WO2004038394A1

WO2004038394A1 - Method for the quality control of connection balls of electronic components

Info

Publication number: WO2004038394A1
Application number: PCT/EP2003/011711
Authority: WO
Inventors: Klaus Neumaier; Günter SCHIEBEL; Klaus Peter Wershofen
Original assignee: Siemens Aktiengesellschaft
Priority date: 2002-10-25
Filing date: 2003-10-22
Publication date: 2004-05-06
Also published as: DE10249850A1; AU2003276146A1

Abstract

The invention relates to a method for the quality control of connection balls (102) of electronic components (100) in which the connection balls (102) are arranged on a flat lower side of the component (100). The lower side of the components (100) is illuminated by an inclined illumination element (103a) and by a flat illumination element (103b), in such a way that different luminous reflections (104a and 104b) can be produced. The quality of each individual connection ball (102) can be determined by comparing the luminous reflections that are produced by the different illuminations, and are respectively associated with a connection ball (102), with reference luminous reflections. A preferred form of embodiment is characterised in that: (a) the inclined illumination element (103a) meets the components (100) perpendicularly from below, (b) the flat illumination element (103b) is produced by an annular illumination unit, enabling the connection balls (102) to be illuminated on all sides, at a defined angle, and (c) the light reflections are detected perpendicularly to the lower side of the components.

Description

description

Process for quality control of connection balls of electronic components

The invention relates to a method for quality control of connection balls of electronic components, in particular of ball grid arrays, chip scale packages, micro ball grid arrays and / or flip chips, in which the connection balls are on a flat underside of the Component are arranged.

Due to the ever increasing integration density on electronic assemblies, the number of connections of electronic components is steadily increasing. In order to meet this trend, assembly and contacting methods have been developed in which the components are contacted via solder balls on the underside of the components with connection surfaces formed on a substrate to be equipped. Such components are, for example, so-called ball grid arrays, chip scale packages, micro ball grid arrays and / or flip chips. In order to ensure reliable contacting, the connections must be inspected precisely before assembly, since faulty connections which lead to poor electrical contact between the component and the connection surfaces can only be detected with great difficulty after assembly.

In the case of BGA components, for example, missing, incomplete or flattened connection balls can lead to incorrect contacting of the entire component.

EP 968522 B1 discloses a method for checking the presence of connecting balls, in particular on ball grid arrays, in which the connecting balls are illuminated with light coming in at an angle from one direction, so that a light reflection from each connecting ball and to the side of the connector closing ball on the underside of the BGA component a shadow is created. The light reflections and the shadows of the individual connection balls are recorded by a camera. An image evaluation unit connected downstream of the camera uses the size of the shadow to be expected at a certain height of the respective connection ball with simultaneous presence of an associated light reflection of the connection ball as a criterion for the presence of the respective connection ball. However, this method has the disadvantage that it does not work with a reflective, ie glossy component housing and only very poorly with an absorbent, ie black component housing.

JP 02-081449 discloses a method for measuring connecting balls, in which the connecting balls are illuminated at an oblique angle and the resulting shadow cast is measured. The size and shape of the shadow cast can be used to determine the size and shape of the respective connection ball. This method also has the disadvantage that the accuracy of the measurement of the connection balls strongly depends on the reflectivity of the respective component housing on which the connection balls are formed.

From WO 99/44408 a method for measuring connecting balls is known, in which a connecting ball provided on the underside of a component is illuminated by light that is incident at an angle on all sides and the associated light reflection is recorded by a camera. The beam path of the illuminating light runs parallel or at least almost parallel to the underside of the component. The camera is arranged in such a way that those light reflections are detected whose beam path runs perpendicular to the underside of the component. In this way, light reflections with an annular structure arise when the connection balls are intact. From the diameter of the ring-shaped structure and the brightness of the light reflections, the size and thus also the size the presence of the respective connection ball can be inferred.

The invention has for its object to provide a method for quality control of connection balls of electronic components, by means of which a large number of possible defects of connection balls can be detected quickly and reliably regardless of the reflectivity of the component housing.

This object is achieved by a method for quality control of connection balls of electronic components with the features of independent claim 1. The invention is based on the knowledge that the separate processing of two different images of the connection balls and a subsequent combination of the results of the two image processing processes the Quality of the connection balls can be determined quickly and reliably. A first image of the connection balls is generated by the flat underside of the component under a steep, i.e. is illuminated at a small angle to the normal of the bottom. The other picture is in flat lighting, i.e. illuminated at a large angle to the normal of the underside. A combination of the two image processing methods enables the quality of the individual connection balls to be determined quickly and reliably. The term quality of a connection ball is to be understood in this context to mean that high-quality connection balls have a slight deviation in their shape and size from a specific reference connection ball, so that it can be predicted before the actual contacting of the components that a perfect electrical contacting of the component can be achieved if all connection balls are of high quality.

Since automatic placement machines for the detection of BGA components usually include not only a component camera but also a high-quality term lighting device with both steep and flat lighting is available, the inventive method can be carried out without major conversions in conventional placement machines.

The sequential lighting according to claim 2, in which the connecting balls are not illuminated simultaneously, but successively by the steep and the flat lighting, has the advantage that all light reflections are particularly clear, i. H. can be captured by the camera with high contrast.

The use of different illuminating colors for different illuminating angles advantageously enables simultaneous detection of the first and second light reflections, provided that a spectrally resolving camera is used. This has the advantage that the method can be carried out particularly quickly.

In the method according to claim 4, there is no overlap between the angle of incidence of the steep lighting and the angle of incidence of the flat lighting. This can be achieved, for example, by choosing a large difference between the angles of incidence of the steep illumination and the angles of incidence of the flat illumination, or by using an illumination light with at least approximately parallel light beams for the steep illumination and / or for the flat illumination ,

In the method according to claim 5, the connection balls are simultaneously illuminated from different sides by the flat lighting. This can be achieved, for example, by segmented flat ring lighting or by quasi-continuous ring lighting, in which a multiplicity of light sources with a height offset perpendicular to the underside of the component are arranged in a ring around the component. It should be noted that the Light sources can also be replaced by a corresponding mirror arrangement, which reflect the illuminating light from one or a plurality of light sources such that the connecting balls are illuminated from different sides at a flat angle of incidence. Instead of a mirror arrangement, it is also possible to use a plurality of optical waveguides which guide the light emitted by the illuminating light sources to the corresponding points, so that the component is also appropriately illuminated.

In the method according to claim 6, the light of the steep illumination is directed perpendicularly onto the underside of the component, so that the first light reflections can be evaluated particularly easily.

According to claim 7, those light rays of the reflected light are detected whose beam paths are perpendicular to the underside.

In conjunction with continuous ring lighting

For rotationally symmetrical connection balls, circular second light reflections result, the diameters of which represent a measure of the volumes of the connection balls. In addition, the completeness of the ring structure of the circular second light reflections is a measure of the symmetry of the connection balls.

In conjunction with vertical lighting (see claim 6), the brightness of the first light reflections is a measure of a possible flattening of the connection balls. In addition, a lateral shift of a first light reflex indicates a possible lateral flattening of the corresponding connection balls.

At this point, it is pointed out that lighting perpendicular to the flat underside of the component combines with illumination relative to the underside vertical detection of the reflected light can be realized by using a conventional beam splitter. Both the vertical illuminating light can be reflected on the beam splitter and the light reflections transmitted through the beam splitter, and conversely the vertical illuminating light can be transmitted and the light reflections to be detected by the camera can be reflected on the beam splitter.

Since coplanar connection balls are required for reliable electrical contacting of a component, it is not the absolute but the relative volume of the individual connection balls that is decisive. For this reason, according to claim 8, the first and / or the second light reflections are compared with reference light reflections, which are determined by a statistical evaluation such as, for example, a simple averaging over different first and second light reflections.

Further advantages and features of the present invention result from the following exemplary description of a currently preferred embodiment.

In the drawing, FIG. 1 a shows a vertical illumination of an intact connection ball and the associated vertical light reflex at an observation angle perpendicular to the underside of the component, FIG. 1 b shows a ring-shaped illumination of an intact connection ball under a flat illumination angle and the associated vertical light reflection, FIG. 2 a an intact connection ball and the corresponding vertical light reflections in the case of vertical and flat lighting, FIG. 2b a missing connection ball and the corresponding light reflections in the case of vertical and flat lighting, and Figure 2c-f four different ways for faulty

Connection balls and the corresponding light reflections for vertical and flat lighting.

Figures la and lb show an electronic component 100 with a connection surface 101, on which an intact connection ball 102 is located. As can be seen from FIG. 1 a, the connecting ball 102 is illuminated by a vertical illumination 103 a. A camera, not shown, detects the light reflection generated due to the vertical illumination 103a, the beam path of which is directed downwards perpendicularly to the underside of the component 100. The beam paths of the vertical illuminating light 103a and the light reflex running perpendicular to the underside of the component 100 are spatially separated in a conventional manner by means of a beam splitter, not shown.

FIG. 1b shows a flat illumination 103b of the connection ball 102, which, according to the exemplary embodiment of the invention shown here, is generated by an annular lighting unit, so that the connection ball 102 is simultaneously illuminated from all sides at a fixed angle. The beam paths of the illumination beams of the flat illumination 103b define the lateral surface of a cone that tapers in the direction of the connection balls 102 to be measured. The camera, not shown, detects the light reflection generated due to the flat illumination 103b, which is directed downwards perpendicularly to the underside of the component 100. The intact connection ball 102 results in an annular light reflection 104b, the diameter of which is a measure of the volume of the connection ball 102.

To determine the quality, ie to measure the shape and size of the connecting ball 102, the light reflections 104a and 104b are each separated from an image processing system evaluated and compared with reference light reflections, which reflect the size and shape of a given intact connection ball. In this way, if at least one of the two light reflections 104a or 104b deviates from a corresponding reference light reflex, a missing or a defective connection ball can be reliably identified.

FIGS. 2a to 2f show, in the form of a tabular overview, different connection balls (left column), associated first light reflections (middle column) generated by vertical illumination and associated second light reflections generated by flat ring illumination (right column). The light reflections shown are recorded by a camera, which captures the flat underside of the component at a vertical angle.

FIG. 2a shows once again an intact connecting ball which, under vertical illumination, produces a light reflection with a point-symmetrical brightness distribution and, in the case of flat, continuous ring illumination, a point-symmetrical ring-shaped light reflection. It is pointed out that due to the re lexions law, according to which the angle of incidence relative to the reflecting surface is equal to the angle of reflection, the bright point in the middle of the first light reflection has a diameter which is significantly smaller than the real diameter of the connecting ball. It also follows from the law of reflection that in the second light reflection the diameter of the circular ring is somewhat smaller than the real diameter of the connecting ball.

Figure 2b shows the first and the second light reflex in the absence of a connecting ball. For vertical lighting, there is a circular reflex that shows the connection surface of the component. Since the connection surfaces usually have a flat surface, there is a circular light reflection that opposes an intact closing ball has a significantly larger diameter. With flat lighting, there is also a circular light reflection, the brightness of which strongly depends on the optical surface properties of the connection surface. If the connection surface is covered with solder residues, a low brightness can be detected. With a bare connection surface, practically no light gets into the camera.

Figure 2c shows a damaged connecting ball, in which a part of the solder ball has broken out on the right side. In the case of vertical illumination, there is a first light reflex, which corresponds to a light reflex of an intact connection ball in the left part. In the smaller ren right partial region, the first light reflection on a _U ndefinierte structure. Flat, circular lighting results in an incomplete circular ring.

FIG. 2d shows a connecting ball with a volume that is too small. Due to the surface tension of the solder material, the connection surface is generally completely wetted with solder, but the surface of the connection ball is significantly flattened compared to an intact connection ball. In this case, there is a first light reflex in the case of vertical illumination, which is generally hardly distinguishable from the light reflex of an intact connecting ball. With flat lighting, however, there is a clear difference compared to an intact connection ball, which consists in the fact that the diameter of the circular ring is reduced compared to the second light reflection of an intact connection ball.

It is pointed out that in the case of a connection ball which has a solder volume which is too large compared to an intact connection ball, an intact connection light with a larger diameter results from an intact connection ball compared to a second reference light reflex. FIG. 2e shows a connection ball which has a flattening parallel to the underside of the component. In this case, in the case of vertical illumination, a circular first light reflection results, which has a bright circular surface in the center, which has a larger diameter than a first reference light reflection of an intact connection ball. In this case, the flat, ring-shaped illumination results in a second light reflex, which differs insignificantly from the second reference light reflex of an intact connecting ball.

FIG. 2f shows a connection ball, which likewise has a flattening, the surface of which runs obliquely to the underside of the component and thus leads to an asymmetrical shape of the connection ball. In the case of vertical illumination, depending on the asymmetry of the connecting ball, a more or less weak first light reflex results, which is laterally displaced compared to a first reference light reflex of an intact connecting ball. In the case of the flat, ring-shaped illumination, if the asymmetry of the connection ball is not excessively pronounced, there is also a second light reflection, which also differs insignificantly from a second reference light reflection of an intact connection ball.

It is pointed out that the connection balls shown in FIGS. 2b, 2c and 2d are generally caused by production errors in the manufacture of the electronic components. The connection balls shown in FIGS. 2e and 2f are often based on improper handling of the electronic components.

It is also pointed out that when measuring a plurality of connection balls, which are distributed on the flat underside of a component, the individual connection balls, in particular of the flat illumination, are each subjected to a slightly different winch. be illuminated. As a result, the corresponding second light reflections in particular have a slightly different structure for each connecting ball. In the case of a fixed spatial position of the component to be measured relative to the lighting unit which generates the annular flat lighting, however, the geometric lighting conditions are fixed for each connecting ball, so that the different lighting angles can be taken into account and compensated accordingly in a subsequent evaluation of the light reflections ,

In summary, the invention provides a method for quality control of connection balls 102 of electronic components 100, in particular of ball grid arrays, chip scale packages, micro ball grid arrays and / or flip chips, in which the connection balls 102 are on a flat surface Bottom of the component 100 are arranged. The underside of the components 100 is illuminated by a steep illumination 103a and by a flat illumination 103b, so that different light reflections 104a and 104b are generated. The quality of each individual connection ball 102 can be determined by comparing the light reflections generated by the different illuminations, which are each assigned to a connection ball 102, with reference light reflections. A preferred embodiment of the invention is characterized in that (a) the steep lighting 103a hits components 100 vertically from below, (b) the flat lighting 103b is generated by an annular lighting unit and thus the connecting balls 102 under one be - Selected angles are illuminated from all sides, and that (c) the light reflections are detected perpendicular to the underside of the components.

Claims

claims

1. Method for quality control of connection balls of electronic components, in particular of ball grid arrays, chip scale packages, micro ball grid arrays and / or flip chips, in which the connection balls (102) on a flat underside of the component (100) are arranged in which

The connection balls (102) are illuminated at an angle of incidence that is steep relative to the underside,

• light reflected by the connecting balls (102) due to the steep illumination (103a) is recorded by a camera, a first light reflex (104a) being assigned to each connecting ball (102), • the connecting balls (102) under one relative to the underside flat angle of incidence are illuminated,

Light reflected by the connection balls (102) due to the flat illumination (103b) is recorded by the camera, a second light reflection (104b) being assigned to each connection ball (102),

• for each connecting ball (102) the first light reflex (104a) is compared separately with a first reference light reflex and the second light reflex (104b) with a second reference light reflex, and • based on the differences between the light reflexes (104a, 104b) and the quality of the connecting balls (102) is determined using the associated reference light reflections.

2. The method of claim 1, wherein the connector balls (102) are illuminated by the steep lighting (103a) when the flat lighting (103b) is off, and by the flat lighting (103b) when the steep lighting ( 103a) is switched off.

3. The method according to any one of claims 1 to 2, in which for the steep lighting (103a) light with another spec- central distribution is used as for flat lighting (103b).

4. The method according to any one of claims 1 to 3, wherein for each connecting ball (102) each light beam of the steep lighting (103a) is directed at a larger angle to the underside than each light beam of the flat lighting (103b).

5. The method according to any one of claims 1 to 4, in which a ring illumination is used for the flat illumination (103b), the light sources of which are arranged in a ring around the component (100) with a vertical offset perpendicular to the underside of the component (100).

6. The method according to any one of claims 1 to 5, wherein the light of the steep illumination (103a) is directed perpendicularly to the underside.

7. The method according to any one of claims 1 to 6, in which those light rays of the reflected light are detected by the camera, which are directed perpendicularly away from the bottom.

8. The method according to any one of claims 1 to 7, in which the first reference light reflections are determined by a statistical evaluation of at least several detected first light reflections (104a) and / or in which the second reference light reflections by a statistical evaluation of at least several detected second light reflections (104b) can be determined.