JPH02163364A - Crowded metal microspherearranged body - Google Patents

Abstract

PURPOSE: To produce a base body consisting of congested metallic microsphere arrays and having discontinuous metallic coatings by forming metallic vapor in a vacuum chamber and adhering the metal vapor onto the adhesive surface of the base body kept at the melting temp. of the metal or above, then cooling and solidifying the metal.

CONSTITUTION: The metal is evaporated from a pot 32 by an electron beam source 30 in the vacuum chamber 20 having a diffusion pump 28. Pb, Sn, In, Bi, Zn, Cd, Ti, their alloys, mixtures, etc., are used as the metal described above. The metal vapor is adhered onto the surface of the web base body 48 transported along a drum 46. The base body 48 is adequately polyimide or Al coated with Al₂O₃. The adhesive surface of the base body 48 is kept at an effective temp. above the melting temp. of the metal at the time of adhesion of the metal vapor. As a result, the discontinuous metallic coatings which are individually and tightly packed with the metallic microspheres having a diameter of about 0.1 to 5.0μm and in which the projecting regions occupy at least 60% of the surface area of the base body 48 are formed. A pressure is applied on the resulted metal coated base body 48 to deform part of the microsphere, by which conductive passages may be formed.

COPYRIGHT: (C)1990,JPO

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to arrays of metal microspheres, particularly to deformable, electrically conductive, closely packed individual metal microspheres.

[Conventional technology]

There are many uses for arrays of closely packed individual metal microspheres supported on a substrate, especially when the microspheres are deformable and electrically conductive. Common areas in which such metal microsphere arrays are used include electrical circuits, microsoldering, and imaging.

In the field of electrical circuits, so-called circuit component boards for electrical circuit testing can be produced by providing an array of closely packed individual electrically conductive deformable metal microspheres.

Electrical circuits can be formed in the array by drawing lines through the microsphere coated surface with a sharp object. Electrical contact is made between the individual microspheres upon which pressure is applied to deform the microspheres, creating the desired electrical path through the otherwise non-conducting surface. If desired, such a circuit can be preserved by coating its surface with a protective plastic or the like.

In a related application, a tamper-evident film can be made by covering an array of such deformable conductive metal microspheres with a protective covering membrane. Tampering can be evidenced by the presence of areas of deformed microspheres that can be detected visually or electrically.

Powders used for fine microsoldering, currently produced by spray atomization, can be produced by removing individual metal microspheres from a substrate. Furthermore, the entire array of metal microspheres can be used to solder, for example by stacking such an array towards the circuit and heating it from the back side of the substrate. When heated, the individual metal microspheres melt and transfer to the circuit as solder.

Arrays of closely packed individual metal microspheres useful for imaging can be made. Such arrays are typically transparent and have a dull appearance. When pressure is applied to the transparent dull microsphere array, the array becomes opaque and shiny in the areas where pressure is applied. The transparency and specular reflection layer depend on the amount of pressure applied to the individual metal microspheres.For example, by pressing a textured surface against an array of such microspheres, various useful images or You can create patterns.

These and other important applications for arrays of closely packed individual metal microspheres, particularly deformable and electrically conductive microspheres, exist in the art. Accordingly, there is a need to provide an array of closely packed individual metal microspheres on a substrate, preferably by commercially available methods. These metal microspheres are deformable, electrically conductive, and extremely densely packed, making it desirable for the array to be useful for the end uses mentioned above.

[Summary of the invention]

The invention provides a substrate having a discontinuous metallization consisting of an array of closely packed individual metal microspheres.The invention also provides a commercially effective method of manufacturing such an array. The metal microspheres are preferably deformable and individually conductive; ``deformable'' is here defined as being deformable by applying slight pressure, such as that applied by pressing with a human fingernail. It is defined as meaning that it can be substantially deformed by

"Individual" is defined here to mean discontinuous discrete parts, such that each line does not touch its neighboring sphere.

"Densely packed" means packed together so that, for example, when one ball is deformed, it inevitably comes into contact with its neighbor. Define.

The metal microspheres of the present invention include lead, tin, indium, bismuth, cadmium, thallium, zinc, alloys of these metals,
Preferably selected from the group of metals consisting of mixtures of such metals and alloys, hereinafter "metal" shall refer to both metals and alloys.

The microspheres of the present invention can have a very wide range of diameters, but for end uses consisting of preferably about 0.
．． 1 μm to about 5.0 μm, preferably 0.1 μm to
It will have an average diameter in the range of about 2.0 μm.

Preferred arrays of closely packed individual metal microspheres of the present invention provide a method in which the uniformly distributed protruding areas of the microspheres account for at least about 60% of the total surface area of the substrate on which they are supported.
It is characterized by occupying .

The microsphere array of the present invention comprises: (a) providing a substrate in a chamber; (b) forming a metal vapor in said chamber; and (c) disposing of individual metal microspheres closely packed on said substrate. It may be manufactured by a method consisting of several steps in which the array is attached.

Preferably, the method includes providing a substantial vacuum in the chamber prior to forming the metal vapor. Preferably, the method also includes depositing a metal vapor onto a deposition surface of the substrate having an effective temperature greater than the melting temperature Tm of the metal.

The effective temperature is defined as the actual temperature of the substrate plus the temperature increase due to the heat of condensation of the metal when deposited on the surface of the substrate.

[Detailed description of the invention]

The present invention provides an array of closely packed individual metal microspheres supported on the surface of a substrate and a method of making such an array. Previous methods of manufacturing metal microsphere arrays supported by a substrate have not been able to provide sufficient packing density. For many end uses, it is important that the metal microspheres are loose but packed very close to each other. In a preferred embodiment of the invention, the metal microspheres are deformable and electrically conductive. . These loose microspheres deform when a small amount of pressure is applied, for example the pressure exerted by a human fingernail, causing the microspheres to deform and interact with the neighboring ball(s). are filled sufficiently close together to form physical and electrical contact. What makes the invention particularly useful is that the spheres are in close proximity while remaining separate. It should be understood that the terms "spheres" and "microspheres" are used herein to refer to each discrete individual metal deposit on a substrate. It will be appreciated that these individual deposits may not actually be spheres, but instead may approximate fragments or portions of spheres.

``The array of the present invention includes two general parts, a substrate and a metal microsphere supported by the substrate. Furthermore, a novel method for attaching these metal microspheres to a substrate is described.

A suitable substrate for use in the present invention should be selected according to the requirements of its end use. The substrate may be flexible or non-flexible, transparent or opaque, may be made from many different materials, may have various thicknesses and widths, etc., forming metal microspheres. A substrate should be selected that has a surface that is not wetted by the liquid metal used in the process.

Second, a substrate should be selected that does not deteriorate due to the temperatures experienced in processing.

The wettability of a liquid placed on a substrate depends, at least in part, on the surface tension between the liquid and the substrate.

Generally speaking, the greater the surface tension, the greater the wetting angle between the droplet and the substrate.If the surface tension is large enough, the liquid will form discrete droplets that will coalesce with neighboring droplets. and will not form a liquid film on the substrate,
Wetting refers to the tendency of a liquid to form a liquid film on a given surface, whereas non-wetting refers to the tendency of a liquid to form individual discrete droplets on a surface.

For the purposes of the present invention, it is sufficient that the selected metal droplets, when deposited on the surface of the substrate, form discrete metal droplets thereon.

When this condition is met, it is referred to as a non-wetting liquid metal with respect to a particular substrate surface.

The substrate selected for use in the present invention should also be able to withstand the temperatures experienced in processing. The surface of the substrate to which the metal is deposited should have an effective temperature above the melting point of the metal when the vapor is deposited thereon. The substrate should be able to withstand the temperatures necessary to provide such a deposition surface temperature.

Examples of polymers that can be used as substrates in the present invention include: polyphenylene oxide;
Polymers of fluorinated olefins such as dorafluoroethylene: silicone polymers; cellulose polymers; polyurethanes; polystyrene, styrene/acrylonitrile copolymers, copolymers containing polymerized styrene, acrylonitrile and butadiene (often referred to as ABSf! polymers) ), styrene/butadiene copolymers, rubber-modified styrenic polymers, styrene/maleic anhydride copolymers and similar polymers of monovinisopolydenic aromatic carbocyclic monomers; phosgene and bisphenol A and ( or) polycarbonates, including those made from phenolphthalein; polyesters such as polyethylene terephthalate; acrylic resins such as poly(methyl methacrylate); polyolefins such as polyacrylonitrile and acrylonitrile/methyl methacrylate coethylene and polypropylene; polyvinyl chloride and chloride; Polyvinyl halides such as vinylidene homopolymers and copolymers, polysulfones, polyarylsulfones and perfluorinated ethylene-propylene copolymers.

Additionally, a metal substrate such as aluminum coated with at least a thin non-wetting aluminum oxide coating (typically
In general, substrates that are wettable with the selected liquid metal and therefore unsuitable for use may be coated with a non-wetting coating to ensure proper adhesion. It is also possible to provide a surface.

Many metals and metal alloys (hereinafter referred to collectively as "metals") are suitable for use in the present invention. the metal is evaporated onto the substrate selected for use in the present invention;
Metal vapor, as used herein, which must be capable of being deposited, refers to suspended metal particles, whether provided by sputtering or evaporation.

The metal microspheres formed from the selected metal are preferably deformable and electrically conductive; these properties provide many advantages for the array of closely packed individual gold i'Wi globules of the present invention. Important for desired end use. The metal is also preferably a low melting point metal, defined as a metal having a melting temperature or range of melting temperatures below 400°C, which allows for the use of a wide range of polymeric substrates. Preferred metals include lead, tin, indium, bismuth, thallium, cadmium, zinc, alloys of these metals, pure metals, and mixtures of alloys.

In order for a metal to be properly deposited on a substrate in the form of discrete droplets, the metal must be deposited at its melting temperature or throughout its melting temperature range after it has been deposited on the substrate. It should have a vapor pressure lower than the effective partial pressure of the surrounding atmosphere. Deposition is preferably accomplished in a vacuum chamber, and the effective partial pressure is therefore defined as the amount of metal vapor at the substrate surface. If the vapor pressure is greater than the effective partial pressure, the metal will evaporate into the surrounding atmosphere and will not form suitable droplets on the heated substrate.

Preferably, the metals used in the arrays of the present invention are relatively soft and deformable, allowing the arrays to be used in many of the end uses mentioned above.
Brinell hardness number (BH
N). BHN values for some metals are as follows: Indium 0.9 Tin 3.5 Approximately 2 Bismuth 7.0 70% Tin/30% Lead 12.0 Lead Alloy 8-24 T. The metal(s) and substrate or web are selected to produce the closely packed array of individual metal microspheres of the present invention. Select a metal with a melting temperature Tm. For alloys that have a melting temperature range, The is defined as the upper end of the melting temperature range. Melting point depends on pressure,
Therefore, T- would be precisely defined as the melting point of the metal at the pressure of deposition, since it may vary slightly between vacuum and standard atmospheric pressure.

Select a substrate that will not be wetted by the metal when the metal is at a temperature above Tl1 (i.e., in a liquid state) Prepare the substrate and deposit the array of metal microspheres onto it. .

A preferred method for depositing a suitable array of microspheres is as follows: first the substrate is placed in a substantially vacuum chamber. A suitable vacuum is typically about 10-4 to 1 O-
5)-L. The effective temperature of the deposition surface of the substrate is above T+s when metal is deposited thereon. The effective temperature of a substrate is defined herein to mean the actual temperature of the surface of the substrate to which it is deposited plus the temperature rise due to the heat of condensation of the metal when deposited on the surface. The heat provided by the source used to evaporate the metal can also increase the temperature of the substrate and must be taken into account, firstly forming metal vapor in the vacuum chamber and increasing the temperature of the substrate at a temperature above Tm. Deposit onto a surface. The metal vapor is deposited in a liquid state onto a heated surface, and the droplets of liquid metal cover the surface.As the metal droplets are allowed to cool, they form individual metal microspheres packed tightly onto the substrate. An array is formed.

Preferably, the metal vapor is generated in the chamber by evaporation of the metal. Deposition on the surface is therefore in the form of condensation from the substrate into a liquid. In addition to evaporation, sputtering can also be used to form a suitable metal vapor. Methods of vaporizing metals include electron beam (E-beam) vaporization and vaporization using resistive heating. E-beam evaporation, such as the embodiment depicted in Figure 1, is preferred.

Regarding the embodiment of the present invention shown in FIG. 1, overall (10)
The microsphere coating device shown in FIG. Device (10)
includes a vacuum chamber (20), an electron beam source (30) and a web conveyor indicated generally at (40).

The web conveyor (40) includes a supply roll (42),
Take-up roll (44), drum (46) and web (
48) is included. The web (48) is fed from a supply roll (42), moves around a drum (46) which is heated to the desired temperature, and then moves around a drum (46) that is heated to the desired temperature and then
4) It is wound around.

The electron beam (30) includes a sample pot (32) in which the metal to be vaporized is placed. An electron beam source (30) provides an electron beam directed at the pot (32) sufficient to vaporize the metal.

The vacuum chamber (205) includes a pair of shielding plates (22), a liquid nitrogen trap (24), a valve means (26), and a diffusion pump (28).
) and a variable orifice (29).

In use, a vacuum is drawn in the chamber (20) by the diffusion pump (28), the metal source is placed in the pot (32), and it is evaporated by the electron beam source (30). The steam is in the chamber (
20) and is guided by the shielding plate (22) and deposits onto the web (48) during its movement over the surface of the drum (46).

The substrate is presented in the vacuum chamber in the form of a heated and moving web, as shown in the embodiment of FIG.
Preferably, the web is heated to a sufficient temperature such that the attachment surface of the substrate has an effective temperature greater than or equal to T+s at the point where the metal vapor condenses. The web may be heated by a heated drum, such as drum (46) in FIG.

After the liquid metal droplets condense on the web or substrate surface, the droplets are cooled. Cooling may be facilitated by cooling rollers (not shown) on the back side of the web, the back side being the side opposite the adhering surface of the web, as shown in FIG. It may also be formed into rolls for future use.

The size and size distribution of the metal microspheres can be determined and controlled. It is believed that the metal vapor first contacts the substrate and fine droplets are formed. Further, as the metal vapor comes into contact with the substrate, the droplet size increases. As droplet size and number increase, droplets that come into contact with other droplets coalesce to form larger droplets. Growth is primarily a function of vapor deposition rate. The operator can adjust the process conditions to control droplet size.

The size of the microspheres can be determined and controlled by two means; one of the metal vapor produced by the source, e.g. an E-beam evaporator, and the rate at which the substrate web moves through the metal vapor in the vacuum chamber. It is. That is, the faster the substrate web moves, the less vapor it deposits.

Similarly, the more units of metal that evaporate per unit time, the more vapor pans are deposited. Increase your web speed,
By keeping the metal evaporation rate low, small microspheres will form. By decreasing the web speed and/or increasing the rate of metal vaporized, the microsphere size increases.6 The distribution range of the microsphere size also decreases and It is thought that this increases as the metal droplet becomes larger. □ An array will be produced in which a large number of relatively large droplets are interspersed with very small droplets.

The diameter of the microspheres of the present invention, as measured at the point of contact between the sphere and the substrate, typically ranges from a few to 10 μm or more, a particularly useful range. Typical average diameters are from about 0.1 μm to about 5.0 μm, preferably from about 0.1 to about 2.0 μm.

A preferred array of microspheres according to the invention is characterized in that the microspheres occupy at least 60% of the total surface area of the substrate, measured by the area projecting above the substrate when viewed at right angles to the substrate. Although it is possible to create an array with a close density at fi, there is no conductivity in the horizontal plane since it is made up of discrete metal microspheres.

The invention will be described by, but not limited to, the following examples.

Example 1 A microsphere array of the present invention was manufactured using an apparatus of the type depicted in FIG. The drum (46) was a resistance heated drum with a diameter of 40 cm. Aero Temescal CV as an electron beam source
-14 power source was used.

300 g of indium metal was placed in the zirconia-lined box I of the electron beam evaporation source. The source was located 25 cm from the drum. The shield formed a 10 ci+X 20 cm window placed symmetrically above the evaporator bot, 2.5 cz from the drum.

The long side of the window was located parallel to the axis of the drum.

Width 15c++, thickness 7.5x 10-'mz, length 3
A roll of 0 m polyimide film (Kapton V film, commercially available from DuPont) was placed in a vacuum chamber of the type shown in FIG. The film was passed around the drum to a take-up roll. Vacuum was applied to the chamber and the pressure was reduced to 2 x 10-5 Torr.

The drum was heated to 200°C. Electron beam voltage is 1°k
A current of 0.13 A at V was delivered to the pot. The drum was rotated to give a web speed of 150 cz/min.

A coating of indium microspheres with an average diameter of 1 μm was formed on a polyimide substrate. The coating has a hollow appearance and no light passes through the array. The electrical resistance of the array exceeded the test equipment limit of 30 MΩ/square. Upon gentle rubbing, the microsphere coating had a shiny opaque appearance and an electrical resistance of 0.5 ohms/square.

Examples 2-6 A series of arrays of the invention were prepared following a procedure similar to that described in Example 1. However, 280. of tin was placed in the pot and the drum was heated to 259°C. The electron beam is 1
Settings were 0 kV and 0,15 A, and the drum was rotated at various speeds. An array of silver microspheres was formed on a polyimide substrate as described in Table I.

Table 1 Ha 2 Education l Web, Agency C degree 0.1 240 0.2 120 0.4 5Q O,83Q 1,. 3 21 Example 7 A microsphere array of the present invention was prepared according to a procedure similar to that outlined in Example 1. However, 300 g of buttons were placed in the pot and the drum was set at 305°C.

The drum was set to rotate at a constant speed giving a constant nib speed of 120 CJI/min. The electron beam voltage is 1
It was set at 0 kV and the current was varied slowly from 0.12 A to 0. At 0.08A, a lead wire with a shoulder diameter of 2-3μ was formed on a polyimide substrate.

At 0.04 A, S() spheres with a diameter of 0.2 μm were formed.

Even if the drum temperature is not higher than the melting point of the button (327℃),
The radiant heat from the pot was sufficient to raise the substrate temperature and cause condensation of the molten lead wire.

Example 8 A microsphere array of the present invention was prepared following a procedure similar to that outlined in Example 1. However, 150° and 5
0g of lead was placed in a pot. The drum was set at 178°C. The electron beam was set at 10 kV and 0.1 OA.

Web speed was set at 240 cz/min.

Since button has a higher vapor pressure than tin, the first microspheres formed were mostly lead. After 3 minutes, the microspheres were mostly buttons. 5 minutes later, IIJ70 heavy plate%, lead 30! u amount%
and microspheres having a diameter of approximately 1-1.3 μm were formed on the polyimide substrate. Again, the radiant heat from the pot provided extra energy to heat the substrate above the melting point of the ship/tin alloy.

Example 9 A microsphere array of the present invention was prepared according to the procedure described in Example 1, except that the aluminum was evaporated using a drum at room temperature and the electron beam was set at 10 kV and 0.29 A. Web speed was 120 cz/min. The aluminum formed a thin uniform film over the polyimide. After coating the polyimide with aluminum, the pot was again coated with 300. of indium was added. Approximately 15 drums
Heating to 0°C allowed the indium to evaporate onto the aluminum coated polyimide. During this coating process, the electron beam was
0kV and 0. IE! Keep A and web speed 120
ct/min to 800cs+/min. At 600 c expansion/min, indium microspheres with a diameter of approximately 0.2 μm were formed on the aluminum coated polyimide. They appeared dark blue in normal light due to interference effects of reflected light from their spheres and the underlying aluminum coating.

[Brief explanation of the drawing]

FIG. 1 is a schematic cross-sectional view of the apparatus used to carry out the method of the invention. FIG. 2 is a photomicrograph showing the grain structure of an array of the present invention consisting of indium metal deposited on polyimide. FIG. 3 is a photomicrograph showing the grain structure of an inventive array of indium metal deposited on polyimide after partial scraping. FIG. 4 is a micrograph showing the grain structure of an inventive array of indium metal on polyimide after rubbing. FIG. 5 is a photomicrograph showing the grain structure of the inventive array of lead metal deposited on polyimide. Agent Asamura Akira Proceedings (Method) Case Description 2008 Patent Application Name of Invention Dense Metal Microsphere Array No. 220154 Name (Name) Minnesota Mining and Manufacturing Company Agent 5. 6゜*nJ correct order size November 28, 1999 None) P
^-05315

Claims (1)

Claims: (1) A metallized substrate having a discontinuous metal coating, the metal coating comprising an array of closely packed individual metal microspheres. (2) The metal-coated substrate according to claim 1, wherein the microspheres are deformable. (3) Metal is Pb, Sn, In, Bi, Zn, Cd, T
2. The metallized substrate of claim 1, wherein the metallized substrate is selected from the group consisting of: i, alloys thereof, and mixtures thereof. (4) The metallized substrate according to claim 2, wherein the metallization allows visible light to pass through. 5. The metallized substrate of claim 1, wherein the microspheres have a diameter ranging from about 0.1 μm to about 5.0 μm. (6) The metal coated substrate of claim 1, wherein the substrate is selected from the group consisting of polyimide and aluminum oxide coated aluminum. 7. The metal-coated substrate of claim 1, wherein the protruding areas of the metal microspheres occupy at least 60% of the surface area of the substrate. (8) The metal-coated substrate according to claim 4, wherein the coating comprises conductive microspheres. (9) A method of forming a discontinuous metal coating on a substrate consisting of an array of closely packed individual metal microspheres, comprising: (a) providing a substrate having an attachment surface in a chamber; (b) said chamber; forming a metal vapor therein, and (c) depositing said metal vapor on said deposition surface, so that an array of closely packed individual metal microspheres is formed on said deposition surface. Method of manufacturing metal coated substrate. 10. The method of claim 9, wherein a substantial vacuum is provided in the chamber prior to forming the metal vapor. 11. The method of claim 9, wherein the metal has a melting temperature Tm and the deposition surface has an effective temperature greater than or equal to Tm when the metal is deposited on the deposition surface. (12) The metal is Pb, Sn, In, Bi, Zn, Cd,
10. The method of claim 9, wherein the material is selected from the group consisting of Ti, alloys thereof and mixtures thereof. 13. The method of claim 9, wherein the microspheres have a diameter ranging from about 0.1 to about 5 μm. 14. The method of claim 14, wherein the microspheres have a diameter ranging from about 0.1 to about 2 μm. 15. The method of claim 9, wherein the metal vapor is deposited on the deposition surface by condensation. (16) The method according to claim 9, wherein the vapor is generated by vaporizing the metal by electron beam irradiation. (17) A substrate with a discontinuous metallization consisting of an array of closely packed individual metal microspheres is provided with a metal coating sufficient to deform some of the array microspheres to form electrical paths between them. A method of forming a conductive passageway comprising applying pressure. (18) A substrate having a discontinuous metal coating produced by the method according to claim 9. (19) A substrate having a discontinuous metal coating produced by the method according to claim 11.