Irregular Terminal Pad Topography for Stronger Solder Ball Bonds
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Solution Overview
Problem
Solder joints in microelectronic component assemblies are prone to failure due to cracking or delamination at the interface between the terminal pad and solder ball, especially under thermal cycling, as the interface has a limited surface area and is susceptible to mechanical stress, leading to open circuits.
Innovation Solution
The terminal pads are designed with an irregular surface topography featuring protruding and recess portions, which increase the bonding surface area and provide a mechanical interlock with the solder balls, enhancing both metallurgical and mechanical strength.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a planar terminal pad surface is used, then the manufacturing process is simple, but the bonding surface area is limited and the interface strength is insufficient
Solution Approach 1:
The terminal pad surface is transformed from a planar geometry to an irregular topography with protruding and recess portions. This curvature modification increases the bonding surface area and creates mechanical interlocking features that enhance the interface strength between the terminal pad and solder ball, directly resolving the contradiction between simple structure and strong bonding.
Solution Approach 2:
The invention transitions from a two-dimensional planar surface to a three-dimensional irregular surface with varying heights and depths. The protruding and recess portions create additional bonding interfaces in the vertical dimension, significantly increasing the effective bonding area and strength without substantially increasing the lateral footprint of the terminal pad.
2Strength
If the terminal pad surface area is increased to improve bonding, then the interface strength improves, but the solder ball volume and pitch must increase
Solution Approach 1:
By utilizing the vertical dimension through protruding and recess portions, the invention increases the bonding surface area without requiring an increase in the lateral dimensions of the terminal pad or solder ball. This allows strong bonding to be achieved while maintaining small solder ball volumes and tight pitches.
Solution Approach 2:
The irregular surface topography concentrates the bonding enhancement in specific localized regions (protruding and recess portions) rather than requiring a uniform increase in overall surface area. This allows the bonding strength to be improved through strategic local features rather than global dimensional increases.
3Reliability
If a planar terminal pad is used, then the manufacturing process is simple, but crack propagation and delamination occur under thermal cycling
Solution Approach 1:
The irregular surface topography with its protruding and recess portions creates a mechanically interlocked structure that resists crack propagation and delamination. The curved and varied surface geometry disrupts the propagation path of cracks that would otherwise travel easily across a planar interface, thereby improving reliability under thermal cycling without complex manufacturing processes.
Data Source
AI summary
An apparatus comprising a substrate having conductive traces and associated integral terminal pads on a surface thereof, the terminal pads having an irregular surface topography formed in a thickness of a single material of the conductive traces and integral terminal pads. Solder balls may be bonded to the terminal pads, and one or more microelectronic components operably coupled to conductive traces of the substrate on a side thereof opposite the terminal pads. Methods of fabricating terminal pads on a substrate, and electronic systems including substrates having such terminal pads are also disclosed.