Protrusion Bump Pads for Bond-on-Trace Testing
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Solution Overview
Problem
In Bond-on-Trace (BoT) processing, the close trace pitch leads to solder bonds inadvertently bridging connections with adjacent traces, making probe testing challenging due to the trace pitch falling below the diameter of common testing probes.
Innovation Solution
The implementation of protrusion bump pads on conductive traces, where the trace portions not covered by bump pads are recessed within the substrate, allowing for reliable electrical connections and preventing short circuits during testing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the trace pitch is reduced to increase fan-out capability, then the connectivity and routing flexibility are improved, but solder bonds inadvertently bridge adjacent traces causing short circuits
Solution Approach 1:
The conductive trace is segmented into two distinct portions: a recessed portion embedded in the substrate and a protruding portion extending above the substrate surface. This segmentation allows the trace to maintain close pitch for fan-out while the protruding portion prevents solder bridge formation, thus resolving the contradiction between connectivity and connection reliability.
Solution Approach 2:
The solution transitions from a two-dimensional planar trace to a three-dimensional structure by making portions of the trace protrude above the substrate surface. This dimensional change enables close trace spacing while maintaining electrical isolation through vertical separation, addressing both fan-out capability and connection reliability.
2Adaptability or versatility
If the trace pitch is reduced to increase fan-out capability, then the routing flexibility is improved, but probe testing becomes challenging due to trace pitch falling below probe diameter
Solution Approach 1:
By making the trace portion protrude vertically above the substrate, the effective testing target is raised to a height where standard probes can easily contact it. This dimensional elevation solves the probe testing difficulty while maintaining the reduced trace pitch for improved routing flexibility.
Solution Approach 2:
The protruding trace portion acts as an intermediary testing interface between the closely-spaced traces and the probe. It provides a raised contact point that mediates the interaction between the small-pitch traces and larger-diameter probes, enabling reliable electrical testing.
3Ease of manufacture
If standard flat bond pads are used on close-pitch traces, then the manufacturing process is simplified, but solder bonds bridge adjacent traces causing short circuits
Solution Approach 1:
The bond pad structure is segmented with a recessed portion in the substrate and a protruding portion extending above the substrate surface. This segmentation prevents solder bridge formation between adjacent pads while maintaining a manufacturing process that builds upon standard PCB fabrication techniques.
Solution Approach 2:
The trace structure has different geometries at different locations: recessed portions for electrical connection and protruding portions for solder bonding and testing. This local differentiation of structure quality prevents solder bridging while maintaining manufacturing feasibility through localized process modifications.
Data Source
AI summary
An embodiment apparatus includes a dielectric layer, a conductive trace in the dielectric layer, and a bump pad. The conductive trace includes a first portion having an exposed top surface, wherein the exposed top surface is recessed from a top surface of the dielectric layer. Furthermore, the bump pad is disposed over and is electrically connected to a second portion of the conductive trace.