maximum torque (45) is reached only after reaching the maximum angle of rotation (49). Method according to Claim 7 , characterized in that the values for the threshold value for the gradient decrease are defined differently for the first and further repetitions of the method. Method according to Claim 8 , characterized in that the values for the threshold value for the slope decrease for a second, third or further implementations of the method become smaller. Method according to one of Claims 7 to 9 , characterized in that the method is limited to two repetitions.

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