GB2211810A

GB2211810A - Transporting apparatus

Info

Publication number: GB2211810A
Application number: GB8828984A
Authority: GB
Inventors: George Battams; Chris Mckeown; Bryan Howes; Denis Bedford
Original assignee: Texas Instruments Ltd
Current assignee: Texas Instruments Ltd
Priority date: 1987-12-22
Filing date: 1988-12-12
Publication date: 1989-07-12
Also published as: GB8828984D0; GB8729917D0

Abstract

An apparatus for transporting items having projecting edge portions includes at least one flexible belt, in the form of a closed loop round pulleys and having at least one longitudinal slit 7, 8 in the front face. When two belts are used they run side by side in the same direction with their front faces facing each other along a straight section, at the start and finish of which each belt passes over a pulley having such a shape that it causes the longitudinal slit 7, 8 to open to receive or relinquish an edge portion of an item carried between the belts. Instead of a slit a discontinuous break or more than one such slit or break may be provided. The slit or breaks may be held closed along the straight section by e.g. channel members 14 engaging the back faces of the belts. Alternatively the belts may include an internal resilient structure for this purpose. <IMAGE>

Description

TRANSPORTATION APPARATUS This invention relates to apparatus for transporting items of relatively small size and especially but not exclusively to apparatus for transporting items having a thin sheet portion projecting at one or more sides.

In the manufacture of integrated circuits, after the semiconductor chips themselves have been produced they are enclosed in protective packages from which project leads providing connections to the chips inside. During the packaging, especially if it consists of encapsulation in a plastics material, the leads are kept in place by being formed as part of a lead frame punched out of suitable sheet material. A lead frame usually has the leads for a plurality of packaged integrated circuits, and the individual circuits with their leads are cut away from the rest of the lead frame as one of the final processes of the manufacture.

Another process that is required to be done is the solder coating or tinning of the leads, and whilst this can be done on the individual integrated circuits after they have been separated from the rest of the lead frame, it would be more convenient to do it whilst all the integrated circuits are still carried on the lead frame since a single lead frame may hold up to a hundred integrated circuits. There are, however, difficulties in supporting the lead frame with all the packaged integrated circuits on it in such a way that the parts of the exposed metal of the lead frame that will form the leads of the integrated circuits can easily be coated with solder. In addition, the lead frame carries important information in printed or other form relating to the integrated circuits on it and the information must not be covered by the solder.

It is an object of the present invention to overcome the difficulties described above.

According to the present invention there is provided apparatus for transporting items having projecting edge portions, including a belt of flexible material formed into a closed loop and having at least one longitudinally extending break in the front face, a plurality of pulleys constraining the belt to follow a particular path including a carrying section between a first of said pulleys and a second of said pulleys, the back face of the belt running in contact with the first and second pulleys which have curved surfaces so shaped in relation to the configuration of the back face of the belt that the break or at least one of the breaks in the front face of the belt opens as it passes over the first and second pulleys to enable it to receive and to relinquish the edge portion cf an item, means effective along the carrying section to constrain the belt so as to close the break or breaks in its front face and hold the edge portion of an item, means for feeding items to the vicinity of the first pulley so as to enable edge portions of the items to enter the opened break or breaks in the pelt, and means for collecting items from the vicinity of the second pulley.

The carrying section may be substantially straight.

The apparatus may include two belts for respectively engaging opposite edge portions of the items.

The belt may be arranged to convey the items through a processing station located between the first and second pulleys. In one example the items are integrated circuit lead frames and the processing station is arranged to apply solder to the leads of the integrated circuits. For use in this example the belt should be made of a material which is not wetted by liquid solder and is not deleteriously affected by heating to the temperatures involved in the soldering. In another example the items are printed circuit boards.

The back face of the belt may be flat when the break is closed and the first and second pulleys may each have a convex, for example biconical, curved surface for causing the break to open. Otherwise the back face of the belt may have a longitudinal ridge and the first and second pulleys may have cylindrical curved surfaces or convex curved surfaces with a groove to receive the ridge.

Each break in the one face of the belt may be a longitudinal slit extending the entire length of the loop.

Otherwise there may be one or more separate breaks, each in the form of a simple, longitudinal slit or a more complex opening, along the length of the belt.

In order that the invention may be fully understood and readily carried into effect examples of it will now be described with reference to the accompanying drawings, of which: FIGURE 1 is a perspective diagram of a part of an example of the invention; FIGURE 2 is a diagrammatic side view of the apparatus of Figure 1 showing an item entering a solder wave; FIGURE 3 shows a pulley of the example of Figure 1 with the belt shown in cross-section; FIGURE 4 shows diagrammatically the means for holding the break in the belt closed in the example of Figure 1; FIGURE 5 shows the cross-section of another form of belt on another form of pulley; and FIGURE 6 shows another form of the means for holding the break in the belt closed.

Referring to the drawings, the part of the apparatus shown in Figure 1 consists of two flexible belts 1 and 2 formed into closed loops round pairs of pulleys 3,4 and 5,6 respectively. The loops have substantially parallel, substantially straight portions between the pulleys. The belts have respective longitudinal slits 7,8 in their outer, front faces. A workpiece 9 is carried by the two belts 1 and 2 with two edge portions of it fitting into the slits 7 and 8 respectively. The loops formed by the two belts are driven by one or more motors (not shown) through the pulleys so that the substantially straight portions of the two loops which are nearer to each other move along parallel paths in the same direction. The belts 1 and 2 serve to carry the workpiece 9 along.Preferably the motor drive is applied to the pulleys 5 and 6 so that the workpiece 9 is pulled along by the tension in the belts 1 and 2.

The curved surfaces of the pulleys 3, 4, 5 and 6 engaged by the belts are so shaped in relation to the back' faces of the belts that contact them that the slits in the front faces of the parts of the belts in contact with the pulleys are opened as indicated at 10 and 11.

A workpiece, which in the present instance is a rectangular integrated circuit lead frame with a number of integrated circuits on it, is brought by a conveyor 12 in the direction of the arrow 13 to the vicinity of the pulleys 3 and 5. The workpiece is guided by means (not shown) so that the leading corners enter the opened parts of the slits 7 and 8. As the workpiece is fed into the slits 7 and 8 and the belts 1 and 2 follow the substantially rectilinear paths from the pulleys 3 and 5 to the pulleys 4 and 6, respectively, so that the slits 7 and 8, released from the opening forces exerted by the pulleys 3 and 5, close on the edge portions of the workpiece. The belts 1 and 2 are preferably made of a material, such as silicone rubber, so that the slits 7 and 8 tend to close because of the resilience of the material.

Two guide members 14 (of which only one is shown in Figure 1), mounted on supports 15 and 16, respectively, press diagonally inwardly on the edges of the belts 1 and 2 so that the workpiece is firmly gripped in the slits 7 and 8. The guide members 14 may be of channel section formed from titanium sheet, titanium being used because it is not wetted by molten solder.

When the workpiece reaches the pulleys 4 and 6, it is passed onwards on to another conveyor 17, the slits 7 and 8 opening, so as to release the workpiece, as the belts 1 and 2 wind round the pulleys 4 and 6.

A particular application of the invention is to convey workpieces in the form of integrated circuit lead frames with integrated circuits thereon through a wave soldering station so as to coat the leads of the integrated circuits with solder. For this application, the belts 1 and 2 are preferably made of a silicone rubber of such a type that it can withstand heating to the temperature of the molten solder without a significant change in its rubber-like properties and which has the additional advantage that the molten solder does not tend to stick to it. Silicone rubber of the grade 701/5 has been found suitable.Because the edge portions of the lead frames are covered by the belts when passing through the wave soldering station, information such as batch numbers can be written stamped or printed on their edge portions without any danger of the information being obliterated by the solder.

The belts 1 and 2 may include embedded fibres to limit the longitudinal stretching, and transverse resilient members, such as spring steel strips, tending to close the slits 7 and 8. If transverse resilient members are provided in the belts 1 and 2, it may be possible to dispense with the guide members altogether or for them to be used merely to support the belts.

Figure 2 shows the workpiece 9 being carried in the direction of the arrow 20 by the belt 2. An edge portion of the workpiece 9 is located in the slit 8. The broken line 21 indicates the surface of the molten solder in the wave soldering station.

Figure 3 shows a side view of one possible shape for the pulley 3 with the belt 1, shown in cross-section, passing over it. The biconical shape of the curved surface of the pulley 3 causes the slit 7 to open as the belt 1 passes round it. The pulleys 4, 5 and 6 are of the same shape as the pulley 3, and the belt 2 has the same cross-section as the belt 1. The belts 1 and 2 may each be provided with a longitudinal ridge on the back face level with the slit 7 or 8; such a ridge helps to strengthen the belt and assists in opening the slit when against a pulley.

Figure 4 is a diagram showing the view in the direction of the arrow 13 (Figure 1) of the workpiece 9 between the guide members 14. As can be seen from Figure 4 the guide members 14 are of polygonal channel section and engage the bounding edges of the back faces of the belts 1 and 2, so as to tend to close the slits 7 and 8 round the edges of the workpiece 9. The members 14 may have lead-in sections to ease the entry of the belts 1 and 2 into full engagement with the members. The members 14 may have a coating of a low friction material such as polytetrafluoroethylene to reduce the drag on the belts 1 and 2.

Figures 5 and 6 show at 30 another possible crosssectional shape for the belts which enables the pulleys, one of which is shown at 31, to have a conventional cylindrical curved surface. Figure 6 shows another possible form for each of the guide members, pairs of inclined rollers 32 and 33 disposed along the length of the belt. The inclined rollers of Figure 6 can also be used with the form of belt described with reference to Figures 1 to 4.

Many different forms of conveyor are possible using the invention. For example, a single belt may be sufficient for some applications and other applications may require three or more belts with side by side parallel running sections conveying the items. Each belt may have more than one longitudinal slit and may be guided over a more complex path than the form of those shown in Figure 1. The slit need not be perpendicular to the surface.of the belt and it may be of any cross-section compatible with the receiving and releasing of workpieces as the belt passes over a suitable pulley.The break in the belt may be discontinuous, the belt having a plurality of shaped recesses disposed along its length with matching protuberances from the back of the belt so that each recess is opened to receive or release a part of a workpiece as the belt passes over a suitable pulley.

A single belt, or each of a pair of belts as shown in Figure 1 for example, may have two or more slots or rows of shaped recesses so that two or more series of items may be conveyed at the same time. A processing station may involve the combining of all or part of items from different series.

If the nature of the process to be carried out on the items requires it, the belt or belts can be stopped when an item is in position and the item pushed down or otherwise moved against the elasticity of the belt or belts to take it to the place where the process is to be performed.

Another possible use of the invention is to convey ,printed circuit boards with components on them through a wave soldering station.

Claims

CLAIMS:

1. Apparatus for transporting items having projecting edge portions, including a belt of flexible material formed into a closed loop and having at least one longitudinally extending break in the front face, a plurality of pulleys constraining the belt to follow a particular path including a carrying section between a first of said pulleys and a second of said pulleys, the back face of the belt running in contact with the first and second pulleys which have curved surfaces so shaped in relation to the configuration of the back face of the belt that the break or at least one of the breaks in the front face of the belt opens as it passes over the first and second pulleys to enable it to receive and to relinquish the edge portion of an item, means effective along the carrying section to constrain the belt so as to close the break or breaks in its front face and hold the edge portion of an item, means for feeding items to the vicinity of the first pulley so as to enable edge portions of the items to enter the opened break or breaks in the belt, and means for collecting items from the vicinity of the second pulley.

2. Apparatus according to claim 1 wherein the carrying section is substantially straight.

3. Apparatus for transporting items having projecting edge portions on both sides, the apparatus including two belts of flexible material formed into closed loops, each belt having at least one longitudinally extending break in its front face, two pluralities of pulleys respectively constraining the belt loops to follow particular paths, each path including a substantially straight carrying section along which in use the belt travels from a first to a second 'of the pulleys of the respective plurality, the carrying sections of the paths of the two belts being parallel with the front faces of the belts facing each other, the back face of each belt running in contact with the first and second pulleys which have curved surfaces so shaped in relation to the configuration of the back face of the belt that the break or at least one of the breaks in the front face of the belt opens as it passes the first and second pulleys to enable it to receive and to relinquish an edge portion of an item, means effective along the carrying sections of the paths to constrain the belts so as to close the breaks in their front faces and hold edge portions of items therein, means for feeding items to the vicinity of the first pulleys so as to enable edge portions of the items to enter the opened breaks in the belts and means for collecting items from the vicinity of the second pulleys.

4. Apparatus according to claim 3 wherein the means effective to constrain the belts comprise guide members pressing diagonally inward on the outer edges of the back faces of the belts.

5. Apparatus according to claim 3 wherein the means effective to constrain the belts comprise a plurality of rollers pressing diagonally inwards on the outer edges of the back faces of the belts.

6. Apparatus according any one of the preceding claims wherein the back face of the or each belt is substantially flat when the or each break in the front face is closed and the pulleys at the start and finish of the carrying section have biconical curved surfaces for causing the break or breaks to open.

7. Apparatus according to any one of claims 1 to 5 wherein the back face of the or each belt has a longitudinal ridge opposite a break in the front face of the belt and the pulleys at the start and finish of the carrying section have X cylindrical curved surfaces or convex surfaces with a groove to receive the ridge.

8. Apparatus according to any one of the preceding claims wherein the or each longitudinally extending break in the or each belt is a lengthwise slit.

9. Apparatus according to any one of claims 1 to 7 wherein the or each longitudinally extending break in the or each-belt is a row of shaped recesses in the belt.

10. Apparatus according to any one of the preceding claims wherein the means effective to constrain the or each belt includes transverse resilient members incorporated in the belt so as to tend to close the break or breaks in its front face.

11. Apparatus according to any one of the preceding claims further including a processing station located in the carrying section so that the apparatus carries items through the processing station.

12. Apparatus according to claim 11 for items which are integrated circuits lead frames in which the processing station is arranged to apply solder to the leads of the integrated circuits, the belt or belts being of a material not adversely affected by liquid solder.

13. Apparatus for transporting items having at least one projecting edge portion substantially as described herein and as illustrated by Figures 1 to 4 of the accompanying drawings or modified as described with reference to Figures 5 and 6 of those drawings.