Patent ID: 12209304

DETAILED DESCRIPTION OF THE INVENTION

The present invention provides a much faster way to fabricate metal lines and patterns on a receiver substrate at a high resolution by applying a solvent layer to metal-coated donor substrate. The laser jetting involves ejecting metal particles, constrained within a solvent membrane, from a metal layer coated on the donor substrate. Once the metal particles have been deposited onto a receiver substrate, the solvent can be evaporated.

Since this printing procedure can be performed with the solvent layer in direct contact with the receiver substrate (or separated therefrom by a small distance), the resolution of the metal lines is very high and depends directly on the laser spot size and defocus. The solvent constrains the droplet size of the metal particles, which can increase or maintain the resolution of the laser beam. As this process is a continuous sequence production, the metal line production can be performed at a very rapid rate.

Before describing the invention in detail, it is helpful to present an overview. The invention generally relates to the laser-assisted deposition of metal particles from a donor substrate12onto a receiver substrate18. As illustrated in the printing system100depicted inFIG.1A, a printing unit10is used to direct a laser beam20towards a donor substrate12that has been coated with a metal layer14, causing metal particles22to be jetted towards the surface of a receiver substrate18. The jetted metal particles22, however, travel in uncontrolled stream (e.g., in a spray or mist form) that can diffuse in air to distant locations. Such uncontrolled (or loosely controlled) trajectory of the metal particles22is undesirable as it reduces the resolution at which the printing of metal on the receiver substrate18can be performed as well as can cause contamination of equipment in the surrounding workspace.

To address such shortcoming of the printing system100, a surface of the metal layer14(facing the receiver substrate18) may be coated with a solvent layer16, as depicted in the printing system102ofFIG.1B. When the printing unit10directs the laser beam20towards the donor substrate12in the printing system102, the metal particles22are constrained within a solvent membrane24as the metal particles22are released from the metal layer14. Such solvent membrane24filled with metal particles22then is then jetted towards the receiver substrate18. The resulting effect is that the trajectory of the metal particles22can be much more stringently controlled (e.g., trajectory can be controlled to be perpendicular to the surface of the receiver substrate18). Accordingly, the resolution at which the metal particles22can be printed on the receiver substrate18can be greater than the resolution possible from the printing system100depicted inFIG.1A.

In one embodiment, the donor substrate12may be a film of plastic or glass. In one embodiment, the donor substrate12is a continuous transparent film substrate. In a preferred embodiment, the donor substrate12is a transparent plastic film to allow a direct contact to more easily be formed between the solvent layer16and the receiver substrate18. One benefit of a direct contact is an increase in the final printing resolution. However, the same printing technique can still be applied with the donor substrate12separated by some distance from the receiver substrate18, albeit with a possible reduction in the printing resolution.

In one embodiment, the donor substrate12may be transparent to the wavelengths of radiation present in the laser beam20. The radiation may include infra-red (IR) light, visible light or ultra-violet (UV) light. Therefore, the films that can be used for the process are almost unlimited, because almost any film of material used as the donor substrate12will be transparent to at least one of the wavelengths mentioned above.

The metal layer14coating a surface of the donor substrate12can be created by any known chemical or physical coating mechanism. However, in a preferred embodiment, a thermal coating process which deposits metal from a metal target is used, because such a process is capable of depositing a very precise and uniform metal layer14on the donor substrate12. The metal layer14can include any metal, but in the most important application of creating metal conduction lines on printed circuit boards (PCBs) and other surfaces, the metal layer14includes copper.

The key properties of the solvents to consider when selecting the solvent are its compatibility to the metal in the metal layer14and its boiling point. The reason is that a non-compatible solvent can increase the oxidation of the metal during the laser jetting or can increase the occurrence of other side reactions. Therefore, it is important to choose a solvent with a low tendency to react with the metal in use. It is also important to choose a solvent with a high enough boiling point so that it will not evaporate from the donor substrate12prior to the jetting of the metal particles22at the start of the process. It is also important that the solvent will have a low enough boiling point so that it will evaporate from the metal particles22during or right after the jetting.

Some metals (e.g., metals that do not tend to react) can be jetted with the aid of any solvent with a high enough boiling point (e.g., water). Other metals will need to be jetted with non-polar solvents such as ISOPAR™ with a medium boiling point or polar solvents such as tetrahydrofuran (THF). However, in a preferred embodiment, solvents with respective boiling points between 50-150° C. and a low number of reactive components (i.e., inert solvents) are used.

FIGS.2A-2Hdepict a sequence of drawings to illustrate a coating process using a coating unit11, followed by a metal jetting process using a printing unit10. As depicted inFIG.2A, a donor substrate12, more specifically its bottom surface, is first coated with a metal layer14. As previously explained, the type of material used for donor substrate12is almost unlimited. Almost any plastic can be used, and even colored films can be considered if they are transparent to the wavelength(s) of the laser beam20. Furthermore, the thickness of the metal layer14on the donor substrate12can be as thin as one nanometer or as thick as one micron. Therefore, the variety of metals and metal thicknesses that can be printed by the jetting process is very high.

However, the most important application for the current process is depicted inFIG.2A, in which a transparent donor substrate12is coated with a copper layer14. In a preferred embodiment, the donor substrate12may be a polyester (PET) film with a thickness of 50 microns that is coated by a copper layer with a thickness of 100 microns.

As depicted inFIG.2B, the surface of the metal layer14facing the receiver substrate18may be coated with a layer of solvent16. In one embodiment, the solvent layer16has a uniform thickness. In a preferred embodiment, the solvent is ISOPAR™ with a 63° C. boiling point and no reactive components on its backbone.

As depicted inFIG.2C, a printing unit10may direct a laser beam20towards the donor substrate12, which causes a region26of the metal layer14to be heated. As previously mentioned, the laser beam20may include light in the ultra-violet (UV), infra-red (IR) and/or visible spectrums. The energy emitted by the laser (not depicted) and the distance between the laser (not depicted) and the focal point of the laser beam20on the metal layer14will determine the spot size and the effect of the laser beam20on the metal layer14. In one embodiment, the laser is a high-frequency laser.

FIG.2Cillustrates the effect of shining the laser beam20on the metal-coated donor substrate12. Heat is absorbed on the side of the metal layer14facing the printing unit10and metal particles22(e.g., on the scale of nanometers) begin to form, as depicted inFIG.2D. At this point in the process, the presence of the solvent layer16becomes relevant: instead of an uncontrolled stream of metal particles22that can travel in the air to all directions, the solvent layer16constrains the trajectories of the respective metal particles22. As a result of the solvent layer16, the metal particles22are enveloped within a solvent membrane24as the metal particles22travel toward the surface of the receiver substrate18in a direction normal to the surface of the donor substrate20, as depicted inFIG.2E.

When the solvent membrane24with the metal particles22therein contacts the surface of the receiver substrate18, as depicted inFIG.2F, the solvent starts to evaporate. The evaporation can occur at ambient conditions if a slow evaporation is desired. Otherwise, the evaporation can occur more quickly at higher temperatures by heating the surface of the receiver substrate18with a heater, a stream of hot air, or the laser beam20to sinter the metallic particles, as depicted inFIG.2G. In one embodiment, the evaporation of the solvent may take place in a controlled environment or in ambient conditions.

At the end of the printing process, the sintering of the metal particles22forms a metallic conductive pattern28on the surface of the receiver substrate18. The conductivity of the metallic conductive pattern28can equal the conductance of a pure metal since no organic material is present in the final metallic conductive pattern28, as shown inFIG.2H.

FIG.3depicts an alternative embodiment in which a dielectric layer13is disposed between the donor substrate12and the metal layer14. The dielectric layer13may include an adhesive such as glue to enhance the adhesion of the metal layer14to the donor substrate12, which is advantageous for some types of metals which would otherwise have difficulty adhering to the donor substrate12.

Thus, systems and methods for printing metal lines and patterns at high resolution have been described. Many other embodiments will be apparent to those of skill in the art upon reviewing the above description. The scope of the invention should, therefore, be determined with reference to the appended claims, along with the full scope of equivalents to which such claims are entitled.

LIST OF REFERENCE NUMERALS

10Printing unit11Coating unit12Donor substrate13Dielectric layer14Metal layer16Solvent layer18Receiver substrate20Laser beam22Metal particles24Solvent membrane26Heated region of metal layer28Deposited metal100Printing system102Printing system