Placement apparatuses in the semiconductor industry need to operate with high precision and high throughput. One example for such placement apparatuses are die-bonders or pick-and-place machines with which components in form of semiconductor chips are placed and bonded on substrates such as lead frames. The components are received in a picking station by the placement head, especially by means of suction, moved via an XYZ handling system of the placement apparatus to the point of placement above the substrate, and placed thereafter at a precisely defined position on the substrate. The placement head is fixed to a placement head support and coupled to the XYZ handling system via said support. The Z direction usually corresponds to the vertical direction, whereas the XY plane forms the horizontal plane.
In addition to a highly precise placement of the components in the XY plane, it is further very important that the components are also placed in a plane-parallel manner on the substrate. Tilted placement of the components can lead to undesirable properties such as reduced holding force, worse or missing electric contacts, uneven heat transfer between the components and the substrate, or damage to the components.
During the placement process it is a considerable problem that when the component is pressed onto the substrate reaction forces will be produced as a result of the generated pressing forces which are far from inconsiderable, which reaction forces can lead to a deformation of the placement head guide device, i.e. the placement head support and/or the XYZ handling system. In a placement head which is rigidly connected to the placement head support this deformation leads to a tilting of the placement head and therefore to an axis error (“tilt”) which produces a respective inclined position of the component relative to the surface of the substrate and furthermore to an undesirable offset of the component in the XY plane.
Such a deformation which occurs in the state of the art is schematically shown in FIG. 2. The axial or inclination error which is caused by the deformation-induced tilting of the placement head 2 together with the placement head support 1, starting from the unloaded position as shown in FIG. 1, is designated there with “tilt”. The additionally occurring lateral offset at the bottom end of the placement head 2 on which the not shown component is held is designated with “a”. “F” indicates the reaction force acting on the placement head 2, which reaction force is produced by the pressing force when the placement head 2 is pressed perpendicularly onto the substrate 3.
It is known for avoiding this undesirable axis error to make the placement head support as stiffly as possible. Despite optimized technology in lightweight construction, this inevitably also leads to a relatively large mass. As a result of the massive configuration, the throughput of the placement apparatus will decrease considerably at given drive power. Furthermore, it can never be prevented entirely even in the case of a highly massive arrangement of the placement head support that the placement head will always yield slightly at its tip which accommodates the components when it is pressed onto the substrate.
It is a further known approach to arrange the placement head support in a symmetrical way. In the case of this symmetrical arrangement, the placement head will be supported evenly on both sides. Although this prevents the tilting of the placement head which is caused by the pressing force, the arrangement of the placement apparatus, and in particular the placement head support and the placement head, will be limited very strongly with respect to its design. This leads to disadvantages in machine design like reduced accessibility, as well as complex or a high number of components.
A placement head holding system is known from WO 2008/052594 A1. The placement head is tiltably fixed there to the tool holder by means of a sliding joint which comprises an air bearing. The compensation of the inclined position of the placement head occurs in such a way that the placement head is placed without the component with released air bearing on the substrate, wherein the placement head will automatically align relative to the placement head support in such a way that the bottom face of the placement head is parallel to the substrate surface. The air bearing is locked thereafter and the placement head lifted from the substrate. The adjusted tilting angle of the placement head relative to the placement head support is maintained in this process and is used for the subsequent placement processes. Furthermore, an adjusting apparatus is indicated in a merely symbolic manner, by means of which a positioning of the placement head is possible with activated air bearings when a specific tilting position is to be set without pressing against substrate. WO 2008/052594 A1 therefore merely concerns a presetting of the placement head which is performed prior to the actual placement process. A continuous compensation of the axis error of the placement head during the placement process is not possible with this known holding system.