GB2618064A

GB2618064A - Ultrasonic collimator

Info

Publication number: GB2618064A
Application number: GB2205622.0A
Authority: GB
Inventors: Cheeseman Anthony; Falcon Tom
Original assignee: ASM Assembly Systems Singapore Pte Ltd
Current assignee: ASMPT SMT Singapore Pte Ltd
Priority date: 2022-04-15
Filing date: 2022-04-15
Publication date: 2023-11-01
Also published as: KR20230148101A; GB202205622D0; JP2023157897A; TW202406758A; CN116907557A

Abstract

Collimator 1 comprising a body with an aperture extending completely through the body in a transmission direction T, the aperture having a width W being the maximum diameter of the aperture along its extent, and a length L in the transmission direction, wherein the ratio of the width to the length is greater than or equal to 1. The collimator is operative to limit the lateral extent of ultrasonic waves orthogonal to the transmission direction. The aperture may have a width to length ratio in the range 2.5 to 3.5. The aperture width may be 3 mm to 4.5 mm and the length may be 0.7 mm to 1.5 mm and it may be of circular cross-section. An ultrasonic sensor may comprise an emitter of ultrasonic waves and the collimator 1 and may detect objects in a target zone separated from the emitter by a dead zone. The collimator may be mounted on the emitter, so it is in the dead zone. The ultrasonic sensor may be part of a pin placement system for placing tooling pins within a printing machine.

Description

Ultrasonic Collimator This invention relates to a collimator for ultrasonic waves, an ultrasonic sensor, a pin placement system and a printing machine.

Background and Prior Art

Industrial screen-printing machines typically apply a conductive print medium, such as solder paste, silver paste or conductive ink, onto a planar workpiece, such as a circuit board, by applying the conductive print medium through a pattern of apertures in a thin planar layer or mask, such as a stencil (which is a patterned solid material such as stainless steel) or a screen which is a mesh material coated with emulsion. The print medium is applied using an angled blade or squeegee. The same machines may also be used to print certain nonconductive media, such as glue or other adhesive, onto workpieces.

To ensure high quality printing, it is necessary to support the workpiece so that the surface to be printed is parallel to the printing screen, generally horizontal, with the workpiece support being capable of withstanding the pressure placed upon it during the printing operation, especially by the downward pressure applied by the squeegee, while maintaining the correct alignment of the workpiece. The simplest type of support is to use a flat surface or platen on which a workpiece may be placed. However, there are many circumstances where this type of arrangement is not possible, in particular where the underside of a workpiece has previously been printed and equipped with components (for example during a so-called "placement" operation), and this underside needs to be supported during a printing operation applied to the topside of the workpiece. The presence of components on the underside of the workpiece means that the workpiece will not be flat, and also the components are liable to damage if they are "squashed" during a printing operation. It will be appreciated that workpieces also need support during other processes, for example during a placement operation. To this end, specialist support solutions, known as "tooling", are used.

Tooling pins -these are thin columns which are positioned to contact the board in use, avoiding contact with any components (or other delicate or critical regions) on the underside. The pins are usually magnetic, i.e. they include either a permanent or an electro-permanent magnet within them, to non-permanently attach the pins to a flat, underlying support plate or "tooling table", which may conveniently be made from a magnetically permeable material such as steel. By way of example, ASM currently uses simple, low-cost, moulded plastics tooling pins with a single Neodymium permanent magnet in the base of each pin.

Tooling pins can be reused for a wide variety of workpieces, and they tend to be cheaper and more convenient than dedicated tooling blocks. Within printing machines, tooling pins are usually manually placed on the tooling table (although auto-place systems are starting to be introduced), while placement machines, such as those produced by ASM, may provide both manual placing and auto-place options. With a manual system it is challenging and time consuming for the operator to place the pins consistently and with the required accuracy. Auto-place systems may save time and reduce defects by placing pins accurately.

An auto-place system typically uses a "pin picker" device operable to engage with a pin, the pin being located either on the tooling table or in a storage magazine, from above. The pin picker may then lift the pin, move it laterally into the desired position, then lower it onto the tooling table.

In ASM's auto-place option, known as "smart pin placement", an ultrasonic measurement device is provided on the pin picker, which may be used to detect foreign objects, such as deposits of print medium or fallen tooling pins, located on the tooling table, and which could negatively impact the placement of a tooling pin at that area. For the present purposes, ultrasound is defined as a sound wave having a frequency of >= 20 kHz. In its default condition, the ultrasonic device emits an ultrasonic beam profile that is wide enough to detect targets outside of the area of interest, which may result in nuisance measurement data being reported.

As is well-known in the art per se, an ultrasonic beam profile may be limited by using a collimator between the ultrasonic device and the beam target. Known ultrasonic collimators are essentially tubes through which the ultrasonic beam is passed, and these are effective at spatially limiting the beam profile.

However, a problem exists with such known collimators in that the tube is relatively long, and in fact may be too long to be accommodated on a pin picker.

The present invention seeks to overcome this problem and provide a collimator which is relatively small, so that it can be fitted within the design envelope available for a pin-picker of a printing machine. Naturally, the presently proposed collimator may be used in other applications away from printing.

In accordance with the present invention this aim is achieved by providing a collimator comprising an aperture of reduced longitudinal extent compared to conventional tube-like collimators, such that the ratio of the width to the depth is greater than or equal to 1. The present inventors have, surprisingly, found that such a thin collimator is still effective at reducing the lateral extent of ultrasonic waves incident upon the collimator.

It should be noted that the term "collimator" as used in this specification refers to a beam limiting device, reducing or limiting the lateral extent of waves, rather than to a device that straightens or concentrates incident waves.

Summary of the Invention

In accordance with a first aspect of the present invention there is provided a collimator for ultrasonic waves, comprising a body with an aperture extending completely through the body in a transmission direction, the aperture having a width being the maximum diameter of the aperture along its extent in the transmission direction, and a length in the transmission direction, wherein the ratio of the width to the length is greater than or equal to 1, such that the collimator is operative to limit the lateral extent of ultrasonic waves orthogonal to the transmission direction.

In accordance with a second aspect of the present invention there is provided an ultrasonic sensor comprising an emitter for emitting ultrasonic waves and the collimator of the first aspect.

In accordance with a third aspect of the present invention there is provided a pin placement system for placing tooling pins within a printing machine, comprising the ultrasonic sensor of the second aspect.

In accordance with a fourth aspect of the present invention there is provided a printing machine comprising the pin placement system of the third aspect.

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

Brief Description of the Drawings

The invention will now be described with reference to the accompanying drawings (not to scale), in which: FIG. 1 schematically shows, in perspective view, a collimator in accordance with the present invention; FIG. 2 schematically shows the collimator of FIG. 1 from the side; FIG. 3 schematically shows the collimator of FIG. 1 from below; FIG. 4 schematically shows an ultrasonic sensor arrangement in accordance with the present invention; and FIG. 5 schematically shows, from the side, part of a pin placement system for a printing machine including an ultrasonic sensor in accordance with the present invention.

Detailed Description of the Preferred Embodiments of the Invention FIGs. 1 to 3 schematically shows, in perspective view, from the side and from below respectively, a collimator 1 in accordance with an embodiment of the present invention, which is operative to limit the lateral extent of ultrasonic waves orthogonal to a transmission direction T of the ultrasonic waves. The collimator 1 shown is monolithic, being formed from a single block of rigid material, such as a metal or a rigid plastics material, formed for example by casting, machining or 3D-printing. The collimator comprises a spacer 2, which includes mounting features 3A, 3B, including in this embodiment a screw hole 3A extending therethrough and an azimuthal key 3B, for attachment to other components of an ultrasonic sensor, as will be described in more detail below. Projecting laterally from the lower extent of the spacer 2 is a body, in this case a plate 4, with an aperture 5 formed therein, which extends completely through the plate 4 between its upper and lower surfaces, along the transmission direction. In use, the spacer 2 ensures that the plate 4 and aperture 5 are suitably spaced from an ultrasonic emitter (see below) of an ultrasonic sensor by a distance H (see FIG. 2). The thickness of the plate 4, which defines the length of the aperture 5, is shown as L (see FIG. 2). The apertures has an aperture width W (see FIG. 3), which is the maximum diameter of the aperture 5 along its extent in the transmission direction, i.e. along its length.

In the embodiment shown, the aperture 5 is of circular section, and so has a constant width W along its length and in all radial directions orthogonal to the transmission direction T. The ratio of the width W to the length L is greater than or equal to 1, optionally the ratio of the width to the length is in the range 2 to 4, optionally the ratio of the width to the length is in the range 2.5 to 3.5. The aperture may have a width in the range from 3.0 mm to 4.5 mm and a length in the range from 0.7 mm to 1.5 mm.

FIG. 4 schematically shows an ultrasonic sensor arrangement in accordance with the present invention, for detecting objects within a target zone 7. The ultrasonic sensor includes an ultrasonic emitter 6 which emits ultrasonic waves in transmission direction T, towards the target zone 7. The ultrasonic transmitter 6 is spaced from collimator 1 by the distance H. The distance H is selected so that the collimator 1 lies within a so-called "dead zone" 8 of the ultrasonic sensor, which is the region proximate to the ultrasonic emitter Sand in which objects cannot be detected by the ultrasonic sensor. A typical dead zone 8 for this application may be extend for around 20-40 mm away from the ultrasonic emitter 6 for

example.

FIG. 5 schematically shows, from the side, part of a pin placement system for a printing machine including an ultrasonic sensor in accordance with the present invention. The collimator 1 is shown mounted under an ultrasonic emitter 6 on a pin placement head 10, which is movably mounted on a gantry (not shown) of a printing machine so that it may selectively place tooling pins (not shown) onto a tooling table 9. The ultrasonic sensor is arranged to detect misplaced tooling pins or fouling objects on the tooling table 9 which could adversely interfere with the pin placement operation. The present collimator 1 is of sufficiently low vertical extent that the pin placement head 10 can move unimpeded over the tooling table 9, which would not be possible with a conventional, tube-like collimator.

The above-described embodiments are exemplary only, and other possibilities and alternatives within the scope of the invention will be apparent to those skilled in the art. For example, the aperture need not be of circular section, but could be shaped so as to provide beam-shaping functionality if required.

While he invention has been described above with particular reference to tooling pin placement systems, there are potentially many other uses, both related and unrelated to printing operations.

Some printing-related uses could include, for example: 1. Topographically mapping the component side of a PCB to learn optimal tooling pin positions when that side is subsequently printed; 2. PCB thickness! warpage measurement; 3. Checking tooling and board clamp height! co-planarity; and 4. Checking height! co-planarity for singulated parts presented to a surround plate for printing.

Reference numerals used: 1-Collimator 2-Spacer 3A -Screw hole 3B -Azimuthal key 4-Plate -Aperture 6-Ultrasonic emitter 7 -Target zone 8-Dead zone

9 -Tooling table

10-Pin placement head L-Aperture length H -Distance between aperture and ultrasonic emitter W -Aperture width T -Transmission direction

Claims

Claims 1. A collimator for ultrasonic waves, comprising a body with an aperture extending completely through the body in a transmission direction, the aperture having a width being the maximum diameter of the aperture along its extent in the transmission direction, and a length in the transmission direction, wherein the ratio of the width to the length is greater than or equal to 1, such that the collimator is operative to limit the lateral extent of ultrasonic waves orthogonal to the transmission direction.
2. The collimator of claim 1, wherein the ratio of the width to the length is in the range 2 to 4.
3. The collimator of claim 2, wherein the ratio of the width to the length is in the range 2.5 to 3.5.
4. The collimator of claim 1, wherein the aperture has a width in the range from 3.0 mm to 4.5 mm and a length in the range from 0.7 mm to 1.5 mm.
5. The collimator of any preceding claim, wherein the aperture is of circular section.
6. An ultrasonic sensor comprising an emitter for emitting ultrasonic waves and the collimator of any of claims 1 to 5.
7. The ultrasonic sensor of claim 6, for detecting objects within a target zone separated from the emitter by a dead zone, wherein the emitter is adapted for emitting ultrasonic waves towards the target zone and the collimator is mounted to the emitter so that it is located within the dead zone.
8. The ultrasonic sensor of claim], wherein the collimator is mounted to the emitter such that ultrasonic waves emitted by the emitter travel to the target zone along the transmission direction.
9. A pin placement system for placing tooling pins within a printing machine, comprising the ultrasonic sensor of any of claims 6 to 8.
10. A printing machine comprising the pin placement system of claim 9.