SE515672C2 - Application of molten metal droplets together with secondary liquid on a substrate - Google Patents

Abstract

When applying solder paste to substrates, for example circuit boards, a jet comprising a fluxing agent (15) on top of a core of molten solder (11) is used. It is achieved by making a jet of molten solder (11) pass through a space filled with the fluxing agent. For suitable conditions the jet (19) is divided into drops (21), when it has passed out of the space filled with fluxing agent. Those drops, which hit the substrate, the consist of a core (22) of solidified solder surrounded by an enclosure (25) of fluxing agent. The applied solder paste thereby becomes completely fresh, which means that only an extremely small amount of oxide exists in the paste. Furthermore, in the corresponding way individual drops of solder can be ejected through the space filled with fluxing agent, which allows a very accurate dosing of the amount of solder paste, since the amount is determined by the number of solder balls and this number can be digitally controlled. This method can generally be used to apply a first liquid material having an enclosure of another liquid material, the first material advantageously being a material such as molten metal, which is significantly more heavy than the material of the enclosure.

Description

530 67 515 672 barability is usually supported by a mechanical vibration, crystal, generated by a beam, generated by a piezoelectric mounted on the capillary which is driven by applying electrical voltage in a suitable manner. In the so-called droplet formation point, selected droplets are electrically charged to enable them to be deflected in an electric field, all in analogy with the "continuous ink-jet" technology. This "continuous solder-jet" technique is briefly described in the article "MPM's Metal Jet Technology - Solving the Materials Applications Tasks of the Future and Enabling Ongoing Reed Miniaturization", Electronics Manufacturing International, Elsevier, Brussels, Nov./Dec. 1996, p. 16, with both application of mechanical oscillations to a plumb beam and electrostatic deflection of formed droplets.

In this technique, the droplets may solidify on their way to the substrate. Thus, what strikes the substrate is either a stream of solid particles or droplets of high temperature, which solidify. they cool on contact with the printed circuit board. as desired. For the solid particles, some form of sticky coating on the printed circuit board is conventionally required for the particles to adhere thereto. Even if any such coating is used, however, the particles cannot stick on top of each other, which is necessary to obtain the desired height of the solder island. In the case of molten droplets, they may possibly melt into each other, but it may be difficult to control the appearance of the solder and to avoid splashes of solder. Another disadvantage is that a flux addition to the solder is required for the subsequent soldering of the components. With the described technique, the flux must be applied separately.

U.S. Patent 4,828,886 discloses the application of small amounts of molten solder from a nozzle. After melting the solder, it is driven forward by a piezoelectric transducer used as a pressure generator.

A fused solder electrodynamic pump is disclosed in U.S. Patent 5,377.96l suitable for the manufacture and application of very small single droplets. An electric current is applied in a reversible direction in a plumb current and a force on the plumb current is obtained by interaction with a surrounding magnet. This is used to separate the droplets. U.S. Patent 5,560,543 discloses how droplets of uniform and predictable size can be formed from a liquid at a high temperature. A jet of the liquid is expelled by means of an electromechanical drive from a nozzle, whereby vibrations are produced in the liquid on its way to the nozzle, so that droplets are formed.

DISCLOSURE OF THE INVENTION It is an object of the invention to provide a method and a device for accurately controlled application of molten metal, for example solder, printed circuit boards, by means of which method and device a the molten metal can be made to securely adhere to the surface of the substrate.

It is a further object of the invention to provide a pre-solder at the same time and with high speed and a device, by means of which molten metal, and a secondary liquid, eg flux, can be accurately applied to a substrate such as a printed circuit board.

By using a combined jet of flux / liquid solder with the molten solder as the primary liquid and flux / resin solution as the secondary liquid, the solder paste is created or manufactured at the same moment as it is needed. The droplets which hit the substrate then consist of a core of solidified solder surrounded by a flux / resin casing and thus form a form of solder paste according to OVafl.

Such a method allows a very accurate dosing of the amount of paste, as the amount is determined by the number of solder balls and this number is digitally controllable. Another advantage is the fact that the solder paste is completely fresh, which means that only a very small amount of oxide is present in the paste. This is favorable from a soldering point of view, as the tendency of the paste to splash during the remelting increases sharply due to increased oxide content in the paste. Solder splashes are a potential short-circuit risk on circuit boards. In addition, the low oxide content of the paste results in a greatly improved wetting against metal surfaces. To further enhance this effect with low oxide content in the paste, for example, an antioxidant gas or generally a shielding gas can be applied around the jets / drops of solder or solder balls surrounded by the flux immediately after formation and up to the substrate.

In inkjet printing technology, there are two basic concepts, namely "continuous ink-jet" and "drop on demand". Above, the application of the "continuous ink-jet" principle for applying solder to substrates has already been discussed.

The "drop on demand" principle means, as the name suggests, that drops are ejected piece by piece, one at a time, when desired or required.

When applying the procedure just described, these droplets may consist of molten solder. As before, the solder droplets constitute a "primary liquid" and are allowed to pass through a secondary liquid of molten flux / resin. In the same way as described above, the primary drop solidifies into a ball and surrounds itself with a flux / resin casing. The droplets can, during and after their formation, be surrounded by a shielding gas to prevent, for example, oxidation of material. The shielding gas flow can be designed, for example, laminarly or in another way, in the droplets on their way to the substrate. so that a stabilizing effect is also obtained on the formation of the droplet flow and on its path towards the substrate.

The advantage of the "drop on demand" principle is that only as much solder paste is produced as is needed to coat the solder surfaces of the printed circuit board; there is thus no "slap" paste. Furthermore, no deflection and thus no electrostatic charge of the droplets is required. However, the ejector and substrate must be moved laterally relative to each other to apply solder paste to desired surfaces of the substrate. However, such a movement is necessary in order for a good accuracy of the ejected droplets to also be for the "continuous ink-jet" method. The reason for this is, obtained, you usually choose to arrange electrostatic charging of selected drops and to divert precisely these charged drops, which you do not want to hit the substrate. These drops end up in and are therefore not used. a "sludge" In the "continuous ink-jet" case, all the droplets which it is desired to hit and be applied to the substrate go straight out of the ejection nozzle. Any other selective control by means of the electrostatic deflection is therefore not used - this only works analogously with a "switch-off / switch-off" or shut-off valve, ie a switch or valve which either provides complete shut-off or releases full flow. Although the process described above could also be applied to liquids which are miscible with each other, it is better suited for immiscible liquids as in the above case with solder = flux / resin = In the case of solder flux / resin the ratio is particularly favorable due to primary fluid, secondary fluid. because the liquids are immiscible with each other and the primary liquid has a significantly higher density than the secondary liquid. The latter means that when applying the secondary liquid to droplets of the primary liquid, only a small amount of kinetic energy is stolen from the primary liquid, ie the speed of the primarily ejected droplets is only moderately affected.

Thus, in general, amounts of material which in the preferred case comprise a metal such as solder and another substance are applied to a substrate.

Such an amount of material can be obtained by first supplying or producing a primary liquid, such as by melting a metal to form the primary liquid. A jet of the primary liquid, in the special case a jet of the molten one, is formed. if this is not present in liquid form, the metal. Furthermore, a secondary liquid of the second substance is formed, such as through the jet of primary liquid may pass through a first space, which heating to melting, to near melting or the like. contains the secondary liquid, so that the amount of primary liquid has a surface coating of secondary liquid, which can then or later mix with the primary liquid, even if this does not happen in the preferred case of molten metal, when the second substance comprises, for example, as a main component or carrier something organic matter. The beam is allowed to pass from the first space through an opening thereof out into a free state directed towards a designated place on the substrate. Furthermore, various essential parameters, such as the properties of the primary liquid and the secondary liquid, in particular surface tension and their wetting in relation to each other, the velocity of the beam, the size of the aperture and the distance from the aperture to the substrate are so selected that the beam the first space forms individual droplets, before it reaches the substrate, i.e. during its path in the direction of the substrate.

Alternatively, instead of a jet, at least one drop of primary liquid can be formed, which drop is given at a high speed. This drop is then, as above, passed through the first space, which contains secondary liquid, so that the drop of primary liquid thereby has a surface coating of secondary liquid. The drop as well as the jet is then caused to pass out of the first space directed towards a designated place on the substrate. A series of such individual droplets of the primary liquid can be formed, which series as well as the jet above then passes through the first space.

When forming a droplet or a series of droplets and expelling it with speed, primary liquid may be present in a second space provided with a nozzle. The nozzle can then have a suitable design and / or is arranged in such a way, for instance by applying vibrations such as from a piezoelectric device, that the primary liquid is divided into individual drops after passage through the nozzle. However, this can only give a series of drops. Alternatively, in order to also produce individual droplets, different devices may be provided for subjecting the primary liquid in the second space to a rapid pressure change and / or a pressure surge and / or a rapid volume change or a consequence of such changes / shocks. , so that in some way an acceleration of at least some part of the primary liquid in the second space is effected. With each such change / shock, a small amount of primary liquid in the form of a drop will then be expelled through the nozzle, if this is suitably placed in relation to how the change / shock or acceleration is formed or located. For example, such devices may include a suitably shaped piston which is movable in the second space or forms a wall therefor, piezoelectric means, devices for shock heating of the primary liquid or a hammer which strikes an outer wall of the second space.

In the preferred case, the primary liquid can have a significantly higher density than the secondary liquid, as in the case of solder and flux.

Furthermore, in the standard case, these liquids are not miscible with each other. The secondary liquid may generally comprise alone or in association substances for modifying the rheological properties of the primary liquid, substances for preserving the primary liquid, substances having a reducing effect on the primary liquid, antioxidants and surfactants, for example, adhesives for attaching droplets of the primary liquid to the substrate.

A shielding gas can be used to protect the expelled amounts of material such as from oxidation and fouling. This is then suitably emitted by an annular nozzle, which surrounds the ejection opening, so that the emitted shielding gas will surround the emitted amounts of material at least partially during their journey towards the substrate.

Such a shielding gas flow can also be designed, for example as a laminar flow, so that a stabilizing effect is obtained on the formation of droplets from the amount of primary liquid together with secondary liquid and / or on the movement of the material quantities or droplets towards the substrate. Furthermore, electrostatic deflection can be used to, for example, divert unwanted drops.

DESCRIPTION OF THE DRAWINGS The invention will now be described as a non-limiting exemplary embodiment with reference to the accompanying drawings, in which - Fig. 1 is a perspective view illustrating a principle for applying solder paste, - Fig. 2 is a section through a device for applying solder paste, in which solder is ejected as a jet or series of drops, - Fig. 3 is a section through a device for applying solder paste, in which solder is ejected as single drops, and - Fig. 4 is a section similar to that in Fig. 2 but the device is here provided with electrostatic deflection.

DESCRIPTION OF PREFERRED EMBODIMENTS In Fig. 1, on a greatly enlarged scale, a principle for applying solder paste by means of a composite beam is illustrated. A jet 11 of primary liquid from any suitable source, not shown, is ejected from the opening in a nozzle 13 and then passes through a secondary liquid 15, which is in open space, which is bounded by a cylindrical, side wall 17 concentric with the nozzle 13 and which surrounds the nozzle 13. The secondary liquid can be kept in the open space due to surface tensioning forces and possibly by means of a suitable design of the side wall 17, which does not have to have the cylindrical design shown in this figure but can be designed conically tapered with a smaller opening. The jet is then surrounded by a casing of the secondary liquid 15 to form a combined jet 19. The combined jet 19 of primary liquid 11 plus secondary liquid 15 then decomposes, with suitable parameters selected for the process, due to surface tension, etc., in droplets. pair 21, which are constituted by a core 22 of primary liquid, surrounded by a shell 25 of secondary liquid.

Fig. 2 shows the application of solder paste to a substrate or printed circuit board 27 placed on a table 29, which is movable in two, perpendicular directions lying in the plane of the table, one direction of which is indicated by the arrow at 31. A jet of primary liquid 11 consisting of for example, molten solder is ejected from a nozzle 13, which is arranged at the lower end of a pipeline 33, at the other end of which primary liquid 11 is supplied, see arrow 35. With a suitable design of the nozzle 13, the ejected jet can, for example, directly form droplets. in the secondary liquid 15. The secondary liquid consisting of eg flux / resin solution, comes from some source, see arrow 37, through a channel 39 perpendicular to the primary liquid pipeline 33 and then passes into a space concentric with the pipeline 41 formed in an exhaust body 43, in which the pipeline 33 is also attached. The secondary liquid 15 is led therefrom to a space 45, also concentric with the pipeline 33 and the nozzle 13 but has which surrounds the nozzle 13 of the primary liquid. This space 45 is lower bent-in edges 47, so that a nozzle for secondary liquid is formed. The droplets or jets of primary liquid pass through the secondary liquid 15 in the space 45 and are thereby surrounded by a casing of secondary liquid. As the droplets consisting of the primary liquid 11 plus the secondary liquid 15 are pushed out of the nozzle of the secondary liquid formed by the edges 47, they will in a similar manner as above consist of a core of primary liquid, surrounded by a shell of secondary liquid. The droplets may be surrounded by a shielding gas entering from any gas source through an annular nozzle 48 located at the outlet of the space 45 adjacent the edges 47 on the outside of the exhaust body 43, to prevent, for example, oxidation of the molten metal on the way to the substrate 27. The gas flow can be laminated with the appropriate design of the annular nozzle 48, compare the arrows 48 ', or otherwise, so that in addition a stabilizing effect is obtained on the formation of the droplet flow and its travel towards the substrate.

The movement of the table 29 relative to the ejector body 43 can easily be effected in known automatic assembly / coating machines, for example by the table 29 being movable in a horizontal direction and the ejector body 43 in a perpendicular, horizontal direction.

Figure 3 shows a cross section through an ejection mechanism for generating single ejected composite droplets. The primary liquid consisting of e.g. molten solder enters through a tube 49, which is partially closed at its lower end to form an opening or nozzle 13 with a suitably shaped, rather small outlet. The tube 49 is arranged in an ejection block 53, which contains means for pushing a small drop through the nozzle. Such means may, for example, bring about a small reduction in the volume of the inner space of the tube 49, where the primary liquid is located. In the embodiment shown, the tube 49, within its portion inside the block 53, is surrounded by an annular body 55 of piezoelectric material, which is connected to suitable electrical circuits, not shown, in order to effect a controlled reduction of the internal the diameter of the annular body 55. The nozzle 13 opens, as in Fig. 2, into a space 45 containing secondary liquid. The secondary liquid consisting of eg flux / resin solution enters through a channel 57 perpendicular to the tube 49 and passes from there through a channel to the lower space 45, which surrounds the nozzle 13 of the primary liquid. This space 45 is concentric with the tube 49 and the nozzle 13. An opening 59 with a suitable design is available from the lower space 45.

When the ejection means 55 is activated, the volume in the tube 49 is reduced and a drop of primary liquid is expelled at speed through the nozzle 13. The drop passes through the secondary liquid in the lower space 45 and is thereby surrounded by a casing of secondary liquid. The composite drop thus formed then passes out through the outer nozzle 59 to be applied at the intended location.

Applying droplets in the manner described above can be combined with electrostatic deflection as in the above-mentioned 10 15 20 25 515 672 10 A device with such deflection is shown circulating and is the "continuous jet" method. schematically in Fig. 4. This has an upper electrically conductive, linear ring or a cylindrical short tube 61, concentric with the upper part of the path of the formed droplets.

An electrically high voltage can be applied between the ring 61 and the housing 43, which is generated by an electrical control unit 63, partly with the ring 61 and partly with the housing 43. The voltage can thus be connected by suitable electrical conductors. pelvis is applied, so that the housing has a negative potential or earth potential, while the ring 61 has a positive potential. When the voltage is applied, a drop, which is separated from the beam emanating from the housing 43, becomes electrostatically charged, provided that the liquid in the drops has some electrical conductivity, and with the exemplary polarity of the high voltage, such a drop becomes drop negatively charged. Below the ring 61 there are electrically conductive plates 65, small with the shaft of the ring 61 and which with their mutually opposite sides and also parallel large surfaces surround a lower part of the path of the ejected drops. The plates 65 are also electrically connected to the control unit 63, between the plates. This voltage diverts the ejected droplets, so that a high electrical voltage is generally permanently located which is electrically charged, so that these are led to some space, not shown, which acts as a "sludge" and can receive a considerable amount of droplets. The ejected droplets, which have no electric charge, instead go straight towards the substrate and hit this and are applied there.

Claims (17)

10 15 20 25 30 35 515 672 ll PATENT REQUIREMENTS A method of applying material amounts comprising a metal, in particular solder, and another substance to a substrate, wherein the metal is melted to form a primary liquid of molten metal and a secondary liquid is formed of the second substance, which comprises an organic or inorganic fluid, especially flux or resin in semi-molten or molten form, selected to enhance the application of a quantity of primary liquid to the substrate and / or the use of a quantity of primary liquid, characterized in that a quantity of primary liquid is allowed to pass through a first space, which contains secondary liquid, so that the amount of primary liquid has a surface coating of secondary liquid, and out of the first space directed towards a designated place on the substrate. of that A method according to claim 1, characterized in that the amount of primary liquid is a jet, a series of drops or a single drop. of that 3. A method according to claim 1, characterized in that the amount of primary liquid is a jet which passes out of the first space through an opening of suitably sized design, so that the jet after the outlet from the opening is divided into individual drops. 4. A method according to claim 3, characterized in that the metal and the second substance are so selected that the individual droplets comprise an inner part of primary liquid and an outer layer of secondary liquid. of that 5. A method according to claim 1, characterized in that the amount of primary liquid is a series of droplets, which are formed by the primary liquid being allowed to pass out of a second space into the first space through a suitably designed and / or arranged nozzle. k ä n n e t e c k n a t A method according to claim 1, in that the amount of primary liquid is a single or single drop, which is formed by allowing primary liquid to pass through or reside and in a second space, which is provided with a nozzle, The primary liquid in the second space is subjected to a rapid pressure change and / or a pressure surge and / or a rapid volume change, whereby a small amount of primary liquid in the form of a drop is expelled through the nozzle. A method according to any one of claims 1 to 6, characterized in that a flow of a shielding gas is emitted to surround the amount of primary liquid together with secondary liquid, when this amount passes out of the first space directed towards a designated place on the substrate , so that the shielding gas surrounds the amount at least in part as it travels towards the substrate. k ä n n e t e c k n a t of flö- especially as a lami- A method according to claim 7, it is emitted by shielding gas in such a manner, near flow, that a stabilizing effect is obtained on the formation of droplets from the quantity of primary liquid together with secondary liquid and / or on the movement of the quantity and droplets towards the substrate. Method according to any one of claims 1 - 8, characterized in that after the amount of primary liquid together with secondary liquid has passed out of the first space directed towards a designated place on the substrate, the amount is electrostatically charged and the amount of primary liquid together with secondary liquid is exposed to an electrostatic field to control the trajectory of the quantity. Device for applying amounts of material comprising a metal, in particular solder, and another substance on a substrate, which substance is capable of forming a primary liquid, as in melting, forming an organic or inorganic fluid, in particular flux or resin in semi-molten or molten form, selected to improve the application of an amount of primary liquid to the substrate and / or the use of an amount of primary liquid, characterized by - means for melting an amount of the metal to form an amount of primary liquid and for expelling it with speed, - a first space, which contains secondary liquid and is located so that the amount of primary liquid passes therethrough and thereby has a coating of secondary liquid, and - an opening out of the first space is placed, so that the amount of material passes therethrough directed towards a designated place on the substrate. 10 15 20 25 30 35 515 672 13 the substrate. 11. ll. Device according to claim 10, characterized in that the means for melting an amount of the metal and for expelling the formed amount of primary liquid at speed are arranged to form a jet of primary liquid or to form a series of droplets or a single drop of primary fluid. Device according to claim 10, characterized in that the means for melting an amount of the metal and for expelling the formed amount of primary liquid at speed are arranged to form a jet and that the opening out of the first space is formed with suitable size, so that the beam after the outlet through the opening during its journey towards the substrate is divided into individual drops. Device according to claim 10, characterized in that the means for melting an amount of the metal and for expelling the formed amount of primary liquid at speed are arranged to form a series of drops and that the device further comprises - a second space , through which primary liquid passes or in which primary liquid resides and which comprises a nozzle which opens into the first space, and - means for causing primary liquid to pass out through the nozzle, - wherein the nozzle has such a design and / or is arranged in such a way that the primary liquid is divided into individual droplets after passage through the nozzle. Device according to claim 10, characterized in that the means for melting an amount of the metal and for expelling the formed amount of primary liquid at speed are arranged to form a drop and that these means further comprise - a second space, in which primary liquid resides and which is provided with a nozzle, and - means for subjecting the primary liquid in the second space to a rapid pressure change and / or a pressure surge and / or a rapid volume change, whereby a small amount of primary liquid in the form of a drop is expelled through the nozzle. 10 15 20 25 30 515 672 14 Device according to any one of claims 10 - 14, characterized by a nozzle connected to a source of a shielding gas for emitting a shielding gas flow, so that it surrounds the amount of material, as it passes out through the opening towards the intended place on the substrate and so that the shielding gas surrounds the amount at least in part during its further travel towards the substrate. of that Device according to claim 15, characterized nozzle for the shielding gas is designed so that the shielding gas is emitted therefrom in such a way, in particular as a laminar flow, that a stabilizing effect is obtained on the formation of droplets from the amount of primary liquid with secondary liquid and / or on the path of the quantity as it travels further towards the substrate. Device according to any one of claims 10 - 16, characterized by - an electrostatic charging device placed at the path which the amount of primary liquid with secondary liquid has, after it has passed out through the opening, the charging device being connected to electric high voltage for charging the amount of primary liquid with secondary liquid coating, - deflection plates placed around the path that the amount of primary liquid with secondary liquid coating has, after it has passed the electrostatic charging device, the plates being electrically connected to a electrostatic deflection of the amount of primary fluid with secondary fluid.