1. Field of the Invention
The present embodiments relate generally to preparing a lens-less light emitting diode array. The present embodiments relate more specifically to preparing an acrylic coated lens-less light emitting diode array that enables high focused light output for a printer.
2. Background of the Invention
Typically, non-impact printers employ an array of light emitting diodes (LEDs) for exposing a photoreceptor drum surface. Minute LEDs are positioned next to a lens so that the images of the LEDs are arrayed across the surface to be illuminated. In some printers, multiple rows of LEDs may be used. As the surface moves past the line of LEDs, the LEDs are selectively activated to either emit light or not, thereby exposing or not exposing the surface of the drum in a pattern corresponding to the LEDs activated.
To obtain good resolution and image quality in such a printer, the physical dimensions of the LEDs must be quite small and very tight position tolerances must be maintained. Dimensional tolerances are often no more than a few tens of micrometers.
A problem arises for these types of LED printers in that the light from the LEDs must pass through a lens. If the lens is dirty, flawed, scratched, or otherwise not in perfect condition, the light emitted from the LEDs onto the surface is compromised.
The present embodiments provide a lens-less LED array that is a high quality light source without the use of lens that can get scratched during use.
A present embodiment is for a method to make a polished lens-less light emitting diode array for use in a printer. Light emitting diodes are adhesively attached to an etched circuit board. Each diode has a top section and a bottom section. The bottom section is connected to the circuit board; the top section has an anode and a cathode.
A clear polymer is added to the top of each diode to form a clear cap. A black or opaque polymer is added to the circuit board to fill the space between the light emitting diodes to cover the anode and the cathode. The black polymer is not filled to the point where the cap of the clear polymer is covered. The polymers are then polished and grounded to provide a lens-less light emitting diode array with a uniform, level, non-light-scattering surface.
The present embodiments are advantageous over the prior are because the methods provide an array resistant to scratching.
In the detailed description of the preferred embodiments presented below, reference is made to the accompanying drawings, in which:
The present embodiments are detailed below with reference to the listed Figures.
Before explaining the present embodiments in detail, it is to be understood that the embodiments are not limited to the particular descriptions and that it can be practiced or carried out in various ways.
The present embodied methods provide a manner to build extremely large LED arrays with high power output. The methods provide a low cost and quick way to build high power LED light arrays.
The present embodiments can be used to create a polished lens-less light emitting diode array that can produce either one color—such as green, red, or blue visible light—or to produce a combination of these colors.
The light emitting diode array is able to transmit about 90% of the light of the bare diode. This transmission rate is a dramatic improvement over normal transmissions.
An embodiment of the method to make a polished lens-less light emitting diode array involves first attaching a plurality of light emitting diodes (LEDs) to an etched circuit board. The LEDs can be attached either using an adhesive or by soldering the LED to the board.
Blue and green LEDs are typically attached to a sapphire substrate with a thermally conductive adhesive, such as Model TC-201P available from Zymet. For longer wavelength red LEDs with a bottom cathode contact, an electrically conductive adhesive, such as a silver-filled Model Epo-Tek H2OE available from Epoxy Technology, can be used. Small amounts of adhesive are typically applied by pin transfer rather than by pneumatic pressure dispensers. Lower cost manufacturing methods are envisioned with the embodied methods that can co-deposit and co-cure the two types of polymers used to make the LED array.
In a preferred embodiment, the array can be used for exposing photographic images or for slitting of photographic images. In one embodiment about thirty LEDs can be secured to the etched circuit board. The number of LEDs can vary as the size of the board or the size of the array varies. In addition, the LEDs can be secured perpendicular to the circuit board or in an angle in order to provide a directed, angled beam depending on the desire of the customer.
Each LED has a top section and a bottom section. The bottom section of each LED is attached to the circuit board. An anode and a cathode can be attached to the top section of each LED. In an alternative embodiment, the cathode can be connected to the bottom section instead of the top section. The anode is typically connected to a modulator that controls a power source. The cathode is typically connected to a grounded section.
A modulator controls the current to the LEDs. By controlling the current to the LEDs, the intensity of the light produced from the LED array can be controlled.
The method involves the applications of a clear polymer directly to the top of each LED. Preferably, the clear polymer is a liquid polymer at room temperature. The clear polymer is typically cured using ultraviolet (UV) light. The clear polymer is preferably an acrylic or an optically clear thixotropic ultraviolet curing adhesive, such as Model NEA 123 available from Norland, Inc. Any polymer that is optically clear at the wavelength of the associated diode is usable. Clear materials with a greater hardness are preferred because the harder materials are easier to polish.
Once the clear polymer has hardened on each LED, the circuit board is covered or flooded with a black polymer, typically a liquid black polymer. The black polymer is added to the circuit board to optically separate the LEDs and to eliminate cross-talk between the LEDs.
The black polymer completely fills the space between the LEDs and covers the anode and cathode, but leaves the top of the hardened clear polymer visible. The black polymer serves to passivate the anode and the cathode forming a monolithic structure. The black polymer is typically cured chemically, usually in less than five minutes. The black polymer can be an epoxy, an acrylic, or an opaque epoxy (such as EPO-Tek 320). Typically, the black polymer is applied to a depth of 25 microns so that all but the top of the LEDs are completely covered.
The hardened epoxy is then polished. The polishing step is typically performed using optical polishing powders or slurries that contain a small amount of abrasive. The polishing step is performed to make the surface a high polish, non-light scattering surface. The high polish, non-light scattering surface provides an efficient transmission of the LEDs in a highly directed fashion.
With reference to the figures,
In the embodiment depicted in
The invention has been described in detail with particular reference to certain preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention.