Raised Chip Mounting Area for Low Profile Wire Bond Encapsulation
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Solution Overview
Problem
The encapsulation of wire bonds between a circuit board and an integrated circuit die poses challenges due to the high profile of the encapsulant bead, which obstructs active surfaces like inkjet printhead nozzles, and the irregular shape of the encapsulant bead leads to inefficient use of wafer real estate and reduced die density.
Innovation Solution
Raising the chip mounting area relative to the conductor mounting area, plastic deformation of wire bonds to reduce their height, and using a profiling blade to shape the encapsulant bead into a lower, more controlled profile, allowing the active surface to be closer to other surfaces without contact.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the encapsulant bead is made tall to fully encapsulate the wire bonds, then the wire bonds are protected and strengthened, but the active surface of the die is obstructed from close proximity to other surfaces
Solution Approach 1:
The support structure introduces a vertical dimension by providing a raised chip mounting area, effectively creating a step configuration. This dimensional change allows the wire bonds to extend vertically from the raised area while the encapsulant bead height is measured from the lower support structure surface, thereby protecting the wire bonds without obstructing the active surface proximity requirements
Solution Approach 2:
The support structure is segmented into two distinct levels: a raised chip mounting area and a lower conductor mounting area. This segmentation allows the wire bonds to be positioned on the raised area where they require full encapsulation, while the overall encapsulant bead height from the lower surface remains minimal, thus resolving the contradiction between wire bond protection and active surface accessibility
2Reliability
If the encapsulant bead is made irregular to accommodate wire bond arcs, then full wire bond coverage is achieved, but wafer real estate is wasted and die density is reduced
Solution Approach 1:
The wire bonds are plastically deformed into a flatter profile before the encapsulant bead is applied. This preliminary action reduces the vertical space required for wire bond arcs, allowing the encapsulant bead to be formed with a more regular, compact shape that minimizes the area occupied on the wafer, thereby improving die density while maintaining adequate wire bond encapsulation
3Adaptability or versatility
If wire bonds are made longer to accommodate thermal expansion and flex, then changes in gap between PCB and contact pads are accommodated, but the wire bond arc height increases
Solution Approach 1:
By providing a raised chip mounting area, the invention creates a vertical offset that absorbs the wire bond length required for thermal expansion and flex accommodation. The wire bonds can be longer to accommodate gap variations, but their arc height is reduced because they extend from the raised area, allowing the encapsulant bead to maintain a low profile from the support structure surface
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach reduces the encapsulant bead height, enabling closer proximity of active surfaces to other components without contact, optimizing wafer real estate and improving die density by maintaining electrical connectivity and structural integrity.
Implementation Method 1
The wire bonds are plastically deformed to reduce their height above the contact pads
Data Source
AI summary
A microprocessor device that has a support structure with a chip mounting area and a conductor mounting area. An inkjet printhead IC is supported on the chip mounting area. The inkjet printhead IC has a back surface in contact with the chip mounting area and an active surface opposing the back surface. The active surface has electrical contact pads and an array of ink ejection nozzles. The active surface has electrical contact pads for its circuitry and functional elements. A plurality of electrical conductors are, at least partially, supported on the conductor mounting area and a series of wire bonds extending from the electrical contact pads to the plurality of electrical conductors supported on the conductor mounting area wherein, the chip mounting area is raised relative to the conductor mounting area. By raising the chip mounting area relative to the rest of the PCB, or at least the conductors connected to the PCB end of the wire bonds, the top of the arc formed by the layer is much closer to the active surface of the die. This, in turn, allows the bead of encapsulant to have a lower profile relative to the active surface. With a lower encapsulant bead, the active surface can be brought into closer proximity with another surface without making contact. For example, the nozzle array on a printhead IC can be 300 microns to 400 microns from the paper path.