Wiring Substrate Bump Height Equalization via Recessed First Metal Layer
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Solution Overview
Problem
The mixing of bumps with different diameters on a wiring substrate can lead to deteriorating connection reliability between the substrate and semiconductor chip, resulting in open failures and short circuits due to insufficient contact and lateral pressure on larger bumps.
Innovation Solution
A wiring substrate design featuring a first metal layer with a recess in the larger opening portion, allowing the second metal layer to fill the recess, ensuring equal top heights for both small and large diameter bumps, thereby improving contact reliability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If bumps of different diameters are formed by plating with the same thickness, then the large-diameter bumps have larger volume of second metal layer, but the top portions of large-diameter bumps become higher than small-diameter bumps
Solution Approach 1:
The patent applies local quality by forming a recess in the first metal layer specifically at the center of large-diameter opening portions, while small-diameter opening portions maintain flat first metal layers. This localized structural difference allows the second metal layer to be contained within the recess for large-diameter bumps, preventing excessive height while maintaining the required volume for electrical connection.
Solution Approach 2:
The recess is formed in the first metal layer before plating the second metal layer. This preliminary action creates a predetermined space that accommodates the second metal layer in large-diameter bumps, ensuring that after plating, the top portions of both small and large diameter bumps achieve equal heights, thereby preventing short circuit failures.
2Reliability
If large-diameter bumps have higher top portions, then the volume of second metal layer is sufficient for power supply connections, but top portions of large-diameter bumps may be pressed to extend laterally and contact adjacent bumps causing short circuit
Solution Approach 1:
The patent introduces a localized recess structure in the first metal layer only for large-diameter opening portions. This local modification contains the second metal layer within the recess, preventing lateral extension and contact with adjacent bumps, thereby eliminating the short circuit hazard while preserving adequate connection reliability.
Solution Approach 2:
By forming the recess in advance before second metal layer plating, the patent preemptively prevents the lateral extension problem. The recess acts as a physical constraint that guides the second metal layer to remain within boundaries, ensuring both connection reliability and prevention of short circuit failures.
3Shape
If small-diameter bumps have lower top portions, then the bump structure is compact, but top portions of small-diameter bumps may not contact electrodes of semiconductor chip sufficiently causing open failure
Solution Approach 1:
The patent applies local quality by creating a recess only in large-diameter opening portions, while small-diameter opening portions maintain flat-topped bumps. This ensures small-diameter bumps achieve sufficient contact height with semiconductor chip electrodes, preventing open failures while maintaining compact structure.
Solution Approach 2:
The patent achieves equipotentiality in terms of bump top heights by differentiating the structure based on diameter. Small-diameter bumps maintain flat tops at a height sufficient for electrode contact, while large-diameter bumps use recesses to achieve the same effective contact height, ensuring uniform electrical connection quality across different bump sizes.
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 design ensures consistent contact between the bumps and semiconductor chip electrodes, preventing open failures and short circuits by maintaining equal top heights for bumps of varying diameters, thus enhancing connection reliability.
Implementation Method 1
first metal layers which are, for example, made of copper are formed by plating in and around the opening portions provided in the solder resist layer, and second metal layers which are, for example, made of tin, solder, or the like, are formed by plating as upper layers on the first metal layers
Implementation Method 2
When only the second metal layers are melted and solidified by a reflow process, bumps each having a spherical shape are formed
Data Source
AI summary
A wiring substrate includes: a wiring layer; an insulating layer covering the wiring layer, and including a first opening portion exposing the wiring layer and a second opening portion exposing the wiring layer, wherein a diameter of the second opening portion is larger than that of the first opening portion; a first metal layer formed in the first opening portion and the second opening portion, and having a recess in the second opening portion; and a second metal layer that is formed on the first metal layer formed in the first opening portion and the second opening portion, wherein a portion of the second metal layer fills the recess. The first metal layer and the second metal layer serve as connection terminals to be electrically connected to an electronic component.