DE69512743T2 - Composite process for silicon chips for inkjet printing - Google Patents

Description

FIELD OF INVENTION

The present invention relates to a method for connecting a silicon chip to the pen body of an inkjet printer.

BACKGROUND OF THE INVENTION

Modern inkjet printing has placed many unprecedented demands on materials and methods for their assembly. The present invention relates to a solution to one such requirement, namely a method for connecting the silicon chip to the pen body of the inkjet printer.

The bond between the inkjet silicon chip and the inkjet printer pen body is subjected to very severe attack, particularly because the temperature during use is very high and the bond is exposed to water-based liquid inks, which usually contain organic co-solvent and also have a very high (basic) pH. Not only must the bond serve to attach the chip to the pen body, but it must also form a leak-resistant bond around the chip to prevent ink transfer to the user.

The binder must also be such that it does not alter the properties of the ink used in the system, and modern color printers typically use three different inks. In addition, the curing temperature of the adhesive must be below the glass transition temperature of the plastic that forms the pen body. To build a multi-color inkjet pen, the paths in the chip generally need to be separated by an adhesive that acts as a barrier or sealing material around each path to prevent ink from entering the chip. Furthermore, the adhesive must act as a seal around the chip to prevent ink mixing. Furthermore, the adhesive must act as a seal around the chip to prevent ink leaking to the outside of the body. Ever-tightening path spacing to deliver ever-higher dots-per-inch (dpi) print resolution places the highest demands on an adhesive to produce a reliable bond in a very harsh environment.

A method of improving adhesion at the adhesive-to-silicon interface is necessary to prevent two failure modes. If an adhesion failure occurs at this interface, then the primaries will flow freely, resulting in ink mixing. Second, if the adhesive-to-chip interface is flawed at the perimeter, then the ink will leak and routine handling can transfer ink to the user. Both types of failures would be considered reliability failures.

DISCLOSURE OF THE INVENTION

The present invention, which is defined in the independent claims, solves the above-mentioned problems. According to this invention, the silicon chip is first covered with a thin coating of a silane coupling agent. This coating is applied to the side of the chip that does not contain the electronic circuitry. The coating of the silane coupling agent is in turn coated with a thin (about 0.5 to about 5.0 µm (microns)) layer of an epoxy resin, which is then cured at a temperature of about 175°C.

In another embodiment of the present invention, the above steps are performed on a multichip silicon wafer, which can then be subjected to subsequent manufacturing operations. Hundreds of chips can be processed on a single silicon wafer.

In the final step of the method of the present invention, the chip is attached to the pen body using an epoxy resin that cures at a temperature of 100°C or less.

DESCRIPTION OF THE DRAWINGS

The understanding of the invention is facilitated with reference to the attached drawings.

Fig. 1 is a cross-sectional view (not to scale) of a coated silicon wafer.

Fig. 2 is a cross-sectional view, not to scale, of an inkjet printhead chip and pen portion.

In Fig. 1, 1 is a silicon wafer; 2 is the circuitry on one side of the wafer; 3 is a layer of an adhesion promoter; and 4 is a layer of an epoxy resin.

In Fig. 2, 1 is the pen body of the inkjet printer nozzle; 2 is the inkjet silicon chip; 3 is an acrylate-based polymer thick film; 4 is the nozzle plate; 5 is a layer of fast/low temperature cure epoxy adhesive; 6 are two thin layers, one of an adhesion promoter and one of an epoxy resin; and 7 is the ink path.

BEST EXAMPLE OF IMPLEMENTATION

A preferred silane coupling agent is Dow Corning's Z6032, a vinylbenzylamine functional silane. The commercial material is prehydrolyzed by adding 5 wt% water to the silane solution. It is then diluted to a 1% functional silane solution using ethanol. This solution is sprayed onto the side of the resting silicon wafer that does not carry circuitry and allowed to sit for 20-30 seconds. The wafer is then rotated at 2000 rpm for 45 seconds to remove the excess and to dry the wafer surface.

A preferred high temperature curing epoxy is a tertiary amine cured compound such as Ablebond 968 from Ablestik Co. This material is used without filler. It is first diluted with gamma-butyrolacetone in a 1 to 1 ratio. Approximately 2 int of this solution is applied to the center of the wafer after the silane is applied. The wafer is rotated at 2500 rpm for 45 seconds. This results in a uniform epoxy film approximately 0.8 µm (microns) thick on the wafer. The wafer is then baked at 175ºC for 2 hours to cure the epoxy.

Finally, the wafer is cut into individual chips that are attached to the pen body using a low-temperature-curing polybenzimidazole epoxy resin, such as Emerson-Cuming's LA3032-78, an epoxy resin that cures at about 100ºC.

Manufacturing processes for inkjet pen products, because they are consumable (often disposable) products, must include low-cost material that can be processed at high throughputs. Pen bodies are most commonly injection-molded thermoplastic materials, such as modified polyphenylene oxide (PPO). The increased temperature resistance of such a material sets a maximum cure temperature that is acceptable for subsequent processes, such as attaching the inkjet chip and nozzle assembly to the body.

Materials are available that cure in the 100ºC or lower range and in shorter times and are resistant to ink formulations when exposed to substrates. However, early adhesion failures are usually observed at the silicon-to-wafer adhesive interface. By applying the silane/epoxy resin Ultra-thin film coating and protecting hundreds of chips simultaneously at an early stage of manufacturing (at the wafer stage). At this stage, high purity, high stoichiometric epoxies can be thoroughly crosslinked at the higher temperatures (at least 175ºC, which gives much better attachment to the silane/silicon wafer). A method of increasing product lifetime while keeping throughput cost-effective is then achieved.

The method of the present invention is characterized by the use of two different epoxies, the first of which cures at a temperature above the heat distortion temperature of the plastic pen body and the second of which cures at a temperature below the heat distortion temperature of the plastic pen body. After attachment to the pen body, the chips have an ink path extending into the chips, bounded by the coupling agent, the first epoxy resin and the second epoxy resin.

Other features of this invention are the following: Insensitivity to production line interruption/processing (as a silane alone would be), and the ultra-thin application provides a minimal additional thermal barrier to heat removal from the wafer.

Claims (9)

1. A method of bonding an inkjet silicon chip to the plastic pen body of an inkjet printer, the method comprising the steps of: 1) Applying a thin coating of a silane coupling agent to the side of the chip that does not contain circuitry; 2) applying a thin coating of a first epoxy resin over the coupling agent; 3) Curing the first epoxy resin at a temperature above the heat distortion temperature of the plastic pen body; 4) Attaching the coated chip to the plastic pen body using a second epoxy resin that is cured at a temperature below the heat distortion temperature of the plastic pen body. 2. A method of connecting an inkjet silicon chip to the pen body of an inkjet printer, the method comprising the steps of: 1) Applying a thin coating of a silane coupling agent to the side of the chip that does not contain circuitry; 2) applying a thin coating of a first epoxy resin over the coupling agent; 3) curing the first epoxy resin at a temperature of about 175ºC; and 4) Attaching the coated chip to the pen body using a second epoxy resin cured at a temperature of 100ºC or less. 3. The method of claim 1, wherein the thin coating of the silane coupling agent and the thin coating of the first epoxy resin are each applied by a spin coating process. 4. The method of claim 1, wherein the application of the thin coating of a silane coupling agent and the application of the thin coating of the first epoxy resin are carried out on a multi-chip silicon wafer. 5. The method of claim 1, wherein the thin coating of the first epoxy resin is about 0.5 to about 5.0 µm (microns) thick. 6. The process of claim 1 wherein the silane coupling agent is a vinylbenzylamine functional silane. 7. A method according to any preceding claim, wherein the chip, when attached to the pen body, has an ink path extending into the chip, bounded by the coupling agent, the first epoxy resin and the second epoxy resin. 8. A method of connecting inkjet silicon chips to the pen body of an inkjet printer, the method comprising the steps of: 1) spin-coating the side of a multichip silicon wafer that does not contain circuitry with a thin coating of a vinylbenzylamine-functional silane; 2) spin coating the thin coating with an approximately 0.8 µm (micron) thick coating of a first epoxy resin; 3) Curing the first epoxy resin at a temperature of about 175ºC; 4) Dividing the multi-chip silicon wafer into individual chips; and 5) Attaching the individual chips to the pen body using a second epoxy resin cured at a temperature of 100ºC or less. 9. The method of claim 8, wherein the chips, when attached to the pen body, have an ink path extending into the chips, bounded by the coupling agent, the first epoxy resin and the second epoxy resin.