Die-Mounting Substrate Dummy Traces for Film Adhesion Planarity
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Solution Overview
Problem
Current die attach methods, such as paste and film adhesives, face challenges in achieving uniform bond line thickness and minimizing interfacial voids due to topographical features on the substrate, leading to unreliable adhesion and potential de-lamination, especially when stacking thin dies with varying sizes and shapes.
Innovation Solution
Incorporating dummy traces with the same design rules as signal traces on the substrate to create a more planar surface, which fills empty regions and provides channels for air escape, thereby improving adhesion and reducing void formation during die attachment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If paste adhesive is used to attach die to substrate, then viscous properties accommodate irregular topographical features and minimize die attach voids, but non-uniform bond line thickness occurs due to die warpage and shrinkage produces reverse fillet
Solution Approach 1:
The patent changes the physical state of the adhesive from viscous paste to thin film form, fundamentally altering how the adhesive interacts with topographical features. The film adhesive maintains uniform thickness through its inherent flexibility while eliminating the shrinkage issues of paste adhesive.
Solution Approach 2:
The patent employs thin film adhesive that can conform to substrate topography while maintaining uniform bond line thickness. The film's flexibility allows it to accommodate irregular surfaces without the void formation associated with rigid fillers, and without the shrinkage problems of paste adhesive.
2Manufacturing precision
If film adhesive is used to attach die to substrate, then uniform bond line thickness is provided and shrinkage is minimized, but interfacial voids form due to rigid nature and topographical features
Solution Approach 1:
The patent uses thin film adhesive that combines the uniform thickness advantage of film adhesive with the ability to conform to topographical features. The film's flexibility allows it to bridge over irregularities without forming voids, while maintaining consistent bond line thickness for reliable adhesion.
Solution Approach 2:
The patent incorporates filler material and mechanical planarization steps before applying the top solder mask layer to create a more uniform substrate surface. This preliminary cushioning of topographical irregularities reduces the formation of interfacial voids when film adhesive is applied.
3Shape
If solid metal fill is used to minimize topographical variations, then substrate planarity is improved, but metal regions are thicker than traces due to etching/plating density
Solution Approach 1:
The patent applies different trace patterns in different regions: dummy traces are placed in empty regions where planarity is needed, while signal traces maintain their functional patterns. This local differentiation allows planarity improvement without compromising electrical functionality or creating excessive thickness variations.
Solution Approach 2:
The patent creates dummy traces that copy the design rules and patterns of signal traces but are placed in non-functional empty regions. These dummy traces replicate the beneficial planarity effect of solid metal fill while maintaining the trace thickness consistency of patterned conductors.
4Shape
If mechanical planarization is used to provide flat surface for film adhesive mounting, then substrate planarity is improved, but additional processing cost and complexity increase
Solution Approach 1:
The patent combines the dummy trace pattern formation with the existing signal trace fabrication process. Both dummy and signal traces are created using the same photolithography and etching steps, merging the planarity improvement function into the existing manufacturing flow without adding separate planarization processing steps.
Solution Approach 2:
The dummy traces serve multiple functions: they improve substrate planarity in empty regions, maintain consistent trace thickness throughout the substrate, and can potentially serve as electrical pads or connection points. This multi-functionality eliminates the need for separate mechanical planarization steps.
Data Source
AI summary
A die-mounting substrate and method incorporating dummy traces for improving mounting film planarity makes the use of film attach possible with a simplified manufacturing process and in applications where film-attach was not previously practical. The die-mounting substrate includes dummy traces that are generated along with signal traces extending into the die mounting area of the substrate. The dummy traces are designed according to the same design rules as the signal traces and are disposed in otherwise empty regions between signal traces and vias within the die mounting area. The result is die mounting area without regions empty of signal traces that previously either lack conductor or are filled completely with conductor, either of which will result in surface variation that compromises the film bond.