Micro-fluid ejection devices continue to be used in a wide variety of applications, including ink jet printers, medical delivery devices, micro-coolers and the like. Of the uses, ink jet printers provide, by far, the most common use of micro-fluid ejection devices. Ink jet printers are typically more versatile than laser printers for some applications. As the capabilities of ink jet printers are increased to provide higher quality images at increased printing rates, fluid ejection heads, which are the primary printing components of ink jet printers, continue to evolve and become more complex.
For example, there is a trend toward use of smaller semiconductor substrates containing more fluid ejection actuators for ink jet printers. The substrates also contain contact pads thereon for providing electrical impulses to the fluid ejection actuators. In some conventional ink jet print heads, flexible circuits containing conductive leads are bonded to contact pads on the substrate. In other conventional ink jet print heads, conductive wires are bonded to the contact pads on the substrate and to contact pads on a flexible circuit. The bonds between the flexible circuit and the substrate can be made through techniques such as hot bar gang soldering or tape automated bonding (TAB).
In either case, the contact pads on the semiconductor substrate must be large enough and spaced far apart enough to enable an electrical connection between the flexible circuit and the substrate to be made. For example, a typical TAB contact pad on a print head substrate has the following dimensions: 283 μm×160 μm. The contact pad size may vary by 25% or more. Such size and spacing of contact pads on the substrate requires valuable substrate surface area to be provided for the contact pads.
In a typical print head, the semiconductor substrate is placed and bonded in a pocket or recessed area of a print head or fluid reservoir. An adhesive or protective underfill material is then used to fill in voids around the substrate to prevent fluid from contacting and corroding the underside of the conductive leads or wires. Because the leads or wires do not conform to the shape of the adhesive or underfill material, there is often a gap between the leads or wires and adhesive or underfill material. Such gap may allow fluid to enter and corrode the leads or wires.
Accordingly, there is a need for improved interconnections between a semiconductor substrate and a circuit device that will enable the use of smaller contact pads and further reduce corrosive effects of fluids on interconnections between the substrate and circuit device.
With regard to the foregoing and other objects and advantages there is provided a method of connecting a circuit device to a semiconductor substrate and a micro-fluid ejection device made by the method. In an exemplary embodiment, the method includes printing an elongate strip of an electrically conductive fluid to electrically interconnect a first contact pad on a semiconductor substrate containing fluid ejection actuator devices with a second contact pad on an electrical trace circuit, wherein the electrical trace circuit is disposed adjacent to and spaced-apart from the semiconductor substrate. The electrically conductive fluid contains a liquid component and a conductive particle component. Subsequently, removing the liquid component from the conductive particle component to provide a solid elongate strip of conductive material interconnecting the first contact pad and the second contact pad.
In another embodiment there is provided a micro-fluid ejection device. The micro-fluid ejection device includes a fluid reservoir body and a semiconductor substrate attached to the fluid reservoir body. The substrate contains fluid ejection actuators and first electrical contact pads electrically connected to the fluid ejection actuators. A circuit device is disposed adjacent to and spaced apart from the semiconductor substrate. The circuit device contains electrical trace circuits terminating in second electrical contact pads. Elongate strips of electrically conductive material are printed to electrically interconnect the first contact pads with the second contact pads.
An advantage of an exemplary embodiment of the disclosure may include providing interconnections across uneven surfaces wherein a printed conductive material conforms to the underlying surface thereby eliminating gaps between the printed connector and the underlying surface. Another advantage may be that conductors can be connected to smaller contact pads with more precision than when using conductive leads or wire bond connectors to make such interconnections.