Extended Bond Pad Profiles for COB Solder Bridging Control
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Solution Overview
Problem
Solder bridging defects in Chip-on-Board (COB) semiconductor device assemblies occur due to incomplete underfill material flow and excessive solder volume, leading to electrical shorts and damage, particularly in the bond-line-thickness (BLT) region between the semiconductor chip and substrate.
Innovation Solution
Extended bond pads with varying cross-sectional profiles, such as protruding or concave surfaces, are fabricated on the substrate to increase the bond-line-thickness (BLT) and reduce solder volume, facilitating better underfill material flow and minimizing the risk of solder bridging by containing solder material within the concave profiles.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional bond pads are used in COB assemblies, then the packaging process is simpler, but solder bridging defects occur due to incomplete underfill material flow and excessive solder volume
Solution Approach 1:
The bond pad structure is modified locally by adding extended portions with varying cross-sectional profiles (protruding or concave surfaces) at specific locations. This local modification changes the solder distribution pattern and underfill flow characteristics only where needed, rather than redesigning the entire bond pad structure, thus preventing solder bridging while maintaining overall structural simplicity.
Solution Approach 2:
The bond pad design transitions from a conventional planar two-dimensional structure to a three-dimensional structure with extended portions having varying cross-sectional profiles. This dimensional change creates additional space for underfill material flow and controls solder distribution in the vertical dimension, effectively preventing solder bridging defects.
2Manufacturing precision
If extended bond pads with varying cross-sectional profiles are fabricated, then underfill material flow is improved and solder bridging is reduced, but manufacturing complexity increases
Solution Approach 1:
The bond pad structure incorporates extended portions with varying cross-sectional profiles by modifying geometric parameters such as height, width, and surface contour (protruding or concave). These parameter changes are achieved through standard semiconductor fabrication processes like selective plating or etching, allowing precise control of underfill flow and solder distribution while using existing manufacturing capabilities.
3Quantity of substance
If extended bond pads are used to reduce solder volume, then solder bridging risk is minimized, but more fabrication steps are required
Solution Approach 1:
The extended bond pad structure with varying cross-sectional profiles is fabricated in advance during the substrate preparation stage, before the solder paste application and bonding processes. This preliminary structuring of the bond pads pre-determines the solder distribution and underfill flow paths, allowing reduced solder volume to be used while minimizing bridging risk, without adding complexity to the subsequent assembly steps.
Data Source
AI summary
A semiconductor device assembly including a semiconductor device having a plurality of pillars disposed on a backside surface of the semiconductor device; and a substrate, including: a solder mask layer disposed on a front side surface of the substrate, a plurality of extended bond pads disposed on the frontside surface of the substrate and surrounded by the solder mask layer, the plurality of extended bond pads each having a top surface higher than a top surface of the solder mask layer, and wherein the semiconductor device is directly attached to the substrate by bonding each of the plurality of pillars of the semiconductor device to the top surface of a corresponding one of the plurality of extended bond pads with a solder connection.