Interconnect Substrate Layout for Flat Pad Surfaces
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Solution Overview
Problem
Existing interconnect substrates with uniformly thick insulating layers and via interconnects result in varying solder bump heights due to recesses on uppermost pads, leading to unreliable connections with semiconductor chips.
Innovation Solution
The interconnect substrate design alternates insulating layers with varying thicknesses, ensuring the uppermost pad surface is substantially flat by making the insulating layer between the second and third pads thicker than the one between the first and second pads, reducing recess depth and height variation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If uniformly thick insulating layers are used in the stacked via structure, then the manufacturing process is simplified, but recesses are formed on the upper surfaces of the uppermost pads causing height variations in solder bumps
Solution Approach 1:
The insulating layers are designed with different thicknesses at different locations in the vertical stacking direction. Specifically, the insulating layer between the first and second pads is thinner than the insulating layer between the second and third pads, creating local thickness variations that compensate for the recess formation and achieve a substantially flat upper surface on the first pad.
2Device complexity
If uniformly thick insulating layers are used, then the structure is simpler, but the solder bump heights vary depending on recess depths leading to unreliable connections
Solution Approach 1:
Different insulating layer thicknesses are implemented at different vertical positions to locally adjust the pad surface height. The thinner first insulating layer and thicker second insulating layer create a compensated structure that eliminates excessive recesses and ensures uniform solder bump heights, thereby improving connection reliability.
3Manufacturing precision
If the insulating layer thickness is increased to compensate for recesses, then pad surface flatness is improved, but the overall substrate thickness increases
Solution Approach 1:
Instead of uniformly increasing all insulating layer thicknesses, the invention applies localized thickness adjustments: the first insulating layer is kept thinner while the second insulating layer is made thicker. This selective approach compensates for recesses and achieves pad surface flatness without causing excessive overall substrate thickness increase.
Data Source
AI summary
An interconnect substrate includes alternately stacked pads and insulating layers, and via interconnects extending through respective ones of the insulating layers, the via interconnects and the pads being alternately stacked in a vertical direction, the pads being electrically connected to each other via the via interconnects, wherein the pads include a first pad disposed on an uppermost one of the insulating layers and electrically connectable to a semiconductor chip, the first pad being an uppermost layer pad, a second pad disposed on a second uppermost one of the insulating layers, and a third pad disposed on a third uppermost one of the insulating layers, and wherein the uppermost one of the insulating layers located between the first pad and the second pad is thicker the second uppermost one of the insulating layers located between the second pad and the third pad.