Multi-Layer Redistribution Board for Self-Aligned Chip Bonding
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Solution Overview
Problem
The small bump pitch of semiconductor chips makes direct mounting onto a printed circuit board difficult, necessitating fan-out structured packages with redistribution layers for scale conversion, but existing self-alignment techniques are inadequate for precise bonding.
Innovation Solution
A multi-layered board with differential pad heights and a redistribution layer design, utilizing self-alignment through surface tension of molten solder bumps to correct initial misalignment during reflow soldering, ensuring accurate chip bonding.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the bump pitch is reduced for miniaturization and multi-functionalization, then the chip functionality is improved, but direct mounting onto the main board becomes difficult
Solution Approach 1:
A redistribution layer (RDL) is introduced as an intermediary between the chip and the main board. The RDL includes multiple conductive layers with different pad pitches that enable scale conversion, allowing fine-pitch chip bumps to be connected to coarser-pitch main board pads through a multi-layer redistribution structure.
Solution Approach 2:
The solution transitions from a single-layer direct connection to a multi-layered three-dimensional structure. The redistribution layer uses multiple stacked conductive layers (first conductive layer, second conductive layer, third conductive layer) connected through vias, enabling pitch conversion in the vertical dimension while maintaining planar connectivity.
2Device complexity
If conventional single-height pads are used, then the structure is simple, but self-alignment accuracy during reflow soldering is insufficient
Solution Approach 1:
Different pad regions are given different heights to perform different functions. First pads (for signal transmission) have a first height, while second pads (for alignment reference) have a second height greater than the first height. This local differentiation enables both electrical connectivity and precise self-alignment during reflow soldering.
Solution Approach 2:
The differential height structure is prepared in advance before soldering. The taller second pads make contact with solder bumps first during reflow, establishing alignment references before the shorter first pads are soldered, thereby pre-establishing the alignment framework for the entire bonding process.
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
The design enables precise and reliable bonding of semiconductor chips by automatically correcting misalignment, enhancing the reliability of solder connections and accommodating thermal expansion differences.
Implementation Method 1
It is known that reflow soldering has an effect of self-alignment of a solder bump with a pad. This self-alignment effect is induced by the surface tension of the molten solder.
Data Source
AI summary
A multi-layered board includes an upper insulating layer, a lower conductive layer including first lower conductive parts, an upper conductive layer between the lower conductive layer and the upper insulating layer and including first upper conductive parts and second upper conductive parts, and a lower insulating layer between the lower conductive layer and the upper conductive layer. The first upper conductive part includes a first pad exposed from a hole of the upper insulating layer. The second upper conductive part includes a second pad exposed from a hole of the upper insulating layer. At least a part of the first pad is in direct contact with the first lower conductive part within a hole of the lower insulating layer. The second pad is outside any hole of the lower insulating layer. A top surface of the second pad is higher than a top surface of the first pad.