Solder Trench Captures Excess Under-fill Flow
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Solution Overview
Problem
The miniaturization of integrated circuit (IC) packages is hindered by the challenges of controlling the height of solder dams, which can obstruct stencil placement during solder paste deposition, leading to imprecise deposition and potential electrical connection issues in IC packages.
Innovation Solution
The use of a solder trench in IC packages allows for precise solder paste deposition by enabling the stencil to be placed closer to the substrate, capturing excess under-fill and reducing the complexity of the fabrication process, while eliminating the need for precise solder dam structures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a solder dam is used to contain under-fill, then under-fill containment is improved, but manufacturing precision deteriorates due to stencil placement obstruction
Solution Approach 1:
The patent transitions from a vertical barrier structure (solder dam protruding above substrate surface) to a horizontal subsurface structure (trench formed within substrate). This dimensional change allows the containment structure to exist below the stencil placement plane, eliminating interference with solder paste deposition while maintaining under-fill containment effectiveness.
Solution Approach 2:
The solder trench is formed within the substrate volume, nesting the containment structure inside the substrate rather than adding it as an external protrusion. This nesting approach allows the containment function to be integrated into the substrate itself without interfering with surface-level fabrication processes.
2Reliability
If solder dam height is increased to improve under-fill containment, then under-fill flow control is improved, but device complexity increases due to alignment sensitivity
Solution Approach 1:
By moving the containment structure from vertical (above substrate) to horizontal (within substrate), the system eliminates the height parameter that creates alignment sensitivity. The trench depth is controlled during substrate fabrication with standard tolerances, while the top surface remains flat for straightforward stencil alignment.
Solution Approach 2:
The solder trench is formed as part of the substrate fabrication process before IC mounting and under-fill application. This preliminary formation of the containment structure eliminates subsequent alignment operations, as the trench is already precisely positioned within the substrate during manufacturing.
3Reliability
If a solder dam is used to protect chip capacitors from under-fill, then component protection is improved, but manufacturing precision deteriorates due to stencil placement errors
Solution Approach 1:
The protection function is achieved by positioning the containment structure in the subsurface dimension rather than the surface dimension. This allows chip capacitors on the substrate surface to remain accessible for precise solder paste deposition while the trench below provides protective containment.
Data Source
AI summary
One embodiment sets forth an integrated circuit package that includes a substrate, one or more devices mounted on the substrate, a layer of under-fill configured to secure the one or more devices on the substrate, and a solder trench formed in the substrate, where the aggregate volume of the solder trench is large enough to capture a flow of excess under-fill during fabrication. One advantage of the disclosed integrated circuit package is that the solder trench is used in lieu of solder dam structures, thereby allowing a stencil to be lowered closer to the substrate surface during fabrication, which facilitates depositing solder paste during fabrication.