Molded Printhead Back-Face Electrical Routing
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Solution Overview
Problem
Conventional inkjet printheads face challenges in making robust electrical connections between the printhead dies and external wiring that withstand ink and mechanical stresses without interfering with low-cost capping and servicing, especially when using tiny printhead die "slivers".
Innovation Solution
The electrical connections are moved to the back of the printhead die and embedded in the molding, with bond wires routed through a printed circuit board embedded in the molding, creating a continuous planar surface on the front face for ink ejection orifices, allowing for robust and protected connections.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If electrical connections are made on the front face of the printhead die, then connections can be easily accessed, but protruding structures interfere with printhead-to-paper spacing and capping/servicing
Solution Approach 1:
The patent inverts the conventional approach by moving electrical connections from the front face to the back face of the printhead die. Bond wires are routed from bond pads on the back of the die through the molding to contact pads on the front, allowing the front surface to remain completely flat while electrical connections are established on the opposite side.
Solution Approach 2:
The patent transitions electrical connections from a two-dimensional surface arrangement on the front face to a three-dimensional routing through the molding depth. Bond wires extend through the molding material from the back face to the front face, utilizing the vertical dimension to resolve the conflict between accessibility and surface flatness.
2Ease of operation
If electrical connections are exposed on the front face, then connections are easily accessible, but connections are vulnerable to ink exposure and mechanical stresses
Solution Approach 1:
The patent extracts the vulnerable electrical connection points from the ink-exposed front face environment and relocates them to the protected back face. Bond pads are positioned on the back of the die away from ink ejection zones, and connection wires are routed through the molding material that provides mechanical protection and chemical isolation from ink.
Solution Approach 2:
The molding material serves as an intermediary that protects bond wires from direct exposure to ink and mechanical stresses. The molding encapsulates the wire routing path, providing both chemical barrier properties against ink and mechanical strength against physical damage while still allowing electrical signal transmission.
3Quantity of substance
If conventional fluidic fan-out is used from microscopic ejection chambers to macroscopic supply channels, then ink supply is adequate, but the die size must be large to accommodate the fan-out structure
Solution Approach 1:
The patent transitions fluidic channels from a planar two-dimensional layout on the die surface to a three-dimensional structure where channels are formed within the molding material. This vertical integration allows macroscopic supply channels to deliver ink directly to microscopic ejection chambers without requiring large horizontal spacing for fluidic fan-out structures.
Solution Approach 2:
The patent merges the fluidic supply function with the structural molding that houses the electrical connections. The same molding material that provides mechanical support and electrical wire routing also contains the fluidic channels, eliminating the need for separate fluidic fan-out structures and reducing overall die area.
Data Source
AI summary
In some examples, a print bar fabrication method comprises placing printhead dies face down on a carrier, placing a printed circuit board on the carrier, wire bonding each printhead die of the printhead dies to the printed circuit board, and overmolding the printhead dies and the printed circuit board on the carrier, including fully encapsulating the wire bonds.