CA2171190A1 - Patterned array of uniform metal microbeads - Google Patents

Patterned array of uniform metal microbeads

Info

Publication number
CA2171190A1
CA2171190A1 CA002171190A CA2171190A CA2171190A1 CA 2171190 A1 CA2171190 A1 CA 2171190A1 CA 002171190 A CA002171190 A CA 002171190A CA 2171190 A CA2171190 A CA 2171190A CA 2171190 A1 CA2171190 A1 CA 2171190A1
Authority
CA
Canada
Prior art keywords
metal
microspheres
array
regions
substrate
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Abandoned
Application number
CA002171190A
Other languages
French (fr)
Inventor
David C. Koskenmaki
Clyde D. Calhoun
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
3M Co
Original Assignee
Individual
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Individual filed Critical Individual
Publication of CA2171190A1 publication Critical patent/CA2171190A1/en
Abandoned legal-status Critical Current

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    • H01L21/04—Manufacture or treatment of semiconductor devices or of parts thereof the devices having at least one potential-jump barrier or surface barrier, e.g. PN junction, depletion layer or carrier concentration layer
    • H01L21/48—Manufacture or treatment of parts, e.g. containers, prior to assembly of the devices, using processes not provided for in a single one of the subgroups H01L21/06 - H01L21/326
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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
    • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
    • B23K35/00—Rods, electrodes, materials, or media, for use in soldering, welding, or cutting
    • B23K35/02—Rods, electrodes, materials, or media, for use in soldering, welding, or cutting characterised by mechanical features, e.g. shape
    • B23K35/0222—Rods, electrodes, materials, or media, for use in soldering, welding, or cutting characterised by mechanical features, e.g. shape for use in soldering, brazing
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Abstract

The present invention provides a method for providing an array of metal microbeads on a substrate, preferably in a regular pattern of very fine, uniform size microspheres or microbeads at precise spacing or scale previously unachievable. The method of the present invention comprises the steps of providing a metal layer (14) on a substrate (12) that is partitioned into metal regions (20); heating the metal layer to a temperature sufficient to melt the metal and to permit beading of the layer into discrete microbeads (22).

Description

2~71 19o WO 9~ C PCT/US94/09507 PAl~RNED ARRAY OP UNIPORM METAL MICROBEADS

TECHNICAL FIELD
The present invention relates to a method for forming a pqttPme~ array of 5 metal mic~b~ds on a s~,l,s~ e and particularly to a method of providing a regular array having precise spacing.

BACKGROUND OF INVENTION
In the el~lunic ~ui~ ent and teleco.-~ icqtinnc inductries there are 10 ~tl~;n~ous r~uil~,llcnls for making ele~t~ q-l cQnnPctinn belween cG...~ ?ntc, often on a very small scale. Semico~uctors, such as inte~,.dted circuits, are forrned on wafers which are then cut into dice or chips that individually may bernoun~d on s~slla~e,s. Typically, the D~slldle has fine rlectrirqlly conductive circuit lines, and e1~trirql and thermal contact must be made bel~æn the D~sl.dte 15 and chip. As el~~ )nic appliqnces, such as COIIIPU~1D, tape players, televisions, t~le~hn~s, and other appliqnres become smaller, thinner, and more portable, the size ~uil~.~lehl~ for s~mir~Qnductors and the means for providing electriçql c~nn~il;c!n bet ~ semi~on~lct~rs and s.lbs~ s, or~æn flexiblecircuits and rigid printed circuits, beool.-es incl~as;ngly de ..qn~;ng.
One method for providing elr~trirql CQ~UGtivity betwæn two electrical clP--.e~ such as belweeil flexible circuits and printed circuits, is through the use of a Z-axis adhesive. A Z-axis adhesive (ç~ U.S. Pateht Nos. 2,822,509 and 4,606,962) typically con~i~t~ of condllctive particles dispersed throughout an adhesive film. When a Z-axis adhesive is used to bond together arrays of 25 condu.l;ve elp ~ nl~ on two in~ul~ting ~S~ ,S, contact belween the conductivee~ .f n~ is made by the cond~ctive particles. As the dem~n-ls for .~ 7~tion cQnl;nue to increase, spacing bel~n particles and precision in spacing bel~n particles beco.--Ps intil~s,ngly i~
A Z-axis adhesive can be made by randomly dispersing conductive metal 30 particles in an adhesive. By randomly dispersing cond~lctive metal particles in an adhesive, the res~ltin~ Z-axis adhesive will have random ~ t~nres between ~ 1 71 1 90 WO 951~.S 236 PCT/US94/09507 individual p~licles, inr.1u~1ing particles touching each other. In order to provide the desired density for el~c~irql connPction of the e1e~trirq-l el~rnPntC~ sufficient particles must be loaded into the adhesive to insure that Z-axis con~uctivity will occur as l~qUil~d. It is typically nPc~c~ to load excess particles so that the S .n~;.nu... random gap between particles does not exceed the spacing r~uire~-~ents for inle.~;onnP~l;on The random loading of conductive particles causes clullllJiAg of l.~licles which will cause shorting of electrir-q-l elPmPntC. Therefore, it is nt to be able to provide positiol-Pd conductive particles.
AccG.dingly, there is a need for a method for providing a patterned array 10 of ullirJllll metal microbeads on a s~sll~te with spacing and precision previously unq'tqinahle There is a need for a method that provides a regular pattern of very fine, unirollll size microspheres or microbeads at precise spacing or scale previously un^~hiP-vable. Such arrays can be used, for ey~mrle~ in a Z-axis adhesive.
SUMMARY OF THE INVENI~ON
The present invention provides a method for providing an array of metal microbeads on a svbst~e. The present invention also provides a substrate, such as a polymeric s~llJc~-AIP, having a iiccqnt;nuo~ls metal coating, the metal coating 20 compric~ a P~ ...P~ array of closely-spaced metal microbeads, the metal microbeads having a srhP-ri~l portion and a flat portion.
The method of the present invention comprices the steps of providing a metal layer on a s~ll.sl-~tP- that is partitioned into metal regions; cont~rtin~ the metal layer with an err~clive amount of a fluxing agent, as needed; heating the 25 metal layer to a lc-..~-~lu~t: suffirierlt to melt the metal and to permit be~inE of the layer into dis-l~t~, microbeads. The metal layer may be depos;led on the ~",I"cl-.~le so as to be partitioned when ~r~s;led, thus l~uiling no sperific partitir~ning step, or de~sited as a conl;nuous layer and then partitinne~. The metal regions do not n~ec~,;ly need to be discrete, but only sllffiriently 30 partitioned to permit be~ling Fluxing is needed only if an oxide layer is present.
The microbeads of the present invention may have a wide range of W095/09436 2 1 7 1 1 9 0 PCT/US~ 507 d;~...P~ ~. Typical average ~ meters are in the range of about 0.2 ~m to about 100 ~m, and more preferably 1 ~m to about 50 ~m. Microbeads can be provided in a very wide range of ~enCitip~ Typically, average den.citi~s are about 600-6,000,000 beads/cm2; pr~fe.dbly 40,000 6,000,000 beads/cm2; more preferably 5 80,000-6,000,000beads/cm2; and mostpç~ dbly 160,000-6,000,000 beads/cm2. Other ~.~nenl~ can be added to the microbeads and substrate. For example, an adhesive layer may be coated onto the microbeads to form a Z-axis adhesive.
"Pe~ul~-" is defined herein as having spacing of a defined or rc~)edtdble 10 pattern.
"Discrete" is defined herein as mP~ning distinct PlPmPnt~ that do not touch, such that each sphere, bead, or region does not touch a neighboring metal ele-mPnt BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is a p~,~live view of a metal coated polymer having the metal layer partitioned into metal regions, as part of the method of the present invention;
Fig. 2 is an declron mic;loE~lal~h shc,wing a ~~ ;tiv-e view of an array of microbedds on a s~st~dle of the present invention;
Fig. 3 is an ele~:llon miclugld~h showing a ~.~ecli~e view of an array 20 of ll,icr~edds of the present invention;
Fig. 4 is an clecllon micrugl~h showing a ~.~e.;live view of an array of ,,,i.;lubeads of the present invention; and Fig. 5 is a photc"~c~g~ph showing a top view of an array of microbeads of the present invention.
DETAILED DESCRIPTION OF THE PRESENI INVENTION
The present invention provides a patterned array of metal microbeads and a method of making such a p~t. ..~d array of metal microbeads. The method of the present in-~ention is capable of providing microbeads on a ~ubsl~te in a 30 precise, regular array of unirùllll sizes, with extremely close center-to-center .
? 1 7 1 1 90 WO 951'~g S?~ PCT/US~ 5507 spacing of the microbeads. "Microbead" or "mi-;lus~hele" will be used throughoutto desclibe each individual discrete sphere-like metal element of an array of the present invention. The metal ll"cr~h~l~ s or microbeads are not likely to be p~lÇectl~ ~l.hr.;l~l, but will have a flat portion. The microbeads will range from 5 almost entirely spherical to lesser portions or segments of a sphere, such as hP.mi~ph~Prical. .
The flat portion of the bead may provide advantages in certain usages. A
flat portion can assist in ~ Ae...Pnt of a microbead on a secondary substrate with the flat portion acting as a base that may aid in providing ele~tric~l connPction 10 b~lween two S~llSllates. If an array of microbeads is transferred to a se~Qn-l~ry s~st~, for ~ Aall~ylc, into an adhesive layer, the flat portions could remain os~d and also assist in providing elPctrir~l connPcl;Qn.
The method of the present invention can make microbeads of a single, ullif~llll size, or of more than one size of beads. The arrays of the present 15 invention include two general parts: the s.Jl,sll~te and the metal microbeads, s,~pol~d by the ~l,sl dte~ The arrays of the invention are made by a novel process by which the metal microbeads are formed on the su~sll~te.
Referring to Fig. 1, a plC~iUl:~ of an array of metal microspheres of the present in~ltion is shown, genP~d1ly dPcign~tPd 10. The pr~u~or of the array 20 includ-ps a ;.~ .l.~; 12, and a metal layer 14. The metal layer 14 in~ des vertical ~,w~es 16 and hc~ nt~l grooves 18, dividing the metal layer 14 into metal regions 20.
Ref~lli.lg to Fig. 2, a ~ live view of an array of metal microspheres of the present invention is shown in the electron mic,og,~ph. The array is 25 gene~lly ~es;gn~'~d 20, in~lu~ling a ~ le 21, with metal mic,usph~.~s 22, provided thereon. The vertical groo~es 23 and ho. ;~.ûn~l g~ es 24 are shown in the S~ a~e 21. The grw~s are a result of the process of the present invention. The mic,us~h. l~ s 22 typically include a spherical portion 25 and a flat portion (not shown) that is in contact with su~sl,~t~ 21.
pPfPrrirlg to Fig. 3, a ~.~cti~e view of an array of metal microspheres of the present invention, gP.nP,T~lly d~P.~igll~t~d 30, is shown. The electron 2~ 71 1 9(1 WO 95,û~ . C PCT/US94/09507 mi~ gl~h shows an array 30, inrl~ ing a s.lbs~ 31, metal ~ usl.heres 32, vertical grou~ s 33, and ho. ;7.or~t~l g~ es 34. The grooves are the result of the process of the present invention. The metal micl.,s~hel~s 32 include spherical portions 35 and flat portions (not shown). The micl~o~l,h~ .~ s 32 are more spherical S in shape than the miclu~ Glcs 22 shown in Fig. 2.
12ere- - ;.~g to Fig. 4, an electron microgld~h showing a pe. ~ e view of an array of metal ,nicr~s~heres of the present invention is shown, the array g~nter~lly dÇCign~trd 40. The array 40 includes a s~slldte 41, metal mic,ùs~hel~s 42, vertical grooves 43, and ho~;~u~ l grooves 44. The miclo~hc~s 42 include 10 a ~phrn~l portion 45, and a flat portion (not shown) that is in contact with the s~sllate 41. Fig. 4 also shows that the microspheres are not perfect portions ofa sphere so-~t~ es having i-,.pe.~clions, including more bell-shaped micr~sl~he.~.
~r~ . .;.~p to Fig. 5, an array of metal mic,osphen_s of the present invention 15 is shown, g~on~lly desi&n~t~ 50. The ~hot<J~ic~oglaph of Fig. 5 is a top viewof the array 50, inr~ ;ng a substrate 51, mi.;~s~he~s 52, first grooves 53, and second gl~O.eS 54. The grooves 53 and 54 form di~mond shapes. The spherical nature of the l..iclos~he~s 52 cannot be seen in the top view of the Fig. S
phOtolllic~gla~h, but the circular cross-section of the micloi,ph~r~ s 52 is shown.

Substlate A wide variety of m~tPri~l~ may be used as aubsl~at~ s in the present invention. Many polymeric and non-polymeric m~tPri~l~ are s~it~hle as Sub5k~lCS.A sub~tr~te which is suitable for use in the present invention should be 25 s~ in accol~ce with the needs of its end use. The sllhst~t~ may be flexible or inflPYihle; ~ l or opaque; made from a wide range of materials; have a wide variety of thi(~L ~ ces and lateral tiimPnsi()ns; and have other char~^tPrictics suited to the particular end use. In many cases, the substrate may be used only as a carrier for the l"iclobeads, or as a means on which to form the microbeads. The 30 mi.;~ubeads of the present invention can be used s~ ely from the ~sl-~te, or used while a~lh~.~d to the s~sl,ate.

WO 95t09436 PCT/US94109507 To use the microbeads ~ ly from the substrate, the microbeads must first be physically removed and coll~ted. This can be accomplich~l by lly scraping or brushing the microbeads off of the s.l,sll~te. After removal, the microbeads are freely ~no~cable relative to one another. They can S be dispersed in a liquid, preferably an adhesive, and coated on a second substrate.
The result is an adhesive film coating cont-Ail~ing a r~ndom t~ .r~io~ of uniform micr~>b~ds. An application of this invention would be a Z-axis adhesive having microbeads of very Unil~lln size and shape, in a randomly dispersed pattern.
~ltern~tively~ the microbeads can be formed on a first s~b~ AIr and then 10 transferred to a second s~bsh~t~; for example, inrlll~ing an adhesive layer. A
At.; iS ~l~t~ based on the wetting characteri~ti~s of the metal to be used.
The i~.lb;~lldle ~ `d should not be entirely wet by the liquid metal used to form the metal micl~eads. In ^ l~lition~ a s~ ldte should be selected which is not de6l~ded by the t ~ t~ ~s ~ c~d in ~rDce-s~ g. One of skill in the art 15 will l~,l.;7e that the polymer must remain intact and fi)nctiQn~l after the heating step.
The wett~ ity of a liquid when placed onto a ~LIbsh~t~ iS at least partially de~ndent on the surface tension between the liquid and the s.~s~ tP. In general terms, the greater the surface tension, the greater the internal wetting angle 20 ~e~oen the droplet of liquid metal and the s.~s~le. If the surface tension issuffi~i~ntly great, the liquid will form discrete droplets. Wetting refers to the te.~denc~ of a liquid to form a liquid film on a given s~ e, as oppos~ to non-wetting where the liquid forms individual disc~te droplets on the s~rf ^e In order to form the desired microbeads of the present invention, it is 25 suffi~i~nt that the metal form discrete, liquid metal droplets on the surface of the substrate when the metal layer is melted. When this con~itiQn is ~tisfi~d~ it will be referred to as a liquid metal which is non-wetting, or which does not wet a particular ~V~ AtÇ s~ e Depen~ling on the desired shape of the microbead, the degree of wetting b~t .~n a given ~.,bs~ P and a given metal can be ~le~t~ so 30 as to control the shape of the micr~eads. The less the metal wets the ~ll sllale surface, the more s~.helic~l the bead.

2 ~ 7~ 1 90 Sul~sllates chosen for use in the present invention should also be capable of withcPn~ling the tt~ dlules mP~ec~g to melt the metal layer in pr~ g.
Metal, glass, cPramic~ and polymeric ~ slla~s are examples of useful subsl~ates for use in the present invention.
S FYamples of polymers that may be used as s~shdtes in the present invention incllJde: polyimides; polyphenylene oxides; polymers of fluorinated olefins such as polytr, ~fllJQr~lbylene; siliconP polymers; ce~ 1nsi~ polymers;
polyùle~ f s eagi~ g plastics such as poly~ly~ne, styrene/acrylo~itril~
copolyme,~, copolymers contAining pol~llle.i~ed styrene, acrylonitrile and 10 b~lt~ipne (often called ABS polymers3, styrene/butadine copolymers, rubber nloAifi~P~ styrene ~ lllcl~, styrene/male.c anhydride co~olylll~.~ and similar polymers of l,lono~inglidene aromatic c~l,ocgclic monollle.~; polyc~l,onales inclu~ling those made from phosgP-ne and biphenol A and/or phPnnlphth~lPin;
polyesters such as polyethylene l~hl~.Al~tP; acrylic resins such as po]y(methyl 5 I~C~ alt;); pol~llides such a nylon, polyolefins, such as polyethylene and pol~ o~lene, polyvinyl halides such as polyvinylchloride and vinyldene chlQride ho",opolymers and copolymers, polysulfones, polyarylsulfones, andperfluorinated-ell~ylcne-propylene copolymer.
In ~ ition~ metal substr~tps such as ~ u~l (typically wet by molten 20 metals) coated with at least a thin non-wetting coating of Al~ ..n oxide, or with another non-wetting coating, may be used. In general, S~Shat~ s which are unCllit~ for use be~ se they are wet by the SPlPct-P~ liquid mehl may be coated with a non-wetting coating to provide a suitable depos;~ g s--rf~(e.
The l1I;C1l n~5~ of the s~sll~te is not particularly in.pG,l~nt to the practice 25 of the present invention and should be del~l",ined by the ch~~ tics and pf~pellies which are d;cl~ted by the end use for which the collll~s;le is ~eci~ned~
Such end use char-tPrictics or pf~Jpellies includes t~nsr~rency~ flexibility, tensile ah'~n~ co~rosion resict~nce, and the like. In some cases, the s~lbsllateo will not be used with the microbeads in the end use and will ll,e,~ro~e be sele~ted 30 only for its p~ c~qr~t.~ ;r.s 2 ~ 7 1 1 90 Metal Microbeads A wide variety of metals may be used. Examples of ~l~ f~.lcd metals for use in forming the metal microbeads of the present invention include tin, lead, bi~muth, zinc, indium, alu,,,inu,,,, alloys (inelurling alloys of these metals with S metals of higher melting points, such as copper, silver, gold, nickel, cobalt, iron), and ."i~lu..s thereof.
Like the s~l,s~ te, the metal will be scl~cted for its end use pro~Glhies.
The metal will also be ~ clP~ based on its wetting cha,~le ;~tics of the s~sll~te, as de~ il~d above.
Fluxin~ A~ent A fluxing agent is used, as nPed~P~, in the present invention. It is d~ignPd to p'~ tP the metal oxide layer that forms on the metal layer and to rli~sip~t~.any metal oxide layer so that when the metal layer is melted, the metal will form 15 discrete metal Illic~S~el~,s on the S~Shale.
A fluxing agent may not be needed if the ~roce~ g con~itirns do not permit the ro"~t;o~ of an oxide layer, such as under vacuum co~ tiQnS.
Examples of suitable fluxing agents include organic acids, such as malic acid or acetic acid; chlnr~es such as zinc ehloritle; l)hosl.hn.;( acid; dilute 20 h~.kor~ )rie acid; other volatile acids; and other known fluxing agents. Fluxing agents are s ~ d based on the particular metal and metal oxide used in the present invention.
The fluxing agent is used in a sufficient conePntr~tiQn to sllffi~;~ntly ipatP any metal oxide layer to allow mic~sl,he,G formation upon melting of the 25 metal layer, but should be weak enough so that it does not dissolve, corrode, or othenvise d~r~tle the sulsll~le, or other co.,.ponent~ utili7~1. Preferably, thefluxing agent is volatile enough so that it will evapol~t~ after it has ~,rol."ed the desired fUnotion- If the fluxing agent eva~r~lcs from the system, it ~-vill not present a risk of s~uent degr~tion to col"~onents of the co"l~sile. It is O
30 plere.led that the fluxing agent be applied to the metal layer in the form of a fine mist.

WO 951'~Q4?6 2 1 7 1 1 9 0 PCT/US94/09507 ;n~ Pdldl~le~
The metal microbeads of the present invention are formed by providing a metal layer on a s-ll,sLIdte that is sufficiently partitioned to permit bP~Aing,con~A~ t;n~ the metal layer with an errec~ e amount of a fluxing agent, if nP~P~, S and heating the metal layer to a le.n~ lure s~fficiPnt to melt the metal and to permit be^ ling of the metal layer into discrete microbeads.
The process of the present invention involves first clepG~;Iing a metal layer onto a ~.~bs~ . A ~-~f~ d method of depo~ition is through vacuum deposition.
A metal vapor is formed in a vacuum ch~mber and a continuous layer of this metal10 is deposited onto a polymeric slll sl~dte. More than one layer of a single metal can be ~ çd to form the metal layer, as well as multiple layers of dirre~nl metals.
A p~f~ed method of forming the metal vapor in the vacuum is through one of several means of t;va~ion~ Sputtering would also be suitable, albeit involving typically slower deposition rates.
A ~ f.ll~d form of eva~l~lion is evaporation by means of heating the metal with an eloclrun beam. Typically, the metal is placed in a small water cooled metal crucible and an elcctron beam is produced and rocused on the metal in the crucible by means of a magnetic field. Typically, a beam co~cist~ of an clecl-un current of about 0.1 to 1 amp accele.aled by 10,000 volts, and dil~c~d 20 to a 0.5 cm2 spot on the metal. An elecllon beam power supply col.. lo~c;ally available from Airco Temesc~1 is an eY~mrle ~f a suitable ap~ lus. Other mPthodS of ev~.pc"~,ting the metal or metals include re~ic~nce and induction heating.
After the metal vapor is created, the vapor moves through the vacuum 25 c~ .b~ ~ until it is de~s;l~ d onto the subs~ e pocitioned above. The subsllalt;
may be a moving web that is passed through the metal vapor in the vacuum c~ hf~ at a speed suffiriPnt to deposit a layer of the metal having a desired thirlrn~cs The thic~n~ of the metal layer should be suffiriently thick relative to the width of the metal region after the partitioning to prevent multiple beads from 30 fo~ g in a given region. The .--;~ u-- desired ratio will depend on the s~ate and metal used, but in general terms, the tllirknPss of the metal layer WO 9_J ~)S . C PCI~/US94/09507 should be at least about 2% of the width or breadth of the metal region.
Dependin~ on the s~sLIdte used, there are other methods for depositing a metal layer onto a s~llJslldte includin~, lqminq.~ing a thin foil or membrane of the desired metal; spraying molten metal, electrolysis and/or electroplating of metal.
Before the metal layer is melted to form the desired microbeads, the metal layer is provided on the ~..I,sl.~tP with metal regions formed in the metal layer in a desired pattern. The metal regions may be formed in a continuous metal layer by a partitionine step, or the metal may be provided on the S~sl~ate in the formof p~crul.-,ed metal regions. There are a number of means to provide the desired10 regions. The metal layer may be p~lilioned by me ns of, for example, lase"c. ;hin~, photolithography~ etching, mech-q-nir~l sc.alching, cracking, or other means. ~ltPrnqtively, the met~ regions may be formed by vapor ~epos;line the metal ~h-uugh a mask, or vapor depo~;l;ne onto a substrate with a pre-embossed pattern such that the deposil~d coating is partitioned by shadowing, or line of sight 15 ~e~S;linm The :~sllate Call be pre-e.--bos~ with a pattern having different depths so as to provide microbeads on an e ~bossFd substrate provided at different depths. Whether dcpos ~d as a contim~Qus metal layer and then partitioned, or ~e~:led as metal regions, the regions need to be suffiripntly partitioned to permit be~in~, which does not n~cc~-~;ly require that the regions be discrete.
The metal regions may be of equal size or may be of one, two, or more dirr~ t sizes so as to form microbeads of the same or varying sizes. The area of the metal layer and the l~ L--~5 of the metal layer det~.,..ine the size of the sphere, in conjunclion with the wetting rel~tior.~hir bzlween the metal and the ~slldte which defines the shape of the microbead. The metal layer may be 25 yatlitioned into shapes inrlu~lin~ squares, tri~nelps~ rnond shapes, or otherdesired shapes to provide the desired microbead. For square metal regions, the bead di~m~ter~ ~c~.J----ne a perfect sphere, will be (6tS2k)l13 where t is the thi~lrn~ of coating and s is the width of the squares. For eY~mpl~, to produce microbeads of 2 ~m in dis.~.~lf, the initial coating should be 0.26 llm thick when 30 the width of the squares is 4 ~m.
After a metal layer is depos;led on the polymeric ~ .dte, the e~sed WO 9Sl'~g ~7C PCT/US~ 07 surface of the metal layer will typically oxi~i7p. The eYros~ surface of the metal means the side of the metal that is not in contact with the ~.~bsl,~le. Oxidation of the c.~pos~ surface of the metal will occur by simply leaving the coated substrate in the p~sence of oxygen. When an oxide layer does form, the use of a fluxing S agent is typically lc~lui~d.
A wide variety of p Il. ..c can be used to provide the desired spacing of spheres, sizes of spheres, and relative pos;l;oI ine of spheres. For example, a metal layer may be partitioned by two int~,~liilg sets of parallel lines formingd;~ shapes with the ~ mnn-~c alte.~atingly bisected into tri~ngI-s. The 10 ~li7~onds will form larger spheres and the tniqngl~s (half liqmo~ s) will form smaller spheres.
The spacing of the microsl.h~,~,s is ~epen~ent on the size of the metal regions. The method of the present invention can produce microbeads having c All~."ely precise and fine center-to-center spacing, e.g., 4 ~m center-to-center 15 spacing or 6,000,000 microbeads/cm2. Typical ~en~itip-s for microbeads useful in Z-axis adhesives will be 40,000-1,000,000 microbeads/cm2. One of the advantages of the method of the present invention is ItS ability to provide microbeads of a fine scale having precise spacing l~ci~el~een.
The ~ A.C of the metal layer prior to m,ltine will typically be 0.2-10 20 ~m, more typically 0.2-2 ~m.
The invention is further descnbed by the following non-Iimiting eYqmp'es.

F..~mrle 1 A sllbst~ having an array of microspheres of the present invention was 25 made by providing a 25 llm thick by 18 cm wide by 10 meter long piece of polyi.l.ide film that was vacuum coated with tin on one side by electron beam c~ alion in a web coating ch~-mbrr evYq~ qt~ to 4x1~5 Torr. The electron beam source was an Airco Temescql CV-14 power supply which provided a voltage of 9.4 kV and 0.13 A to melt and V~)OliZc tin in a hearth charged with 30 200 grams of tin. The hearth of mo- ;n tin was 25 cm below a 40 cm rii-meter drum with which the web was in contact and which drove the web at a speed WO 95~0~ t?~ PCT/US94/09507 valying from 0.6 m/min to 16 m/min. Under these conditions the polyimide was coated with 0.5-0.02 ~m of tin. A circular piece of the tin coated web 3.2 cm inAi~m~otPr was cut from the web at a lo~ ion where the tin thir~nPss was 0.2 ~m.
This piece was e",bossed at room lGIIIPG1~lUrG in a hydraulic press using a nickel 5 e,.,bo.~;ng die and a pr~s~.-,G of 28,000 psi or 190 MPa. The nickel die had asawtooth pattern of parallel ridges with a 8 ~m spacing and a 4 ~um depth. The emhoscing step was ~pealed after turning the embossing die 90 so as to create an emboc~d pattern of 8 ~m squares in the tin layer. The embossed tin coated polyimide sample was then exposed to HCl vapor by placing the sample over the 10 top of a 150 ml beaker CQn~;~h-ing 1 ml of conc~nt-dtGd HCl for S sPwn~c- This e;A~3~11G to HCl vapor formed a very thick fog on the surface of the tin which acted as a flux to ~lic~;p~lP oxide during the melting step. The sample was thenplaced on a hot plate with a surface le ~pP ~II e of 280C for 2 seconrlc to melt the tin squares fo.",ing a square array of tin hemispheres which measured 15 3 ~m in ~ and had a center-to-center spacing of 8 ~m. The r~es~-ltin~ array of spheres is ill~ ed in Figure 3.

Example 2 A second array of the present invention was provided by cutting a second 20 piece of tin coated polyimide from the web of Example 1 from a region in which the tin coating was d~ t~.,l,ined to be 0.07 ~Lm in thir~nPss. The metal layer was e ..bos~ in a manner similar to the method used in Example 1 except that the emboscing tool had a ~l~lh pattern of parallel ridges with 4 ~m spacing. The embossed tin was ~-l os~ to HCl vapor in a manner similar to Example 1 and 25 then heated to melt the tin. The e.,lbossed tin formed a square array pattern of beads which were approxim~tply half spheres with a ~i~mPtPr of about 1.5 ~Lm anda center-to-center spacing of 4 ~m. The res~lPng pattern of hPmi~phP.res is i1l,j$n~d in Fig. 2.

FYa--'- 3 A third PY~mrl~ of the present invention was made from a 25 ~Lm thick by WO 95/09436 PCTIUS~ 5507 18 cm wide by 5 m piece of polyimide film that was vacuum coated with tin on one side using the same con~litionc as in F ~ ,lc 1 except that the web speed was held consts nl at 0.7 m/min. The web was reversed after 4 m and then reversed again after 2 m. These reversals were l~i)ealt;d 10 more times so that a section5 of the web b~ ~n 2 m and 4 m was coated with 12 layers of tin each roughly 0.5~m thick. This plocedul~, was I~S,C~y to produce a relatively thick coating of tin (6.5 ~m) without o~,. hF~ g the polyimide s~sLI~te. A 3 cm by 3 cm sample was cut out of this web and embos~ in a manner similar to that used in PY~mr'~
1 except that a nickel tool which produced a ~ mond shaped embos~d pattern was 10 used. The edges of the embossed pattern were spaced 400 ~m apart. After fluxing and heating steps similar to Example 1, the reslllting beads were found to have a ~ ne ~r of 125 ~Lm and a spacing of 400 ~m. The resulting array of beads is shown in the pholu."icn~g~ ,h of Figure 5.

Claims (29)

WHAT IS CLAIMED IS:
1. A method of providing an array of microspheres on a substrate, comprising the steps of:
a) providing a metal layer (14) on a substrate (12), said metal layer sufficiently partitioned into a plurality of metal regions (20) to permit beading of the metal regions;

b) heating said metal layer (14) to a temperature sufficient to melt the metal regions (20) and to permit beading of the metal regions (20) into discrete microspheres (22), thereby providing an array of discrete microspheres (22) on a substrate.
2. The method of claim 1 wherein the metal regions are provided by depositing said metal layer on said substrate followed by a step wherein said metal layer is partitioned into metal regions.
3. The method of claim 1 wherein said metal layer is deposited onto said substrate so as to be sufficiently partitioned into metal regions as deposited.
4. The method of claim 1 wherein said metal regions are defined by a first set of parallel grooves (16) intersecting a second set of parallel grooves (18), such that said metal regions are parallelograms.
5. The metal of claim 1 wherein said metal regions have three sides.
6. The method of claim 1 wherein said metal layer has a thickness of about 0.2 - 10 µm.
7. The method of claim 6 wherein said metal layer has a thickness of about 0.2 - 2 µm.
8. The method of claim 1 further including the step of contacting said layer with an effective amount of a fluxing agent sufficient to permit beading of said metal regions.
9. The method of claim 1 wherein said microspheres are formed having an average density of about 600-6,000,000 beads/cm2.
10. The method of claim 9 wherein said metal microspheres have an average density of about 40,000-6,000,000 beads/cm2.
11. The method of claim 10 wherein said metal microspheres have an average density of about 80,000-6,000,000 beads/cm2.
12. The method of claim 1 wherein said array of metal microspheres is a regular array.
13. The method of claim 1 wherein said metal regions are all of a single uniform surface area, thereby forming a regular array of microbeads of a single size.
14. The method of claim 1 wherein said metal regions have 2 or more uniform sizes.
15. The method of claim 1 wherein the diameter of said microspheres is about 0.2 - 100 µm.
16. The method of claim 15 wherein the diameter of said microspheres is about 1 - 50 µm.
17. The method of claim 1 further including a step of transferring said array of metal microspheres to a second substrate.
18. The method of claim 17 further including an adhesive layer on said second substrate with said array of metal microspheres transferred into said adhesive layer.
19. An array of metal microspheres on a substrate comprising a regular array of closely-spaced metal microspheres, said metal microspheres having a spherical portion and a flat portion and having an average density of about 600-6,000,000 beads/cm2.
20. The array of microspheres of claim 19 wherein said average density of said microspheres is about 40,000-6,000,000 beads/cm2.
21. The array of microspheres of claim 20 wherein said average density of said microspheres is about 80,000-6,000,000 beads/cm2.
22. The array of microspheres of claim 19 further including an adhesive layer coated over said metal microspheres.
23. A population of particles wherein said particles comprise metal microspheres (22) having a nonrandom distribution of diameter and shape, said shape being partially spherical (25) and partially flat, said diameter being less than 100 µm.
24. The population of particles according to claim 23 wherein said microspheres are dispersed in a liquid.
25. The population of particles according to claim 24 wherein said liquid comprises an adhesive composition.
26. The population of particles according to claim 23 wherein the diameter of said microspheres is about 0.2 -100 µm.
27. The population of particles according to claim 26 wherein the diameter of said microspheres is about 1 - 50 µm.
28. The population of particles according to claim 23 wherein said microspheres exist as independently mobile elements.
29. The population of particles according to claim 23 wherein said microspheres have 2 or more selected diameters.
CA002171190A 1993-09-30 1994-08-24 Patterned array of uniform metal microbeads Abandoned CA2171190A1 (en)

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US08/129,668 US5366140A (en) 1993-09-30 1993-09-30 Patterned array of uniform metal microbeads
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KR960705352A (en) 1996-10-09
CN1132570A (en) 1996-10-02
JPH09503100A (en) 1997-03-25
US5486427A (en) 1996-01-23
EP0721659B1 (en) 2000-11-02
EP0721659A1 (en) 1996-07-17
US5366140A (en) 1994-11-22
WO1995009436A1 (en) 1995-04-06
DE69426237D1 (en) 2000-12-07

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