SE2150599A1 - Liquid metal jetting - Google Patents

Abstract

A method and a device for using jetting to provide a suspension of metal particles in flux on a substrate. The method comprises providing a substrate (112), and individually jetting one or more droplets (122) of flux (123) on an area (114) of the substrate. The method further comprises individually jetting one or more droplets (132) of molten metal (133) towards the one or more droplets (124) of flux, thereby causing the one or more droplets of molten metal to solidify and to end up suspended in the flux as metal particles (134). The device includes a substrate receiver (110), a first jetting head (120) configured to individually jet one or more droplets of flux towards the substrate receiver, and a second jetting head (130) configured to individually jet one or more droplets of molten metal towards the substrate receiver.

Description

LIQUID METAL JETTING Technical field The present disclosure generally relates to application of viscous medium on a substrate. ln particular, the present disclosure relates to using non-contactdispensing, i.e. jetting, in order to provide a suspension of metal particles in flux on a substrate.

BackgroundSolder paste normally includes metal particles suspended in a flux and is regularly used to form electrical connections. Solder paste is regularly usedwithin the field of surface mount technology (SMT). For example, solder pastemay be used to form electrical connections (and a physical bond) betweenterminals of electronic components and contact pads of printed circuit boards.Solder paste may further be used in packaging applications. For example,solder paste may be used to form electrical connections (interconnects) withina component or package, such as in Package-on-Package (PoP) solutions, orin Chip Scale Packages (CSP). ln addition to more traditional techniques,such as screen printing and/or contact dispensing, jetting (i.e. non-contactdispensing) has proven itself as a viable technique for the application of solder paste during printed circuit board manufacturing.

As the size of various electronic components continues to shrink, there is aneed to create smaller and smaller deposits of solder paste on e.g. thevarious contacting pads on a circuit board. Forjetting to remain a viabletechnology, a controlled way ofjetting smaller and smaller droplets of solderpaste is therefore required. However, in order to produce smaller droplets,smallerjetting nozzles (jetting nozzle outlets) may be required. Therefore, asthe size of the droplet shrinks, the solder particles get relatively larger in size,which increases a risk of clogging of a nozzle through which the droplets ofsolder paste are ejected during the jetting. Such clogging may causeunwanted variations in e.g. the resulting droplet size or, in a worst-case scenario, even inhibit the functioning of the nozzle itself.

SummaryThe present disclosure seeks to remedy the above discussed issue at least partly. To achieve this, a method and device for using jetting to provide asuspension of metal partic|es in flux on a substrate as defined in theindependent claims are provided. Further embodiments are provided in thedependent claims.

According to a first aspect of the present disclosure, there is provided amethod of using jetting to provide a suspension of metal partic|es in flux on asubstrate. The method includes providing a substrate. The method includesindividually jetting one or more droplets of flux on an area of the substrate.The method further includes individually jetting one or more droplets of moltenmetal towards the one or more droplets of flux, thereby causing the one ormore droplets of molten metal to solidify and to end up suspended in the fluxas metal partic|es.

The use of molten metal may reduce or completely remove the issue of metalpartic|es interfering with the nozzle and may therefore enable jetting of muchsmaller droplets than with traditional ejector technology. ln addition, byavoiding the use of relatively expensive solder paste and instead relying onvarious individual, cheaper off-the-shelf components such as flux and metal(e.g. tin), the cost of producing the metal partic|es suspended in flux may alsobe reduced. Further, a need to re-qualify the jetting process for differentsolder paste compositions may also be eliminated.

For the purpose of this application, it is to be noted that the term “jetting”should be interpreted as a non-contact dispensing process. More specifically,jetting relates to the non-contact generation of a droplet/volume of a viscousmedium (e.g. flux or molten metal), wherein an impulse is applied to theviscous medium, thereby generating a momentum which causes a droplet tobreak off from the main volume of viscous medium, and be ejected through anozzle (onto a substrate). The droplet formation is therefore controlled byinertial forces and/or surface tension.

Ajetting device (orjetting head) generally comprises an eject chambercommunicating with a supply of viscous medium, and a nozzlecommunicating with the eject chamber. Prior to the jetting of a droplet, theeject chamber is supplied with viscous medium. Then, an impulse is appliedto the volume of viscous medium in the eject chamber, causing a well-definedamount of viscous medium to be forced with high velocity out of the orifice orexit hole of the nozzle and onto a substrate, thus forming a deposit or dot ofviscous medium on the substrate. The impulse may for example be in theform of a rapid volume change, an electromagnetic impulse, or an acousticimpulse. The jetted amount is hereinafter referred to as a droplet. During theactual jetting phase, the jetted viscous medium passes through the orifice ofthe nozzle and breaks off from the viscous medium remaining in the ejectchamber, thus forming a droplet (orjet) travelling towards the substrate. Anexample of a jetting device is described with reference to Figs 4-5c inWO02089545A1 (see p.18, l.21-p.20, l.32).

As used above, the term “metal particles” refers to metal in a non-moltenform, e.g. in the form of balls/spheres or other solid form. lt is envisaged thatthe solidification of the droplets of molten metal may at least in part be causedby the inclusion of the droplets in the flux. Alternatively, or additionally, thesolidification of the droplets of molten metal may at least in part be caused bycontact with surrounding air or gas during the flight between exiting the nozzle and entering the flux. ln some embodiments, the method may include providing an active cooling ofthe one or more droplets of flux. Actively cooling the flux may help to controlthe process of solidifying the metal particles. ln some embodiments, actively cooling the one or more droplets of flux mayinclude actively cooling at least a major part of the substrate (towards which the one or more droplets of flux are jetted). ln some embodiments, actively cooling the one or more droplets of flux mayinclude locally cooling the area of the substrate (onto which droplets of flux are jetted, have been jetted, and/or will be jetted) using a cooling gas. ln some embodiments, actively cooling the one or more droplets of flux mayinclude providing the cooling gas during (e.g. in parallel with, at a same timeas) the jetting of the one or more droplets of mo|ten metal. lt is also envisagedthat the cooling gas may instead, or in addition, be applied e.g. just prior tothe jetting of the one or more droplets of mo|ten metal. ln some embodiments, actively cooling the one or more droplets of flux mayinclude at least temporarily providing the substrate on a heatsink. ln some embodiments, the substrate may be a printed circuit board (PCB). ln some embodiments, individually jetting one or more droplets of mo|tenmetal may include adjusting a distance between a nozzle used for the jettingof the one or more droplets of mo|ten metal and the substrate, such that theone or more droplets of mo|ten metal at least partially solidify before enteringthe (one or more droplets of) flux. For example, it is envisaged that at least asurface of the one or more droplets of mo|ten metal may solidify beforeentering the flux. Adjusting the distance between the nozzle and substratemay help to control the time the droplets of mo|ten metal spend between thenozzle and the substrate, and thereby how much they are allowed to solidifydue the cooling of e.g. the air or other gas between the nozzle and substrate.

According to a second aspect of the present disclosure, a device for providinga suspension of metal particles in flux on a substrate is provided. The deviceincludes a substrate receiver (or holder). The device includes a first jettinghead. The first jetting head is configured to individually jet one or moredroplets of flux towards the substrate receive/holder (and i.e. towards asubstrate, such as that of a printed circuit board, which may be held by thesubstrate receiver). The device further includes a second jetting head. Thesecond jetting head is configured to individually jet one or more droplets ofmo|ten metal towards the substrate receiver (and i.e. towards the substrate, and in particular towards the one or more droplets of flux having already beenjetted on the substrate using the firstjetting head). The device is furtherconfigured to receive (or hold), by the substrate receiver/holder, a substrate.The device is further configured to individuallyjet, by the firstjetting head, oneor more droplets of flux onto an area of the substrate. The device is furtherconfigured to individually jet, by the second jetting head, one or more dropletsof molten metal towards the one or more droplets of flux, thereby causing theone or more droplets of molten metal to solidify and to end up suspended inthe flux as metal particles.

The device may be configured to, using at least the substrate receiver, thefirst jetting head, and the second jetting head, provide a suspension ofsolidified metal particles in flux on the substrate, according to the methoddescribed herein according to the first aspect or any embodiment related thereto. ln some embodiments, the device may include a spray cooler configured toprovide a cooling gas for locally cooling the area of the substrate. Locallycooling the area of the substrate may provide active cooling of the one or more droplets of flux. ln some embodiments, the device may include a heatsink as part of thesubstrate receiver, configured to provide an active cooling of the one or more droplets of flux. ln some embodiments, the device may further include means for adjusting adistance between a nozzle of the second jetting head and the substrate receiver.

The present disclosure relates to all possible combinations of features recitedin the claims. Objects and features described according to the method of thefirst aspect may be combinable with, or replaced by, objects and features described according to the device of the second aspect, and vice versa.

Further objects and advantages of the various embodiments of the presentdisclosure will be described below by means of exemplifying embodiments.

Brief description of the drawingsExemplifying embodiments will be described below with reference to the accompanying drawings, in which: Figure 1 schematically illustrates various steps of an embodiment of a method according to the present disclosure; Figure 2 schematically illustrates a cooling step of an embodiment of amethod according to the present disclosure; Figure 3 schematically illustrates a step of an embodiment of a methodaccording to the present disclosure. ln the drawings, like reference numerals will be used for like elements unlessstated otherwise. Unless explicitly stated to the contrary, the drawings showonly such elements that are necessary to illustrate the example embodiments,while other elements, in the interest of clarity, may be omitted or merelysuggested. As illustrated in the figures, the sizes of elements and regionsmay be exaggerated for illustrative purposes and, thus, are provided to illustrate the general structures of the embodiments.

Detailed descriptionWith reference to Figure 1, the main concept of the present disclosure will now be described in more detail.

Figure 1 schematically illustrates various steps S101-S103 of an embodimentof method as envisaged herein. ln the step S101, a substrate 112 is firstprovided. The substrate 112 may for example be provided on a substratereceiver/holder 110 of a jetting device in accordance with the second aspectof the present disclosure. ln this example, the substrate 112 is a printedcircuit board (PCB) and has one or more contact pads 114 to which terminalsof various electronic components (not shown) are to be soldered in a laterpart of a manufacturing process. A firstjetting head 120 is used to individuallyjet, through a nozzle 125, one or more droplets 122 of flux 123 on an area ofthe substrate 112. ln this example, the area of the substrate 112 corresponds to the contact pad 114. As a result, a build-up 124 of flux is created on the contact pad 114. The flux on the contact pad 114 is in a viscous, i.e. non-solidstate. ln a next step S102, a second jetting head 130 is used to individually jet,through a nozzle 135, one or more droplets 132 of molten metal 133 towardsthe one or more droplets (e.g. the build-up 124) of flux now located on thecontact pad 114. ln a next step S103, the one or more droplets 132 of molten metal hassolidified, and has ended up suspended in the flux 124 as metal particles 134.

Consequently, by performing the above steps S101-S103, the methodprovides a composition of flux 124 having suspended metal particles 134therein, e.g. a composition similar or identical to a normal solder paste. lt isenvisaged that a manufacturing process may then include positioning one ormore electronic components on the contact pads, and that, during a solderingstage, electrical connections may then be created between the contact padsand terminals of the electronic components using the solder paste-likecomposition of flux 124 and suspended metal particles 134 just as ifa normalsolder paste had been used. However, as the metal particles 134 has notpassed through any nozzle of a jetting device in a solidified state, the problem of such metal particles clogging the nozzle has been avoided.

A device for providing a suspension of metal particles in flux on a substrate isused to perform the method steps S101-S103 illustrated in Figure 1. Thedevice comprises the substrate receiver/holder 110, which is configured tohold/receive the substrate 112. The device further comprises the first jettinghead 120, which is configured to hold an amount of flux 123, and toindividuallyjet droplets 122 of the flux through a nozzle 125, towards thesubstrate receiver 110 (e.g. while a substrate 112 is being held by thesubstrate receiver 110). The device further comprises the second jetting head130. The second jetting head is configured to hold an amount of molten metal133, and to individuallyjet, through a nozzle 135, droplets 132 of the moltenmetal towards the substrate receiver 110. Specifically, the droplets 132 of molten metal are jetted towards the buildup/droplets 124 of flux on thesubstrate 112 being held by the substrate receiver 110.

With reference to Figure 2, an optional method step S204 of providing anactive cooling of the one or more droplets of flux will be described in moredetail.

The method step of S204 of providing an active cooling of the one or moredroplets of flux, e.g. the buildup 124 of flux, may be performed simultaneouslywith the method step S102 of individually jetting one or more droplets ofmolten metal towards the one or more droplets of flux. Alternativeiy, oradditionally, the method step of S204 of providing an active cooling of the oneor more droplets of flux, may be performed e.g. just prior to the method stepS102 of individually jetting one or more droplets of molten metal towards theone or more droplets of flux.

Cooling the droplet(s) of flux may increase the viscosity of the flux.

The method step S204 of providing an active cooling may include locallycooling the area 114 of the substrate 112 on which the droplets/buildup 124 offlux have been jetted using a cooling gas 243. For example, the cooling gas243 may be provided as a spray 242 (spray cooling) using a gas nozzle 240.A device for providing a suspension of metal particles in flux on a substrate,may comprise a gas nozzle 240 for providing/spraying a cooling gas 243towards the substrate receiver 110. ln some embodiments, the gas nozzle240 may be integrated in one of the otherjetting heads 120, 130 of the device.

Providing a cooling gas 243 simultaneously with jetting the droplets 132 ofmolten metal may further provide that the droplets 132 of molten metal atleast partially solidify prior to entering the flux 124.

Alternativeiy, or additionally, the method step S204 of providing an activecooling may include at least temporarily providing the substrate 112 on aheatsink 241. ln a device for providing a suspension of metal particles in flux on a substrate, the heatsink 241 may be included as part of the substrateholder 110.

With reference to Figure 3, an optional method step S302 of adjusting adistance between a nozzle used forjetting the droplets of molten metal will bedescribed in more detail. The method step S302 may be an alternative (orcomplement) to the method step S102 described above, with reference to Figure 1. ln the method step S302, a means 350 for adjusting a distance d between anozzle 135 of the second jetting head 130 and the substrate receiver/holder110 may for example be used to adjust the distance between the nozzle used forjetting the molten metal and the substrate 112.

The distance d may be adjusted such that the one or more droplets 132 ofmolten metal may at least partially solidify before entering the flux 124. Forexample, at least a surface of the one or more droplets 132 may solidify, dueto e.g. the surrounding air or gas between the nozzle and the flux, prior toentering the flux 124.

Although features and elements may be described above in particularcombinations, each feature or element may be used alone without the otherfeatures and elements or in various combinations with or without other features and elements.

Additionally, variations to the disclosed embodiments may be understood andeffected by the skilled person in practicing the claimed invention, from a studyof the drawings, the disclosure, and the appended claims. ln the claims, thewords “comprising” and “including” does not exclude other elements, and theindefinite article “a” or “an” does not exclude a plurality. The mere fact thatcertain features are recited in mutually different dependent claims does notindicate that a combination of these features cannot be used to advantage.

Claims (12)

1. A method of using jetting to provide a suspension of metal particles influx on a substrate, comprising: providing a substrate (112); individually jetting one or more drop|ets (122) of flux (123) on an area(114) ofthe substrate, and individually jetting one or more drop|ets (132) of mo|ten metal (133)towards the one or more drop|ets of flux (124), thereby causing the one ormore drop|ets of mo|ten metal to solidify and to end up suspended in the fluxas metal particles (134).

2. The method of claim 1, further comprising providing an active coolingof the one or more drop|ets of flux.

3. The method of claim 2, wherein said active cooling includes activelycooling at least a major part of the substrate.

4. The method of claim 2 or 3, wherein said active cooling includes locallycooling said area of the substrate using a cooling gas.

5. The method of claim 4, wherein said active cooling includes providingthe cooling gas during the jetting of the one or more drop|ets of mo|ten metal.

6. The method of any one of claims 2-5, wherein said active coolingincludes at least temporarily providing the substrate on a heatsink (241).

7. The method of any one of the preceding claims, wherein the substrateis a printed circuit board, PCB.

8. The method of any one of the preceding claims, wherein saidindividually jetting one or more droplets of molten metal includes adjusting adistance between a nozzle used for said jetting and the substrate such thatthe one or more droplets of molten metal at least partially solidify beforeentering the flux.

9. A device for providing a suspension of metal particles in flux on asubstrate, comprising:a substrate receiver (110);a first jetting head (120) configured to individually jet one or moredroplets of flux towards the substrate receiver, anda second jetting head (130) configured to individually jet one or moredroplets of molten metal towards the substrate receiver,wherein the device is further configured to:receive, by the substrate receiver, a substrate;individually jet, by the first jetting head, one or more droplets offlux on an area of the substrate;individually jet, by the second jetting head, one or more dropletsof molten metal towards the one or more droplets of flux, therebycausing the one or more droplets of molten metal to solidify and to endup suspended in the flux as metal particles.

10.to provide a cooling gas for locally cooling said area of the substrate. The device of claim 9, further including a spray cooler (240) configured

11.of the substrate receiver/holder, said heatsink being configured to provide an The device of claim 9 or 10, further including a heatsink (241) as part active cooling of the one or more droplets of flux.

12.for adjusting a distance between a nozzle of the second jetting head and the The device of any one of claims 9 to 11, further including means (350) substrate receiver.