GB2187707A - Method of placing an article - Google Patents

Abstract

A method of mounting electronic components (c) at predetermined positions on a printed circuit board and which is capable of simultaneously correcting the misregistration of a plurality of electronic components by one cycle of operations. Misregistration of individual electronic components with respect to suction tubes (3) of a suction head (2) is corrected immediately after the suction tubes (3) have sucked up the electronic components (c) from the cavities (1) of a jig in which the electronic components are charged to thereby place each of the suction tubes (3) at a predetermined or exact suction position on the electronic component. After the components have been sucked up the tubes are moved in both the x and y directions to cause impact of the mis-positioned components with the walls of the cavities and thus cause them to be correctly positioned by relative movement between the components and the tubes. <IMAGE>

Description

SPECIFICATION Method of placing an article This invention relates to a method for placing an article substantially at a predetermined coordinate and is applicable to methods for mounting electronic compounds at predetermined positions of a printed circuit board.

Recently, various kinds of automatic chip-mounting apparatuses have been used for automatically positioning maniaturized electronic components of cylindrical shape, plate-l ike shape, disc-like shape orthe like, such as, for example, resistors, capacitors or the like (hereinafter referred to as "chips") on a printed circuit board and fixedly mounting such chips thereon.

Generally, the automatic chip-mounting apparatus includes a jig having a plurality of cavities into which chips are charged. The cavities are arranged to correspond with those positions of a printed circuit board at which the chips are to be mounted. The chips are fed to the cavities of the jig by a suitable means. The jig charged with the chips is shifted to a predetermined position where the chips are sucked up from the cavitites onto a plurality of suction tubes provided at suction heads of the chip-mounting apparatus which are arranged in alignment with the cavities of the jig.The chips sucked up onto the suction tubes are transferred to the printed circuit board where suction is released so that the chips may fall to be precisely positioned on the printed circuit board corresponding to the arrangement of the chips in the cavities and securely adhered thereto by means of an adhesive applied onto the printed circuit board in advance. Then, the adhesive is allowed to dry and the printed circuit board having the chips mounted thereon is transferred to a soldering station so that the chips may be properly soldered to the board.

However, during the mounting operations of the chips on the printed circuit board described above, it is extremely difficult to arrange the chips precisely on predetermined positions of the board. The chips are liable to be misregistered with respect to the printed circuit board by upto about 0.3mm in the longitudinal direction (y-axial direction) andlorthe lateral direction (x-axial direction) of the printed circuit board.

The misregistration is caused due to the inaccuracy or variation of dimensions of individual chips. A chips has considerable variability in dimensions due to various factors occurring in the manufacturing process such as a dimensional error of the chip to be finished, variation in dimensions of the chips caused by the work on the chip such as the coating on the chip, and the like. For example, a chip having nominal dimensions of 1.25mm x 2.00mm has a possible dimensional error of about 0.25mm in each direction. In orderto allow for such a dimensional error of the chip.The cavities of the jig each must be formed to have a size sufficient to receive therein a chip having a maximum dimensional error of, for example, 0.25mm and therefore must provide a clearance of, for example, 0.25mm defined around the chip received therein. In this example, the cavity must have a size of about 1.7-2.4mm x 2.4-2.5mm.

Accordingly, the charging of a chip having nominal dimensions of,forexample, 1.25mm x 2.00mm in the cavity creates a clearance of about 0.25mm around the chip. When the chip has a dimensional error, the clearance is, of course, different. This does not cause any problem when the chip is precisely positioned atthe centre ofthe cavity, however, the initial position of the chip is about 0.75mm off in maximum when it deviates from the precise positionin the cavity.

On the other hand, the suction tubes of the suction head and the corresponding cavities of the jig can be mechanically designed with high accuracy to a degree sufficient to align the centre of each ofthe suction tubes with that of the corresponding cavities on the same centre line and carry out the mounting ofthe chips in a mannerto permit the suction tube to descend to suck up the chips charged in the cavities, ascend while holding the chips thereon and then mount the chips on the predetermined position of the printed circuit board. Accordingly, when the chip is sucked up onto the suction tube at a position deviating from the predetermined or exact suction position thereof, the chip is mounted on a position of the printe circuit board deviating from the intended mounting position thereof.

This resregistratjon of the chip is relatively easy to correct in an automatic chip-mounting apparatus of the single-mount type which is adapted to perform the sucking and mounting of chips onto the printed circuit board one by one, because the correction of the misregistration can be carried out individually.

However, an automatic chip-mounting apparatus of the multi-mounttype renders the correction of the misregistration substantially impossible during the mounting operation, because it is constructed in a manner such that a plurality of suction tubes provided at the suction head such as, for example, vacuum tubings have to concurrently suck up simultaneously a plurality of chips, for example, several tens to several hundreds of chips, from a plurality of the cavities provided at the jig and mount them on the predetermined various positions of the printed circuit board.

Thus, misregistration of the chips cannot be eliminated by the convention automatic chip-mounting apparatus ofthe multi-mounttype.

Accordingly, it has been attempted to decrease the misregistration by increasing the dimensional accuracy of individual chips so asto minimize the clearance of each cavity. However, this is not effective with miniaturized chips.

The present invention has been made in view of the foregoing disadvantage of the prior art having regard to the fact that the best chance of correcting the misregistration of the chip is during the time for which the chip is received in the cavity of the jig.

An object ofthe present invention is to provide a method of placing an article whose location is approximately known substantially at a predetermined coordinate in a simple and rapid manner.

Another object of the present invention is to provide a method of correcting the suction position of a chip which is capable of simultaneously correcting the misregistration of a plurality of chips and simultaneously positioning and mounting the chips on a printed circuit board in a simple manner with high accuracy.

It is another object of the present invention to provide a method of mounting a chip at a predetermined position of a printed circuit board in a simple and rapid manner.

According to one aspect of the invention, there is provided a method of placing an article substantially at a predetermined coordinate in which: said component is placed between first and second stop means having predetermined positions relative to said coordinate; said component is held by releasable holding means having a predetermined positional relationship to said first and second stop means; and the holding means is advanced successively towards the first and second stop means by respective predetermined distances, and said holding means permitting the component to change its position relative thereto where said at least one stop means obstructs movement of the component.

According to a further aspect of the invention, there is provided a method of mounting electronic components at predetermined positions of a printed circuit board, comprising the steps of: charging said components into respective cavities of a jig; lifting said components by means of respective holding devices; moving said suction tubes laterally of said cavities to cause impact of any miscentered components with walls of said cavities to centre said components on respective lifting devices; transferring said components to said printed circuit board by means of said lifting devices; and releasing said components from said lifting devices.

Preferably, the cavities each have an x-axial dimension Lx1 and a y-axial dimension Ly1, and components each have an x-axial dimension Lx2 and ay-axial dimension Ly2, thereby creating positive and negative clearances fx in the x-axial direction between each of the cavities and the components and positive and negative clearances ty in the y-axial direction between each ofthe cavities and the components. The holding devices, which may be suction tubes, are lowered into the cavities to lift up the components and then upwardly moved by a predetermined distance within the cavities.Then, the holding devices are preferably moved by a distance of fx in each of the positive and negative x-axial directions and returned to the centre of the cavities. Subsequentlythe devices may be moved by a distanceofty in each of the positive and negative y-axial directions and then returned to the centre of the cavities, to thereby permit the periphery of each ofthe components to collide with the innerwall of the cavity in the positive and negative x-and y-axial directions, and the centre ofthe holding device, electronic component, and cavity to align with one anotherdueto relative motion of the holding devices with respect to the components.The holding devices each having a respective component held atthe correct position thereon are moved onto a printed circuit board and the components are then released for mounting at predetermined positions ofthe printed circuit board with high precision.

The present invention will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings in which like reference characters designate like parts throughout and in which: Figure 1fa) is a schematic sectional view showing suction tubes of a suction head which have sucked up chips charged in cavities of a jig and have been lifted by a predetermined distance; Figure 1(b) is a schematic plan view showing dimensional relationships between a cavity of a jig and a chip charged in the cavity;; Figures 2(a) to 2/do are schematic plan views showing a sequential order of moving and positioning a chip in the positive and negativex-axial directions, and Figures 2(e) to 2(g) are schematic plan views showing the sequential order of moving and positioning a chip in the positive and negative y-axial directions.

Now, a method of correcting the position of a chip in a jig and with respectto a suction tube of an automatic chip-mounting apparatus will be described hereinafter with reference to the accompanying drawings.

First, a suction position correcting method in accordance with one embodiment of the present invention will be described with reference to Figures 1 (a) and 1 (b). Briefly, the method comprises the steps of charging chips by means of suction tubes 3 of a suction head 2, upwardly moving the suction head 2 while holding the chips Cthereon, lowering it onto a printed circuit board, and releasing the chips C from the suction tubes 3 so that the chips may be mounted on predetermined positions of the printed circuit board.

As shown in Figure 1 the chip charging cavities 1 each have an x-axial dimension Lx1 and a y-axial dimension Ly1 ,the chips C each have an x-axial dimension Lx2 and a y-axial diemnsion Ly2.

Accordingly, the upper and lower clearances or positive and negative clearances fx in the x-axial direction between the chip charging cavity 1 and the chip C each are indicated byes, which is equal to (lox1 - Lx2)/2, and the right and left clearances or positive and negative clearances ty in they-axial direction tehrebetween each are indicated by ty, which is equal to (Ly1 - Ly2)/2.

The suction tubes3 are downwardly moved for insertion into the corresponding cavities 1, to thereby suck up the chips Ctherefrom, and are then upwardly moved by a predetermined distance within the cavities 1 so as to hold and maintain the chips at predetermined positions in respective cavities.

These operations are carried out simultaneously with respectto all the suction tubes.

Then, all the suction tubes 3 are moved in x-axial and y-axial directions parallel to the jig A in accordance with the following sequential steps by actuating the suction head 2.

(a) First, the suction tubes 3 are moved by a distance of cox in the positive x-axial direction or the right direction in Figure 1 (b).

(b) Then, the suction tubes 3 are moved by a distance of 2fx in the negative x-axial direction or the left direction in Figure 1 (b) from the position described above in (a); (c) Thesuctiontubes3arethen moved bya distance of & in the positive x-axial direction from the position (b); (d) Then, the suction tubes 3 are moved by a distance of liy in the positive y-axial direction from the position (c); (e) Subsequently, the suction tubes 3 are moved by a distance of 24y in the negative y-axial direction from the position (d); and (f) Thereafter, the suction tubes 3 are moved by a distance of ty in the positive y-axial direction from the position (e) and then stopped.

In other words, all the suction tubes 3 each having its centre positioned on the centre line ofthe corresponding cavity 1 are moved by a distance of#x in each of the positive and negativex-axial directions and then returned to the original position. Further, the suction tubes 3 are moved by a distance of ty in each of the positive and negative y-axial directions and then returned to the original position. The movement of the suction tubes 3 in both x-axial and y-axial directions by a distance corresponding to each of the clearances causes the periphery of each of the chips to collide with the inner wall of the cavity 1, to thereby displace the suction position of the chip due to relative motion between the suction tube 3 and the chip C, thus aligning the centres ofthe suction tubes 3, chips C and cavities 1 with one another.Then, the suction tubes3, each holding a respective chip C at the correct suction position thereof, are moved onto a printed circuit board, and then the chips C are released from the suction tubes and mounted on the predetermined positions of the printed circuit board.

The method described above can obtain satisfactory results when the following preconditions are satisfied: (1) The cavities 1 are formed to have the same dimensions in respect of each of the chips C to be charged in the cavities. This can be readily accomplished using conventional precision machining techniques.

(2) The centre of each of the suction tubes 3 is aligned with that of the corresponding cavity 1 and the predetermined position of the printed circuit board on which the chip is to be mounted.

(3) The clearances fx and ~eyaredetermined based on the basic dimensions ofthechip C, andthe positive and negative allowable dimensional errors of each of the chips are neglected.

Accordingly, if there is a dimensional error in the chip, the centre of the suction tube cannot be exactly aligned with the centre of the chip and the alignment between the suction tube and the chip is "apparent alignment". Nevertheless, the misregistration of the chip dueto the apparent alignment is one tenth to one hundredth of that in the prior art.

Now, the method of the present invention will be described in more detail in connection with an example shown in Figures 2(a) and 2(9).

In the example shown in Figure2,thechipCis determined to have dimensions of 1.25mm 1 .25mm x 2.00mm and the cavity 1 has dimensions of 1 .75mm x 2.50mm. Accordingly, each of the positive and negative clearances in each of the x- and y-axial directions is 0.25mm when the chip C is positioned at the centre of the cavity. In the example shown in Figure 2, the chip C is charged in the cavity 1 in a position deviating from the centre of the cavity 1 towards the lower left-hand corner as shown in Figure 2(a). The method of aligning the centre ofthe suction tube with that of the chip is effected as follows: (a) First, the suction tube 3 is moved by a distance of 0.25mm (fix) in the positive x-axial direction as shown in Figure 2(b).In this case, the chip C does not collidewith the innerwall ofthe cavity because the clearance in this direction is above 0.25mm.

(b) Then, the suction tube 3 is moved by a distance of 0.5mm (2fix) in the negative x-axial direction from the position (a) described above or that shown in Figure 2(b). This causes the chip Cto collidewiththeinnerwall ofthecavitywhenthechip C is moved by a distance of 0.25mm, and the movement of the chip C is stopped and onlythe suction tube 3 is forcibly moved by the distance of 0.5m m. Acco rdi n g ly, the suction position of the suction tube 3 with respect to the chip C is moved due to relative motion, to thereby align the centre of the chip C on the x-axis thereof with that ofthe suction tube 3 as shown in Figure 2(c).

(c) When the suction tube 3 is moved or returned by 0.25mm (fix) in the positive x-axial direction fromt he position (b), this causes the x-axial centres of the suction tube 3, chip C and chip charging hole 1 to be aligned with one another as shown in Figure 2(d).

(d) Then, the suction tube 3 is moved by a distance of 0.25mum (try) in the positive y-axial direction from the position (c) or that shown in Figure 2(d). This movement does not cause the collision between the chip C and the innerwall ofthe cavity 1 as shown in Figure 2(e), because the clearance in this direction is above 0.25mm.

(e) Subsequently, the suction tube 3 is moved by 0.5mm (2my) in the negative y-axial direction from the position (d). This causes the chip C to collide with theinnerwall of the cavity when the chip C is moved by a distance of 0.25mm, and the movement ofthe chip C is stopped and only the suction tube 3 is forcibly moved by the distance of 0.5mm.

Accordingly, the suction position of the suction tube 3 with respect to the chip C is moved due to relative motion, to thereby align the centre of the chip C on the y-axis thereof with that of the suction tube 3 as shown in Figure 2(f).

(f) Thereafter, the suction tube 3 is returned by a distance of 0.25mm in the positive y-axial direction from the position (e) or that shown in Figure 2(f). This results in the centre ofthe suction tube 3, chip C and cavity 1 being aligned with one another on they-axial direction as shown in Figure 2(g).

Thus, it will be noted that the operations (a)-(f) described above cause the centre of the suction tube 3, chip C and cavity 1 in the x- and y-axial directions to be made exactly coincident or aligned with one another, andthe misalignment ofthechip Cwhich had deviated from the predetermined correct suction position thereof is corrected to the exact position.

The above operations are carried out simultaneously with respectto all the suction tubes corresponding to the cavities ofthe jig. More particularly, the movements in the positive and negativex- and y-axial directions are each simultaneously carried outwith respect to all the suction tubes, and one cycle of the operations permits all the chips to be simultaneously corrected in suction position and mounted on the predetermined mounting positions of the printed circuit board with high precision.

The method is to suck up chips charged in the cavities of the jig by means of the suction tubes, move the suction tubes to the printed circuit board while holding the chips thereon and mountthe chips on the printed circuit board. Accordingly, any suitable means can be used forfeeding chips one by one to the cavities, such as, for example, a chip feederforfeedingthechipthrough a chip feeding pipe, a chip feeding magazine, a chip feeding tape and the like.

Thus the misregistration of individual chips with respect to suction tubes of the suction head is corrected atthe time immediately after the suction tubes suck up the chips from the cavities ofthe jig,to thereby place each of the suction tubes on the predetermied or exact suction position of the chips or align the centre of the chips with that ofthe corresponding suction tube.

While a preferred embodiment of the invention has been described with a certain degree of particularity with reference to the drawings, obvious modifications and variations are possible in the light ofthe above teachings. It is therefore to be understood that with in the scope of the appended claims, the invention may be practiced otherwise than as specifically described.

For example, holding devices 3 for lifting and lowering the chips C need not be suction tubes. Any suitable form of holding device may be employed provided it is ableto hold and release a chip upon command and provided it can permit the requisite degree of lateral relative movement between the holding device and the chip held thereby.

Furthermore, although in the specific embodiment the actual position of the individual chip (in two dimensions) is adjusted, it is possible, of course, to apply the conceptofthe invention to situations in which it is desired to adjust the magnitude of only one coordinate of an article, or even to adjust all three spatial coordinates or an article if desired, e.g.

in robotics.

Claims (18)

1. A method of placing an article substantially at a predetermined coordinate in which: said component is placed between first and second stop means having predetermined positions relative to said coordinate; said component is held by releasable holding means having a predetermined positional relationship to said first and second stop means; and the holding means is advanced successively towards the first and second stop means by respective predetermined distances, and said holding means permitting the component to change its position relative thereto where said at least one stop means obstructs movement of the component.

2. A method according to Claim 1 wherein said holding means is a suction device.

3. A method according to Claim 1 or 2 wherein said holding means is returned to said predetermined position after the operations of Claim 1.

4. A method according to any one of the preceding claims in which said predetermined position is equidistant from said first and second stop means.

5. A method according to any one of the preceding claims in which said first and second stop means are opposed walls of a cavity.

6. A method according to any one of the preceding claims in which the holding means also has a predetermined positional relationship to third and fourth stop means, and is moved by respective predetermined ammounts, perpendicular to its motion towards first and second stop means, towards said third and fourth stop means successively, in orderto place said article substantially at a second predetermined coordinate.

7. A method according to Claim 6 when dependent on Claim Sin which said third and fourth stop means are further opposed walls of said cavity.

8. A method according to Claim 7 wherein said article is an electrical or electronic component and said cavity is provided in a location jig.

9. A method according to any one of Claims 1 to 8 in which said article is released from said holding means after placing at said coordinate(s).

10. A method of mounting electronic components at predetermined positions of a printed circuit board, comprising the steps of: charging said components into respective cavities of a jig; lifting said components by means of respective holding devices; moving said holding devices laterally of said cavities to causeimpactofanymiscentered components with walls of said cavities to centre said components on respective holding devices; transferring said components to said printed circuit board by means of said holding devices; and releasing said components from said holding devices.

11. A method according to Claim 10 in which said cavities each have an x-axial dimension Lx1 and a y-axial dimension Lye, and said electronic components each have an x-axial dimension Lx2 and a y-axial dimension Ly2, thereby creating a first and second clearances x in the x-axial direction between each of said cavities and said electronic components and a first and second clearances yin they-axial direction between each of said cavities and said electronic components and in which said moving step includes:: moving each holding device in first and second x-axial directions; returning each holding device to the centre of its cavity by movement in the x-axial direction; moving each holding device in first and second y-axial directions; returning each holding device to the centre of its cavity by movement in the y-axial direction, thereby permitting each of said electroniccomponentsto collide with an innerwall of said cavity in thefirstand second x- and y-axial directions and permitting the centres of said holding device, electronic component cavity to align with one another due to relative motion of said holding device with respect to said electronic component.

12. A method as claimed in Claim 11 wherein each of said first and second clearances in the x-axial direction is represented by the expression of Lx1-Lx2/2.

13. A method as claimed in Claim 11 or 12, wherein each of said first and second clearances in the y-axial direction is represented by the expression of Ly1 -Ly2/2.

14. A method as claimed in anyone of Claims 11 to wherein each holding device is moved by a distance equivalent to said clearance fx in the first x-axial direction and then moved by a distance equivalent to twice said clearanceex in the second x-axial direction.

15. A method according to any one of Claims 11 to 14 wherein each holding device is moved by a distance equivalentto said clearance tyinthefirst y-axial direction and then moved by a distance equivalent to twice said clearance in the second y-axial direction.

16. A method according to anyone of Claims 10 to 15 in which said holding devices are suction tu bes.

17. A method of placing an article substantially at a predetermined coordinate substantially as hereinbefore described with reference to the accompanying drawing.

18. A method of mounting electronic components at predetermined positions of a printed circuit board substantially as hereinbefore described with reference to the accompanying drawing.