WO1999044402A1

WO1999044402A1 - A deposition method and apparatus therefor

Info

Publication number: WO1999044402A1
Application number: PCT/GB1999/000556
Authority: WO
Inventors: Peter John Wellesley Noble
Original assignee: Moore, Royston
Priority date: 1998-02-25
Filing date: 1999-02-24
Publication date: 1999-09-02
Also published as: GB9803972D0; AU2631699A

Abstract

A method of depositing a deposition material (4) on a substrate (1) comprising the steps of: overlaying a sheet (3) comprising a carrier film (5) of said deposition material (4) over the substrate (1); directing an energy source (11) having a spot area onto a pre-selected area of the sheet (3) to deposit the pre-selected area of the deposition material (4) from the sheet (3) onto the substrate (1); and removing the remainder of the sheet (3).

Description

- 1 -

"A deposition method and apparatus therefor"

THIS INVENTION relates to a deposition method and apparatus therefor and more particularly to a method of depositing material on a substrate.

The precise delivery and placement of electrically conductive pastes, solders and adhesives and other such materials on such items as printed circuit boards and ceramic substrates has in the past been carried out using developments of screen printing technology.

The methods used by such systems have utilised a mask, stencil or screen in order to define both the thickness and the area of material to be deposited. This is a well known process and has been used in the electronics industry for many years. Recent developments have led to a process called 'metal jetting' which deposits solder on a substrate by directing a stream of molten solder toward the substrate and deflecting the stream of solder by a magnetic field to control the area on which the solder is to be deposited.

The present invention seeks to provide a deposition method and apparatus therefor which does not require the use of masks, screens or stencils and does not use any aspect of metal jetting technology.

Accordingly, one aspect of the present invention provides a method of depositing a deposition material on a substrate comprising the steps of : overlaying a sheet of said deposition material over the substrate; directing a concentrated energy source having a spot area onto a pre-selected area of the 2 sheet to deposit a pre-selected area of the deposition material from the sheet onto the substrate; and removing the remainder of the sheet.

Another aspect of the present invention provides an apparatus for moving the sheet of deposition material into contact with the substrate and moving the substrate at the same speed as the sheet past the concentrated energy source such that there is no relative movement between the substrate and the deposition material as the substrate and deposition material pass the concentrated energy source.

In order that the present invention may be more readily understood, embodiments thereof will now be described, by way of example, with reference to the accompanying drawings, in which:

FIGURE 1 is a schematic side view of an apparatus embodying the present invention; and

FIGURE 2 is a cross-section of a length of deposition material fixed to a carrier film for use with an embodiment of the present invention.

Referring to Figure 1, a deposition apparatus embodying the present invention comprises deposition means to deposit deposition material onto a substrate and a feeder (not shown) for carrying a substrate 1 such as an electrical or electronic circuit board into proximity with the deposition means.

The feeder is preferably a conveyor having a number of jigs or fastening means to which each substrate may be attached. The conveyor is driven at a substantially constant speed. Thus, a train of substrates secured to the conveyor move at a constant speed past the deposition means. 3 The deposition apparatus comprises two spaced apart rollers 2,3. The first roller 2 is a source roller 2 and carries a rolled length 3 of the material to be deposited on the substrate. Referring to Figure 2, the deposition material 4 to be deposited on the substrate 1 is held on a substantially transparent carrier film 5 either by its own adhesion or by an adhesive applied to the carrier film 5 or the deposition material to adhere the deposition material 4 to the carrier material 5. The deposition material 4 is a solder, paste, adhesive, powder or whatever other material is required to be deposited on the substrate 1. The deposition material is held together on the carrier by a binding agent such as a solder flux, paste or other material which forms a binding agent. Thus, the deposition material 4 could comprise solder balls or powder held in place by the solder flux and a binding agent.

The deposition material 4 is adhered to the carrier film 5 by the adhesive as a uniform layer of constant thickness across the width of the carrier film 5. Preferably, the carrier film 5 has a thickness of the order of 10 to 50 microns and the deposition material 4 has a thickness of the order of 20 to 100 microns.

Referring to Figure 1, the film 3 is fed from the source roller 2 toward the feeder carrying the substrates 1 and around a first pressure roller 6 which, in use, is held against the substrate 1, the film 3 being sandwiched between the pressure roller 6 and the substrate 1 with the deposition material 4 contacting the substrate 1 and the carrier film 5 contacting the pressure roller 6.

A second pressure roller 7 is spaced apart from the first pressure roller 6 by a predetermined distance and the film 3 is fed from the first pressure roller 6 across the predetermined distance in contact with the substrate 1 and around the second pressure roller 7 which also pushes the film 3 against the substrate 1 4 such that the deposition material 4 makes contact with the substrate 1 and the carrier film 5 makes contact with the second pressure roller 7.

The film 3 is then fed from the second pressure roller 7 to a take-up roller 8 so that the film 3 which has passed from the source roller 2, under the first and second pressure rollers 6, 7 is stored on the take-up roller 8.

The source roller 2 and the take-up roller 8 are driven such that the speed of the film 3 between the first and second pressure rollers 6, 7 is synchronised to the speed of the substrate 1 passing under the first and second pressure rollers 6, 7 so that there is substantially no relative movement between the substrate 1 and the film 3 over the predetermined distance between the first and second pressure rollers 6, 7 when the deposition material 4 is in contact with the substrate 1.

A laser 9 or other concentrated energy source is located above the film 3 such that the laser beam of the laser 9 is focused by a focusing lens 10 located between the laser 9 and the film 3 onto the film 3 between the first and second pressure rollers 6, 7.

The area of the film 5 illuminated by the laser 9 is known as the spot area.

The focusing lens 10 is controllable so as to direct the focused laser beam 11 on any point along the width of the film 3. The laser 9 can be switched rapidly on or off or the beam 11 can be directed away from the film 3 to control which areas of the film 3 are illuminated by the laser beam 11. 5 In operation- substrates 1 are delivered to the deposition apparatus by the feeder at a predetermined speed. The film 3 is travelling at the same predetermined speed as the substrates 1 between the two pressure rollers 6, 7 so that over the distance between the two pressure rollers 6, 7 there is no relative movement between the film 3 and the substrate 1. Over the distance between the two pressure rollers 6, 7, the deposition material 4 on the film 3 is in contact with or in close proximity to the substrate 1.

A microprocessor or the like is operable to control the focusing lens 10 and the laser 9 such that the laser beam 11 can scan across the width of the film

3 as the film travels under the laser beam 11. Those areas of the substrate 1 upon which the deposition material is to be deposited are illuminated by the spot area of the laser beam 11 and those areas upon which no deposition material is to be deposited are not illuminated by the laser beam 11. Only these areas of the film 3 illuminated by the spot area of the laser 9 will be imparted with sufficient energy to melt the adhesive which holds the deposition material

4 on the carrier film 5, thereby releasing the deposition material 4 from the carrier film 5. In addition, the laser beam 11 melts, for example, the solder flux of the deposition material 4 such that the solder flux adheres to the substrate 1 thereby transferring the deposition material 4 to the substrate 1. As a consequence of being illuminated by the laser beam 11, the deposition material 4 on the film 3 is removed from the film 5 and deposited onto the substrate 1. The energy of the laser beam is controlled such that the removal of the deposition material from the carrier film 5 is by melting the adhesive and at least a part of the deposition material 4 such that the deposition material 4 attaches to the carrier film 5.

In embodiments where no adhesive is applied between the carrier film and the deposition material, the step of melting the deposition material 4 6 releases the deposition material from the carrier film 5 and attaches the deposition material 4 to the substrate 1.

The combination of the movement of the substrate 1 under the laser beam 11 and the ability of the laser beam 11 to scan across the width of the substrate 1 allows the laser beam 11 to be directed to and therefore remove the deposition material 4 from any point of the film 3 in contact with the substrate 1. This arrangement provides a particularly easily controllable method of depositing deposition material 4 from the film 3 onto the substrate 1 at preselected areas such as where solder pads, adhesive pads and any other structures to be deposited on the substrate 1 are required.

Examples of the deposition material 4 are the solder pastes used in surface mount technology, solder bumps used in silicon wafer bumping, conductive adhesives used in surface mount technology and pastes and inks used in hybrid assembly and similar applications.

As previously described, the carrier film 5 is transparent such that little or no energy from the laser beam 11 is absorbed by the carrier film 5. However, the deposition material 4 is substantially opaque and thus absorbs the laser energy. The laser energy melts the deposition material 4 which, in contact with the substrate 1, is transferred to the substrate 1, thereby removing the deposition material 4 from the carrier film 5.

Whilst the above described apparatus uses a single laser beam 11, it is envisaged that an array of such laser beams could be provided to scan predetermined widths of the film 3 above the substrate 1. 7 The ability to control the movement of the laser beam 11 or other concentrated energy source across the film 3 above the substrate 1 can be implemented in a number of ways and is not limited to movement of the laser beam 11 normal to the direction of travel of the substrate 1 nor to the use of a controllable focusing lens 10.

The constant feeding of substrate 1 under the film 3 provides a deposition method which can be readily integrated into production lines. Additionally, the method and system of the invention do not require the use of masks or stencils of the like which require troublesome registration with the substrate 1 to ensure accurate positioning of the deposition material 4 on the substrate 1.

The pattern to be deposited may be derived from assembly data and delivered to the apparatus by electronic means or may be derived by using an optical scanner to create the data from the original substrate at an earlier point in the process.

It is envisaged that the used film 3 running off from the second pressure roller 7 and onto the take-up roller 8 can be recycled for future use as it is quite clear that, in most applications, not all of the deposition material 4 carried on the film 3 will actually be deposited on the substrate 1. Only those pre-selected areas of deposition material 4 will be deposited. Another option is to provide a continuous supply of film 3 in a never-ending loop such that used film 3 is passed under a deposition material applicator which fills areas where the deposition material has been removed with fresh deposition material so that the renewed film 3 can be fed around the source roller 2 and back under the first pressure roller 6. 8

It is envisaged that the entire system of film control including driving the source roller 2, take-up roller 8, the pressure roller 6, 7 and the control of the pressures which the pressure rollers 6, 7 apply to the substrate 1 may be included in a single control unit such that the entire deposition apparatus can be manufactured and produced as a stand alone and replaceable unit.

In a basic embodiment of the deposition apparatus, an embodiment more suited to low volume applications, the film 3 is provided as discrete sheets which can be manually or otherwise located over a substrate 1 such that the deposition material 4 is in contact with the substrate 1. The laser beam 11 can then be directed over pre-selected areas 5 of the film 3 so as to deposit the deposition material on the substrate 1 in the pre-selected areas. Such an embodiment requires the laser beam 11 to be controllable in two axes rather than just one since there is no relative movement of the substrate 1 with respect to the laser 9. It is, however, envisaged that a movable jig may be provided upon which the substrate 1 can be placed. The laser beam 11 remains stationary and the movable jig controls movement of the substrate 1 in the two axes necessary to allow the laser beam to cover the entire area of the film 3 above the substrate 1.

It is envisaged that the laser 9 could be replaced with some other form of energy means, such as a heat source, which is focused enough to position accurately the spot area on the film so that only the area of the carrier illuminated (or heated) by the spot area is deposited on the substrate 1.

The deposition material 4 may comprise a powder in micro-capsule form which, upon heating, deposits the contents of the capsules onto the substrate. 9

It is envisaged that position or negative air pressure can be used to enhance the contact between the substrate 1 and the film 5 over the contact region between the pressure rollers 6, 7.

Claims

10CLAIMS:

1. A method of depositing a deposition material on a substrate comprising the steps of: overlaying a sheet of said deposition material over the substrate; directing an energy source having a spot area onto a pre-selected area of the sheet to deposit the pre-selected area of the deposition material from the sheet onto the substrate; and removing the remainder of the sheet.

2. A method according to Claim 1, comprising the further step of moving the sheet of deposition material into contact with the substrate and moving the substrate at the same speed as the sheet past the energy source such that there is no relative movement between the substrate and the deposition material as the substrate and deposition material pass the energy source.

3. A method according to Claim 2, wherein the energy source is directable across the sheet in a direction substantially normal to the direction of travel of the substrate.

4. A method according to any preceding claim, wherein the energy source is controllable to be directed onto the sheet to deposit deposition material on the substrate or away from the sheet to prevent deposition from the sheet.

5. A method according to Claim 4, wherein the energy source is switchable on or off such, when on and directed at the sheet, deposition material is deposited on the substrate.

6. A method according to any preceding claim, wherein the sheet comprises a carrier film and the step of depositing the deposition material onto 11 the substrate comprises melting the deposition material off the carrier film and onto the substrate.

7. A method according to Claim 6, wherein the sheet is recyclable.

8. An apparatus for depositing a deposition material on a substrate, the apparatus comprising means to overlay a sheet of deposition material on a substrate; and concentrated energy means to direct a spot area of an energy source to a pre-selected area of the deposition material.

9. An apparatus according to Claim 8, wherein feed means are provided to move the substrate with respect to the spot area of the energy source; and means are provided to move the sheet of deposition material with respect to the spot area of the energy source, wherein there is no relative movement between the sheet of deposition material and the substrate.

10. An apparatus according to Claim 9, wherein the means to move the sheet of deposition material with respect to the spot area of the energy source comprises an arrangement to move the sheet along a first axis and direction means to move the spot area of the concentrated energy means along a second axis substantially normal to the first axis.

11. An apparatus according to Claim 10, wherein the direction means comprises a controllable lens to focus the spot area at a predetermined position along the second axis.

12. An apparatus according to any one of Claim 8 to 10, wherein the direction means comprises means to move the energy source along the second axis. 12

13. An apparatus according to any one of Claims 8 to 10, wherein the direction means comprises an array of a plurality of sources of energy located along the second axis, each source being operable to provide a spot area along a predetermined portion of the second axis.

14. An apparatus according to any one of Claims 10 to 13, wherein the arrangement is a roller arrangement and the sheet of deposition material is in the form of a roll.

15. An apparatus according to Claim 14, wherein a pair of spaced apart rollers are provided and, in use, the roll of deposition material is fed across the rollers, the rollers being arranged to press the portion of the roll of deposition material between the rollers into contact, or close proximity, with the substrate.

16. An apparatus according to Claim 14 or 15, wherein a source roller is provided having a supply of deposition material in roll form and a take-up roller is provided to hold used roll.

17. An apparatus according to Claim 16, wherein applicator means are provided to pass used roll from the take-up roller, renew the roll of deposition material for future use and feed the source roller with the renewed roll.

18. A sheet of deposition material comprising a carrier film to which a deposition material is affixed.

19. A sheet of deposition material according to Claim 18, wherein an adhesive is provided between the carrier film and the deposition material to affix the deposition material to the carrier film. 13

20. A sheet of deposition material according to Claim 18 or Claim 19, wherein the deposition material is a paste, solder or adhesive.

21. A sheet of deposition material according to any one of Claims 18 to 20, wherein the deposition material comprises a plurality of micro-capsules, each micro-capsule, in use, upon being heated to a predetermined temperature, releasing its contents comprising material to be deposited on a substrate.

22. A sheet according to any one of Claims 18 to 21 for use with the method or apparatus of any one of Claims 1 to 17.

23. A method substantially as hereinbefore described with reference to and as shown in the accompanying drawings.

24. An apparatus substantially as hereinbefore described with reference to and as shown in the accompanying drawings.

25. Any novel feature or combination of features disclosed herein.